A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor

A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor

Accepted Manuscript Title: A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor Authors: Daqi Chen, Kaihuan Zhang, Hui Zh...

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Accepted Manuscript Title: A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor Authors: Daqi Chen, Kaihuan Zhang, Hui Zhou, Guokang Fan, You Wang, Guang Li, Ruifen Hu PII: DOI: Reference:

S0925-4005(18)30111-4 https://doi.org/10.1016/j.snb.2018.01.105 SNB 23954

To appear in:

Sensors and Actuators B

Received date: Revised date: Accepted date:

13-6-2017 1-12-2017 9-1-2018

Please cite this article as: Daqi Chen, Kaihuan Zhang, Hui Zhou, Guokang Fan, You Wang, Guang Li, Ruifen Hu, A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor, Sensors and Actuators B: Chemical https://doi.org/10.1016/j.snb.2018.01.105 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A wireless-electrodeless quartz crystal microbalance with dissipation DMMP sensor Daqi Chen1, Kaihuan Zhang1, Hui Zhou2, Guokang Fan2, You Wang1, Guang Li1 and Ruifen Hu1,* 1

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State Key Laboratory of Industrial Control Technology, Institute of Cyber Systems and Control, Zhejiang University, Hangzhou 310027, China; E-Mails: [email protected] (D.C.); [email protected] (G.L.) 2 School of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China; E-Mail: [email protected] * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel. /Fax: +86-571-8795-2268 (ext. 8232).

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microbalance with dissipation gas system.

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 Hollow ball-like indium oxide and Au-decorated indium oxide

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were synthesized and tested as sensing films.  A noncontact, real-time and high sensitive DMMP gas sensor was

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achieved.

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 The dissipation value was monitored during the experiment, showing a visco-elastic variation and a proper model was chosen

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to explain overshoot in this and some other researches.

Abstract Highly sensitive chemical warfare agents (CWAs) detection is demanded against the usage of the CWAs for war or terrorism aims. A dimethyl methylphosphonate (DMMP), simulant for sarin, monitoring sensor based on a homemade wireless-electrodeless quartz crystal microbalance with dissipation (QCM-D) was developed. With this noncontact configuration, deterioration of the sensing ability cause by the electrodes and drilling on the gas chamber for wire lead was avoided. Nano-structured hollow ball-

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like indium oxide (In2O3) was synthesized using a facile hydrothermal method and then decorated with cubic gold particles (In2O3-Au). Both of them were applied as the sensing films to detect DMMP. The In2O3-Au based QCM-D sensor exhibited 2.1 Hz/ppm to DMMP range from 5 ppm to 50 ppm, which was 400% higher compared to the undecorated one. Moreover, with the simultaneously monitored dissipation value, desorption processes of DMMP was further investigated and the overshoot that appear in some researches was explained in terms of visco-elastic variations in mechanical stiffness. The results suggest that the wireless-electrodeless QCM-D could be a promising strategy for observation of materials under dynamic conditions.

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Keywords: wireless-electrodeless QCM-D; indium oxide; nobel metal decoration; visco-elastic property; overshoot

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1. Introduction Intentional uses of chemical warfare agents (CWAs) for war or terrorism aims have motivated researches for development of early warning systems especially after the sarin attacks in the Tokyo subway in 1995. Sarin, which is a kind of dangerous G-type nerve agents, is very dangerous even in a few ppm levels. Dimethyl methylphosphonate (DMMP), due to its nontoxicity and organophosphorus compound elemental composition, is commonly considered as a simulant for sarin[1-3]. Many researches have been done to detect DMMP at the ppm level by semiconductor sensors[3, 4], quartz crystal microbalances (QCM) sensors[5-7], surface acoustic wave (SAW) sensors[8-10], surface plasmon resonance (SPR) sensors[11] and so on. Among them, QCM-based sensors was a popular choice because of their high sensitivity, rapid response and room temperature working conditions[12]. To develop a QCM based DMMP sensor, nano-structured metal oxide is a good choice for the sensing film because of the large specific surface area, non-toxicity and easy for doping in gas sensing applications. Zhao et al.[13, 14] used WO3 nano-flakes and Flower-like one to detect DMMP and found Flower-like WO3 had better performance due to its larger surface areas. Fan et al.[12, 15] respectively synthesized solid ball-like and hollow ball-like Fe2O3. Then he applied them as sensing films for monitoring DMMP and found hollow ball-like Fe2O3 perform much better and monitored DMMP at the concentration from 1 to 10 ppm. Except synthesizing nano-structured metal oxide of different morphology, researchers also tried decorating the metal oxide with noble metals, which they found it could get ultra-fine grains, combine the advantages of all components and possess better sensing performance[16-19]. Improving sensing film material was a good way to achieve better performance. However, improving the sensor itself is also another good way to improve the performance and have the potential to overcome some drawbacks of conventional QCMs. These drawbacks are: (1) Metal electrodes of the conventional QCMs, which are deposited on the both sides of the crystals, are more likely to be corroded and would limit the life-span of the sensors in corrosive conditions[20, 21]. (2) The electrodes also deteriorate the performance of the QCM sensor because the metal electrodes increase the loaded mass of the sensor. This can limit the available frequency range with QCM

