Anurat Wisitsoraat

Electrolytically Exfoliated Graphene-Loaded Flame-Made Ni-Doped SnO2 Composite Film for Acetone Sensing

In this work, flame-spray-made SnO2 nanoparticles are systematically studied by doping with 0.1-2 wt % nickel (Ni) and loading with 0.1-5 wt % electrolytically exfoliated graphene for acetone-sensing applications. The sensing films (∼12-18 μm in thickness) were prepared by a spin-coating technique on Au/Al2O3 substrates and evaluated for acetone-sensing performances at operating temperatures ranging from 150 to 350 °C in dry air. Characterizations by X-ray diffraction, transmission/scanning electron microscopy, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that Ni-doped SnO2 nanostructures had a spheriodal morphology with a polycrystalline tetragonal SnO2 phase, and Ni was confirmed to form a solid solution with SnO2 lattice while graphene in the sensing film after annealing and testing still retained its high-quality nonoxidized form. Gas-sensing results showed that SnO2 sensing film with 0.1 wt % Ni-doping concentration exhibited an optimal response of 54.2 and a short response time of ∼13 s toward 200 ppm acetone at an optimal operating temperature of 350 °C. The additional loading of graphene at 5 wt % into 0.1 wt % Ni-doped SnO2 led to a drastic response enhancement to 169.7 with a very short response time of ∼5.4 s at 200 ppm acetone and 350 °C. The superior gas sensing performances of Ni-doped SnO2 nanoparticles loaded with graphene may be attributed to the large specific surface area of the composite structure, specifically the high interaction rate between acetone vapor and graphene-Ni-doped SnO2 nanoparticles interfaces and high electronic conductivity of graphene. Therefore, the 5 wt % graphene loaded 0.1 wt % Ni-doped SnO2 sensor is a promising candidate for fast, sensitive and selective detection of acetone.

Fast cholesterol detection using flow injection microfluidic device with functionalized carbon nanotubes based electrochemical sensor

This work reports a new cholesterol detection scheme using functionalized carbon nanotube (CNT) electrode in a polydimethylsiloxane/glass based flow injection microfluidic chip. CNTs working, silver reference and platinum counter electrode layers were fabricated on the chip by sputtering and low temperature chemical vapor deposition methods. Cholesterol oxidase prepared in polyvinyl alcohol solution was immobilized on CNTs by in-channel flow technique. Cholesterol analysis based on flow injection chronoamperometric measurement was performed in 150-μm-wide and 150-μm-deep microchannels. Fast and sensitive real-time detection was achieved with high throughput of more than 60 samples per hour and small sample volume of 15 μl. The cholesterol sensor had a linear detection range between 50 and 400 mg/dl. In addition, low cross-sensitivities toward glucose, ascorbic acid, acetaminophen and uric acid were confirmed. The proposed system is promising for clinical diagnostics of cholesterol with high speed real-time detection capability, very low sample consumption, high sensitivity, low interference and good stability.

A review of monolithic multichannel quartz crystal microbalance: a review.

Monolithic multichannel quartz crystal microbalance (MQCM) is an emerging technology for advanced sensing and measurement applications. In this report, a comprehensive review of MQCM technology is presented. Firstly, basic MQCMs design, simulation and characterization with emphasis on acoustic interference are described. Next, various MQCM schemes to minimize interference and enhance sensitivity of conventional MQCM devices based on modification of quartz substrate structure are digested. These include mesa, convex and x-axis inversion structures. Three important MQCM sensing platforms and their application areas are then discussed. These comprise MQCM as a static multichannel detector, series MQCM as a multichannel detector for the flow injection analysis and multi-frequency QCM for multi-sensitivity/multi-dynamic range detection. Finally, potential MQCM applications including electronic noses, bio-sensor arrays, and photocatatalytic measurement are illustrated and prospective MQCM applications including electronic tongues and electrochemical measurement are suggested.

