Recent progress in tissue optical clearing for spectroscopic application

Recent progress in tissue optical clearing for spectroscopic application

Accepted Manuscript Recent progress in tissue optical clearing for spectroscopic application A.Yu. Sdobnov, M.E. Darvin, E.A. Genina, A.N. Bashkatov,...

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Accepted Manuscript Recent progress in tissue optical clearing for spectroscopic application

A.Yu. Sdobnov, M.E. Darvin, E.A. Genina, A.N. Bashkatov, J. Lademann, V.V. Tuchin PII: DOI: Reference:

S1386-1425(18)30111-2 https://doi.org/10.1016/j.saa.2018.01.085 SAA 15804

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date: Revised date: Accepted date:

13 December 2017 25 January 2018 31 January 2018

Please cite this article as: A.Yu. Sdobnov, M.E. Darvin, E.A. Genina, A.N. Bashkatov, J. Lademann, V.V. Tuchin , Recent progress in tissue optical clearing for spectroscopic application. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Saa(2017), https://doi.org/10.1016/j.saa.2018.01.085

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ACCEPTED MANUSCRIPT Recent progress in tissue optical clearing for spectroscopic application A.Yu. Sdobnov1,2*, M.E. Darvin3, E.A. Genina2,4, A.N. Bashkatov2,4, J. Lademann3, V.V. Tuchin2,4,5

*Corresponding Author: [email protected]

Faculty of Information Technology and Electrical Engineering, University of Oulu, Oulu

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90570, Finland

Research-Educational Institute of Optics and Biophotonics, Saratov State University (National

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Research University of Russia), Astrakhanskaya 83, 410012 Saratov, Russian Federation Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology,

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Venerology and Allergology, Charité – Universitätsmedizin Berlin, corporate member of Freie

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Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Charitéplatz 1, 10117 Berlin, Germany

Interdisciplinary Laboratory of Biophotonics, Tomsk State University (National Research

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University of Russia), Lenin’s av. 36, 634050 Tomsk, Russian Federation 5

Laboratory of Laser Diagnostics of Technical and Living Systems, Institute of Precision

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Mechanics and Control RAS, Rabochaya 24, 410028 Saratov, Russian Federation

Keywords: optical clearing agent, multiphoton microscopy, Raman spectroscopy, Raman microscopy, optical coherence tomography, laser speckle contrast imaging, tissue, skin 

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Highlights:

In this review, the progress in optical clearing for multiphoton microscopy, Raman

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microscopy, NIR spectroscopy, confocal microscopy, optical coherence tomography, and speckle contrast imaging has been described in detail. 

The physical, molecular and physiological mechanisms of optical clearing have been described



Future perspectives of using optical clearing was discussed

Abbreviations: BABB - Benzyl Alcohol/ Benzyl Benzoate; CARS - coherent anti-Stokes Raman spectroscopy; CLSM – confocal laser scanning microscopy; CM – confocal microscopy; 1

ACCEPTED MANUSCRIPT CRM - confocal Raman microscopy; DMSO - dimethyl sulphoxide; FPT – fructose, PEG-400 and thiazone mixture; FSOCA - footpad skin optical clearing agent; Hb – hemoglobin; LSCI – laser speckle contrast imaging; LSSCA - Laser Speckle Spatial Contrast Analysis;

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LSTCA - Laser Speckle Temporal Contrast Analysis; MPM - multiphoton microscopy;

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MRI - magnetic resonance imaging; NIR – near-infrared;

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OC – optical clearing; OCT – optical coherence tomography; PBS - Phosphate Buffer Solution;

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PEG - polyethylene glycols;

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OCA – optical clearing agent;

RBC – red blood cell; RS – Raman spectroscopy;

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SC - stratum corneum;

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SERRS - surface-enhanced resonance Raman scattering; SERS - surface-enhanced Raman scattering; SHG - second harmonic generation;

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TDE - 2,2’-thiodiethanol;

TPEAF - two-photon excited autofluorescence;

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US – ultrasound;

Abstract

This paper aims to review recent progress in optical clearing of the skin and over naturally turbid biological tissues and blood using this technique in vivo and in vitro with multiphoton microscopy, confocal Raman microscopy, confocal microscopy, NIR spectroscopy, optical coherence tomography, and laser speckle contrast imaging. Basic principles of the technique, its safety, advantages and limitations are discussed. The application of optical clearing agent on a tissue allows for controlling the optical properties of tissue. Optical clearing-induced reduction of tissue scattering significantly facilitates the observation of deep-located tissue regions, at the 2

ACCEPTED MANUSCRIPT same time improving the resolution and image contrast for a variety of optical imaging methods suitable for clinical applications, such as diagnostics and laser treatment of skin diseases, mucosal tumor imaging, laser disruption of pathological abnormalities, etc.

Graphical abstract This paper aims to review recent progress in optical clearing of the skin and over naturally turbid biological tissues and blood using this technique in vivo and in vitro with multiphoton

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microscopy, confocal Raman microscopy, confocal microscopy, NIR spectroscopy, optical coherence tomography, and laser speckle contrast imaging. Basic principles of the technique, its

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safety, advantages and limitations are discussed.

Structural images of different skin layers obtained ex vivo for porcine ear skin samples at

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application of OmnipaqueTM and glycerol solutions during 60 min. Red color corresponds to

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TPEAF signal channel. Green color corresponds to SHG signal channel.

1. Introduction For the last few decades, biomedical photonics has been of great interest with the focus on non-invasive in vivo tissue imaging and analysis. This field allows for clinical structural and functional analysis of tissues and cells at high resolution, cancer diagnostics and therapy control. Compared to other methods such as X-ray imaging, magnetic resonance imaging (MRI) and ultrasound imaging, optical methods are safer and simpler. Recently, a large variety of noninvasive in vivo optical tissue diagnostic techniques has been developed, such as optical coherence tomography (OCT) [1, 2], laser speckle contrast imaging (LSCI) [2, 3], confocal microscopy (CM) or, more specifically, confocal laser scanning microscopy (CLSM) [4, 5], Raman and coherent anti-Stokes Raman spectroscopy (CARS) [6, 7], Raman microscopy [8-11], 3

ACCEPTED MANUSCRIPT surface-enhanced Raman scattering (SERS) [12-14], fluorescence spectroscopy [15, 16], multiphoton microscopy (MPM) [4, 5, 17-21], including CARS tomography [22], fluorescence lifetime imaging [23, 24], second harmonic generation (SHG) imaging [25], etc. However, the main limitations of the optical imaging techniques are due to strong light scattering in tissue layers and blood, which causes low contrast and spatial resolution, as well as a small probing depth for visible and near-infrared light [26-28]. The optical clearing (OC) technique, which was developed and has been intensively

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studied since the nineties of the last century, allows for controlling tissue optical properties, particularly, effectively reducing the light scattering in tissue. Suppression of scattering provides

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greater probing depths and better contrast, light focusing ability and spatial resolution of optical diagnostic methods [26, 29]. Nowadays, many optical imaging methods such as OCT [30-32],

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LSCI [3], 3D-confocal microscopy [33], optical projection tomography [34], polarized microscopy [35], ultramicroscopy [36] and multiphoton imaging [20, 37-40] are used in

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combination with OC. An approximate evaluation of the number of publications related to the optical clearing of tissues using the databases Web of Science, Scopus, PubMed, and other

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available sources shows an exponential grow [41] (see Fig.1). Thus, an understanding of the mechanisms of interaction of the optical clearing agents (OCAs) with tissue, cells and biological molecules is an important goal for non-invasive clinical examinations by using different

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spectroscopies.

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Number of papers

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80 60 40 20

0 1990

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2005

2010

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Years

Fig.1 Approximate evaluation of the number of publications related to the optical clearing of tissues from 1990 to 2017. The dependences are plotted using the databases Web of Science, Scopus, PubMed. This article presents recent progress in tissue optical clearing technique applied in vitro and in vivo for two-photon microscopy, confocal Raman microscopy, near-infrared spectroscopy, confocal microscopy and laser speckle contrast imaging. 4

ACCEPTED MANUSCRIPT 2. Main mechanisms of tissue optical immersion clearing It was found that scattering anisotropy factor (g) and scattering coefficient (μs) depend on a refractive index mismatch between cellular components such as membranes, organelles cytoplasm, etc. [26]. For fibrous tissues (skin dermis, muscles, cartilages, etc.), an index mismatch between interstitial medium and long formations of scleroprotein fibers plays main role [42]. The refractive index has been calculated for large amount of tissues, and tissue

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components such as the nucleus and the cytoplasmic organelles in mammalian cells (n=1.381.41 at 589 nm wavelength) [43], nuclei (nnc = 1.39) [44], connective tissue fibers

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(n=1.41) [45], interstitial fluid and human blood plasma (n=1.331.35) [26, 46], dry RBCs (n=1.611.66 at 550 nm wavelength) [47,48], hemoglobin (Hb) with of 32 g/dl concentration

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(n=1.42) [49], etc.

Three hypothesized mechanisms of tissue OC were suggested [50]. The first one is

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matching of refractive indices (n) between tissue components and interstitial fluid modified by an OCA diffused into the tissue [26, 29-31, 50-55]. Others are related to the interaction of an

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OCA with the tissue compounds and can be associated with reversible dissociation of collagen fibers [52, 56-59] and tissue dehydration process [26, 30, 51, 52, 60-62], induced by hyperosmolarity of the applied agent. Some OCAs are capable of destabilizing the collagen

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structure by interaction of hydrogen bonds between collagen and an OCA (collagen-reversible

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solubility). It leads to decreasing of light scattering from collagenous tissues because of a reduction of scatter size [62]. These and possibly other not known OC mechanisms usually work not independently but simultaneously with different relative contributions depending on tissue,

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OCA and delivery method. It was suggested that dehydration could reduce scattering in soft tissues by displacing water from the space between collagen fibrils, decreasing the refractive

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index mismatch [26, 63-67]. Also, refractive index matching causes replacement of water with OCA as well as scattering coefficient reduction and increasing of single scattering directness. For fibrous tissues, reduction of scattering coefficient can be extremely high [29, 67-71]. Changes in structure can lead to tissue shrinkage and thus significantly increase tissue transmittance even at some refractive index mismatch [61]. Also, tissue swelling may appear as one of the factors that influences on OC [26, 50, 61, 62, 69-72]. For collagen-based tissues, reversible solubility in sugars and sugar alcohols may take place as well as destabilization of collagen structure leading to reduction of optical scattering [57]. For the use of hyperosmotic agents, osmotic pressure may play a significant role. Efficiency of tissue OC can vary due to differences in the refractive indices of the used OCAs, their osmolarity and initial state of turbidity (tissue structure). Selection of the optimal 5

ACCEPTED MANUSCRIPT parameters allows for effective OC of soft tissues as well as hard ones. Therefore, OC technique opens the way for the least-invasive diagnostics and therapy of tissues hidden under bones, cartilages, tendons, etc. For example, optical immersion clearing of the cranial bone under action of anhydrous glycerol was investigated [73]. It was shown that a cranial bone sample, exposed during 1 hour, decreased the reduced scattering coefficient of superficial tissue layers by approximately 25% in the wavelength range of 1400–2000 nm. It was experimentally found that the main aspect of OC process is the replacement of water in the interstitial space by the

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immersion substance [73]. The solution of Iohexol in water (x-ray contrast named OmnipaqueTM) has been used for cartilage-bone boundary visualization by OCT [63]. The effect

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of OC became noticeable after 15 min of OCA application. Also, it was found that for 0.9 mm thick cartilage optical clearing process is saturated after 50 min with an increase of the refractive

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index from 1.386 ± 0.008 to 1.510 ± 0.009.

As far as blood immerses or goes through practically all tissues, development of effective

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blood OC methods is an important goal for the successful optical imaging. Blood scattering is caused by the refractive-index mismatch between RBC cytoplasm and blood plasma, as well as

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by specific size and structure of RBC [26, 49, 55, 61]. The refractive index of RBC cytoplasm is defined mostly by the hemoglobin concentration [74]. The volume and shape of a single RBC are defined by blood plasma osmolarity [74, 75]. Also, aggregation and disaggregation capability

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of RBCs has an influence on the blood scattering [76]. Introduction of OCAs into blood, causes

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matching between plasma and RBCs refractive indices [55, 61]. It was shown that minimal light scattering occurs at a glucose concentration in blood of 0.65 g/ml. However, residual scattering is still can be noticed. [77]. For safety purposes, large concentrations of glucose could only be

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applied locally and for a short time period. It was demonstrated that using OCT and CM supported by injection of small amounts of OCA (dextran, glucose, or OmnipaqueTM) allows one

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to visualize an atherosclerotic plaque or coronary stented lesions through a blood layer at high contrast [61, 78]. A 30-40% reduction of the blood scattering coefficient in the spectral range of 400-1000 nm, with an increase in the local hemolysis (up to 20% of RBC in the vicinity of the optical probe) was described theoretically [79]. Then, this prediction was successfully proved experimentally [80, 81]. Also, it was demonstrated that efficiency of blood OC depends not only on refractive-index matching but also on size and shape of RBCs as well as their aggregation ability [55]. The results presented in this section relate mostly to in vitro measurements. For in vivo OCAs application, additional physiological aspects such as the metabolic reaction of living tissue on the clearing agent, the tissue functioning aspects and tissue physiological temperature should be taken into account [26, 31, 50, 61, 62, 68, 82-84]. In a living tissue, the refractive index is a 6

ACCEPTED MANUSCRIPT function of tissue physiological or pathological state. According to the specificity of the tissue state, the refractive index of the scatters and/or the background may be different (increased or decreased), and therefore light scattering may correspondingly change [26, 61]. Topical application or injection of OCA such as glycerol and glucose into skin also influence the state of blood microcirculation in dermis. The OCA diffuses to vessel net area, partly penetrates vessel walls, interacts with endothelial and blood cells and leads to local osmotic stress and follow up dehydration of tissue and cells [85]. It was shown on chick chorioallantoic membrane that the

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vessels blocking effect causing reduction of blood flow depending on the dosage of OCAs, as

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well as on application time [86].