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measurements and restrict the increase of resonance frequency[22] because the influence of the metallic electrodes enlarges and could become significant at high resonance frequencies. (3)This configuration is only applicable in the case when the sensing film is firmly attached to the quartz crystal surface, oscillating rigidly together with the crystal throughout the experiment[23]. When there are visco-elastic changes of the deposited film, the frequency response would not be a linear relationship with the mass loaded and the experiment result may get wrong. Researches have been done to improve the performance of QCM-based sensors. In 1996, Rodahl et al.[24] developed the QCM-D system which can simultaneously monitor the frequency and dissipation value. Owing to this the application of the QCM was expanded and can be used in the visco-elastic interfacial films situation. Recently, wireless-electrodeless QCM (WE-QCM) systems have been proposed by Ogi et al.[2527] and Stevenson et al.[28-31] respectively which removed both electrodes from the quartz disc and could oscillate and receive the frequency signal in a non-contact way. The wireless-electrodeless QCM in a noncontact configuration can avoid deterioration of the sensing ability, be operated at higher frequency and have a better long-term stability in corrosive conditions. In this work, we first tried to combine both the benefits of the QCM-D and the WEQCM technique and a wireless-electrodeless QCM with dissipation system was developed. Both frequency shift and energy dissipation of the oscillating crystal, which corresponds to the variation of the loaded mass and the visco-elatic property of the sensing film respectively were monitored simultaneously during the experiment. Then, hollow ball-like In2O3 is synthesized via a simple template-free method and cubic Au particles were decorated on the surface of the In2O3 hollow balls via a facile aqueous solution method. Both two materials were utilized as the sensing films of the homemade wireless-electrodeless QCM-D system to monitor DMMP and other interfering gases. The thicknesses of the sensing films were optimized and both the sensitivity and selectivity of the sensors were investigated. The results indicate that the sensors loaded with In2O3-Au films worked better on both sensitivity and selectivity. Finally, using the simultaneously obtained dissipation value, the DMMP desorption process was studied further and a proper model was chosen to explain the abnormal peak in desorption process.

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2. Experimental 2.1. Materials All the chemicals and reagents were analytical grade. Dimethyl methylphosphonate (DMMP) was purchased from Qindao Hanhua Fireproofing Material Ltd., China. Indium nitrate (In(NO3)3), chloroauric acid hydrate (HAuCl4·4H2O), 1,2phenylenedioxydiacetic acid, and urea were purchased from Sinopharm Chemical Reagent Co., Ltd. Ethanol, chloroform, ethyl acetate, acetaldehyde (40% v/v) and benzene were purchased from Sigma–Aldrich (Shanghai, China). The AT–cut 6.0 MHz quartz crystal discs were purchased from Kesheng Electronics (Yantai) Ltd, China. 2.2. A homemade wireless-electrodeless QCM-D gas sensing system

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The wireless-electrodeless QCM-D reported herein consists of an AT-cut 6.0 MHz blank quartz disc, a couple of copper coil (the radius was 1 cm), a function generator (Tektronix AFG3102C), an oscilloscope (Tektronix TDS5054B), a homemade narrow band amplifier (60 dB), an impedance matching network (mAT-125E) and a PC. Unlike traditional QCM devices, there is not a well-defined electric field distribution between two metal electrodes of the quartz disc. The electric field generated by the transmitting coil is more complicated and the quasi-static electric field is suggested to be the main electric field that stimulates the quartz disc to oscillate[22]. As shown in Fig. 1a, the quartz disc is stimulated by a remote planar copper coil ( transmitter ) located immediately beneath the disc(5 mm), which produced a radio frequency (RF) electric field. After the stimulation, the crystal’s vibrations are detected by another planar cooper coil (receiver) which is located beside the transmitter, through piezoelectric effect. The frequency shift (Δf) and dissipation factor (D) are measured by periodically disconnecting the oscillating crystal from the function generator. The decay of the QCM oscillation is further amplified and is recorded on the digital oscilloscope and is shown in Fig. 2a. Finally, the signal is transferred into a PC for curve fitting to calculate the Δf and the D. For comparison, operation without the quartz disc is showed in Fig. 2b. Fig. 3 shows the amplitude-frequency curve of our quartz disc. Only when the frequency of RF signal was within this range, the quartz disc could be oscillated (freely oscillation signal in Fig. 2a can be observed). The glass chamber for gas detection was designed and shown in Fig. 4. The quartz crystal was placed at the bottom center of the chamber where a 9 mm diameter blindhole was fabricated to fix the disc. Both the transmitting coil and the receiving coil mentioned above were placed outside the chamber and right below the quartz plate. The volume capacity of the chamber was 1 L. A small plastic airbag was linked to the top of the chamber to keep the pressure at 1 atm during the whole experiment.