Multi-Walled Carbon Nanotube-Doped Tungsten Oxide Thin Films for Hydrogen Gas Sensing

In this work we have fabricated hydrogen gas sensors based on undoped and 1 wt% multi-walled carbon nanotube (MWCNT)-doped tungsten oxide (WO3) thin films by means of the powder mixing and electron beam (E-beam) evaporation technique. Hydrogen sensing properties of the thin films have been investigated at different operating temperatures and gas concentrations ranging from 100 ppm to 50,000 ppm. The results indicate that the MWCNT-doped WO3 thin film exhibits high sensitivity and selectivity to hydrogen. Thus, MWCNT doping based on E-beam co-evaporation was shown to be an effective means of preparing hydrogen gas sensors with enhanced sensing and reduced operating temperatures. Creation of nanochannels and formation of p-n heterojunctions were proposed as the sensing mechanism underlying the enhanced hydrogen sensitivity of this hybridized gas sensor. To our best knowledge, this is the first report on a MWCNT-doped WO3 hydrogen sensor prepared by the E-beam method.

Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H(2) Gas Sensor.

Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2–2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5–20 nm wide and 20–40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al2O3 substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H2) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H2 sensitivity of ∼164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature.

Ultrasensitive detection of Vibrio cholerae O1 using microcantilever-based biosensor with dynamic force microscopy

This work presents the first demonstration of a cantilever based cholerae sensor. Dynamic force microscopy within atomic force microscope (AFM) is applied to measure the cantilevers resonance frequency shift due to mass of cell bound on microcantilever surface. The Vibrio cholerae O1, a food and waterborne pathogen that caused cholera disease in human, is a target bacterium cell of interest. Commercial gold-coated AFM microcantilevers are immobilized with monoclonal antibody (anti-V. cholerae O1) by self-assembled monolayer method. V. cholerae O1 detection experiment is then conducted in concentrations ranging from 1×10(3) to 1×10(7) CFU/ml. The microcantilever-based sensor has a detection limit of ∼1×10(3) CFU/ml and a mass sensitivity, Δm/ΔF, of ∼146.5 pg/Hz, which is at least two orders of magnitude lower than other reported techniques and sufficient for V. cholerae detection in food products without pre-enrichment steps. In addition, V. cholerae O1 antigen-antibody binding on microcanilever is confirmed by scanning electron microscopy. The results demonstrate that the new biosensor is promising for high sensitivity, uncomplicated and rapid detection of V. cholerae O1.

Facile preparation of graphene–metal phthalocyanine hybrid material by electrolytic exfoliation

In this article, we present a new, facile and efficient electrochemical method for the production of a stable aqueous dispersion of a graphene–metal phthalocyanine hybrid material. The material has been prepared by electrolytic exfoliation of graphite in an electrolyte containing copper phthalocyanine-3,4′,4′′,4′′′-tetrasulfonic acid tetrasodium salt (TSCuPc). Single- and few-layer graphene sheets, decorated with metal phthalocyanine molecules, are generated during the electrolysis and stably dispersed in the electrolyte with no further chemical treatment. Scanning electron/atomic force microscopic characterization shows that the TSCuPc–graphene hybrid structure has a sharp-edged particle morphology with thicknesses ranging from 2 nm to 6 nm, corresponding to 1 to 6 graphene-stacked layers and largely varied lateral dimensions from a few tens to several hundreds of nanometers. In addition, Raman/FTIR/UV-Vis spectra and X-ray diffraction reveal characteristic peaks that suggest that the TSCuPc–graphene hybrid is formed by non-covalent π–π interactions between graphene sheets and metal phthalocyanine and indicate a high quality graphene hybrid structure that can potentially be used in practical applications.

