Showing papers by "Adisorn Tuantranont published in 2013"

Metamaterial-based microfluidic sensor for dielectric characterization

Abstract: A microfluidic sensor is implemented from a single split-ring resonator (SRR), a fundamental building block of electromagnetic metamaterials. At resonance, an SRR establishes an intense electric field confined within a deeply subwavelength region. Liquid flowing in a micro-channel laid on this region can alter the local field distribution and hence affect the SRR resonance behavior. Specifically, the resonance frequency and bandwidth are influenced by the complex dielectric permittivity of the liquid sample. The empirical relation between the sensor resonance and the sample permittivity can be established, and from this relation, the complex permittivity of liquid samples can be estimated. The technique is capable of sensing liquid flowing in the channel with a cross-sectional area as small as (0.001 λ 0 ) 2 , where λ 0 denotes the free-space wavelength of the wave excitation. This work motivates the use of SRR-based microfluidic sensors for identification, classification, and characterization of chemical and biochemical analytes.

Ultra-sensitive H2 sensors based on flame-spray-made Pd-loaded SnO2 sensing films

Abstract: In this paper, ultra-sensitive hydrogen (H 2 ) gas sensors based on flame-spray-made Pd-catalyzed SnO 2 nanoparticles is presented. Pd-loaded SnO 2 crystalline nanoparticles with high specific surface area and well-controlled size were synthesized by flame spray pyrolysis (FSP) in one step. The particle properties were characterized by XRD, BET, SEM, TEM and EDS analyses. The H 2 -sensing performances in terms of sensor response, response time and selectivity were optimized by varying Pd concentration between 0.2 and 2 wt%. An optimal Pd concentration for H 2 sensing was found to be 0.2 wt%. The optimal sensing film (0.2 wt% Pd/SnO 2 , 10 μm in thickness) showed an ultra-high sensor response of ∼10 4 to 1 vol% of H 2 at 200 °C and very short response time within a few seconds. Moreover, the optimum sensing temperature of Pd-loaded SnO 2 films was shifted to a lower value compared with that of unloaded SnO 2 film. The significant enhancement of H 2 sensing performances was attributed to highly effective spillover mechanism of well-dispersed Pd catalyst in SnO 2 matrix at low Pd-loading concentration. Furthermore, the catalyst selectivity of Pd toward H 2 was found to be significantly higher than those of two other noble metals including Pt and Ru, respectively. Therefore, the flame-made 0.2 wt% Pd/SnO 2 sensors is one of the most promising candidates for highly sensitive and selective detection of H 2 .

NO2-sensing properties of WO3 nanorods prepared by glancing angle DC magnetron sputtering

Abstract: In this work, the NO 2 -sensing properties of the tungsten trioxide (WO 3 ) nanorods prepared by dc magnetron sputtering with glancing-angle deposition (GLAD) technique are comparatively studied with that of WO 3 thin film deposited by normal sputtering process. The crystal structure and morphologies were characterized by grazing-incidence X-ray diffraction and field emission scanning electron microscopy, respectively. As-deposited WO 3 structure deposited at glancing angle of 85° exhibited amorphous crystal structure with uniform isolated columnar nanorod morphology with average length, diameter and spacing between nanorods of around 400 nm, 50 nm and 10 nm, respectively. Annealing at 400 and 500 °C resulted in polycrystalline phase and more porous nanorod network with very large effective surface area. The NO 2 sensing response of WO 3 nanorods was found to be higher than that of WO 3 thin film by a factor of 2–5 depending on operating temperature and gas concentration. In addition, WO 3 nanorod annealed at 500 °C exhibited an optimum response of ∼27–2.0 ppm of NO 2 at 250 °C. Therefore, GLAD using reactive dc magnetron sputtering has been demonstrated as a practical method for fabrication of well-aligned metal oxide nanostructures and is potential for gas-sensing applications.

A disposable amperometric biosensor based on inkjet-printed Au/PEDOT-PSS nanocomposite for triglyceride determination

Abstract: The work presents a new and highly sensitive disposable amperometric triglyceride (TG) biosensor based on Au/PEDOT-PSS nanocomposite inkjet-printed on screen-printed carbon electrodes (SPCEs) and co-immobilization of lipase, glycerol kinase and glycerol-3-phosphate oxidase. One-step chemically synthesized Au/PEDOT-PSS nanocomposite deposited by inkjet printing is demonstrated to produce in nanorod structures on SPCE surface. The electrochemical responses are found to be significantly enhanced by Au nanoparticles and optimal preparation conditions of gold nanoparticle formation for electrochemical detection are found to be 0.015 M EDOT and 6.25 mM gold precursor. For TGs determination in blood, SPCE electrode with 5 layers of inkjet printed Au/PEDOT-PSS nanocomposite provides optimum performances when operated with the operating potential of 0.4 V in 0.1 M sodium phosphate buffer pH of 7.0. Wide dynamic range (0–531 mg/dL), moderate sensitivity (2.66 μA/mM), modest response time (30 s), low detection limit (7.88 mg/dL), low interference, good reproducibility and satisfactory life time (40% loss of response current after 30 days of storage at 4 °C) have been achieved. Therefore, inkjet-printed Au/PEDOT-PSS nanocomposite on SPCEs is a promising candidate for TGs determination.