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2.3. Preparation and characterization of nanostructured hollow ball-like indium oxide and Au-decorated indium oxide 2.3.1. Synthesis of nanostructured hollow ball-like indium oxide The nanostructured hollow ball-like In2O3 was synthesized firstly by dissolving 0.0226 g 1,2-phenylenedioxydiacetic acid, 0.2190 g CTAB and 0.3003 g urea in 9.5 ml deionized water. After stirring for 5 min, 0.5 ml indium nitrate aqueous solution (0.20 M) was gradually injected into the continuously stirred solution. The mixture was stirred for another 10 minutes and then shift to a 20 ml autoclave and treated in a 120 °C oven for 6 hours. After the reaction completed, the deposition was collected and washed with deionized water and ethanol subsequently for five times and dried at a 60 °C in a vacuum drying oven. The product was annealed at 450 °C for 2 h to get the indium oxide hollow ball (In2O3). 2.3.2. Preparation of Au-decorated indium oxide As-prepared indium oxide hollow balls (0.2 g) were dispersed in 20 ml deionized water. Then the solution was stirred quickly and 5.37 ml HAuCl4 (9.7 mM) was added to the stirring solution. After stirred for another 10 minutes, 0.3162 g urea was added into the

solution. The solution was then heated and refluxed for 15 h in dark. The precipitate was washed with deionized water 5 times and dried in a vacuum stove at 100 °C for 24 h. Finally, the product was annealed at 300 °C for 2 h to get the Au-Decorated indium oxide (In2O3-Au).

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2.3.3 Characterization The X-ray diffraction (XRD) analysis for phase identification was performed using a X-ray diffraction device (X’Pert PW3050/60, PANalytical, Nijmegen, The Netherlands) running with Cu Kα radiation at an angle degree range from 20° to 80° (2θ). The scanning electron microscopy (SEM) analysis for morphology and microstructure investigation was performed with a S4800 Field-Emission Scanning Electron Microscope (Hitachi, Tokyo, Japan). Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption data were obtained on a Micromeritics Analyzer (ASAP 2460, Micromeritics Instrument Corporation, Norcross, GA, USA) at 77 K.

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2.4 Fabrication of a QCM gas sensor The quartz plates were respectively washed with deionized water and anhydrous alcohol for 15 min in an ultrasonic oscillator. Then the quartz plates were dried by the flowing high–purity N2. Then 1 mg as-prepared In2O3 was dispersed in the deionized water to form a 10mg/mL In2O3 solution. Finally, the In2O3 solution sample was evenly smeared onto the surface of the quartz plates. After then, the quartz plates were dried for 24 h at room temperature. The QCM sensors coated with In2O3 were obtained. The same procedure was carried out to fabricate the In2O3-Au coated QCM sensors.

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2.5 Preparation of measured vapors The vapors to be measured in the experiment were DMMP, ethanol, chloroform, ethyl acetate, acetaldehyde (40% v/v) and benzene. All of them are in liquid state at room temperature. To make a mixed gas with a certain concentration, small amounts of the analyte solutions were injected into 2 L airbag full of high–purity N2. According to the equation (1), the volume of the analyte solutions injected were calculated except for DMMP. 𝑉𝑥 =

𝑉×𝐶×𝑀 273 + 𝑇𝑅 × 10−9 × 22𝑛. 4 × 𝑑 × 𝑃 273 + 𝑇𝐵

(1)

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Where Vx is the volume of analyte solution (ml), V is the volume of the airbags (ml), C is the target concentration of the measured vapors (ppm), M is the molecular weight of the analyte, d is the density of the analyte solution (g/cm3), P is the purity of the analyte solution (%), TR is the room temperature and TB is the airbag temperature. At last, to make a known concentration mixed gas of DMMP, excess amount of DMMP was injected into the 2 L airbag to get a saturated DMMP vapor, whose concentration was 1095 ppm at room temperature. 2.6 Gas sensing experiments

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The fundamental resonance frequency (f0) of the quartz disc was calibrated by frequency sweeping method and then the frequency of the burst RF signal for stimulation was set to f0 and was held. Before all the injections, the injected vapor was dried with allochroic silicagel to remove the water. In every experiment, high-purity N2 was firstly injected to purge the chamber and to desorb the sensors at the velocity of 120 L/min until the resonant frequency of the sensor reached a stable baseline. Afterwards, precise volumes of mixed gas of the measured vapors were injected into the chamber to obtain appropriate concentrations of the vapors in the chamber and stand for 5 minutes. Finally, N2 was injected to desorb the sensor until its resonant frequency returned back to the baseline again. The frequency and the dissipation value were continuously recorded during the whole experiment.

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3. Results and discussion 3.1 XRD diffraction The X-ray diffraction spectrum of pristine In2O3 hollow balls and those decorated with Au particles were shown in Fig. 5. The main feature peaks were at 21.4, 30.5, 35.2, 41.6, 45.6, 50.9, 55.9 and 60.5 degrees and were well matched with the standard data of the indium oxide, syn(JCPDS card no. 65-3170), indicating that the sample was In2O3. However, the crystalline structures of In2O3 and In2O3-Au can be hardly identified merely from the XRD patterns, because of the low content of Au in the product.