3. OCAs overview

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In the last few years, a wide amount of substances was found suitable for application as OCAs for tissue optical clearing. In general, OCAs can be roughly classified by several groups:

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(i) polyatomic alcohols (e.g., glycerol, polyethylene glycols (PEGs), polypropylene glycol, combined mixtures with a base of polypropylene glycols and polyethylene glycols, mannitol,

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sorbitol and xylitol [60, 63, 68, 70, 71, 73, 83, 85, 86-93]); (ii) sugars (e.g., glucose, dextrose, fructose, ribose and sucrose [51, 57, 58, 82, 84, 85, 86, 94-97]); (iii) organic acids (e.g., oleic and linoleic acids [98, 99]); (iv) other organic solvents such as dimethyl sulphoxide (DMSO) [52, 98-

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101] or thiazone [3, 98, 101-108], and (v) x-ray contrast agents (e.g., Verografin™,

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Trasograph™, Hypaque™, and Omnipaque™ [31, 109]). The most frequently used OCAs are glycerol, glucose and PEG as their biocompatibility and pharmacokinetics render them suitable for tissue treatment [3, 20, 30, 32, 40, 55, 103]. These OCAs were successfully used for

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measurements with OCT [30, 32, 55, 63, 97, 110, 111], Raman spectroscopy [112], two-photon microscopy [20, 37, 113], confocal Raman microscopy (CRM) [114], and LSCI [3, 115].

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Also, OC methods for in vitro imaging should be separately mentioned. Zhu et al. [116] gave an excellent review of in vitro clearing. Here, we will list in brief the most commonly used methods. CLARITY has been presented as technique based on chemical transformation of intact tissue into a nanoporous hydrogel-hybridized form [117]. Such kind of form is fully assembled but optically transparent and permeable for macromolecules. FocusClear was first presented by Chiang et al. [118] as a mixture of DMSO, diatrizoate acid, glucamine, and other chemical agents. Scale, a method based on a serendipitous discovery of urea’s clearing ability, was introduced for rendering the whole mouse brain transparent [53, 54]. Also, SeeDB (saturated solution of fructose (80.2% wt/wt) in water with 0.5% α-thioglycerol) [119], Benzyl Alcohol/ Benzyl Benzoate (BABB), solution comprised of two parts benzyl benzoate and one

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ACCEPTED MANUSCRIPT part benzyl alcohol [120] clearing agents and CUBIC protocol [121] are widely used for in vitro optical clearing.

4. Safety and toxicity of OCA The most commonly used OCAs (e.g. glucose, glycerol and propylene glycol) are generally nontoxic agents. However, prolonged treatment with a highly concentrated OCA can cause the negative effect on tissue such as local hemostasis, shrinkage and even tissue necrosis.

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Glycerol can cause alteration in the skin morphology due to a dissociation of the collagen fibers [56, 58]. Also, it was found that anhydrous glycerol causes anhydrous effect on the cutaneous

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vasculature [122]. This study revealed that the glycerol effect on vessels is reversible with hydration. In addition, transition from oxygenated form of Hb to deoxygenated form for rat skin

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related to local hemostasis during 84.4% glycerol treatment in vivo has been investigated [30]. Moreover, it was found that the topical application 75%-glycerol solution on the mesenteric

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microvessels of a rat in vivo within 1–3 s led to reduction of blood flow velocity in all microvessels and to stasis appearing after 20 s [85]. Also, it was shown that 75%-glycerol

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solution does not induce any loss of collagen organization [60]. However, irreversible changes of the collagen structure under the action of anhydrous glycerol are possible [56]. It was found that long-term application of OCAs on tissues containing blood vessels can

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cause changes in vessels, even stop flow in them. The results have shown that after glycerol

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treatment, the flow velocity in blood vessels was recovered to different extents, and new blood vessels developed after 2 days [85]. Investigation of glucose long-term impact on blood perfused tissues showed that there were no new blood vessels developed in 2 days [86].

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In a number of studies, some side effects of OC in terms of irritation and edema, were noted [60, 68, 69, 82, 84].

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Therefore, it is critically important to find an optimal agent and the safest concentration for application on living tissues. Recent studies revealed that Iohexol (N,N´-bis(2,3dihydroxypropyl)-5-[N-(2,3-dihydroxypropyl)-acetamido]-2,4,6-triiodoisophthalamide) a nonionic, water-soluble radiographic contrast medium with a molecular weight of 821.14 g/mol manufactured by GE Healthcare Ireland, Cork, Ireland, known by the trademark Omnipaque™ (with Iodine concentration 300 mg/mL [110, 111, 114] and 350 mg/mL [63]), can be a promising OCA for in vivo applications. Low osmolarity (465 mOsm/L) allows one to avoid both drastic structural skin deformation and barrier function impairment. Moreover, Omnipaque™ has significant OC effect without noticeable sample shrinkage [63] because of less dehydration. Compared to glycerol, Omnipaque™ has a lower viscosity (11.8 cp) which allows Omnipaque™ solutions to penetrate faster into the skin and start the clearing process. 8

ACCEPTED MANUSCRIPT 5. Enhancers of OCA diffusion The OC efficacy depends on the type and concentration of OCAs as well as on its treatment time. It was shown that mouse brain immersed in Scale became transparent after several weeks of treatment [53]. Compared to other tissues, optical clearing of skin is difficult and requires an extended treatment time, as the barrier function of the stratum corneum (SC) prevents the OCAs from penetrating into deeper layers. Lower concentrations of OCA cannot

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provide enough clearing efficiency, while long treatment with highly concentrated OCAs could possible induce skin tightening, irritation and follow up edema. Thus, for faster, more effective

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and safer optical clearing, physical, chemical and a combination of these enhancement methods should be introduced.

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Ethanol, propylene glycol, DMSO, linoleic and oleic acids, azone and thiazone are typically used as penetration enhancers of OCA diffusivity through the SC [32, 50, 52, 97, 100-

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102, 104, 106-108, 123-133]. Sometimes, DMSO and thiazone alone are used as the OCA [52, 89, 99, 101, 134-137]. Ethanol has ability to modify the skin barrier property as well as enhance

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pore transport [126, 127]. Also, application of ethanol leads to the defatting of skin surfaces which facilitates the OCA penetration. It was shown that mixtures of OCAs with propylene glycol can enhance the effectiveness of OC, while the clearing effect induced by propylene

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glycol itself is lower than that induced by the other OCAs [125]. The permeability of different

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OCA enhancers including DMSO, methanol, boric acids, etc. has been investigated on nails [128]. Also, it was found that the permeability enhancing mechanism for DMSO acts in two ways. First, DMSO can induce the transition of ceramide bilayers from the gel phase to the

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liquid crystalline phase. Second, DMSO can weaken the lipid bilayers in the SC that consist of a high amount of ceramides [129].

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Besides chemical enhancers, physical methods have also been used for advanced OC. Large amount of methods such as tape stripping [138], microdermabrasion [139], low intensive and high intensive laser irradiation of skin surface [140, 141], iontophoresis [142], ultrasound [143] and photomechanical (shock) waves [144], needle-free injection [145], photothermal and mechanical microperforation [146], or microdamaging of epidermis [147] are widely used for reduction of the skin barrier function.

6. Multiphoton microscopy Multiphoton microscopy is a fluorescence imaging technique based on the two- or threephoton excitation of fluorophores. The two-photon microscopy is allowed for in vivo applications [23]. It represents an alternative to single-photon confocal microscopy [17]. One of 9

ACCEPTED MANUSCRIPT the main advantages of multiphoton microscopy is the possibility to investigate 3D distributions of chromophores excited in the ultraviolet range in thick samples. Such an investigation becomes possible because excitation of chromophores (e.g., at the wavelength of 380 nm) caused by laser radiation at a wavelength around 760 nm where a tissue has a high transparency. For skin measurements, the two-photon excited autofluorescence (TPEAF) is produced by NAD(P)H, keratin, elastin and melanin, while the second harmonic generation (SHG) is due to collagen type I molecule response. The excitation wavelengths used in multiphoton microscopy are longer than

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the wavelengths of the emitted TPEAF and SHG signals. Scattering in tissues drastically reduces penetration depths to depths much lower than that of the equivalent single photon fluorescence,

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while resolution stays unchanged [148]. Thus, application of OCAs for two-photon measurements can be very useful.

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Yeh et al. [56] first investigated the OCA effect using multiphoton microscopy. It was suggested that OC has a molecular mechanism. This was evidenced by the fact that glycerol

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application in rodent dermis and rat tissue leads to a loss of order in fibril organization. The change in collagen organization and size can lead to a significant reduction in tissue light

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scattering.

Cicchi et al. [20] presented the first studies of two-photon in-depth enhancement under treatment with OCAs. Human dermis was treated with hyperosmotic agents (glucose, glycerol

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and polypropylene glycol) within a few minutes. Glycerol showed the best but slowest clearing

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result (with relative contrast 16.3 at 20 µm). Propylene glycol proved to be similarly efficient (relative contrast is 12.6 at 20 µm). Glucose was the least effective (relative contrast is 5.1 at 20 µm) but three-times faster than glycerol.

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It was shown that simultaneous usage of confocal/two-photon microscopy systems allows for non-invasive microscopic examination of the scaffold structure, which would be a valuable

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tool to advanced studying of biomaterials and their interactions with the molecule/cell of interest within the scaffold in an integrated fashion [148]. The integration of FocusClear OCA mediated OC, confocal/two-photon microscopy and 3-D image rendering provided a useful approach to microscopic examination of the scaffold structure. Additionally, it was found that comparing to DMSO and glycerol, FocusClear can provide significantly better transmittance at 488, 543 and 633 nm, and fluorescent emission at 505 nm. Additional morphological information was obtained by SHG microscopy with two-photon excitation fluorescence microscopy [149]. It was shown that multiphoton imaging allows for temporally separating two processes during collagen optical clearing after glycerol application [37]. The first one is a relatively slow process of glycerol penetration into the interfibrillar space of collagen. The second one is a fast process of tissue dehydration with collagen shrinkage. Using of less glycerol concentration 10

ACCEPTED MANUSCRIPT induced a less-expressed clearing effect because water molecules are partially substituted with glycerol molecules. Also it was found that the effects caused by phosphate-buffered saline and glycerol application are reversible. Moreover, possibility of fiber morphology and SHG signal intensity recovery was noticed after the removal of OCAs from Achilles tendon, chicken skin and chicken tendon. Plotnikov et al. [40] found that the key mechanism of OC in muscle after glycerol application is a combined effect of cytoplasmic protein concentration reduction and concomitant

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decrease in the secondary inner filter effect on the SHG signal. Moreover, it was suggested that refractive index matching plays only a minor role in OC of muscle. However, reduction in

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protein concentration has been observed after long OCA application (24 hours) while short time application (up to 1 hour) lead to increase of protein concentration due osmotic effect.

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Wen et al. [60] showed that glycerol application leads to decrease of skin reflectance. In addition, after treatment during 30 min by 75% glycerol in water solution, the thickness of

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dermis and the diameter of collagen fibrils decreased from 1459 µm to 1287 µm and from 109 nm to 79 nm, respectively, and skin became transparent. Nevertheless, no collagen fiber was

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dissolved or fractured. So, it was suggested that the important mechanisms of OC are changes in tissue thickness and concomitant more compact tissue fiber packing. A Monte Carlo simulation and experimental validation showed that reduction of the

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primary inner filter effect following glycerol treatment dominates the axial attenuation response

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in both muscle and tendon [39]. Primary inner filter is an effect related to the nonlinear dependence of the fluorescence intensity on the concentration of the fluorescent substance. However, OC mechanisms for these types of tissue are different. In the acellular tendon,

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application of glycerol leads to the scattering reducing due to the index matching effect. The OC mechanism in striated muscle is a consequence of the refractive index matching of the cytoplasm

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cells with that of the surrounding higher-index collagenous perimysium as well as with sarcoplasm and myosin filaments. It was found that a decrease in the scattering coefficient depending on glycerol concentration growth can be well approximated applying the Mie theory. Ke et al. [150] showed that fixed mouse brains, which have been treated for a few days with the water-based optical clearing agent SeeDB, can be imaged using two-photon microscopy at millimeter-scale level (up to 6 to 7 mm), and up to 1 to 2 mm in depth using confocal microscopy. The use of 2,2’-thiodiethanol (TDE) solutions using optical clearing agent has been successfully demonstrated [151]. Fixed mouse brain was placed in TDE solution (30 min in case of 400 µm thick slices) for enhancing of the observation depth for two-photon measurements. Dendritic spines along single dendrites at deep positions have been successfully visualized. 11

ACCEPTED MANUSCRIPT Hippocampus has been successfully visualized at 2 mm depth also. Moreover, it was found that after treatment by 97% TDE in Phosphate Buffer Solution (PBS) solution fluorescent signals became highly detectable but rapidly decreased in intensity. Further immersing of the same sample in PBS and subsequently in 60% TDE solutions allows recovering the fluorescence signal. ScaleS technology has been introduced as an OCA for mouse brain imaging [53, 54]. Compared to other clearing agents (CUBIC, 3DISCO, SeeDB), fluorescence was firmly

fluorescence detection from thick samples of brain tissue.

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preserved in ScaleS-treated samples. Presumably, only ScaleS may be able to improve the

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Chang et al. [152] were the first to demonstrate a possibility for imaging intact mouse brain cleared by the CLARITY technique combining diffusion tensor imaging and two-photon

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microscopy. It was found that fractional anisotropy is sensitive to axon myelination. Also, it was

factors contributing to the diffusion signal.

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shown that a 3D CLARITY analysis can be useful method for resolving of various molecular

An approach towards 3D observation of multilayered organization of placental

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membranes supported by OC has been presented [153]. Placental membrane was immersed in aqueous 50%-TDE solution for 2 h and then in pure TDE overnight at room temperature for optimal OC. OC allowed full-depth imaging of amniochorion and deciduas.

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Sdobnov et al. [113] have showed that a topical application of both glycerol and

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Omnipaque™ solutions on the porcine skin can significantly improve the depth and contrast of the TPEAF and SHG images within 1 hour (see Fig. 2). By utilizing 40%, 60% and 100% glycerol, and 60% and 100% Omnipaque™, it was demonstrated that both agents can improve

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TPEAF and SHG signals from the skin ex vivo. Although glycerol was more effective than Omnipaque™, tissue shrinkage and cell morphology changes were found for high concentrations

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of glycerol solutions. Omnipaque™, on the contrary, increases the safety and causes no or minimal tissue shrinkage during the optical clearing process. Moreover, it was suggested that Omnipaque™ allows for robust multimodal optical/х-ray imaging with automatically matched optically cleared and х-ray contrasted tissue volumes.

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Fig. 2. Structural images of different skin layers obtained ex vivo for porcine ear skin samples at application of OmnipaqueTM and glycerol solutions during 60 min. Red color

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corresponds to TPEAF signal channel. Green color corresponds to SHG signal channel.

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7. Raman microscopy

A Raman spectrum represents a molecular fingerprint of the sample and provides quantitative information regarding its chemical composition. Any changes in cells and tissues

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can lead to significant changes in the Raman spectra. Raman spectroscopy (RS) provides

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information regarding the inelastic scattering, which occurs when vibrational or rotational energy of target molecules is exchanged with incident probe radiation. Thus, RS is a powerful and useful technique allowing measuring the chemical composition of various tissue types [154-156].

