P2.3.3 VOC gas detection using solvatochromic dye coated side polished optical fiber

We propose a design for a highly sensitive volatile organic compounds (VOCs) sensor based on evanescent wave coupling of a side-polished optical fiber. The surface of the side-polished optical fiber coupled with a coated solvatochromic dye has charge-transfer (CT) properties. In the proposed model, the application of these optical properties and the novel solvatochromic dye helped overcome problems caused by limited sensitivity, selectivity, and dynamic range that are encountered in typical gas sensors. The different polarities of the VOCs cause changes in the effective refractive index of the sensing membrane owing to CT properties. This can lead to a change in the resonance wavelength of the side-polished optical fiber. To ascertain the effectiveness of the sensor, five VOCs dimethylamine, acetic acid, toluene, benzene, and ethanol were tested, and the enhance in sensitivity was analyzed for varying concentrations. According to the results, the proposed gas sensor showed high sensitivity and resolution.

All-fiber-optic VOC gas sensor based on side-polished fiber wavelength selectively coupled with cholesteric liquid crystal film

We have developed an optical gas sensor for detection of volatile organic compounds (VOCs) gases. The side-polished optical fiber coupled with the polymer planar waveguide (PWG) which has high sensitive to change refractive index. The PWG was fabricated by coating the solvatochromic dye with a polyvinyl pyrrolidone (PVP). The fabricated gas sensor system was tested with five-types of VOCs gases. The different polarities of the VOC gases cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. According to the results, the proposed gas sensor showed high sensitivity.

In this paper, we proposed a new type high sensitive volatile organic compounds (VOCs) gas sensor array that is based on the pulse width modulation technique. Four different types of solvatochromic dyes and two different types of polymers, were used to make the five different types of sensing membranes. These were deposited on the five side-polished optical fibers by a spin coater to make the five different sensing elements of the array. In order to ascertain the effectiveness of the sensors, five VOC gases were tested. Finally, principal component analysis (PCA) has been used to discriminates different types of VOCs.

Transparent ZnO gel was synthesized by sol-gel process. In order to getting fine powder of ZnO, at the beginning, ZnO gel was disposed with the pre-firing at 300°C. And then, ZnO powder was calcined at different temperature of 500 °C, 700 °C and 900 °C, the grain size of ZnO powder was different. This paper reports the sensitivity of ZnO gas sensor to three volatile organic compound (VOC) gases (acetone, ethanol and toluene). As we all know, these VOC gases are deleterious to global environment and our health. For different VOC gases, the optimum operating currents and the corresponding sensitivities were different. This paper also researched a nicely sensitive indirect- heating type thick film ZnO gas sensor by adding TiO2. TiO2 was mixed in weight percentage of 2%. The compound oxide sensor debased the optimum working currents of ethanol and toluene. And this sensor also showed rapid response-recovery time, which was propitious to practicability of ZnO gas sensor.

We are developing micropreconcentrators based on micro/nanotechnology to detect trace levels of volatile organic compound (VOC) gases contained in human and canine exhaled breath. The possibility of using exhaled VOC gases as biomarkers for various cancer diagnoses has been previously discussed. For early cancer diagnosis, detection of trace levels of VOC gas is indispensable. Using micropreconcentrators based on MEMS technology or nanotechnology is very promising for detection of VOC gas. A micropreconcentrator based breath analysis technique also has advantages from the viewpoints of cost performance and availability for various cancers diagnosis. In this paper, we introduce design, fabrication and evaluation results of our MEMS and nanotechnology based micropreconcentrators. In the MEMS based device, we propose a flower leaf type Si microstructure, and its shape and configuration are optimized quantitatively by finite element method simulation. The nanotechnology based micropreconcentrator consists of carbon nanotube (CNT) structures. As a result, we achieve ppb level VOC gas detection with our micropreconcentrators and usual gas chromatography system that can detect on the order of ppm VOC in gas samples. In performance evaluation, we also confirm that the CNT based micropreconcentrator shows 115 times better concentration ratio than that of the Si based micropreconcentrator. Moreover, we discuss a commercialization idea for new cancer diagnosis using breath analysis. Future work and preliminary clinical testing in dogs is also discussed.