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3.2 SEM and BET studies of sensing films The SEM technique was used to investigate the morphology and nanostructure of the In2O3 and In2O3-Au films. In Fig. 6a, the In2O3 sample presented a hollow ball-like morphology with the radius about 300 nm. While in Fig. 6b, the Au-decorated In2O3 sample remains the hollow ball-like morphology but with the Au particles distributed on the surface of the inherited In2O3 hollow balls, forming a rougher surface. BET analyses were conducted to investigate the specific surface area and pore structures of the sensing films. Table 1 lists the BET data of In2O3 and Au-decorated In2O3. Both the BET surface area of In2O3 and Au-In2O3 were about 60 m2/g, with the Au-decorated one a bit larger than undecorated one.

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3.3 Optimization of the thickness of the sensing films Previous investigations showed that the thickness of the sensing film on the quartz plate was a key factor to the sensitivity[19, 32, 33]. In2O3 and the In2O3-Au films in different thicknesses respectively were fabricated by controlling the volume of the In2O3 and the In2O3-Au solution loaded on the quartz crystals. The responses of all the sensors to 30 ppm DMMP vapor were measured and are shown in Fig. 7. The response of the sensor is proportional to the thickness of both the In2O3 and In2O3-Au films when the loaded mass is below 1.57 μg/mm2 and 1.96 μg/mm2, respectively and then the responses of the sensors reach a saturation level. Compared with the In2O3 coated QCM sensors, the In2O3-Au coated ones have higher responses to DMMP with the films in the same thickness. The optimal thickness of In2O3 film used during the afterward experiments

was 1.96 μg/mm2 which was the value after the turning point and that of the In2O3-Au film was 2.36 μg/mm2.

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3.4 Sensitivity and repeatability The responses of the sensors loaded with the In2O3-Au (2.36 μg/mm2) to DMMP vapor were tested with the concentration in a range from 5 ppm to 50 ppm. Fig. 8 shows the response curves of the In2O3-Au coated QCM sensor when 15, 25 and 50 ppm DMMP vapor were injected into the chamber. For each concentration, three cycles were carried out to test the repeatability and the stability of the sensor. The results in Fig. 8 illustrate that the response time is less than 100 seconds and the recovery time is nearly 200 seconds. For comparison, the same experiment was carried out using the In2O3 coated sensor and the results are shown in Fig. 9. The responses of both the In2O3 and In2O3Au film coated QCM sensors are linearly proportional to the concentration of the DMMP until the concentration gets above 30 ppm, and then the response increases more slowly. Both of the sensors were highly sensitive to DMMP because the nano-sized hollow ball structure possessed a large specific surface area with more active sites and surface accessibility. Furthermore, the sensitivity of the In2O3 based sensor functionalized with Au particles was 4 times higher compared with that of the pristine In2O3 coated sensor. The detection limit of the In2O3-Au sensor reduced to 1/3 of the In2O3 sensor and achieved as low as 5 ppm (calculated as three times the signal–to– noise ratio). The main reason of the performance improvement of the In2O3-Au sensor might be that the voids and interspaces caused by the doping of Au particles among the interconnected hollow balls greatly facilitate the gas diffusion and transport in the sensing layers. Another reason was that the addition of catalytically active noble metal particles like Au resulted the catalytic activation and chemical sensitization that can thus enhance the gas adsorption responses.

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3.5 Selectivity To investigate the selectivity of the sensor, diverse VOCs interferences, whose concentration were all 30 ppm, including ethanol, chloroform, ethyl acetate, acetaldehyde and benzene were tested in the same procedure as DMMP. As it is shown in Fig. 10, the responses of the In2O3 and In2O3-Au coated QCM sensors to the DMMP gas are much higher than those of other inferences. The easily interaction between the P=O function group and the -OH groups of the nanostructured In2O3 surface by hydrogen bond was the main reason for the good selectivity. It should be noted that the sensitivity of the Au doped QCM gas sensor was enhanced for all the vapors because the addition in specific surface area after Au particle was decorated onto the In2O3. However, the enhanced level of sensitivity was different for these gases, especially for the DMMP, which was enhanced more than 4 times and larger than others. Fig. 11 shows the polar plot of response ratios (R1/R2, R1 and R2 represent the responses of the In2O3-Au QCM and In2O3 QCM, respectively) to the vapors. The response ratios were all between than 200% and 300% except DMMP, which was larger than 400%. In fact, as an n-type semiconductor, In2O3 has both electronic and chemical sensitization. The addition of Au particles will greatly facilitate the formation of hydrogen bonds

between the DMMP molecules and the sensing film so that more DMMP molecules will be absorbed and the response would be enhanced. This is the main reason why the enhancement of sensitivity level of DMMP was larger than other vapors. 3.6 Dissipation monitoring during the gas sensing process In most QCM gas sensing researches, Sauerbrey model is the basic model and is popularly employed. The model is expressed in Equation (2): 2𝑓02 𝐴√𝜇𝑞 𝜌𝑞