Carbon doped tungsten oxide nanorods NO2 sensor prepared by glancing angle RF sputtering

Abstract: Metal oxide semiconductor nanostructures offer potential advantages in sensing applications due to their large surface to volume ratio, lower electron recombination rate, and high stability. However, most methods produce nanostructures with random sizes, distribution and orientations, which are not reliable for practical applications because of poor reproducibility. In this work, homogeneous carbon-doped WO3 nanorods are developed based on the glancing angle deposition (GLAD) technique using radio-frequency magnetron sputtering and investigated for NO2 gas sensing application. The carbon doping is achieved by using acetylene gas as a carbon source. Characterization based on scanning electron microscopy, Auger electron spectroscopy and X-ray diffraction confirm the formation of uniform carbon-doped crystalline WO3 nanorods. The gas-sensing results reveal that carbon-doped WO3 nanorods sensor exhibits not only high response and selectivity to NO2 (0.5–5 ppm) but also at low operating temperature (150 °C) compared with the undoped ones. The observed gas-sensing enhancement may be attributed to the increase of specific surface area and the decrease of activation energy by carbon doping.

A disposable screen printed graphene–carbon paste electrode and its application in electrochemical sensing

Abstract: In this work, an innovative, low cost and effective screen printed graphene–carbon paste electrode (SPGE) for advanced electrochemical sensing is reported. The SPGE is prepared by mixing electrolytically exfoliated graphene powder with carbon paste and is then screen printed on polyvinyl chloride substrate. The electrochemical device comprises three electrodes including SPGEs as the working and counter electrodes and silver/silver chloride paste as the reference electrode. Material characterization by electron microscopy and Raman spectroscopy confirms that the size of the multilayer graphene is in the range of 250–400 nm and that the carbon paste matrix is composed of 20–30 nm carbon nanoparticles. The electrochemical performances of the SPGE towards three of the most common electroactive analytes including hydrogen peroxide (H2O2), nicotinamide adenine dinucleotide (NAD+/NADH) and ferri/ferro cyanide (Fe(CN)63−/4−) redox couples are characterized. It is found that graphene inclusion considerably enhances electrochemical responses towards the analytes, with 10% being an optimum graphene concentration. The oxidation signals for H2O2, NADH and K4Fe(CN)6 of the SPGE with the optimal graphene concentration are found to be ∼2.0, ∼1.8 and ∼1.7 times higher than those of a screen printed carbon paste electrode, respectively. In addition, excellent analytical features with relatively wide dynamic ranges, high sensitivities, low detection limits and high reproducibility are achieved. Therefore, the SPGE is a promising candidate for low-cost and advanced electrochemical sensing applications.

Inkjet-printed sol–gel films containing metal phthalocyanines/porphyrins for opto-electronic nose applications

Abstract: In this work, five metal porphyrins and phthalocyanines embedded in transparent sol–gel films were deposited by piezoelectric inkjet printing, characterized and used as gas sensors. Explored compounds include magnesium/manganese(III) chloride/zinc 5,10,15,20-tetraphenyl-21H,23H-porphyrin, magnesium 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine, and zinc 2,9,16,23-tetratertbutyl-29H,31H-phthalocyanine. Porphyrin/Phthalocyanine was blended with sol–gel solution to produce inks that were printed on glass substrates. The printed films were used as sensing layers for discrimination of volatile organic compounds (VOCs). Printed films were characterized by UV/vis spectroscopy, FTIR spectroscopy, and scanning electron microscopy. The employed sensing compounds are promising materials for optical gas sensors due to selective spectral alterations when exposed to oxidizing and reducing gases as well as VOCs. These alterations were observed by UV/vis spectroscopy and used to distinguish between several VOCs. To do so, a single printed sensing layer was exposed to methanol, ethanol, acetone and isopropanol vapor, respectively. During exposure the absorbance spectrum was continually measured and split into several wavelength intervals. By calculating the area integral of each interval and considering these as separate sensors it is possible to use a single sensing film to emulate sensor arrays. The results showed that the fabricated layers exhibit reversible optical modulations in the UV/vis spectra when exposed to various VOCs. The data have been analyzed by principal component analysis (PCA) and cluster analysis (CA). Results demonstrate the analytes to be distinguishable as isolated clusters in the PCA domains. The best results were obtained from ZnTPP and MgTPP containing films, whereas layers doped with Mn(III)ClTPP give unusable response.