Volatile organic compounds (VOCs) gas sensor based on gated lateral bipolar junction transistor (LBJT) was developed in this study. The device was fabricated using 0.35-μm logic process by Magnachip-Hynix Co. Ltd. under the Integrated Circuit Design education Center Multi Project Wafer (IDEC-MPW) program. Solvatochromic dye as the sensing membrane was coated on the floating gate of the device. A semiconductor test and analyzer (STA-EL421, ELECS) was used to measure the sensing results. Following the results, we found that the sensing device which used the gated LBJT device has fast responsibility and reversibility to VOC gases (acetone etc.).

We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolidone). To confirm the effectiveness of the sensor, five different sensing membranes were fabricated by coating the side-polished optical-fiber using the solvatochromic dyes Reinhardt's dye, Nile red, 4-aminophthalimide, 4-amino-N-methylphthalimide, and 4-(dimethylamino)cinnamaldehyde, which have different polarities that cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. The fabricated gas detection system was tested with five types of VOC gases, namely acetic acid, benzene, dimethylamine, ethanol, and toluene at concentrations of 1, 2,…,10 ppb. Second-regression and principal component analyses showed that the response properties of the proposed VOC gas sensor were linearly shifted bathochromically, and each gas showed different response characteristics.

In this paper, we propose an Au-polypyrrole (Ppy) nanorod gas sensor for the detection of volatile organic compound (VOC) gases. This gas sensor operates on the principle of localized surface plasmon resonance (LSPR). The Au-Ppy nanorods used in this experiment were synthesized using an anodic aluminum oxide template by the electrochemical deposition method. Using field emission scanning electron microscopy, we confirmed that the Au-Ppy nanorod arrays were successfully fabricated with a uniform size. By depositing gold, the Au-Ppy nanorods exhibited both optical and LSPR interference. The gas sensing properties of the fabricated nanorods were tested for VOCs such as acetic acid, benzene, and toluene with a short response time (~1 min). Moreover, the proposed VOC gas sensing system was tested with three types of VOC gases over a wide concentration range from 10 to 100 ppm. Highest sensitivity was observed for acetic acid gas, which had a linear relation with the gas concentration, indicating that the system can be used as a gas sensor.

Room temperature VOC gas detection using a gated lateral BJT with an assembled solvatochromic dye

Investigation on fabrication and VOC sensing properties of PDMS fiber based optical sensor

Application of micro-electro-mechanical system (MEMS) technology for controlling the evanescent field is attractive because the dimension of the evanescent field is of the same order as that of the movement distance of the MEMS device. Two different types of MEMS-based devices are proposed and developed for controlling the evanescent field generated at the surface of the side-polished optical fiber. The first one is a hybrid type and the other is a monolithic type. Both devices have merit and demerit from the aspects of process ease and alignment. The hybrid-type of device has a problem of close contact of the diaphragm with the side-polished optical fiber. The monolithic-type of device is a pre-aligned structure but has a difficulty in terms of polishing depth control on the single mode fiber. A change in the transmission spectrum due to device operation (movement of diaphragm with respect to polished optical fiber surface) has been noticed. However, the extent of change in transmission has to be improved. Fine control of polishing depth and parallel alignment of side-polished fiber with a diaphragm are the critical factors for effective interaction of the diaphragm with an evanescent field.