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Where f0 is the fundamental frequency of the unloaded quartz crystal, A is the area of the quartz crystal, ρ and µ is respectively the density of and the shear modulus of crystal quartz. In Sauerbrey model, there is a linear relationship between mass loaded and frequency shift. Base on this model, the frequency response should decrease after the N2 injection which indicates desorption of the DMMP from the sensing film. However in fact, unusual frequency shift was observed in a few seconds after N2 was injected to desorb the sensor (Fig. 8). Similar phenomena have been observed in many literatures [19, 3234]. Three reasons have been suggested for the frequency peaks during the absorption and desorption process. (1) Intermediates were formed during the absorption or desorption process[35]. However, in our paper, the operating temperature was room temperature much lower than the working temperature (200 °C) in the reference and the overshoot happened at the beginning of the desorption rather than absorption. Therefore, forming intermediates might not be the main reason. (2) The start/stop of the gas flow that cause a pressure change of the chamber [32, 34, 36]. However, in our work the gas chamber was big (about 1 L), and an airbag was used to maintain the pressure. Therefore, changing of the pressure might not be the main reason. (3) Change in the stiffness of the sensing film[20, 23]. In our work, due to using the drop-coating method, the sensing film was loosely bounded together in a sponge-like structure. After N2 was injected to desorb the sensor, the concentration of DMMP deceased and DMMP molecules would get away from the sensing film due to the concentration gradient. However, the DMMP molecules were still bound to the sensing film through the hydrogen bonds. So, the sensing film would be pulled outwards at the very beginning of desorption until the hydrogen bond finally ruptured, causing the sensing film expanded and became less rigid. As a result, slippage between the internal layers of the sensing film and interface of the sensing film and the quartz disc became larger which made the frequency decline (response) even larger. So, a big increase was seen in the frequency response. However, this increase would not stand for long, with desorption of more and more DMMP molecules, the frequency response soon dropped because of the sufficient reduction of mass loaded and the gradually weakened pulling force. The big increase and drop in the frequency response formed the peak we seen. Therefore, changing stiffness of the

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sensing film might be the main reason. As for data to support our analysis, the frequency response and the dissipation value was simultaneously used. Fig. 12a, b and c show the f-t, D-t and D-f plots of the whole absorption and desorption process of the In2O3-Au coated QCM sensors to 50 ppm DMMP. In Fig. 12a, after DMMP was injected and during the absorption process, the frequency response gradually rises and then levels off. Meanwhile, the dissipation value (Fig. 12b) changes very little and the slope of the D-f plot (Fig. 12c phase I) was 0.29*10-6/10Hz. No abnormal peaks or valleys was seen. However, after N2 was injected to desorb the sensor, a big increase was observed in the dissipation value (Fig. 12b), showing a large perturbation in the stiffness of the sensing film. The slope of the D-f plot (Fig. 12c phase II) abruptly grew 4 times larger (1.33*10-6/10Hz), meaning that the sensing film expanded during the time. What we found in D-f plot (phase II) was very like what Shen et al. found in his work when the sensing film was considered expanded (They found a great increase in the slope of motional resistance versus frequency response when the sensing film was considered expanded). So, we can first assume that the expansion of sensing film which increase the energy dissipation was the main reason of the overshoot in the frequency response. Then, we analyzed the overshoot in angle of mathematics. Sauerbrey equation is only applicable in the case when the mass is firmly attached to the quartz crystal surface, oscillating rigidly together with the crystal throughout the experiment. When changes occurred to the visco-elastic property of the sensing film, Eq. (2) should add a viscoelastic term and change to Eq. (3)[23]: (3)

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Where hf is the thickness of the deposited film, Vs is the acoustic velocity across the deposited film thickness, ρ is the density of the film, μ is the stiffness of the film. The mass uptake can be expressed as Δm=ΔρAhf (A is sensing area). So, the first term of Eq. (3) is the usual Sauerbrey equation and the second term in Eq. (3) explains the frequency shifts being related to the mechanical stiffness of the film. According to our D-f plot, the sensing film expanded, so the ∆μ in equation (3) was a negative value. This will cause an increase in frequency response (Δf) so that it was reasonable to see a larger frequency response (an overshoot in f-t plot). Our assumption that the overshoot was cause by expansion of the sensing film was right in the angle of mathematics. So we suggested that change in the stiffness of the sensing film was the real cause for the overshoot. Furthermore, thickness of sensing films is an important factors that affects the viscoelastic property and the responses of different thickness sensing films were studied. Fig. 12d shows the D-f plots of responses of QCMs with different thickness (0.392, 1.568, 2.352 and 3.136 μg/mm2) of sensing film to 30 ppm DMMP. Whatever thickness the sensing films were, the slope of the D-f plot all increased after N2 injection. What’s more, the thicker the sensing film was, the larger the dissipation changed and the higher the overshoot in the frequency response (can be seen from the change of D and f in

phase II). This phenomenon is also in accord with the equation (3).