Optical H2 sensing properties of vertically aligned Pd/WO3 nanorods thin films deposited via glancing angle rf magnetron sputtering

Abstract: In this work, the optical H2-sensing properties of Pd/tungsten trioxide (WO3) nanorods prepared by rf magnetron sputtering with glancing-angle deposition (GLAD) technique are investigated. From grazing-incidence X-ray diffraction and field emission scanning electron microscopic characterizations, annealed WO3 structure deposited on a quartz substrate at glancing angle of 85° exhibited polycrystalline monoclinic crystal structure with uniform partially isolated columnar nanorod morphology. The nanorods have the average length, diameter and rod separation of around 400 nm, 50 nm and 20 nm, respectively. The developed sensors show remarkable gasochromic absorbance response when exposed to H2. Cumulative absorbance in 650–1000 nm wavelength range is increased by approximately 51% toward H2 with 0.1% concentration in synthetic air, which is more than an order of magnitude higher than that of WO3 dense film prepared by conventional sputtering method. Moreover, WO3 nanorod based sensor is much more promising for practical use due to its much faster response. Therefore, the developed Pd/WO3 nanorod based optical sensors are highly potential for low H2 concentration sensing with highly sensitivity, fast and stable responses and low operating temperature.

Graphene-Based Chemical and Biosensors

Abstract: Graphene is a novel and promising material for chemical and biosensing due to its extraordinary structural, electronic, and physiochemical properties. Recently, a large number of graphene-based chemical and biosensors with different structures and fabrication methods have been reported. In this chapter, graphene’s synthesis methods, properties, and applications in chemical and biosensing are extensively surveyed. Graphene-based chemical and biosensors may similarly be classified into three main groups including chemoresistive, electrochemical, and other sensing platforms. Chemoresistive graphene-based chemical sensors have been widely developed for ultrasensitive gas-phase chemical sensing with single molecule detection capability. Graphene-based electrochemical sensors for chemical and biosensing have shown excellent performances toward various non-bio and bio-analytes compared to most other carbon-based electrodes due to its very high electron transfer rate of highly dense edge-plane-like defective active sites, excellent direct electrochemical oxidation of small biomolecules and direct electrochemistry of enzyme while graphene FET chemoresistive biosensors for detections of DNA, protein/DNA mixture, and other antibody-specific biomolecules have been reported with high sensitivity and specificity. In addition, the graphene’s performance considerably depends on synthesis method and surface functionalized graphene oxides prepared by chemical, thermal, and particularly electrochemical reductions are demonstrated to be highly promising for both electrochemical and chemoresistive sensing platforms. However, large-scale economical production of graphene is still not generally attainable and graphene-based chemical and biosensors still suffer from poor reproducibility due to difficulty of controlling graphene sensor structures. Therefore, novel methods for well-controlled synthesis and processing of graphene must be further developed. Furthermore, effective doping methods should be developed and applied to enhance its sensing behaviors. Lastly, graphene’s chemical and biological interaction and related charge transport mechanisms are not well understood and should be further studied.

Design and development of data glove based on printed polymeric sensors and Zigbee networks for Human-Computer Interface.

Abstract: Current trends in Human-Computer Interface (HCI) have brought on a wave of new consumer devices that can track the motion of our hands. These devices have enabled more natural interfaces with computer applications. Data gloves are commonly used as input devices, equipped with sensors that detect the movements of hands and communication unit that interfaces those movements with a computer. Unfortunately, the high cost of sensor technology inevitably puts some burden to most general users. In this research, we have proposed a low-cost data glove concept based on printed polymeric sensor to make pressure and bending sensors fabricated by a consumer ink-jet printer. These sensors were realized using a conductive polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) [PEDOT:PSS]) thin film printed on glossy photo paper. Performance of these sensors can be enhanced by addition of dimethyl sulfoxide (DMSO) into the aqueous dispersion of PEDOT:PSS. The concept of surface resistance was successfully adopted for the design and fabrication of sensors. To demonstrate the printed sensors, we constructed a data glove using such sensors and developed software for real time hand tracking. Wireless networks based on low-cost Zigbee technology were used to transfer data from the glove to a computer. To our knowledge, this is the first report on low cost data glove based on paper pressure sensors. This low cost implementation of both sensors and communication network as proposed in this paper should pave the way toward a widespread implementation of data glove for real-time hand tracking applications.

The development of graphene-based flex sensors using printed electronics for physical rehabilitation and assistive applications

Abstract: Flex sensors have several promising uses as measurement devices in physical rehabilitation and assistive applications. Most commercial conductive-ink based flex sensors, however, are prone to delamination due to cracking and humidity. Size and flexibility of sensor substrates are also hurdles for practical device designs. This paper presents the development of flex sensors based on the printed technology. The experimental results report the effect of various combination of fabrication settings, i.e., different contact point materials during measurement, the use of graphene-modified vs. pure carbon pastes as the first layer material, different pattern parameters (i.e., sensor width, sensor length, pattern length and interval length), and measurement before and after one week time.