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Raman spectroscopy and microscopy are widely used in dermatology and skin physiology for in vivo skin analysis [157-160]. The penetration of xenobiotics through the skin can also be

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investigated [161]. Since skin depths suitable for in vivo investigation with Raman microscopy are usually limited to the epidermis (approx. 40 µm), Raman microscopy becomes an object of interest for optical clearing. Enejder et al. [162] measured Raman spectra for different glucose concentrations in nondiabetic volunteers using an oral glucose tolerance protocol. For better simplicity, a spectral region between 400 and 2000 cm-1, called the ”fingerprint region”, is employed for data comparison. Different molecular vibrations lead to Raman scattering in the fingerprint region. In many cases, bands can be assigned to specific molecular vibrations or molecular species, aiding the interpretation of the spectra in terms of tissue biochemical composition [163, 164]. Owing to the reduction of elastic light scattering at tissue optical clearing, a more effective interaction of a probing laser beam with the target molecules is expected. Caspers et al. [130] showed the time 13

ACCEPTED MANUSCRIPT dependence of DMSO distribution in human skin. Most doses of DMSO permeated through the SC within 20 min. Also, changes in the amide I region were recorded. DMSO has been used as OCA. Penetration monitoring was possible due DMSO unique spectra. OCAs can increase the signal-to-noise ratio and significantly improve the Raman signal as well as reduce the systematic error caused by misdetection of surface and subsurface spectra [163]. Schulmerich et al. [165] first demonstrated Raman spectroscopic diffuse tomographic imaging at optical clearing. In vivo Raman images were obtained for canine bone under glycerol

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treatment. The glycerol OC effect on the bone tissue was also studied [112]. It was shown that glycerol reduced the noise in the raw spectra and significantly improved the cross-correlation

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between the recovered bone factor and the exposed bone measurement in a low signal-to-noise region of the bone spectra.

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Zimmerley et al. [166] presented studies of combined SHG imaging and coherent antiStokes Raman scattering microscopy for investigation of optical clearing in human skin with

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DMSO solutions. It was suggested that DMSO interferes with the collagen fibers structure by changing the interfibril spacing at a sub-micron scale. The collagen fibers were decomposed

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further up to concentrations of 20 v/v% of the clearing agent. Higher concentrations were not compromised the SHG response from dermal collagen. However, the tissue scattering continued to decline up to DMSO concentrations of 40 v/v%. Thus, these studies confirmed that the

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mechanism of refractive index matching as well as the structural changes of collagen I fibers

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play significant role in the OC process. Also, changes of the DMSO concentration with depth at different times has been presented [166]. As a result, a depth-resolved behavior of the DMSO diffusion coefficient was detected. The maximum DMSO concentration in tissue decreased from

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40% to 10% due to tissue dehydration and the reduction of the skin barrier function provided by the SC. These results proved that Raman spectroscopy can be a useful tool for quantitative

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monitoring of the OC process. Huang and colleagues [167] investigated the OC effect of glycerol by Raman microspectroscopy at time intervals from 0 to 75 min. It was found that application of glycerol significantly improved the depth of Raman measurements as well as contributed to a better recovery of skin tissue Raman spectra that were not overlapped with the glycerol Raman spectra over time. Since it was shown that glycerol solutions with higher concentrations provided a better clearing effect, the intensity of the band at 1003 cm−1 could be increased for improved cancer detection [168, 169]. It was also found, that the Raman signals resembled well the native spectrum of the molecules in porcine skin with a negligible frequency shift. CRM was employed to investigate Omnipaque™ as an OCA for improved investigation of collagen hydration in porcine ear skin ex vivo [114]. Omnipaque™ was compared to glycerol 14

ACCEPTED MANUSCRIPT after 30 and 60 min of treatment. The intensity of the skin-related Raman peaks significantly increased starting from the depth 160 μm for Omnipaque™ and 40 μm for glycerol after 60 min of treatment. Both OCAs induce skin dehydration but the effect of OmnipaqueTM treatment is

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less.

Fig. 3. Depth-dependent Raman spectra of porcine skin without OCA treatment (a), after 30 min (b) and 60 min (c) of OmnipaqueTM treatment and after 30 min (d) and 60 min (e) of glycerol treatment. The dotted vertical lines indicate OmnipaqueTM-related Raman peaks at 774 and 1516 cm-1 (b) and (c) and glycerol-related Raman peaks at 486 and 1056 cm-1 (d) and (e). The figure is taken from [114] and reproduced with journal´s permission.

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ACCEPTED MANUSCRIPT Kim et al. [170] experimentally showed that the Raman spectrum of porcine skin depends on the skin’s water content. A Monte Carlo simulation showed a similar correlation. The diagnostic accuracy is therefore assumed to be affected by spectral alterations due to the variation of skin water content. Cui et al. [171] proposed single-cell OC method for imaging of plasmonic nanoprobes by hyperspectral dark-field microscopy. This method based on a combining of delipidation and refractive index matching with highly biocompatible agents. Delipidation has been achieved by

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application of mild delipidation solvent and was controlled by stimulated Raman scattering. This procedure allows to eliminate lipid-enriched granular structures which are complicates

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penetration of OCA.

The Raman signal strongly depends on elastic scattering [172, 173]. Long treatment with

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highly concentrated OCAs can reduce the scattering too much that can lead to some loss of the Raman signal, because of decrease of light interaction length. These are a trade-off between the

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Raman signal attenuation for strongly turbid media [174] and efficiency of Raman signal excitation for highly transparent ones [172, 174]. Thus, it is important for Raman measurements

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to find the most suitable OCA, its concentration and treatment time for optimal relation between optical clearing and Raman signal intensity.

The long-term application of OCAs can lead to additional decrease of the Raman signal

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that should be taken into consideration in analysis of deep-located tissue regions. As far as strong

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tissue scattering and weak Raman scattering intensity results in decreasing of both resolution and contrast of Raman spectra at high observation depths, surface-enhanced Raman scattering (SERS) [12-14,175] and surface-enhanced resonance Raman scattering (SERRS) [176] allows to

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significantly improve sensitivity of Raman measurements and extend its applications into subcutaneous or even deeper layers.

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Zhang et al. [177] first introduced the OC technique for assisting SERS imaging in vivo. SERS nanoprobe, AuNS-Cy7 has been subcutaneously injected in mouse dorsum after OCA treatment. FPT, a multicomponent OCA combining fructose, PEG-400 and thiazone showed the best optical clearing effect in vivo by suppressing light scattering in the skin. FPT showed the best efficiency at 15 min after treatment. Compared to fructose, FPT was much more effective for in vivo measurements (the signal-to-background ratio was 3.5 times bigger). Simultaneous using of SERS imaging and OC technique demonstrated the feasibility of assisting the handheld Raman detector in imaging in vivo.

8. NIR spectroscopy

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ACCEPTED MANUSCRIPT NIR (near-infrared) spectroscopy is a powerful spectroscopic method for the noninvasive measurement of tissue composition as biological tissue is relatively transparent to the light in the NIR region, the so-called therapeutic/diagnostic window [26, 178-182]. NIR is advantageous for its quick spectra acquisition and possibility to predict physical and chemical parameters from a single spectrum. Tissue OC can be a useful tool for better visualization of glucose bands in tissue reflectance spectra. For example, using of an OCA without a peak in 1600 nm region can cause dehydration of tissue as well as decreasing of the water peak and the light-scattering suppression.

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So, the glucose peak at 1600 nm can be better differentiated. The major problem of glucose monitoring by NIR technique is necessity to use the calibration models [183, 184]. NIR

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frequency-domain reflectance techniques are based on a change in glucose concentration, which influence the refractive index mismatch between the interstitial fluid and tissue fibers, and hence

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μs coefficient. Scattering is decreasing with blood glucose increment. Thus, changes of scattering coefficient should be measured carefully for successfully using of this approach. Also, it is

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important to distinguish the changes in scattering from changes in absorption [185]. Evidently, other physiological effects related to the glucose concentration alterations can also influence on

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the measured μs value. The effect of glucose on the blood flow in the tissue may cause additional errors.

Genina et al. [186] demonstrated OC of dura mater using 1.5M and 3.0M glucose

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solutions (see Fig.4). They established that a few processes support the glucose diffusion. The

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fast process of replacing the water molecules with glucose molecules causes rapid increase of the optical transparency of the tissue (6-8 min). The slow process of tissue swelling under pH reduction in the interstitial fluid results in a decrease of the collimated transmittance of the

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samples after achieving the maximal OC efficiency and by the increase of the sample thickness due to the swelling. A relative increase in the transmittance of rat cranial bone during treatment

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by the immersion solution with inclusion of thiazone by 80% was obtained in Ref. [187].

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Fig. 4. Typical spectral (a, c) and temporal (b, d) dependences of the collimated

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transmittance of the dura mater samples under the action of glucose aqueous solutions with the

journal´s permission.

9. Confocal microscopy

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concentrations 1.5М (a, b) and 3М (c, d). The figure is taken from [186] and reproduced with

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Confocal microscopy (CM) is a powerful optical imaging technique widely used for the

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visualization of the internal structure of biological tissues on a cellular and subcellular level [148, 188]. A confocal microscope illuminates and detects the scattered or fluorescent light from the same small volume within the specimen. One of the main advantages of CM technique is the

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possibility to obtain high-quality images with a micron-level spatial resolution and high contrast. The main limitation of CM using for skin studies is high scattering reducing the quality of CM

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images. It was predicted theoretically based on Monte Carlo simulations of the point-spread function of the confocal reflectance microscope that skin can be investigated precisely at bigger depths. Thus, even the reticular dermis can be investigated [189, 190]. The application of OCAs can improve the penetration depth of reference light, image contrast and spatial resolution of CM. Dickie et al. [191] have introduced a technique that permits to resolve the microvasculature of murine tissues by CM to depths of up to 1500 μm below the specimen surface owing to optical clearing of thick tissue sections. FocusClear has been used as an OCA for confocal visualization of cockroach Diploptera punctata brains [192]. The application of the Focus Clear provided 3D mapping of an entire brain that measures more than 500 μm in thickness. Also, possibility to permeate and reduce the opacity of mouse colon and ileum by using of FocusClear has been demonstrated [193]. 18

ACCEPTED MANUSCRIPT Saline, pure glycerol and 80% DMSO solution influence on dorsal mouse skin has been investigated by CM [136] (see Fig. 5). Reflectance images measured at a wavelength of 488 nm showed that glycerol significantly increased the anisotropy of dermis scattering (from 0.7 to 0.99) with little changes in the scattering coefficient. At the same time, DMSO and saline has only a slight effect. It was suggested that the glycerol-related clearing effect starts when reducing the angular deviation of scattering. Moreover, an increase in anisotropy of scattering with a minor change in the scattering coefficient should cause an increase in the size of the scattering

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particles meaning swelling of collagen fibers in dermis.

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Fig. 5. Sagittal views of the skin samples from three mice (Expt#1, Expt#2, and Expt#3), showing the reflected signal, R(z’f,x), in the original lab units of detector volts [V] acquired by the microscope as a function of the apparent depth of focus (z’f) and lateral position (x). The

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color indicates the log10(Detector[V]). The top bright surface is the glass/sample interface (arrow). The signal decays as the microscope scans deeper into the tissue. The glycerin image is

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darker, indicating less reflectance from the glass/glycerin interface and from within the skin sample. The figure is taken from [136] and reproduced with journal´s permission.

It was found that DMSO application within 30 min allows increasing the fluorescence signal by the factor of 9 [194]. Moreover, further treatment with OCA within 105 min showed 13× signal increment. This enhancement was observed at depths up to 2 mm for mouse dorsal skin. Song et al. [195] presented their investigation of glycerol and FocusClear on mouse skin by CM. For 3 hours pinna treatment with glycerol, no significant enhancement in the imaging depth and contrast was observed. However, a noticeable optical clearing with enhanced factor of

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ACCEPTED MANUSCRIPT 2 was obtained on dorsal skin. Compared to glycerol, FocusClear proved to be more efficient for both pinna and dorsal skin. Puelles et al. [196] presented a method combining immunofluorescence, optical clearing, confocal microscopy and 3D analysis for observation of podocyte depletion in renal glomeruli. Optical clearing of sliced kidney was achieved by embedding the slices in agarose, which were subsequently dehydrated through changes in methanol and cleared by BABB. The 3D visualization of healthy mouse brains and tissues with diffuse, infiltrative

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grooving GBM8 brain tumors was demonstrated using optical clearing [197]. Optical clearing allowed a 10-fold increase of imaging depths.

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Shi et al. [198] introduced a new footpad skin optical clearing agent (FSOCA), which is mixture of saturated fructose solution, ethanol, dimethyl sulfoxide, polyethylene glycol-400 and

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thiazone. Application of FSOCA allowed monitoring of cutaneous blood vessel with improved contrast by laser speckle contrast technique. Moreover, imaging of fluorescent cells by laser

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scanning confocal microscopy became possible with higher fluorescence signal intensity and improved observation depth. No observable effects on blood flow distribution and cellular

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morphology have been noticed.

10. Laser Speckle Contrast imaging

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Laser Speckle Contrast Imaging (LSCI), first introduced in the early 1980s [199], is a

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powerful, easy to use and low cost method allowing noncontact, full-field and real-time flow systems mapping. If any parts of the illuminated object are moving, temporal fluctuations in the single speckle intensity occur. These fluctuations are manifested in blurring of the speckle

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pattern during observation with fixed camera exposure duration. The blurring leads to a reduction in speckle contrast and can be used to obtain information about movement in object by

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statistically analyzing the blurring degree. The LSCI technique provides images of the twodimensional blood flow distribution at high spatial and temporal resolutions. LSCI became an object of interest for researchers due to possibility to monitor the influence of OCAs on the blood flow in tissues. Galanzha et al. [85] firstly showed that topical application of glucose on mesenteric microvessels caused a decrease in blood flow. After 5 s interaction with OCA blood flow rate in venule with 11 µm diameter decreased from 1075 µms-1 to 202 µms-1. Moreover, after 20 s of interaction stasis appeared in venule. Glycerol also caused stasis after 20-30 s. Zhu et al. [86] introduced LSCI technique for investigation of long-term and short-term effects of glycerol and glucose as OCAs. It was shown that direct topical application of the OCAs on blood vessels in the chick chorioallantoic membrane can decrease the blood flow 20

ACCEPTED MANUSCRIPT velocity. Also blocking of blood vessels has been noticed. Long-term observations indicate that OCAs slowed down development of blood vessels. The blood flow can be recovered to different extents if the blood vessel is not blocked completely. It was shown that long-term application of glucose has stronger negative effects than short-term. Mao et al. [200] investigated influence of 30% glycerol solution on the dermal blood vessels of flap window of rat skin using LSCI. It was found that the blood flow velocity decreased initially and began to recover after 16 min. It was suggested that the short-term effect

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on the blood flow of the skin flap window can be revisable after the application of glycerol. Zhu et al. [201] developed an OC method allowing for imaging of the dermal blood flow

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through the skin after 40 min of OCA treatment. Mixture of PEG400 and thiazone has been used for maximal clearing effect. It was demonstrated that the speckle contrast improves after topical

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application of the OCA. Thus, more data related to the dermal blood vessels or blood flow can be

vessels become invisible very quickly.