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4. Conclusions In this paper, a homemade wireless-electrodeless QCM-D based nano-structured hollow ball-like In2O3-Au decorated DMMP sensor is presented. With the noncontact configuration, wires or electrodes were removed so that deterioration of the sensing ability cause by the electrodes and damage to the chamber for wire lead were avoided. The frequency shift and dissipation value was simultaneously monitored during the experiment, which provide us more information about the sensing film so that desorption process of the DMMP was studied further. Then, proper model for the experiment was chosen and the abnormal peak after N2 was injected to desorb the sensor was explained in the angle of both mathematics and chemical bond. Finally, the In2O3-Au coated sensor achieved sensitivity of 2.14 Hz/ppm, which was 4 times higher compared with that of the pristine In2O3 coated sensor. Besides, a limit of detection 5 ppm was achieved. The results indicate that the wireless-electrodeless QCM-D system is a good candidate for monitoring low concentration of VOCs and for monitoring the mechanical properties of the coated materials. In the future, more work needs to be done to make good use of this new kind of wireless-electrodeless QCM-D sensor. By simultaneously monitoring the frequency and dissipation value, proper model would be proposed and more phenomena during the gas sensing experiment can be better understood. Moreover, operating in higher harmonics will be investigated in the future to research the relationship between D and f in viscoelastic conditions and how it changes in different harmonics. This would be important for us to do more deep researches on dynamic properties of the loaded materials.

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Acknowledgments The work is supported by the Natural Science Foundation of China (Grant No. 61403339), the Research Program of the Education Department of Zhejiang Province (Grant No. Y201328881) and Autonomous Research Project of the State Key Laboratory of Industrial Control Technology, China (Grant No. ICT1704).

References [1] C. Tasaltin, I. Gurol, M. Harbeck, E. Musluoglu, V. Ahsen, Z.Z. Ozturk, Synthesis and DMMP sensing properties of fluoroalkyloxy and fluoroaryloxy substituted phthalocyanines in acoustic sensors, Sensors and Actuators B: Chemical, 150(2010) 781-7. [2] Z. Ying, Y. Jiang, X. Du, G. Xie, J. Yu, H. Wang, PVDF coated quartz crystal microbalance sensor for DMMP vapor detection, Sensors and Actuators B: Chemical, 125(2007) 167-72. [3] S.C. Lee, H.Y. Choi, S.J. Lee, W.S. Lee, J.S. Huh, D.D. Lee, et al., The development of SnO2-based recoverable gas sensors for the detection of DMMP, Sensors and Actuators B: Chemical, 137(2009) 23945.

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[4] T. Alizadeh, L.H. Soltani, Reduced graphene oxide-based gas sensor array for pattern recognition of DMMP vapor, Sensors and Actuators B: Chemical, 234(2016) 361-70.

[5] H. Li, Q. Zheng, J. Luo, Z. Cheng, J. Xu, Impacts of meso-structure and organic loadings of

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fluoroalcohol derivatives/SBA-15 hybrids on nerve agent simulant sensing, Sensors and Actuators B: Chemical, 187(2013) 604-10.

[6] Q. Zheng, Y. Zhu, J. Xu, Z. Cheng, H. Li, X. Li, Fluoroalcohol and fluorinated-phenol derivatives functionalized mesoporous SBA-15 hybrids: high-performance gas sensing toward nerve agent, J Mater Chem, 22(2012) 2263-70.

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[7] Z. Zhang, J. Fan, J. Yu, S. Zheng, W. Chen, H. Li, et al., New poly(N,N-dimethylaminoethyl methacrylate)/polyvinyl alcohol copolymer coated QCM sensor for interaction with CWA simulants, ACS

N

applied materials & interfaces, 4(2012) 944-9.

[8] Y. Long, Y. Wang, X. Du, L. Cheng, P. Wu, Y. Jiang, The Different Sensitive Behaviors of a Hydrogen-

A

Bond Acidic Polymer-Coated SAW Sensor for Chemical Warfare Agents and Their Simulants, Sensors,

M

15(2015) 18302-14.

[9] V.B. Raj, A.T. Nimal, M. Tomar, M.U. Sharma, V. Gupta, Novel scheme to improve SnO2/SAW sensor performance for NO2 gas by detuning the sensor oscillator frequency, Sensors and Actuators B:

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Chemical, 220(2015) 154-61.

[10] V.B. Raj, H. Singh, A.T. Nimal, M. Tomar, M.U. Sharma, V. Gupta, Origin and role of elasticity in the enhanced DMMP detection by ZnO/SAW sensor, Sensors and Actuators B: Chemical, 207(2015) 375-82.

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[11] S.M. Daly, M. Grassi, D.K. Shenoy, F. Ugozzoli, E. Dalcanale, Supramolecular surface plasmon resonance (SPR) sensors for organophosphorus vapor detection, Journal of Materials Chemistry, 17(2007) 1809.

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[12] G. Fan, Y. Wang, M. Hu, Z. Luo, K. Zhang, G. Li, Template free synthesis of hollow ball-like nanoFe2O3 and its application to the detection of dimethyl methylphosphonate at room temperature, Sensors, 12(2012) 4594-604. [13] Y. Zhao, H. Chen, X. Wang, J. He, Y. Yu, H. He, Flower-like tungsten oxide particles: synthesis, characterization and dimethyl methylphosphonate sensing properties, Analytica chimica acta, 675(2010)

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36-41.