Flow injection based microfluidic device with carbon nanotube electrode for rapid salbutamol detection

A microfabicated flow injection device has been developed for in-channel electrochemical detection (ECD) of a beta-agonist, namely salbutamol. The microfluidic system consists of PDMS (polydimethylsiloxane) microchannel and electrochemical electrodes formed on glass substrate. The carbon nanotube (CNT) on gold layer as working electrode, silver as reference electrode and platinum as auxiliary electrode were deposited on a glass substrate. Silver, platinum, gold and stainless steel catalyst layers were coated by DC-sputtering. CNTs were then grown on the glass substance by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. 100-microm-deep and 500-microm-wide PDMS microchannels fabricated by SU-8 molding and casting were then bonded on glass substrate by oxygen plasma treatment. Flow injection and ECD of salbutamol was performed with the amperometric detection mode for in-channel detection of salbutamol. The influences of flow rate, injection volume, and detection potential on the response of current signal were optimized. Analytical characteristics, such as sensitivity, repeatability and dynamic range have been evaluated. Fast and highly sensitive detection of salbutamol have been achieved. Thus, the proposed combination of the efficient CNT electrode and miniaturized lab-on-a-chip is a powerful platform for beta-agonists detection.

H2 Sensing Response of Flame-Spray-Made Ru/SnO2 Thick Films Fabricated from Spin-Coated Nanoparticles

High specific surface area (SSABET: 141.6 m2/g) SnO2 nanoparticles doped with 0.2–3 wt% Ru were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The specific surface area (SSABET) of the nanoparticles was measured by nitrogen adsorption (BET analysis). As the Ru concentration increased, the SSABET was found to linearly decrease, while the average BET-equivalent particle diameter (dBET) increased. FSP yielded small Ru particles attached to the surface of the supporting SnO2 nanoparticles, indicating a high SSABET. The morphology and accurate size of the primary particles were further investigated by TEM. The crystallite sizes of the spherical, hexagonal, and rectangular SnO2 particles were in the range of 3–10 nm. SnO2 nanorods were found to range from 3–5 nm in width and 5–20 nm in length. Sensing films were prepared by the spin coating technique. The gas sensing of H2 (500–10,000 ppm) was studied at the operating temperatures ranging from 200–350 °C in presence of dry air. After the sensing tests, the morphology and the cross-section of sensing film were analyzed by SEM and EDS analyses. The 0.2%Ru-dispersed on SnO2 sensing film showed the highest sensitivity and a very fast response time (6 s) compared to a pure SnO2 sensing film, with a highest H2 concentration of 1 vol% at 350 °C and a low H2 detection limit of 500 ppm at 200 °C.

Ultrasensitive NO2 Sensor Based on Ohmic Metal–Semiconductor Interfaces of Electrolytically Exfoliated Graphene/Flame-Spray-Made SnO2 Nanoparticles Composite Operating at Low Temperatures

In this work, flame-spray-made undoped SnO2 nanoparticles were loaded with 0.1-5 wt % electrolytically exfoliated graphene and systematically studied for NO2 sensing at low working temperatures. Characterizations by X-ray diffraction, transmission/scanning electron microscopy, and Raman and X-ray photoelectron spectroscopy indicated that high-quality multilayer graphene sheets with low oxygen content were widely distributed within spheriodal nanoparticles having polycrystalline tetragonal SnO2 phase. The 10-20 μm thick sensing films fabricated by spin coating on Au/Al2O3 substrates were tested toward NO2 at operating temperatures ranging from 25 to 350 °C in dry air. Gas-sensing results showed that the optimal graphene loading level of 0.5 wt % provided an ultrahigh response of 26,342 toward 5 ppm of NO2 with a short response time of 13 s and good recovery stabilization at a low optimal operating temperature of 150 °C. In addition, the optimal sensor also displayed high sensor response and relatively short response time of 171 and 7 min toward 5 ppm of NO2 at room temperature (25 °C). Furthermore, the sensors displayed very high NO2 selectivity against H2S, NH3, C2H5OH, H2, and H2O. Detailed mechanisms for the drastic NO2 response enhancement by graphene were proposed on the basis of the formation of graphene-undoped SnO2 ohmic metal-semiconductor junctions and accessible interfaces of graphene-SnO2 nanoparticles. Therefore, the electrolytically exfoliated graphene-loaded FSP-made SnO2 sensor is a highly promising candidate for fast, sensitive, and selective detection of NO2 at low operating temperatures.