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obtained. The afterward treatment of observed skin can reduce the image contrast. So, dermal

OC has been applied to skull for vessel imaging [202]. It was shown that the OC method

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can enhance the contrast of white-light images as well as the speckle images, providing an innovative transparent cranial window for LSCI. This method allows one to obtain information about cortical structure and functionality with higher resolution.

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LSCI was implemented for the blood flow monitoring through a capillary system

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embedded within various tissue phantoms at different depths and flow velocities [113]. Glycerol was mixed with Intralipid at different concentrations for reduction of tissue phantom scattering. The data analysis have showed that the OC method can effectively enhance the image contrast,

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imaging depth, and sensitivity to blood flow velocity. It was also found that for typical turbid tissue, the sensitivity to velocity estimated by the Laser Speckle Temporal Contrast Analysis

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(LSTCA) is twice of that by the Laser Speckle Spatial Contrast Analysis (LSSCA); while the sensitivity to velocity estimated by using the two analytic methods is 10 times higher. Abookasis et al. [203] demonstrated an approach using a standard LSCI system combined with lens array placed in front of a camera. This combination allows obtain multiple speckle contrast map projection. The application of OCA allowed enhancing the contrast-to-noise ratio. Moreover, the experiment showed that an increase in temperature from 22ºC to 28ºC causes a contrast-to-noise ratio growth [204]. Further, Moshe et al. [205] presented an improvement of this technique using combining multiple elliptical polarized speckle contrast projections with the use of OCAs. Wang et al. [97] evaluated optical clearing effects of three sugars (fructose, glucose, and ribose) through a molecular dynamics simulation and in vitro experiments. Fructose showed the 21

ACCEPTED MANUSCRIPT optimal clearing potential. Also, it was shown that application of a mixture of fructose with PEG-400 and thiazone allows for imaging vessels at high contrast and resolution. The effect of mixture is higher than effect of pure fructose. After 24 min of immersion in fructose, the glucose and ribose resolution was improved up to 14.3, 27.3 and 39.6 µm, respectively. It was shown that OC could improve the performance of LSCI for monitoring the cutaneous vascular structure and function, including the imaging resolution, contrast and sensitivity of the blood flow’s dynamical response to vasoactive drug [3]. In addition, based on the rebuilt arteries-veins separation

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method, the blood flow dynamical response time and amplitude, as well as the recovery process in arteries and veins can be quantitatively assessed and compared.

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The blood microcirculation of the pancreas in rats with diabetes after application of Omnipaque™ was studied using LSCI [206]. These investigations showed that the disease

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development in animals causes changes in the response of the microcirculatory system to the application of OCA. Omnipaque™ has caused a significant increase of the blood flow in the

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pancreatic vessels only in diabetic mice. It was also demonstrated that the diameter of the vessel after application of OCA did not change. So, it was suggested that the application of

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Omnipaque™ could be used not only for obtaining speckle images with enhanced resolution, but also for monitoring some complications related to increased vascular endothelial permeability

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like in diabetes.

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11. Optical coherence tomography Optical coherence tomography (OCT) is a noninvasive method of imaging the internal structure of optically inhomogeneous objects that allows for the study of tissue at high resolution

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and without disturbing its integrity [207]. In particular, it can be successfully used for differentiation of inhomogeneities in skin and mucosa [208, 209]. However, the multiple

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scattering essentially worsens the image resolution, probing depth, and the precision of localization.

Using OCT with immersion OC, surface tissue layers can be rapidly impregnated with OCAs. In Refs. [210, 211] it was demonstrated by Wang et al. that the application of immersion liquids increases the probing depth nearly by 3.5 folds and significantly improves the image contrast of the internal inhomogeneities. Also, the possibility of observation of subepidermal cavity, malignant melanoma diagnostics, and control of the human skin scattering properties under the application of glycerol and propylene glycol to its surface was shown by the example of OCT imaging in vitro and in vivo [61]. Moreover, the variation rate of the OCT A-scan slope in the course of optical clearing allows an additional differentiation of the healthy and tumour tissue [88,212-214]. 22

ACCEPTED MANUSCRIPT The use of enhancer-OCA solutions contributed to improve the OCT images significantly [30]. For example, visualization of cerebral blood vessels can be realized using Doppler OCT without any damaging impact of the cranial bone. Also, the velocity of blood flow in the vein can be determined [187]. The use of sonication with enhancer-OCA solutions on skin can significantly improve OCT imaging depth, which was demonstrated in several studies [133,215-217]. Thus, in Ref. [216] it was shown that after complex processing with thiazone, PEG-400, and ultrasound (US)

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the observation depth increased by 41.3% in comparison with the non treated control samples. On the basis of OCT data presented in Ref. [133] it was demonstrated that the maximal

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efficiency for 20 min of skin OC in vivo was observed under the combined use of US-DMSOOCA (about 33%), compared to US-OCA (about 18%) and DMSO-OCA (about 9%).

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Liu et al. [218] showed that increment of glucose concentration cause changes in stiffness of cartilage tissues. The stiffness decreased by 44%, 55% and 76% for 30%, 40% and 70%

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glucose solutions respectively. It was suggested that stiffness decreased due to the OCA replacing water in the extracellular matrix and partly dehydrating the cartilage.

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Zhao et al. [219] demonstrated possibility of strong enhancement in OCA permeability and optical clearing effect by applying of US and glucose synergy. It was found that the permeability of glucose in cancerous tissue ((12.1±0.34)10-6cm/s) was 1.95-fold greater than in

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normal tissue ((6.3±0.16)10-6cm/s) within the same OCA treatment time. Genina et al. used US

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combining with chemical enhancer DMSO for improvement of glycerol and PEG-400 clearing effect on skin [220]. Application of US-DMSO-OCA (4 min treatment), US-OCA (4 min treatment), DMSO-OCA (20 min treatment) and only OCA (20 min treatment) has been

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investigated and compared. Results showed that attenuation coefficient of intact skin decreased by 31%, 19% and 5% for US-DMSO, US-OCA and DMSO-OCA combinations respectively.

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Using of only OCA without US and DMSO did not provide any noticeable clearing effect within treatment time.

Topical application of OCA solution can reduce the tissues electro-kinetic response [221]. Moreover, it was found that topical application of OCA cause tissue cooling allowing reducing the temperature induced by the electric current by a several degrees. Investigation of 40% glucose solution influence on bovine skeletal muscle in vitro showed 4-fold increase in the image contrast for OCT measurements at the depth of 360 µm [222]. Also, significant increase in image contrast (2.4-fold) has been obtained at the depths up to 800 µm. Bykov et al. [223] investigated iohexol solution (OmnipaqueTM) capability for optical clearing of cartilage tissue. It was shown that optical clearing saturated after 50 min allowing 23

ACCEPTED MANUSCRIPT observing depths by OCT up to 0.9 mm. However, even after 15 min it is possible to detect rear cartilage boundary. Moreover, results showed that low osmolality provides minimal changes of sample thickness. The topical application of OCA on melanoma tissues in vivo showed enhancement of melanoma microvasculature observation depth by OCT from 300 µm to 750 µm [224]. Zhernovaya et al. [225] showed that intravenous injection of PEG-300 combining with intradermal injection of fructose saline solution cause fast clearing effect in mice in vivo, while

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injection of OCAs only into blood vessels does not provide any significant clearing effect. However, the use of fractional ablation of epidermis for improvement of skin

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permeability in vivo can impair the OC of the skin, especially immediately after application of OCA. It was shown that skin surface ablation leads to local edema of the affected region that

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increases the scattering coefficient. In the upper layers, the intense evaporation of water from the ablation zone facilitates the OC at the expense of tissue dehydration. Nevertheless, at a depth

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150-400 µm, the dehydration of upper layers cannot completely compensate for an increase in light scattering [226]. Therefore, the optical probing depth of OCT does not increase for at least

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than 30 min post ablation [227].

12. Conclusion

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This paper provides a review of recent developments, specific features, methods and

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application of the optical clearing techniques with the focus on in vivo application of optical methods to the tissue and especially to the skin. The physical, molecular and physiological mechanisms have been described. In this review, the progress in skin optical clearing for

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multiphoton microscopy, Raman microscopy, NIR spectroscopy, confocal microscopy, optical coherence tomography, and speckle contrast imaging has been described in detail.

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The application of OCA on a tissue allows for controlling the optical properties of tissue. Reduction of tissue scattering gives significantly bigger observation depths for a variety of optical imaging methods suitable for clinical applications. In particular, the application of OCAs allows for imaging mouse brain with two-photon microscopy 7 mm in depth and up to 2 mm in depth with confocal microscopy. 400-500 µm in depth have been reached in skin after OCA treatment. The application of OCAs allows one to improve the relative contrast for multiphoton measurements by the factor of 16.0 and 3.0 fold increases in raw signal for NIRs measurements. Moreover, OCA application provides incensement of resolution for speckle contrast measurements and 13 fold fluorescence signal increase. The application of OCAs can increase the probing depth by almost 3.5 times for OCT measurements and significantly improve the image contrast of the internal inhomogeneities. 24

ACCEPTED MANUSCRIPT In general, the mechanism of optical clearing is usually combination of several factors: molecular dynamical reactions between tissue and optical clearing cause dehydration of tissue; refractive index matching; collagen dissociation. The most commonly used OCAs are generally nontoxic and safe for using with biological tissues in vivo. However, long application of highly concentrated OCAs can induce negative effect on tissue such as local hemostasis, tissue shrinkage, etc. So, further understanding of the optical clearing mechanisms and searching for safe and non-toxic clearing agents is an important goal for noninvasive clinical optical imaging

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and spectroscopy of the tissues. Finally, it should be noted that majority of OCAs are cryoprotectors and widely used to

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keep living tissues due to their unique properties of high osmolarity and low-temperature freezing ability that prevent formation of ice crystals and allow for keeping tissue undamaged at

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low temperatures [228, 229].

As far as OC is becoming an effective and cheap tool for significant improvement of

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optical imaging methods, we belive that in near future a lot of new OCAs will be developed with aim to provide fast and safe clearing. Also, a lot of researches will be focused on these fingings

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for effective enhancement of the depths under investigation during the spectroscopic analysis of the tissue, such as dermis, mucous, bone, etc.

The efficiency of tissue investigations can be considerably improved by combined use of

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several optical techniques simultaneously with OC. So, new multimodal clinical optical imaging

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systems and technologies will be implemented. Moreover, in-built OC can be used in these systems.

Only few tissues such as cerebral membrane, skin and eye sclera has been studied more

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or less fully. However, more accurate studies of these and other tissues should be continued. The mucosal tissue of different organs, esophagus, muscle, myocardium, vessel wall, liver lymph

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node, brain, stomach, kidney and liver tissues are of great interest to be cleared for light diagnostic, therapy or surgery. For hard tissues, OC of dentin and cement, tendon, cranial bone, tooth enamel, cartilage and ligament could be important to provide more efficient laser therapy and surgery. So, laser disruption of pathological abnormalities, laser tattoo removal, mucosal tumor imaging, etc. will be significantly improved in combination with OC technique. Thus, OC technique has a great potential for spectroscopic investigations in life science owing to its simplicity, low cost and low risk.

Acknowledgements This article was supported by the Research Program of Saratov National Research State University, the Russian Ministry of Education and Science grant 17.1223.2017/AP, the Russian 25

ACCEPTED MANUSCRIPT Governmental grant 14.Z50.31.0044, Tomsk State University Competitiveness Improvement Programme and The Foundation for Skin Physiology of the Donor Association for German Science and Humanities.

Disclosures The presenting authors do not have any financial conflicts of interest regarding the content of

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this manuscript.

[1]

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References

W. Drexler, J.G. Fujimoto (Eds.), Optical Coherence Tomography: Technology and

SC

Applications, 2nd ed. Springer International Publishing Switzerland, Cham, Heidelberg, New York, Dordrecht, London, 2015

V. V. Tuchin (Ed.), Handbook of Coherent-Domain Optical Methods: Biomedical

NU

[2]

Diagnostics, Environmental Monitoring and Materials Science, 2nded., Springer Reference,

[3]

MA

Science & Business Media, New York, 2013.

R. Shi, M. Chen, V.V. Tuchin, D. Zhu, Accessing to arteriovenous blood flow dynamics

response using combined laser speckle contrast imaging and skin optical clearing, Biomed. Opt.

M.E. Darvin, H. Richter, Y.J. Zhu, M.C. Meinke, F. Knorr, S.A. Gonchukov, K. Koenig,

PT E

[4]

D

Exp. 6 (2015) 1977-1989.

J. Lademann, Comparison of in vivo and ex vivo laser scanning microscopy and multiphoton tomography application for human and porcine skin imaging, Quantum Electronics 44 (2014)

[5]

CE

646-651.

M. Ulrich, M. Klemp, M.E. Darvin, K. Konig, J. Lademann, M.C. Meinke, In vivo

detection of basal cell carcinoma: comparison of a reflectance confocal microscope and a

[6]

AC

multiphoton tomograph, J. Biomed. Opt. 18 (2013) 061229. R. Vyumvuhore, A. Tfayli, O. Piot, M. Le Guillou, N. Guichard, M. Manfait, A. Baillet-

Guffroy, Raman spectroscopy: in vivo quick response code of skin physiological status, J. Biomed. Opt. 19 (2014) 111603. [7]

V. D'Elia, G. Montalvo, C.G. Ruiz, V.V. Ermolenkov, Y. Ahmed, I.K. Lednev,

Ultraviolet resonance Raman spectroscopy for the detection of cocaine in oral fluid, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 188 (2018) 338-340. [8]

C.-S. Choe, J. Schleusener, J. Lademann, M.E. Darvin, Keratin-water-NMF interaction

as a three layer model in the human stratum corneum using in vivo confocal Raman microscopy, Scientific Reports, 7(1) (2017) 15900. 26

ACCEPTED MANUSCRIPT [9]

C. Choe, J. Lademann, M.E. Darvin, Analysis of Human and Porcine Skin in vivo/ex

vivo for Penetration of Selected Oils by Confocal Raman Microscopy, Skin Pharmacol. Physiol. 28 (2015) 318-330. [10]

C.-S. Choe, J. Lademann, M.E. Darvin, A depth-dependent profile of the lipid

conformation and lateral packing order of the stratum corneum in vivo measured using Raman microscopy, Analyst 141 (2016) 1981-1987. [11]

C.-S. Choe, J. Lademann, M.E. Darvin, Depth profiles of hydrogen bound water

PT

molecule types and their relation to lipid and protein interaction in the human stratum corneum in vivo, Analyst 141 (2016) 6329-6337.