[14] Y. Zhao, J. He, M. Yang, S. Gao, G. Zuo, C. Yan, et al., Single crystal WO(3) nanoflakes as quartz crystal microbalance sensing layer for ultrafast detection of trace sarin simulant, Analytica chimica acta, 654(2009) 120-6. [15] G. Fan, Y. Wang, M. Hu, Z. Luo, G. Li, Synthesis of flowerlike nano-SnO2and a study of its gas sensing response, Measurement Science and Technology, 22(2011) 045203. [16] J. Zheng, G. Li, X. Ma, Y. Wang, G. Wu, Y. Cheng, Polyaniline–TiO2 nano-composite-based trimethylamine QCM sensor and its thermal behavior studies, Sensors and Actuators B: Chemical,

133(2008) 374-80. [17] N. Tamaekong, C. Liewhiran, A. Wisitsoraat, A. Tuantranont, S. Phanichphant, NO2 sensing properties of flame-made MnOx-loaded ZnO-nanoparticle thick film, Sensors and Actuators B: Chemical, 204(2014) 239-49. [18] Z. Pei, X. Ma, P. Ding, W. Zhang, Z. Luo, G. Li, Study of a QCM dimethyl methylphosphonate sensor based on a ZnO-modified nanowire-structured manganese dioxide film, Sensors, 10(2010) 8275-90. [19] K. Zhang, G. Fan, R. Hu, G. Li, Enhanced Dibutyl Phthalate Sensing Performance of a Quartz Crystal Microbalance Coated with Au-Decorated ZnO Porous Microspheres, Sensors, 15(2015) 21153-68. [20] D. Shen, Monitor the Adsorption of Bromine Vapor on Zeolitic- Imidazolate Framework-8 Film by

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an Electrodeless Quartz Crystal Microbalance in Overtone, International Journal of Electrochemical Science, (2016) 3664-79.

[21] Q. Kang, X. Zhu, X. Ma, L. Kong, W. Xu, D. Shen, Response of an electrodeless quartz crystal

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microbalance in gaseous phase and monitoring adsorption of iodine vapor on zeolitic-imidazolate framework-8 film, Sensors and Actuators B: Chemical, 220(2015) 472-80.

[22] H. Ogi, K. Motoshisa, T. Matsumoto, K. Hatanaka, M. Hirao, Isolated electrodeless high-frequency quartz crystal microbalance for immunosensors, Anal Chem, 78(2006) 6903-9.

[23] A. Erol, S. Okur, N. Yağmurcukardeş, M.Ç. Arıkan, Humidity-sensing properties of a ZnO nanowire

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film as measured with a QCM, Sensors and Actuators B: Chemical, 152(2011) 115-20.

[24] M. Rodahl, B. Kasemo, A simple setup to simultaneously measure the resonant frequency and the

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absolute dissipation factor of a quartz crystal microbalance, Review of Scientific Instruments, 67(1996) 3238.

A

[25] H. Ogi, K. Motohisa, K. Hatanaka, T. Ohmori, M. Hirao, M. Nishiyama, Concentration dependence

M

of IgG-protein A affinity studied by wireless-electrodeless QCM, Biosensors & bioelectronics, 22(2007) 3238-42.

[26] H. Ogi, Y. Fukunishi, H. Nagai, K. Okamoto, M. Hirao, M. Nishiyama, Nonspecific-adsorption behavior

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of polyethylenglycol and bovine serum albumin studied by 55-MHz wireless-electrodeless quartz crystal microbalance, Biosensors & bioelectronics, 24(2009) 3148-52. [27] H. Ogi, T. Yanagida, M. Hirao, M. Nishiyama, Replacement-free mass-amplified sandwich assay with 4819-22.

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180-MHz electrodeless quartz-crystal microbalance biosensor, Biosensors & bioelectronics, 26(2011) [28] A.C. Stevenson, C.R. Lowe, Magnetic–acoustic–resonator sensors (MARS) - a new sensing

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methodology, Sensors and Actuators A: Physical, (1999). [29] A.C. Stevenson, B. Araya-Kleinsteuber, R.S. Sethi, H.M. Mehta, C.R. Lowe, Hypersonic evanescent waves generated with a planar spiral coil, The Analyst, 128(2003) 1175. [30] A.C. Stevenson, B. Araya-Kleinsteuber, R.S. Sethi, H.M. Metha, C.R. Lowe, Planar coil excitation of multifrequency shear wave transducers, Biosensors & bioelectronics, 20(2005) 1298-304.

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[31] R. Hu, A.C. Stevenson, C.R. Lowe, An acoustic glucose sensor, Biosensors & bioelectronics, 35(2012) 425-8. [32] R. Hu, K. Zhang, G. Fan, Z. Luo, G. Li, Development of a high-sensitivity plasticizer sensor based on a quartz crystal microbalance modified with a nanostructured nickel hydroxide film, Measurement Science and Technology, 26(2015) 055102. [33] Y. Wang, P. Ding, R. Hu, J. Zhang, X. Ma, Z. Luo, et al., A dibutyl phthalate sensor based on a nanofiber polyaniline coated quartz crystal monitor, Sensors, 13(2013) 3765-75. [34] S.M. Ballantyne, M. Thompson, Superior analytical sensitivity of electromagnetic excitation

compared to contact electrode instigation of transverse acoustic waves, The Analyst, 129(2004) 219-24. [35] H.T. Fan, X.J. Xu, X.K. Ma, T. Zhang, Preparation of LaFeO3 nanofibers by electrospinning for gas sensors with fast response and recovery, Nanotechnology, 22(2011) 115502. [36] X. Ji, W. Yao, J. Peng, N. Ren, J. Zhou, Y. Huang, Evaluation of Cu-ZSM-5 zeolites as QCM sensor

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coatings for DMMP detection, Sensors and Actuators B: Chemical, 166-167(2012) 50-5.