Volatile organic compounds (VOCs) that easily evaporate at room temperature have caused detrimental to respiratory, allergic, and/or immune effects in humans. Increased awareness of toxicity on these VOC gases has led many studies to focus on direct measurement of these harmful VOCs with high sensitivity at lower operating temperature. Gas sensors based on surface chemical reaction of semiconducting metal oxides are readily available commercially. To improve gas sensing performance with lowered operating temperature and high sensitivity, adequate catalysts are commonly used. However, there is still limit to lower sensing temperature of metal oxides to room temperature. It has been reported that graphene oxide (GO), a graphene sheet linked to oxygen functional groups, has potential to realize room temperature operation. Additional advantage of the GO includes large scale and low cost production for commercial application. In this study, GO thin films were deposited by drop coating and thermally reduced under Ar to eliminate the functional groups from GO films. The electrical properties of GO transformed from an insulator to semiconductor support GO to easily be activated for sensing gases. To enhance selective gas sensing at room temperature, many types of noble metals such as Pt and Au can be considered as an activators or sensitizers. We investigated GO with silver catalyst with relatively low cost. The formation of Ag island clusters driven by deposition conditions and their VOC gas sensing was characterized to find optimal condition of catalysts. The morphologies of silver catalyst decoated GO film were analyzed with SEM, TEM, and XRD, and the quantity of the silver catalyst was measured by EDS. Gas sensing response to VOCs was measured at room temperature to extract characteristic feature. In order to determine selective detection of specific VOC gas, 2 types and 5 types of mixed gases such as formaldehyde, benzene, styrene, toluene, and xylene were used. Detailed discussion on and the mechanism of silver catalytic effect on GO will be given. AcknowledgementThis research was partially supported by the Korea Institute of Energy Technology Evaluation and Planning (20158520000210) grant funded by the Korea Government Ministry of Trade, Industry and Energy, a grant from a Strategic Research Project (2013-0132) funded by the Korea Institute of Construction Technology, and Auburn University IGP.References Vlachos, D. S., C. A. Papadopoulos, and J. N. Avaritsiotis. "On the electronic interaction between additives and semiconducting oxide gas sensors." Applied physics letters 69.5 (1996): 650-652.Tyagi, Punit, et al. "Metal Oxide Catalyst assisted SnO2 thin film based SO2 gas sensor." Sensors and Actuators B: Chemical (2015).Ahn, Hosang, et al. "Volatile gas sensing properties of phase and composition gradient SnOx thin films by combinatorial sputter deposition." ECS Solid State Letters 2.1 (2013): P11-P13.Li, Yongjie, et al. "Catalytic performance of Pt nanoparticles on reduced graphene oxide for methanol electro-oxidation." Carbon 48.4 (2010): 1124-1130.Wang, Jianwei, et al. "Dielectrophoretic assembly of Pt nanoparticle-reduced graphene oxide nanohybrid for highly-sensitive multiple gas sensor." Sensors and Actuators B: Chemical 220 (2015): 755-761.Park, Hyejin, et al. "Transition of gas sensing behavior in non-reduced graphene oxides with thermal annealing." Materials Letters 136 (2014): 164-167.

In the current study, XRD analysis shows the polycrystalline form an inverse spinel Fe3O4 structure. Fe3O4 film is prepared by dip coating method on MEMS gas sensors to test the sensitivity on volatile organic compound (VOC) gas. VOC is being tested at 92 mW (∼300 °C) power consumption with different VOC gas concentrations and also tested with different gases like NO2, SO2, NH3 and CO gas. The results showed that the Fe3O4 gas sensor has better selectivity and high response with VOC 1.2 ppm concentration. Structural morphology is seen and reaction mechanism when VOC gas reacts with Fe3O4 material is also being discussed.

In this paper, we report the fabrication and experiment results of carbon nanotube (CNT) based micropreconcentrator. In our micropreconcentrator, the CNT are applied as the adsorption structures to trap and detect trace level volatile organic compounds (VOC) gas for human breath analysis. Our CNT based micropreconcentrator is designed and its performance is investigated quantitatively by simulation study. As a result of quantitative simulation study, we could confirm that the number of adsorbed particles of CNT based models is at least 4 times to 23 times more than that of our previous Si based models for the same structure areas. We have also fabricated CNT based micropreconcentrator and evaluated it by gas chromatography with 5 ppb toluene-d8 (C7H8-d8) VOC gas sample. As a result, we could successfully confirm the ppb level VOC gas detection.