Y. Ozaki, K. Kneipp, R. Aroca (Eds.), Frontiers of surface-enhanced Raman scattering:

RI

[12]

single nanoparticles and single cells, John Wiley & Sons, 2014.

Y.S. Yamamoto, M. Ishikawa, Y. Ozaki, T. Itoh, Fundamental studies on enhancement

SC

[13]

and blinking mechanism of surface-enhanced Raman scattering (SERS) and basic applications

[14]

NU

of SERS biological sensing, Frontiers of Physics 9 (2014) 31-46. Y. Wang, W. Ji, Z. Yu, R. Li, X. Wang, W. Song, W. Ruan, B. Zhao, Y. Ozaki,

MA

Contribution of hydrogen bonding to charge-transfer induced surface-enhanced Raman scattering of an intermolecular system comprising p-aminothiophenol and benzoic acid, Physical Chemistry Chemical Physics 16 (2014) 3153-3161. R. Gillies, G. Zonios, R.R. Anderson, N. Kollias, Fluorescence excitation spectroscopy

D

[15]

[16]

PT E

provides information about human skin in vivo, J. Invest. Dermatol. 115 (2000) 704-707. I. Ferulova, A. Lihachev, J. Spigulis, Photobleaching effects on in vivo skin

autofluorescence lifetime, J. Biomed. Opt. 20 (2015) 051031. W. Denk, J.H. Strickler, W.W. Webb, Two-photon laser scanning fluorescence

CE

[17]

microscopy, Science 248 (1990) 73-76. K. König, A.P. Raphael, L. Lin, J.E. Grice, H.P. Soyer, H.G. Breunig, M.S. Roberts,

AC

[18]

T.W. Prow, Applications of multiphoton tomographs and femtosecond laser nanoprocessing microscopes in drug delivery research, Advanced Drug Delivery Reviews 63 (2011) 388-404. [19]

B.G. Wang, K. König, K.J. Halbhuber, Two-photon microscopy of deep intravital

tissues and its merits in clinical research, J. Microsc. 238 (2010) 1-20. [20]

R. Cicchi, F.S. Pavone, D. Massi, D.D. Sampson, Contrast and depth enhancement in

two-photon microscopy of human skin ex vivo by use of optical clearing agents, Optics Express 13 (2005) 2337-2344. [21]

C. Czekalla, K.H. Schönborn, S. Markworth, M. Ulrich, D. Göppner, H. Gollnick, J.

Röwert-Huber, M.E. Darvin, J. Lademann, M.C. Meinke, Technical parameters of vertical in

27

ACCEPTED MANUSCRIPT vivo multiphoton microscopy: a critical evaluation of the flyscanning method, Laser Physics Letters 12 (2015) 085602. [22]

M. Weinigel, H.G. Breunig, M. Kellner-Höfer, R. Bückle, M.E. Darvin, M. Klemp, J.

Lademann, K. König, In vivo histology: optical biopsies with chemical information using clinical multiphoton/CARS tomography, Laser Physics Letters, 11 (2014) 055601. [23]

K. Konig, Clinical multiphoton tomography, J. Biophotonics 1 (2008) 13-23.

[24]

E.A. Shirshin, Y.I. Gurfinkel, A.V. Priezzhev, V.V. Fadeev, J. Lademann, M.E. Darvin,

PT

Two-photon autofluorescence lifetime imaging of human skin papillary dermis in vivo: assessment of blood capillaries and structural proteins localization, Sci Rep. 7 (2017) 1171. F.S. Pavone and P. J. Campagnola (Eds.), Second Harmonic Generation Imaging, CRC

RI

[25]

Press, Taylor & Francis Group, Boca Raton, London, New York, 2014. V.V. Tuchin, Tissue Optics: Light Scattering Methods and Instruments for Medical

SC

[26]

Diagnosis, Bellingham, SPIE Press, 2015.

D.A. Boas, A fundamental limitation of linearized algorithms for diffuse optical

NU

[27]

tomography, Optics Express 1 (1997) 404-413.

C.L. Smithpeter, A.K. Dunn, A.J. Welch, R. Richards-Kortum, Penetration depth limits

MA

[28]

of in vivo confocal reflectance imaging, Appl. Opt. 37 (1998) 2749-2754. [29]

V.V. Tuchin, I.L. Maksimova, D.A. Zimnyakov, I.L. Kon, A.H. Mavlutov, A.A. Mishin,

D

Light propagation in tissues with controlled optical properties, J. Biomed. Opt. 2 (1997) 401-

[30]

PT E

417.

K.V. Larin, M.G. Ghosn, A.N. Bashkatov, E.A. Genina, N.A. Trunina, V.V. Tuchin,

Optical clearing for OCT image enhancement and in-depth monitoring of molecular diffusion,

[31]

CE

IEEE Journal of Selected Topics in Quantum Electronics 18 (2012) 1244-1259. D. Zhu, K. Larin, Q. Luo, V.V. Tuchin, Recent progress in tissue optical clearing, Laser

[32]

AC

& Photonics Reviews 7 (2013) 732-757. X. Wen, S.L. Jacques, V.V. Tuchin, D. Zhu, Enhanced optical clearing of skin in vivo

and optical coherence tomography in-depth imaging, J. Biomed. Opt. 17 (2012) 066022. [33]

Y.-Y. Fu, S.-C. Tang, Optical clearing facilitates integrated 3D visualization of mouse

ileal microstructure and vascular network with high definition, Microvascular Research 80 (2010) 512-521. [34]

J. Sharpe, Optical projection tomography, Annual Review of Biomedical Engineering 6

(2004) 209-228. [35]

O. Nadiarnykh, P.J. Campagnola, Retention of polarization signatures in SHG

microscopy of scattering tissues through optical clearing, Optics Express 17 (2009) 5794–5806.

28

ACCEPTED MANUSCRIPT [36]

O.I. Efimova, K.V. Anokhin, Enhancement of Optical Transmission Capacity of Isolated

Structures in the Brain of Mature Mice, Bull. Exp. Biol. Med. 147 (2009) 3–6. [37]

V. Hovhannisyan, P.-S. Hu, S.-J. Chen, C.-S. Kim, C.-Y. Dong, Elucidation of the

mechanisms of optical clearing in collagen tissue with multiphoton imaging, J. Biomed. Opt. 18 (2013) 046004. [38]

O. Nadiarnykh, P. J. Campagnola, SHG and optical clearing, in F.S. Pavone, P.J.

Campagnola (Eds.), Second Harmonic Generation Imaging, CRC Press, Taylor & Francis

[39]

PT

Group, Boca Raton, London, New York, 2014, pp. 169-189. R. LaComb, O. Nadiarnykh, S. Carey, P.J. Campagnola, Quantitative second harmonic

RI

generation imaging and modeling of the optical clearing mechanism in striated muscle and tendon, J. Biomed. Opt. 13 (2008) 021109.

S. Plotnikov, V. Juneja, A.B. Isaacson, W.A. Mohler, P.J. Campagnola, Optical clearing

SC

[40]

for improved contrast in second harmonic generation imaging of skeletal muscle, Biophysical J.

[41]

NU

90 (2006) 328-339.

E.A. Genina, A.N. Bashkatov, Yu.P. Sinichkin, I.Yu. Yanina, V.V.Tuchin, Optical

MA

clearing of biological tissues: prospects of application in medical diagnostics and phototherapy, Journal of Biomedical Photonics & Engineering 1 (2015) 22-58. [42]

V.V. Tuchin, L.V. Wang, D.A. Zimnyakov, Optical Polarization in Biomedical

R. Drezek, A. Dunn, R. Richards-Kortum, Light scattering from cells: finite-difference

PT E

[43]

D

Applications, Springer-Verlag, New York, NY, USA, 2006.

time-domain simulations and goniometric measurements, Appl. Opt. Vol. 38 (1999) 3651-3661. [44]

K. Sokolov, R. Drezek, K. Gossage, R. Richards-Kortum, Reflectance spectroscopy with

[45]

D.W. Leonard, K.M. Meek, Refractive indices of the collagen fibrils and extrafibrillar

AC

317.

CE

polarized light: is it sensitive to cellular and nuclear morphology, Optics Express 5 (1999) 302-

material of the corneal stroma, Biophysical J. 72 (1997) 1382-1387. [46]

A.G. Borovoi, E.I. Naats, U.G. Oppel, Scattering of light by a red blood cell, J. Biomed.

Opt. 3 (1998) 364-372. [47]

A.N. Yaroslavsky, A.V. Priezzhev, J. Rodriguez, I.V. Yaroslavsky, H. Battarbee, Optics

of blood, in: Handbook of Optical Biomedical Diagnostics, V.V. Tuchin (Ed.), PM107 SPIE Press, Bellingham, WA, USA, 2002, pp. 169–216. [48]

G. Mazarevica, T. Freivalds, A. Jurka, Properties of erythrocyte light refraction in

diabetic patients, J. Biomed. Opt. 7 (2002) 244-247.

29

ACCEPTED MANUSCRIPT [49]

M. Friebel, M. Meinke, Model function to calculate the refractive index of native

hemoglobin in the wavelength range of 250-1100 nm dependent on concentration, Appl. Opt. 45 (2006) 2838-2842. [50]

E.A. Genina, A.N. Bashkatov, V.V. Tuchin, Tissue optical immersion clearing, Expert

Review of Medical Devices 7 (2010) 825-842. [51]

D.K. Tuchina, R. Shi, A.N. Bashkatov, E.A. Genina, D. Zhu, Q. Luo, V.V. Tuchin, Ex

vivo optical measurements of glucose diffusion kinetics in native and diabetic mouse skin, J.

[52]

PT

Biophotonics 8 (2015) 332-346. A.K. Bui, R.A. McClure, J. Chang, C. Stoianovici, J. Hirshburg, A.T. Yeh, B. Choi,

RI

Revisiting optical clearing with dimethyl sulfoxide (DMSO), Lasers Surg. Med. 41 (2009) 142148.

H. Hama, H. Kurokawa, H. Kawano, R. Ando, T. Shimogori, H. Noda, K. Fukami, A.

SC

[53]

Sakaue-Sawano, A. Miyawaki, Scale: a chemical approach for fluorescence imaging and

[54]

NU

reconstruction of transparent mouse brain, Nature Neurosci. 14 (2011) 1481–1488. H. Hama, H. Hioki, K. Namiki, T. Hoshida, H. Kurokawa, F. Ishidate, T. Kaneko, T.

MA

Akagi, T. Saito, T. Saido, A. Miyawaki, Sca/eS: an optical clearing palette for biological imaging, Nature Neurosci. 18 (2015) 1518-1529. [55]

V.V. Tuchin, X. Xu, R.K. Wang, Dynamic optical coherence tomography in studies of

D

optical clearing, sedimentation, and aggregation of immersed blood, Appl. Opt. 41 (2002) 258-

[56]

PT E

271.

A.T. Yeh, B. Choi, J.S. Nelson, B.J. Tromberg, Reversible dissociation of collagen in

tissues, J. Invest. Dermatol. 121 (2003) 1332-1335. J. Hirshburg, B. Choi, J. S. Nelson, A.T. Yeh, Correlation between collagen solubility

CE

[57]

and skin optical clearing using sugars, Lasers Surg. Med. 39 (2007) 140-144. J.M. Hirshburg, K.M. Ravikumar, W. Hwang, A.T. Yeh, Molecular basis for optical

AC

[58]

clearing of collagenous tissues, J. Biomed. Opt. 15 (2010) 055002. [59]

J. Hirshburg, B. Choi, J.S. Nelson, A.T. Yeh, Collagen solubility correlates with skin

optical clearing, J. Biomed. Opt. 11 (2006) 040501. [60]

X. Wen, Z. Mao, Z. Han, V.V. Tuchin, D. Zhu, In vivo skin optical clearing by glycerol

solutions: mechanism, J. Biophotonics 3 (2010) 44-52. [61]

V.V. Tuchin, Optical Clearing of Tissues and Blood, PM154, SPIE Press Bellingham,

WA, USA, 2006. [62]

V.V. Tuchin, A clear vision for laser diagnostics (Review), IEEE J. Selected Topics in

Quantum Electronics 13 (2007) 1621-1628.

30

ACCEPTED MANUSCRIPT [63]

A. Bykov, T. Hautala, M. Kinnunen, A. Popov, S. Karhula, S. Saarakkala, M.T.

Nieminen, V. Tuchin, I. Meglinski, Imaging of subchondral bone by optical coherence tomography upon optical clearing of articular cartilage, J. Biophotonics 9 (2016) 270-275. [64]

G.A. Askar’yan, The increasing of laser and other radiation transport through soft turbid

physical and biological media, Sov. J. Quantum Electron. 9 (1982) 1379-1383. [65]

A.P. Ivanov, S.A. Makarevich, A.Ya. Khairulina, Propagation of radiation in tissues and

liquids with densely packed scatterers, J. Appl. Spectrosc. 47 (1988) 662–668. P. Rol, P. Nieder, U. Durr, P-D. Henchoz, F. Fankhauser, Experimental investigations on

PT

[66]

the light scattering properties of the human sclera, Laser and light in Ophthalmol. 3 (1990) 201-

[67]

RI

212.

E.K. Chan, B. Sorg, D. Protsenko, M. O’Neil, M. Motamedi, A.J. Welch, Effects of

SC

compression on soft tissue optical properties, IEEE J. Selected Topics in Quantum Electronics 2 (1996) 943-950.

G. Vargas, E.K. Chan, J.K. Barton, H.G. Rylander III, A.J. Welch, Use of an agent to

NU

[68]

reduce scattering in skin, Lasers Surg. Med. 24 (1999) 133-141. E.A. Genina, A.N. Bashkatov, V.V. Tuchin, Glucose-induced optical clearing effects in

MA

[69]

tissues and blood, in: Handbook of Optical Sensing of Glucose in Biological Fluids and Tissues, V.V. Tuchin (Ed.), Taylor & Francis Group LLC, CRC Press, FL, USA, 2009, 657–

E.A. Genina, A.N. Bashkatov, V.I. Kochubey, V.V. Tuchin, Optical clearing of human

PT E

[70]

D

692.

dura mater, Optics and Spectroscopy 98 (2005) 470-476. [71]

A.N. Bashkatov, E.A. Genina, Yu.P. Sinichkin, V.I. Kochubey, N.A. Lakodina, V.V.