Author biography Daqi Chen received the B.S. degree in control science and engineering at Zhejiang University in 2013. He is pursuing his Ph.D. in control science and engineering at Zhejiang University. His area of interests is applications of wireless-electrodeless QCM-D sensors.

Kaihuan Zhang is pursuing his Ph.D. in control science and engineering at Zhejiang

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University. His area of interests is gas sensors.

Hui Zhou received her MSc Degrees in physical chemistry at Nanjing Normal

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University, China, in 2008. She became a lecturer of School of Chemical Engineering

at Yangzhou Polytechnic Institute from 2008. Now she is also a doctoral student in Chemistry and Chemical Engineering at Yangzhou University. She is interested in the

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photocatalysis and the mechanism of photocatalysis.

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green synthesis of nanosized semiconductor metal dioxide, the applications of

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Guokang Fan is a lecturer working at School of Chemistry and Chemical Engineering,

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Yangzhou University. He received his Ph.D. in detection technology and automatic equipment from Zhejiang University. His main research interests is in synthesis of

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nanomaterials and gas sensors.

You Wang is an associate professor at the College of Control Science and Engineering,

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Zhejiang University. He received his Ph.D. degree in Biomeidical Engineering from Zhejiang University, P.R. China, in 2007. His research interests are biosensors, gas

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sensors and their application in industry and medical device.

Guang Li is a professor at the College of Control Science and Engineering, Zhejiang

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University. He received a PhD degree from the Centre for Biological and Medical Systems at Imperial College of Science, Technology and Medicine, London, UK and held the post of a post-doc engineer in the University of Glasgow and Moor Instruments Co Ltd., UK. His current research interests include sensors, medical instruments and neuro informatics.

Ruifen Hu received her Ph.D. in chemical engineering and biotechnology from

University of Cambridge and now is an assistant professor at the College of Control

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Science and Engineering, Zhejiang University. Her main research interests is biosensors.

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Figure 1. The schematic illustration of the wireless-electrodeless QCM-D system. The signal generator generates the burst radio frequency signal and sends it to the transmitting coil (left) to oscillate the quartz crystal. The receiving coil (right) receives the decaying oscillation signal and sends it to the narrowband amplifier then to the oscilloscope. Finally, the digitalized signal was sent to the PC for analyzing.

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Figure 2. The received signal of the digital oscilloscope. The constant sinusoidal signal on the initial part of the figure is the RF signal used to oscillate the quartz disc. (a) Operated with the quartz disc. The decaying sinusoidal signal on the later part of the figure is the freely oscillation signal of the quartz disc. (b) Operated without the quartz disc. No decaying sinusoidal signal is seen.

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Figure 3. The amplitude-frequency curve of the quartz disc. Only when the RF signal used for oscillation was within this range could the quartz disc be oscillated (freely oscillation signal can be observed).

Figure 4. The homebuilt electrodeless QCM gas chamber. Transmitting and receiving coils are placed right below the quartz plate outside the chamber, which are used to excite the quartz oscillator and receive the vibrational signals of the oscillator. The quartz disc is placed at the bottom of the chamber and above the middle of two coils.

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Figure 5. XRD patterns of the crystalline In2O3 and In2O3-Au.

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Figure 6. SEM morphology of the In2O3 and In2O3-Au sample. (a) In2O3, (b) In2O3-Au.

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Figure 7. Response curve of the In2O3 and In2O3-Au QCM sensors to 30 ppm DMMP with different thicknesses of sensing films.

Figure 8. Response curves of the In2O3-Au coated QCM sensor to 15, 25, and 50 ppm (from bottom to top) of DMMP.

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Figure 9. Calibration curves of the In2O3 and In2O3-Au coated QCM sensors to different concentrations of DMMP vapor. The inset indicates the calibration curves of the linear range

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Figure 10. Responses of the In2O3 and In2O3-Au coated QCM sensors to various organic vapors. The concentration of all the tested vapor was 30 ppm.

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Figure 11. Polar plot of response ratio (R1/R2) between the In2O3-Au coated and the In2O3 coated QCM.

Figure 12. Responses of the In2O3-Au coated QCM sensors to 50 ppm DMMP. (a) f-t graph, (b) D-t graph and (c) D-f graph. In plot c, phase I represents the absorption process and phase II and III represents the desorption process. (d) Responses of the

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different thickness (0.392, 1.568, 2.352 and 3.136 μg/mm2) In2O3-Au coated QCM sensors to 30 ppm DMMP, phase II represents desorption process right after the injection of N2.

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Pore diameter (nm) 16.05 18.86

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Table 1 BET surface area analyses of PANI and graphene/PANI. Samples BET Surface Pore Volume Area (cm3/g) (m2/g) 56.04 0.22 Undecorated 61.36 0.29 Au-decorated