[72]

Y. Huang, K.M. Meek, Swelling studies on the cornea and sclera: the effects of pH and

AC

3318.

CE

Tuchin, Glucose and mannitol diffusion in human dura mater, Biophys. J. 85 (2003) 3310-

ionic strength, Biophysical J. 77 (1999) 1655-1665. [73]

E.A. Genina, A.N. Bashkatov, V.V. Tuchin, Optical clearing of cranial bone, Advances

in Optical Technologies 2008 (2008) 267867. [74]

A. Roggan, M. Friebel, K. Dorschel, A. Hahn, G. Muller, Optical properties of

circulating human blood in the wavelength range 400-2500 nm, J. Biomed. Opt. 4 (1999) 3646. [75]

M. Friebel, J. Helfmann, M. Meinke, Influence of osmolarity on the optical properties of

human erythrocytes, J. Biomed. Opt. 15 (2010) 055005. [76]

I. Fine, B. Fikhte, L.D. Shvartsman, RBC aggregation assisted light transmission

through blood and occlusion oximetry, Proc. SPIE 4162 (2000) 130-139. 31

ACCEPTED MANUSCRIPT [77]

A.N. Bashkatov, D.M. Zhestkov, E.A. Genina, V.V. Tuchin, Immersion clearing of

human blood in the visible and near-infrared spectral regions, Optics and Spectroscopy 98 (2005) 638-646. [78]

Y. Ozaki, H. Kitabata, H. Tsujioka, S. Hosokawa, M. Kashiwagi, K. Ishibashi, K.

Komukai, T. Tanimoto, Y. Ino, S. Takarada, T. Kubo, K. Kimura, A. Tanaka, K. Hirata, M. Mizukoshi, T. Imanishi, T. Akasaka, Comparison of contrast media and low-molecular-weight dextran for frequency-domain optical coherence tomography, Circulation J. 76 (2012) 922–997. V.V. Tuchin, D.M. Zhestkov, A.N. Bashkatov, E.A. Genina, Theoretical study of

PT

[79]

immersion optical clearing of blood in vessels at local hemolysis, Optics Express 12 (2004)

[80]

RI

2966-2971.

G. Popescu, T. Ikeda, C. Best, K. Badizadegan, R.R. Dasari, M.S. Feld, Erythrocyte

SC

structure and dynamics quantified by Hilbert phase microscopy, J. Biomed. Opt. 10 (2005) 060503.

O. Zhernovaya, V.V. Tuchin, and M. J. Leahy, Blood optical clearing study by optical

NU

[81]

coherence tomography, J. Biomed. Opt. 18 (2013) 026014. E.A. Genina, A.N. Bashkatov, Yu.P. Sinichkin, V.V. Tuchin, Optical clearing of the eye

MA

[82]

sclera in vivo caused by glucose, Quantum Electronics 36 (2006) 1119-1124. [83]

G. Vargas, J.K. Barton, A.J. Welch, Use of hyperosmotic chemical agent to improve the

A.N. Bashkatov, A.N. Korolevich, V.V. Tuchin, Yu.P. Sinichkin, E.A. Genina, M.M.

PT E

[84]

D

laser treatment of cutaneous vascular lesions, J. Biomed. Opt. 13 (2008) 021114.

Stolnitz, N.S. Dubina, S.I. Vecherinski, M.S. Belsley, In vivo investigation of human skin optical clearing and blood microcirculation under the action of glucose solution, Asian J.

[85]

CE

Physics 15 (2006) 1-14.

E.I. Galanzha, V.V. Tuchin, A.V. Solovieva, T.V. Stepanova, Q. Luo, H. Cheng, Skin

AC

backreflectance and microvascular system functioning at the action of osmotic agents, J. Phys. D: Appl. Phys. 36 (2003) 1739-1746. [86]

D. Zhu, J. Zhang, H. Cui, Z. Mao, P. Li, Q. Luo, Short-term and long-term effects of

optical clearing agents on blood vessels in chick chorioallantoic membrane, J. Biomed. Opt. 13 (2008) 021106. [87]

E.A. Genina, A.N. Bashkatov, A.A. Korobko, E.A. Zubkova, V.V. Tuchin, I.

Yaroslavsky, G.B. Altshuler, Optical clearing of human skin: comparative study of permeability and dehydration of intact and photothermally perforated skin, J. Biomed. Opt. 13 (2008) 021102.

32

ACCEPTED MANUSCRIPT [88]

Z. Zhu, G. Wu, H. Wei, H. Yang, Y. He, S. Xie, Q. Zhao, X. Guo, Investigation of the

permeability and optical clearing ability of different analytes in human normal and cancerous breast tissues by spectral domain OCT, J. Biophotonics 5 (2012) 536-543. [89]

B. Choi, L. Tsu, E. Chen, T.S. Ishak, S.M. Iskandar, S. Chess, J.S. Nelson,

Determination of chemical agent optical clearing potential using in vitro human skin, Lasers Surg. Med. 36 (2005) 72-75. [90]

Z. Mao, D. Zhu, Y. Hu, X. Wen, Z. Han, Influence of alcohols on the optical clearing

[91]

PT

effect of skin in vitro, J. Biomed. Opt. 13 (2008) 021104. E.A. Genina, A.N. Bashkatov, Yu.P. Sinichkin, V.V. Tuchin, Optical clearing of skin

RI

under action of glycerol: ex vivo and in vivo investigations, Optics and Spectroscopy 109 (2010) 225-231.

S.G. Proskurin, I.V. Meglinski, Optical coherence tomography imaging depth

SC

[92]

enhancement by superficial skin optical clearing, Laser Physics Letters 4 (2007) 824-826. M.H. Khan, B. Choi, S. Chess, K.M. Kelly, J. McCullough, J.S. Nelson, Optical clearing

NU

[93]

of in vivo human skin: Implications for light-based diagnostic imaging and therapeutics, Laser

[94]

MA

Surg Med. 34 (2004) 83-85.

M.G. Ghosn, V.V. Tuchin, K.V. Larin, Depth-resolved monitoring of glucose diffusion

in tissues by using optical coherence tomography, Opt. Lett. 31 (2006) 2314–2316. A.N. Bashkatov, E.A. Genina, V.V. Tuchin, Measurement of glucose diffusion

D

[95]

PT E

coefficients in human tissues, in: Handbook of Optical Sensing of Glucose in Biological Fluids and Tissues, V.V. Tuchin (Ed.), Taylor & Francis Group LLC, CRC Press, 2009, 587–621. [96]

A.N. Bashkatov, E.A. Genina, Yu.P. Sinichkin, V.I. Kochubei, N.A. Lakodina, V.V.

CE

Tuchin, Estimation of the glucose diffusion coefficient in human eye sclera, Biophysics 48 (2003) 292-296.

J. Wang, N. Ma, R. Shi, Y. Zhang, T. Yu, D. Zhu, Sugar-induced skin optical clearing:

AC

[97]

from molecular dynamics simulation to experimental demonstration, IEEE J. Selected Topics in Quantum Electronics 20 (2014) 7101007. [98]

J. Jiang, R.K. Wang, Comparing the synergistic effects of oleic acid and dimethyl

sulfoxide as vehicles for optical clearing of skin tissue in vitro, Phys. Med. Biol. 49 (2004) 5283–5294. [99]

Y. Liu, X. Yang, D. Zhu, Q. Luo, Optical clearing agents improve photoacoustic

imaging in the optical diffusive regime, Optics Letters 38 (2013) 4236-4239. [100]

X. Xu, R.K. Wang, Synergistic effect of hyperosmotic agents of dimethyl sulfoxide and

glycerol on optical clearing of gastric tissue studied with near infrared spectroscopy, Phys. Med. Biol. 49 (2004) 457–468. 33

ACCEPTED MANUSCRIPT [101]

J. Jiang, M. Boese, P. Turner, R. K. Wang, Penetration kinetics of dimethyl sulphoxide

and glycerol in dynamic optical clearing of porcine skin tissue in vitro studied by Fourier transform infrared spectroscopic imaging, J. Biomed. Opt. 13 (2008) 021105. [102]

Z. Deng, L. Jing, N. Wu, P. Iv, X. Jiang, Q. Ren, C. Li, Viscous optical clearing agent

for in vivo optical imaging, J. Biomed. Opt. 19 (2014) 076019. [103]

L. Guo, R. Shi, C. Zhang, D. Zhu, Z. Ding, P. Li, Optical coherence tomography

angiography offers comprehensive evaluation of skin optical clearing in vivo by quantifying

[104]

PT

optical properties and blood flow imaging simultaneously, J. Biomed. Opt. 21 (2016) 081202. X. Jin, Z. Deng, J. Wang, Q. Ye, J. Mei, W. Zhou, C. Zhang, J. Tian, Study of the

[105]

RI

inhibition effect of thiazone on muscle optical clearing, J. Biomed. Opt. 21 (2016) 105004. Y. Ding, J. Wang, Z. Fan, D. Wei, R. Shi, Q. Luo, D. Zhu, X. Wei, Signal and depth

SC

enhancement for in vivo flow cytometer measurement of ear skin by optical clearing agents, Biomed. Opt. Exp. 4 (2013) 2518– 2526.

J. Wang, R. Shi, D. Zhu, Switchable skin window induced by optical clearing method

NU

[106]

for dermal blood flow imaging, J. Biomed. Opt. 18 (2013) 061209. H. Zhong, Z. Guo, H. Wei, L. Guo, C. Wang, Y. He, H. Xiong, S. Liu, Synergistic effect

MA

[107]

of ultrasound and Thiazone - PEG 400 on human skin optical clearing in vivo, Photochemistry and Photobiology 86 (2010) 732-737.

R. Shi, L. Guo, C. Zhang, W. Feng, P. Li, Z. Ding, D. Zhu, A useful way to develop

D

[108]

[109]

PT E

effective in vivo skin optical clearing agents, J. Biophotonics 10 (2017) 887-895. A.N. Bashkatov, Control of tissue optical properties by means of osmotically active

immersion liquids, Ph. D. thesis, Saratov State University, Saratov, Russia, 2002. I.V. Larina, E.F. Carbajal, V.V. Tuchin, M.E. Dickinson, K.V. Larin, Enhanced OCT

CE

[110]

imaging of embryonic tissue with optical clearing, Laser Physics Letters 5 (2008) 476-479. N. Sudheendran, M. Mohamed, M.G. Ghosn, V.V. Tuchin, K.V. Larin, Assessment of

AC

[111]

tissue optical clearing as a function of glucose concentration using optical coherence tomography, J. Innov. Opt. Health Sci. 3 (2010) 169-176. [112]

M.V. Schulmerich, J.H. Cole, K.A. Dooley, M.D. Morris, J.M. Kreider, S.A. Goldstein,

Optical clearing in transcutaneous Raman spectroscopy of murine cortical bone tissue, J. Biomed. Opt. 13 (2008) 021108. [113]

A.Yu. Sdobnov https://orcid.org/0000-0001-7282-7179, M.E. Darvin, J. Lademann,

V.V. Tuchin, A comparative study of ex vivo skin optical clearing using two-photon microscopy, Journal of Biophotonics. – 2017 Jan 30. doi: 10.1002/jbio.201600066. [Epub ahead of print]

34

ACCEPTED MANUSCRIPT [114]

A.Yu. Sdobnov https://orcid.org/0000-0001-7282-7179, V.V. Tuchin, J. Lademann,

M.E. Darvin, Confocal Raman microscopy supported by optical clearing treatment of the skin - influence on collagen hydration, J. Phys. D: Appl. Phys. 50 (2017) 285401. [115]

J. Wang, D. Zhu, M. Chen, X. Liu, Assessment of optical clearing induced improvement

of laser speckle contrast imaging, J. Innov. Opt. Health Sci. 3 (2010) 159-167. [116]

T. Yu, Y. Qi, H. Gong, Q. Luo, D. Zhu, Optical clearing for multi-scale biological

tissues, Journal of Biophotonics (2017). https://doi.org/10.1002/jbio.201700187 K. Chung, J. Wallace, S.-Y. Kim, S. Kalyanasundaram, A.S. Andalman, T.J. Davidson,

PT

[117]

J.J. Mirzabekov, K.A. Zalocusky, J. Mattis, A.K. Denisin, S. Pak, H. Bernstein, C.

RI

Ramakrishnan, L. Grosenick, V. Gradinaru, K. Deisseroth, Structural and molecular interrogation of intact biological systems, Nature 497 (2013) 332-337. A.-S. Chiang, Aqueous tissue clearing solution, U.S. Patent No. 6,472,216. 29 Oct.

SC

[118] 2002.

M.T. Ke, S. Fujimoto, T. Imai, SeeDB: a simple and morphology-preserving optical

NU

[119]

clearing agent for neuronal circuit reconstruction. Nature neuroscience 16 (2013) 1154-1161. H.U. Dodt, U. Leischner, A. Schierloh, N. Jährling, C. P. Mauch, K. Deininger, K.

MA

[120]

Becker, Ultramicroscopy: three-dimensional visualization of neuronal networks in the whole mouse brain, Nature Methods 4 (2007), 331-336. E. A. Susaki, K. Tainaka, D. Perrin, F. Kishino, T. Tawara, T. M. Watanabe, T. Abe,

D

[121]

PT E

Whole-brain imaging with single-cell resolution using chemical cocktails and computational analysis, Cell 157 (2014), 726-739. [122]

G. Vargas, A. Readinger, S.S. Dozier, A.J. Welch, Morphological changes in blood

CE

vessels produced by hyperosmotic agents and measured by optical coherence tomography, Photochem. Photobiol. 77 (2003) 541–549. P.A. Timoshina, E.M. Zinchenko, D.K. Tuchina, M.M. Sagatova, O.V. Semyachkina-

AC

[123]

Glushkovskaya, V.V. Tuchin, Laser speckle contrast imaging of cerebral blood flow of newborn mice at optical clearing, Proc. SPIE 10336 (2017) 1033610. [124]

X. Xu, Q. Zhu, Evaluation of skin optical clearing enhancement with azone as a

penetration enhancer, Opt. Commun. 279 (2007) 223–228. [125]

Z. Zhi, Z. Han, Q. Luo, D. Zhu, Improve optical clearing of skin in vitro with propylene

glycol as a penetration enhancer, J. Innov. Opt. Health Sci. 2 (2009) 269–278. [126]

T. Kurihara-Bergstrom, K. Knutson, L.J. de Noble, CY. Goates, Percutaneous

absorption enhancement of an ionic molecule by ethanol–water system in human skin, Pharm. Res. 7 (1990) 762–766.

35

ACCEPTED MANUSCRIPT [127]

E.A. Genina, A.N. Bashkatov, V.V. Tuchin, Effect of ethanol on the transport of

methylene blue through stratum corneum, Med. Laser Appl. 23 (2008) 31–38. [128]

I. Vejnovic, L. Simmler, G. Betz, Investigation of different formulations for drug

delivery through the nail plate, Int. J. Pharmaceutics 386 (2010) 185-194. [129]

R. Notman, W.K. Den Otter, M.G. Noro, W.J. Briels, J. Anwar, The permeability

enhancing mechanism of DMSO in ceramide bilayers simulated by molecular dynamics, Biophys. J. 93 (2007) 2056–2068. P.J. Caspers, A.C. Williams, E.A. Carter, H.G.M. Edwards, B.W. Barry, H.A. Bruining,

PT

[130]

G.J. Puppels, Monitoring the penetration enhancer dimethyl sulfoxide in human stratum

[131]

RI

corneum in vivo by confocal Raman spectroscopy, Pharm. Res. 19 (2002) 1577-1580. C.-H. Chang, E.M. Myers, M.J. Kennelly, N.M. Fried, Optical clearing of vaginal

SC

tissues, ex vivo, for minimally invasive laser treatment of female stress urinary incontinence, J. Biomed. Opt. 22 (2017) 018002.

A.P. Funke, R. Schiller, H.W. Motzkus, C. Gunther, R.H. Muller, R. Lipp, Transdermal

NU

[132]

delivery of highly lipophilic drugs: in vitro fluxes of antiestrogens, permeation enhancers, and

[133]

MA

solvents from liquids formulations, Pharm. Res. 19 (2002) 661-668. E.A. Genina, A.N. Bashkatov, E.A. Kolesnikova, M.V. Basko, G.S. Terentyuk, V.V.

Tuchin, Optical coherence tomography monitoring of enhanced skin optical clearing in rats in

P. Liu, Y. Huang, Z. Guo, J. Wang, Z. Zhuang, S. Liu, Discrimination of dimethyl

PT E

[134]

D

vivo, J. Biomed. Opt. 19 (2014) 021109.

sulphoxide diffusion coefficient in the process of optical clearing by confocal micro-Raman spectroscopy, J. Biomed. Opt. 18 (2013) 020507. S.R. Millon, K.M. Roldan-Perez, K.M. Riching, G.M. Palmer, N. Ramanujam, Effect of

CE

[135]

optical clearing agents on the in vivo optical properties of squamous epithelial tissue, Lasers

[136]

AC

Surg. Med. 38 (2006) 920-927. R. Samatham, K.G. Phillips, S.L. Jacques, Assessment of optical clearing agents using

reflectance-mode confocal scanning laser microscopy, J. Innov. Opt. Health Sci. 3 (2010) 183188. [137]

G. Vargas, K.F. Chan, S.L. Thomsen, A.J. Welch, Use of osmotically active agents to

alter optical properties of tissue: effects on the detected fluorescence signal measured through skin, Lasers Surg. Med. 29 (2001) 213-220. [138]

H.-J. Weigmann, J. Lademann, S. Schanzer, U. Lindemann,·R. von Pelchrzim, H.

Schaefer, W. Sterry, V. Shah, Correlation of the local distribution of topically applied substances inside the stratum corneum determined by tape stripping to differences in bioavailability, Skin Pharmacol. Appl. Skin Physiol. 14 (2001) 98–102. 36

ACCEPTED MANUSCRIPT [139]

W.-R. Lee, R.-Y. Tsai, C.-L. Fang, C.-J. Liu, C.-H. Hu, J.-Y. Fang, Microdermabrasion

as a novel tool to enhance drug delivery via the skin: an animal study, Dermatologic Surgery 32 (2006) 1013-1022. [140]

C. Liu, Z. Zhi, V.V. Tuchin, D. Zhu, Combined laser and glycerol enhancing skin

optical clearing, Proc. SPIE 7186 (2009) 71860D. [141]

O.F. Stumpp, A.J. Welch, T.E. Milner, J. Neev, Enhancement of transepidermal skin

clearing agent delivery using a 980 nm diode laser, Laser Surg. Med. 37 (2005) 278-285. A.K. Nugroho, G.L. Li, M. Danhof, J.A. Bouwstra, Transdermal iontophoresis of

PT

[142]

rotigotine across human stratum corneum in vitro: influence of pH and NaCl concentration,

[143]

RI

Pharm. Res. 21 (2004) 844–850.

A. Tezel, S. Mitragotri, Interaction of inertial cavitation bubbles with stratum corneum

[144]

SC

lipid bilayers during low-frequency sonophoresis, Biophys. J. 85 (2003) 3502–3512. S. Lee, D.J. McAuliffe, N. Kollias, T.J. Flotte, A.G. Doukas, Photomechanical delivery

NU

of 100-nm microspheres through the stratum corneum: implications for transdermal drug delivery, Laser Surg. Med. 31 (2002) 207–210.

O. Stumpp, A.J. Welch, Injection of glycerol into porcine skin for optical skin clearing

MA

[145]

with needle-free injection gun and determination of agent distribution using OCT and fluorescence microscopy, Proc. SPIE 4949 (2003) 44–50. V.V. Tuchin, G.B. Altshuler, A.A. Gavrilova, A.B. Pravdin, D. Tabatadze, J. Childs,

D

[146]

PT E

I.V. Yaroslavsky, Optical clearing of skin using flashlamp-induced enhancement of epidermal permeability, Lasers Surg. Med. 38 (2006) 824-836. [147]

O. Stumpp, B. Chen, A.J. Welch, Using sandpaper for noninvasive transepidermal

[148]

CE

optical skin clearing agent delivery, J. Biomed. Opt. 11 (2006) 041118. S.-J. Tseng, Y.-H. Lee, Z.-H. Chen, H.-H. Lin, C.-Y. Lin, S.-C. Tang, Integration of

AC

optical clearing and optical sectioning microscopy for three-dimensional imaging of natural biomaterial scaffolds in thin sections, J. Biomed. Opt. 14 (2009) 044004. [149]

R. Cicchi, S. Sestini, V. De Giorgi, D. Massi, T. Lotti, F.S. Pavone, Nonlinear laser

imaging of skin lesions, J. Biophotonics 1 (2008) 62-73. [150]

M.-T. Ke, T. Imai, Optical clearing of fixed brain samples using SeeDB, Current

Protocols in Neuroscience 66 (2014) 2.22.1-2.22.19. [151]

Y. Aoyagi, R. Kawakami, H. Osanai, T. Hibi, T. Nemoto, A rapid optical clearing

protocol using 2, 2′-thiodiethanol for microscopic observation of fixed mouse brain, Plos One 10 (2015) e0116280. [152]

E.H. Chang, M. Argyelan, M. Aggarwal, T.S.S. Chandon, K.H. Karlsgodt, S. Mori, A.K.

Malhotra, The role of myelination in measures of white matter integrity: combination of 37

ACCEPTED MANUSCRIPT diffusion tensor imaging and two-photon microscopy of CLARITY intact brains, NeuroImage 147 (2017) 253-261. [153]

L. Richardson, G. Vargas, T. Brown, L. Ochoa, J. Trivedi, M. Kacerovsky, M. Lappas,

R. Menon, Redefining 3Dimensional placental membrane microarchitecture using multiphoton microscopy and optical clearing, Placenta 53 (2017) 66-75. [154]

K. Kong, C. Kendal, N. Stone, I. Notingher, Raman spectroscopy for medical

diagnostics - From in-vitro biofluid assays to in-vivo cancer detection, Advanced Drug

[155]

PT

Delivery Reviews 89 (2015) 121-134. C. Krafft, M. Schmitt, I.W. Schie, D. Cialla-May, C. Matthäus, T. Bocklitz, J. Popp,

RI

Label-Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches, Angew. Chem. Int. Ed. Engl. 56 (2017) 4392-4430. M. Jermyn, J. Desroches, K. Aubertin, K. St-Arnaud, W.-J. Madore, E. de Montigny,

SC

[156]

M.-C. Guiot, D. Trudel, B.C. Wilson, K. Petrecca, F. Leblond, A review of Raman

NU

spectroscopy advances with an emphasis on clinical translation challenges in oncology, Phys. Med. Biol. 61 (2016) R370-R400.

M.E. Darvin, I. Gersonde, S. Ey, N.N. Brandt, H. Albrecht, S.A. Gonchukov, W. Sterry,

MA

[157]

J. Lademann, Noninvasive detection of beta-carotene and lycopene in human skin using Raman spectroscopy, Laser Phys. 14 (2004) 231-233.

L. Binder, S. SheikhRezaei, A. Baierl, L. Gruber, M. Wolzt, C. Valenta, Confocal

D

[158]

PT E

Raman spectroscopy: In vivo measurement of physiological skin parameters - A pilot study, J Dermatol Sci. 2017 doi: 10.1016/j.jdermsci.2017.08.002 [159]

C.-S. Choe, J. Schleusener, J. Lademann, M.E. Darvin. Age related depth profiles of

CE

human stratum corneum barrier-related molecular parameters by confocal Raman microscopy in vivo, Mechanisms of Ageing and Development, Accepted, 19 August 2017. DOI:

[160]

AC

10.1016/j.mad.2017.08.011 R.J. Richters, D. Falcone, N.E. Uzunbajakava, B. Varghese, P.J. Caspers, G.J. Puppels,

P.E. van Erp, P.C.van de Kerkhof, Sensitive Skin: Assessment of the Skin Barrier Using Confocal Raman Microspectroscopy, Skin Pharmacol. Physiol. 30 (2017) 1-12. [161]

S. Mujica Ascencio, C.-S. Choe, M.C. Meinke, R.H. Müller, G.V. Maksimov, W.

Wigger-Alberti, J. Lademann, M.E. Darvin, Confocal Raman microscopy and multivariate statistical analysis for determination of different penetration abilities of caffeine and propylene glycol applied simultaneously in a mixture on porcine skin ex vivo, Eur. J. Pharmaceutics and Biopharmaceutics 104 (2016) 51-58.

38

ACCEPTED MANUSCRIPT [162]

A.M.K. Enejder, T.G. Scecina, J. Oh, M. Hunter, W.-C. Shih, S. Sasic, G. Horowitz,

M.S. Feld, Raman spectroscopy for noninvasive glucose measurements, J. Biomed. Opt. 10 (2005) 031114. [163]

R.J. McNichols, G.L. Coté, Optical glucose sensing in biological fluids: an overview, J.

Biomed. Opt. 5 (2000) 5–16. [164]

A.

Quatela,

L.

Miloudi,

A.

Tfayli,

A.

Baillet-Guffroy,

In

vivo

Raman

Microspectroscopy: Intra- and Intersubject Variability of Stratum Corneum Spectral Markers,

[165]

PT

Skin Pharmacol. Physiol. 29 (2016) 102-109. M. V. Schulmerich, K. A. Dooley, T. M. Vanasse, S. A. Goldstein, and M. D. Morris,

RI

Subsurface and transcutaneous Raman spectroscopy and mapping using concentric illumination rings and collection with a circular fiber optic array, Appl. Spectrosc. 61 (2007) 671–678. M. Zimmerley, R.A. McClure, B. Choi, E.O. Potma, Following dimethyl sulfoxide skin

SC

[166]

optical clearing dynamics with quantitative nonlinear multimodal microscopy, Appl. Opt. 48

[167]

NU

(2009) D79-D87.

D. Huang, W. Zhang, H. Zhong, H. Xiong, X. Guo, Z. Guo, Optical clearing of porcine

[168]

MA

skin tissue in vitro studied by Raman microspectroscopy, J. Biomed. Opt. 17 (2012) 015004. A. Nijssen, T.C.B. Schut, F. Heule, P.J. Caspers, D.P. Hayes, M.H.A. Neumann, G.J.

Puppels, Discriminating basal cell carcinoma from its surrounding tissue by Raman

M. Gniadecka, H.C. Wulf, O.F. Nielsen, D.H. Christensen, J. Hercogova, Distinctive

PT E

[169]

D

spectroscopy, J. Invest. Dermatol. 119 (2002) 64–69.

molecular abnormalities in benign and malignant skin lesions: studies by Raman spectroscopy, Photochem. Photobiol. 66 (1997) 418–423. S. Kim, K.M. Byun, S.Y. Lee, Influence of water content on Raman spectroscopy

CE

[170]

characterization of skin sample, Biomed. Opt. Exp. 8 (2017) 1130-1138. [171]

Y. Cui, X. Wang, W. Ren, J. Liu, J. Irudayaraj, Optical clearing delivers ultrasensitive

3143. [172]

AC

hyperspectral dark-field imaging for single-cell evaluation, ACS nano, 10(3) (2016), 3132-

B.H. Hokr, V.V. Yakovlev, Raman signal enhancement via elastic light scattering,

Optics Express 21 (2013) 11757–11762. [173]

P. Matousek, Raman signal enhancement in deep spectroscopy of turbid media, Appl.

Spectrosc. 61 (2007) 845–854. [174]

D. Oelkrug, B. Boldrini, K. Rebner, Comparative Raman study of transparent and turbid

materials: models and experiments in the remote sensing mode, Anal. Bioanal. Chem. 409 (2017) 673–681.

39

ACCEPTED MANUSCRIPT [175]

Y.J. Zhu, C.-S. Choe, S. Ahlberg, M.C. Meinke, U. Alexiev, J. Lademann, M.E. Darvin,

Penetration of silver nanoparticles into porcine skin ex vivo using fluorescence lifetime imaging microscopy, Raman microscopy and surface enhanced Raman microscopy, Journal of Biomedical Optics, 20(5) (2015) 051006. [176]

Y. Zhang, D. Li, X. Zhou, X. Gao, S. Zhao, C. Li, Enhancing sensitivity of SERRS

nanoprobes by modifying heptamethine cyanine-based reporter molecules, Journal of Innovative Optical Health Sciences, 9(04) (2016), 1642005. Y. Zhang, H. Liu, J. Tang, Z. Li, X. Zhou, R. Zhang, L. Chen, Y. Mao, C. Li, Non-

PT

[177]

invasively Imaging Subcutaneous Tumor Xenograft by Handheld Raman Detector with

RI

Assistance of Optical Clearing Agent, ACS Applied Materials & Interfaces 9 (2017) 1776917776.

B.G. Osborne, T. Fearn, P.H. Hindle, P.T. Hindle, Practical NIR spectroscopy with

SC

[178]

applications in food and beverage analysis, Longman Scientific and Technical, 1993. M. Blanco, I. Villarroya, NIR spectroscopy: a rapid-response analytical tool, TrAC

NU

[179]

Trends in Analytical Chemistry 21 (2002) 240-250.

H.W. Siesler, Y. Ozaki, S. Kawata, H.M. Heise (Eds.), Near-infrared spectroscopy:

MA

[180]

principles, instruments, applications, John Wiley & Sons, 2008. [181]

Q. Kang, Q. Ru, Y. Liu, L. Xu, J. Liu, Y. Wang, Y. Zhang, H. Li, Q. Zhang, Q. Wu, On-

D

line monitoring the extract process of Fu-fang Shuanghua oral solution using near infrared

152 (2016) 431-437. [182]

PT E

spectroscopy and different PLS algorithms, Spectrochim. Acta Part A Mol. Biomol. Spectrosc.

L. Shi, L.A. Sordillo, A. Rodriguez-Contreras, R. Alfano, Transmission in near-infrared

[183]

CE

optical windows for deep brain imaging, J. Biophotonics 9 (2016) 38-43. K. Maruo, M. Tsurugi, M. Tamura, Y. Ozaki, In vivo nondestructive measurement of

AC

blood glucose by near-infrared diffuse reflectance spectroscopy, Appl. Spectrosc. 57 (2003) 1236–1244. [184]

H.M. Heise, P. Lampen, R. Marbach, Near-infrared reflection spectroscopy for non-

invasive monitoring of glucose – established and novel strategies for multivariate calibration, in: Handbook of Optical Sensing of Glucose in Biological Fluids and Tissues, V.V. Tuchin (Ed.), Taylor & Francis Group LLC, CRC Press, FL, USA, 2009, 115–156. [185]

R. Liu, W. Chen, X. Gu, R.K. Wang, K. Xu, Chance correlation in non-invasive glucose

measurement using near-infrared spectroscopy, J. Phys. D: Appl. Phys. 38 (2005) 2675-2681. [186]

E.A. Genina, A.N. Bashkatov, V.V. Tuchin, Optical clearing of human dura mater by

glucose solutions, J. Biomed. Photonics & Eng. 3 (2017) 010309.

40

ACCEPTED MANUSCRIPT [187]

E.A. Genina, A.N. Bashkatov, O.V. Semyachkina-Glushkovskaya, V.V. Tuchin, Optical

Clearing of Cranial Bone by Multicomponent Immersion Solutions and Cerebral Venous Blood Flow Visualization, Izv. Saratov Univ. (N.S.), Ser. Physics, 17 (2017) 98–110. [188]

A. Gerger, S. Koller, T. Kern, C. Massone, K. Steiger, E. Richtig, H. Kerl, J. Smolle,

Diagnostic applicability of in vivo confocal laser scanning microscopy in melanocytic skin tumors, J. Invest. Dermatol. 124 (2005) 493-498. [189]

I.V. Meglinskii, A.N. Bashkatov, E.A. Genina, D.Yu. Churmakov, V.V. Tuchin, Study

PT

of the possibility of increasing the probing depth by the method of reflection confocal microscopy upon immersion clearing of near-surface human skin layers, Quantum Electronics

[190]

RI

32 (2002) 875-882.

I.V. Meglinski, A.N. Bashkatov, E.A. Genina, D.Y. Churmakov, V.V. Tuchin, The

SC

enhancement of confocal images of tissues at bulk optical immersion, Laser Physics 13 (2003) 65-69.

R. Dickie, R.M. Bachoo, M.A. Rupnick, S.M. Dallabrida, G.M. DeLoid, J. Lai, R.A.

NU

[191]

DePinho, R.A. Rogers, Three-dimensional visualization of microvessel architecture of whole-

[192]

MA

mount tissue by confocal microscopy, Microvascular Research 72 (2006) 20-26. A.-S. Chiang, Y.-C. Liu, S.-L. Chiu, S.-H. Hu, C.-Y. Huang, C.-H. Hsieh, Three-

dimensional mapping of brain neuropils in the cockroach Diploptera punctata, J. Comp.

Y.-Y. Fu, C.-W. Lin, G. Enikolopov, E. Sibley, A.-S. Chiang, S-C. Tang, Microtome-

PT E

[193]

D

Neurol. 440 (2001) 1–11.

free 3-dimensional confocal imaging method for visualization of mouse intestine with subcellular-level resolution, Gastroenterology 137 (2009) 453–465. S. Karma, J. Homan, C. Stoianovic, B. Choi, Enhanced fluorescence imaging with

CE

[194]

DMSO-mediated optical clearing, J. Innov. Opt. Health Sci. 3 (2010) 153-158. E. Song, Y.-J. Ahn, J. Ahn, S. Ahn, C. Kim, S. Choi, R.M. Boutilier, Y. Lee, P. Kim,

AC

[195]

Optical clearing assisted confocal microscopy of ex vivo transgenic mouse skin, Optics & Laser Technology 73 (2015) 69-76. [196]

V.G. Puelles, J.F. Bertram, S. Firth, I. Harper, BABB Clearing and Imaging for High

Resolution Confocal Microscopy: Counting and Sizing Kidney Cells in the 21st Century, Science Lab, 2016. [197]

T. Lagerweij, S.A. Dusoswa, A. Negrean, E.M.L. Hendrikx, H.E. de Vries, J. Kole, J.J.

Garcia-Vallejo, H.D. Mansvelder, W.P. Vandertop, D.P. Noske, B.A. Tannous, R.J.P. Musters, Y. van Kooyk, P. Wesseling, X.W. Zhao, T. Wurdinger, Optical clearing and fluorescence deep-tissue imaging for 3D quantitative analysis of the brain tumor microenvironment, Angiogenesis (2017) 1-14 DOI 10.1007/s10456-017-9565-6 41

ACCEPTED MANUSCRIPT [198]

R. Shi, W. Feng, C. Zhang, Z. Zhang, D. Zhu, FSOCA-induced switchable footpad skin

optical clearing window for blood flow and cell imaging in vivo, Journal of Biophotonics (2017) DOI 10.1002/jbio.201700052 [199]

A.F. Fercher, J.D. Briers, Flow visualization by means of single-exposure speckle

photography, Optics Communications 37 (1981) 326-330. [200]

Z. Mao, X. Wen, J. Wang, D. Zhu, The biocompatibility of the dermal injection of

glycerol in vivo to achieve optical clearing, Proc. SPIE 7519 (2009) 75191N. D. Zhu, J. Wang, Z. Zhi, X. Wen, Q. Luo, Imaging dermal blood flow through the intact

PT

[201]

rat skin with an optical clearing method, J. Biomed. Opt. 15 (2010) 026008. J. Wang, Y. Zhang, T.H. Xu, Q.M. Luo, D. Zhu, An innovative transparent cranial

RI

[202]

window based on skull optical clearing, Laser Physics Letters 9 (2012) 469-473. D. Abookasis, T. Moshe, Feasibility study of hidden flow imaging based on laser

SC

[203]

speckle technique using multiperspectives contrast images, Optics and Lasers in Engineering 62

[204]

NU

(2014) 38-45.

D. Abookasis, T. Moshe, Reconstruction enhancement of hidden objects using multiple

MA

speckle contrast projections and optical clearing agents, Optics Communications 300 (2013) 5864. [205]

T. Moshe, M.A. Firer, D. Abookasis, Object reconstruction in scattering medium using

D

multiple elliptical polarized speckle contrast projections and optical clearing agents, Optics and

[206]

PT E

Lasers in Engineering 68 (2015) 172-179. P.A. Timoshina, A.B. Bucharskaya, D.A. Alexandrov, V.V. Tuchin, Study of blood

microcirculation of pancreas in rats with alloxan diabetes by laser speckle contrast imaging, J.

[207]

CE

Biomed. Photonics & Eng. 3 (2017) 020301. R.K. Wang, and V.V. Tuchin, Optical coherence tomography. Light scattering and

AC

imaging enhancement, Chap. 16 in Handbook of Coherent-Domain Optical Methods. Biomedical Diagnostics, Environmental Monitoring, and Material Science, 2nd ed., V. V. Tuchin, Ed., pp. 665-742, New York, Heidelberg, Dordrecht, London: Springer (2013) [208]

E. Zagaynova, N. Gladkova, N. Shakhova, G. Gelikonov, V. Gelikonov, Endoscopic

OCT with forward-looking probe: clinical studies in urology and gastroenterology, J. Biophotonics 1 (2008) 114-128. [209]

P.D. Agrba, M.Yu. Kirillin, A.I. Abelevich, E.V. Zagaynova, V.A. Kamensky,

Compression as a method for increasing the informativity of optical coherence tomography of biotissue, Optics and Spectroscopy 107 (2009) 853-858.

42

ACCEPTED MANUSCRIPT [210]

R.K. Wang, V.V. Tuchin, Enhance light penetration in tissue for high resolution optical

imaging techniques by the use of biocompatible chemical agents, J. X-Ray Science and Technol. 10 (2002) 167-176. [211]

R.K. Wang, J.B. Elder, Propylene glycol as a contrasting agent for optical coherence

tomography to image gastrointestinal tissues, Lasers Surg. Med. 30 (2002) 201-208. [212]

H. Xiong, Z. Guo, C. Zeng, L. Wang, Y. He, and S. Liu, Application of hyperosmotic

agent to determine gastric cancer with optical coherence tomography ex vivo in mice, J.

[213]

PT

Biomed. Opt. 14 (2009) 024029. H.Q. Zhong, Z.Y. Guo, H.J. Wei, J.L. Si, L. Guo, Q.L. Zhao, C.C. Zeng, H.L. Xiong,

RI

Y.H. He, S.H. Liu, Enhancement of permeability of glycerol with ultrasound in human normal and cancer breast tissues in vitro using optical coherence tomography, Laser Physics Letters 7

[214]

SC

(2010) 388-395.

Q.L. Zhao, J.L. Si, Z.Y. Guo, H.J. Wei, H.Q. Yang, G.Y. Wu, S.S. Xie, X.Y. Li, X. Guo,

NU

H.Q. Zhong, L.Q. Li, Quantifying glucose permeability and enhanced light penetration in ex vivo human normal and cancerous esophagus tissues with optical coherence tomography, Laser

[215]

MA

Phys. Lett. 8 (2011) 71–77.

X. Xu, Q. Zhu, C. Sun, Combined effect of ultrasound-SLS on skin optical clearing,

IEEE Photonic Technol. Lett. 20 (2008) 2117–2119. H. Zhong, Z. Guo, H. Wei, L. Guo, C. Wang, Y. He, H. Xiong, S. Liu, Synergistic effect

D

[216]

PT E

of ultrasound and thiazone–PEG 400 on human skin optical clearing in vivo, Photochem. Photobiol. 86 (2010) 732–737. [217]

Z. Zhu, H. Wei, G. Wu, H. Yang, Y. He, S. Xie, Synergistic effect of hyperosmotic

CE

agents and sonophoresis on breast tissue optical properties and permeability studied with spectral domain optical coherence tomography, J. Biomed. Opt. 17 (2012) 086002. C.H. Liu, M. Singh, J. Li, Z. Han, C. Wu, S. Wang, R. Idugboe, R. Raghunathan, E.N.

AC

[218]

Sobol, V.V. Tuchin, M. Twa, K.V. Larin, Quantitative Assessment of Hyaline Cartilage Elasticity During Optical Clearing Using Optical Coherence Elastography. Medical Technologies in Medicine/Sovremennye Tehnologii v Medicine, 7 (2015) 44-51. [219]

Q. Zhao, H. Wei, Y. He, Q. Ren, C. Zhou, Evaluation of ultrasound and glucose synergy

effect on the optical clearing and light penetration for human colon tissue using SD-OCT, J. Biophotonics 7 (2014) 938-947. [220]

E.A. Genina, A.N. Bashkatov, E.A. Kolesnikova, M.V. Basko, G.S. Terentyuk, V.V.

Tuchin, Optical coherence tomography monitoring of enhanced skin optical clearing in rats in vivo, J. Biomed. Opt. 19 (2014) 021109.

43

ACCEPTED MANUSCRIPT [221]

A. Doronin, V.V. Tuchin, I. Meglinski, Monitoring of interaction of low-frequency

electric field with biological tissues upon optical clearing with optical coherence tomography, J. Biomed. Opt. 19 (2014) 086002. [222]

E.A. Genina, A.N. Bashkatov, M.D. Kozintseva, V.V. Tuchin, OCT study of optical

clearing of muscle tissue in vitro with 40% glucose solution, Optics and Spectroscopy, 120 (2016) 20-27. [223]

A. Bykov, T. Hautala, M. Kinnunen, A. Popov, S. Karhula, S. Saarakkala, I. Meglinski,

PT

Imaging of subchondral bone by optical coherence tomography upon optical clearing of articular cartilage, J. Biophotonics, 9 (2016) 270-275.

L. Pires, V. Demidov, I.A. Vitkin, V. Bagnato, C. Kurachi, B.C. Wilson, Optical

RI

[224]

clearing of melanoma in vivo: characterization by diffuse reflectance spectroscopy and optical

[225]

SC

coherence tomography, J. Biomed. Opt. 21 (2016) 081210.

O. Zhernovaya, V.V. Tuchin, M.J. Leahy, Enhancement of OCT imaging by blood

NU

optical clearing in vessels–A feasibility study, Photonics & Lasers in Medicine, 5 (2016) 151159.

E.A. Genina, N.S. Ksenofontova, A.N. Bashkatov, G.S. Terentyuk, V.V. Tuchin, Study

MA

[226]

of the epidermis ablation effect on the efficiency of optical clearing of skin in vivo, Quantum Electronics 47 (2017) 561 – 566.

N.S. Ksenofontova, E.A. Genina, A.N. Bashkatov, G.S. Terentyuk, V.V. Tuchin, OCT

D

[227]

PT E

study of skin optical clearing with preliminary laser ablation of epidermis, J. Biomed. Photonics & Eng. 3 (2017) 020307. [228]

G.D. Elliott, S. Wang, B.J. Fuller, Cryoprotectants: A review of the actions and

CE

applications of cryoprotective solutes that modulate cell recovery from ultra-low Temperatures, Cryobiology (2017), doi: 10.1016/j.cryobiol.2017.04.004. J.M. Fox, R.C. Wiggins, J.W.J. Moore, C. Brewer, A.C. Andrew, F. Martin,

AC

[229]

Methodology for reliable and reproducible cryopreservation of human cervical tissue, Cryobiology 77 (2017) 14-18.

44

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Highlights : 

In this review, the progress in optical clearing for multi-photon microscopy, Raman microscopy, NIR spectroscopy, confocal microscopy, optical coherence tomography, and speckle contrast imaging has been described in detail. The physical, molecular and physiological mechanisms of optical clearing have been

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described

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Future perspectives of using optical clearing was discussed

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Graphics Abstract

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5