High Sensitivity Electrochemical Cholesterol Sensor Utilizing a Vertically Aligned Carbon Nanotube Electrode with Electropolymerized Enzyme Immobilization

In this report, a new cholesterol sensor is developed based on a vertically aligned CNT electrode with two-step electrochemical polymerized enzyme immobilization. Vertically aligned CNTs are selectively grown on a 1 mm2 window of gold coated SiO2/Si substrate by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. CNTs are then simultaneously functionalized and enzyme immobilized by electrochemical polymerization of polyaniline and cholesterol enzymes. Subsequently, ineffective enzymes are removed and new enzymes are electrochemically recharged. Scanning electron microscopic characterization indicates polymer-enzyme nanoparticle coating on CNT surface. Cyclic voltammogram (CV) measurements in cholesterol solution show the oxidation and reduction peaks centered around 450 and −220 mV, respectively. An approximately linear relationship between the cholesterol concentration and the response current could be observed in the concentration range of 50–300 mg/dl with a sensitivity of approximately 0.22 μA/mg·dl−1, which is considerably higher compared to previously reported CNT bioprobe. In addition, good specificity toward glucose, uric acid acetaminophen and ascorbic acid have been obtained. Moreover, sensors have satisfactory stability, repeatability and life time. Therefore, the electropolymerized CNT bioprobe is promising for cholesterol detection in normal cholesterol concentration in human blood

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

Enhancement of H2S-sensing performances with Fe-doping in CaCu3Ti4O12 thin films prepared by a sol-gel method

In this work, the effects of Fe-doping on structural and gas-sensing properties of CaCu3Ti4O12 (CCTO) thin film prepared by a sol-gel method were systematically studied. Sol-gel-derived CCTO thin films with different Fe-doping concentrations were deposited on alumina substrates by spin-coating and Au/Cr interdigitated electrodes were patterned onto the films by photolithography, sputtering and lift-off processes. Characterizations by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and X-ray absorption near edge structure confirmed the perovskite CCTO phase with TiO2 and CuO secondary phases and suggested the substitution of Fe3+ ions at Ti4+ sites of CCTO structure. From gas-sensing measurements, Fe dopants greatly enhance H2S response, response time and H2S selectivity against NH3, CO, C2H2, CH4, ethanol and NO2. In particular, 9 wt% (∼3 at%) Fe-doped CCTO sensor exhibited the highest response of ∼126 to 10 ppm H2S, which was more than one order of magnitude higher than that of the undoped CCTO sensor at a low optimum operating temperature of 250 °C. The roles of Fe-dopant on gas-sensing mechanisms of CCTO sensor were proposed.Fil: Pongpaiboonkul, Suriyong. Chulalongkorn University; TailandiaFil: Phokharatkul, Ditsayut. Nanoelectronics and MEMS Laboratory; TailandiaFil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Chulalongkorn University; TailandiaFil: Wisitsoraat, Anurat. Nanoelectronics and MEMS Laboratory; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi

Highly selective sub–10 ppm H2S gas sensors based on Ag-doped CaCu3Ti4O12 films

The detection of the toxic H2S gas is of great practical, environmental and industrial interest. This work presents sensing devices fabricated with Ag-doped CaCu3Ti4O12 (CCTO) thin films using a cost effective sol-gel deposition method. When compared with undoped CCTO sensors, very low doping levels of Ag cause a dramatic improvement of the response towards H2S gas. The Ag-doped CCTO films were found to be remarkable sensors towards H2S in the concentration range of 0.2–10 ppm. In addition, the response of these sensors towards NH3, H2, NO2 and ethanol vapor was up to two orders of magnitude lower than that for H2S, yielding a highly selective mean of detecting and quantifying H2S. Gas sensing experiments were conducted at operating temperatures ranging from 150 to 350 °C with an optimum response found at 250 °C. In the studied temperature range, Ag-doped CCTO film sensors also showed much shorter response times than that of undoped one. It is found that Ag plays a role promoting the adsorption and catalytic oxidation of H2S leading to drastic changes in the electrical resistance via electron injection into CCTO.Fil: Natkaeo, Aukrit. Chulalongkorn University; TailandiaFil: Phokharatkul, Ditsayut. Carbon-based Devices And Nanoelectronics Laboratory; TailandiaFil: Hodak, Jose Hector. Chulalongkorn University; Tailandia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; ArgentinaFil: Wisitsoraat, Anurat. Carbon-based Devices And Nanoelectronics Laboratory; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi

H2S sensing characteristics of Ni-doped CaCu3Ti4O12 films synthesized by a sol-gel method

The problem of detecting the toxic hydrogen sulfide (H2S) gas at part per million levels in air by means of simple solid state gas sensors is relevant to environmental and gas processing industries. In this work, high-performance H2S gas sensors are developed based on nickel-doped calcium copper titanate (Ni-doped CCTO) thin films synthesized by a sol-gel method. From gas-sensing measurements, the response of Ni-doped CCTO sensing films increased substantially with increasing Ni doping level from 1.5 to 7.3 wt%, revealing a catalytic effect of Ni on the surface reactions with adsorbed H2S molecules. In particular, 7.3 wt% Ni-doped CCTO sensors offered a high response of 120 for 10 ppm of H2S at the optimal operating temperature of 250 °C, an order of magnitude higher than that of undoped one. In addition, the response time dropped significantly from ∼80 s to ∼4 s while the recovery time slightly improved as the Ni doping content increased from 0 to 7.3 wt%. Moreover, the Ni-doped CCTO sensors exhibited good reproducibility and high H2S selectivity against ethanol, H2, NO2 and NH3. Therefore, the Ni-doped CCTO sensors are highly promising for sensitive and selective detections of H2S.Fil: Boontum, Arisara. Chulalongkorn University ; TailandiaFil: Phokharatkul, Ditsayut. Carbon-based Devices And Nanoelectronics Laboratory; TailandiaFil: Hodak, Jose Hector. Chulalongkorn University ; Tailandia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; ArgentinaFil: Wisitsoraat, Anurat. B Carbon-based Devices And Nanoelectronics Laboratory; Tailandia. Thammasat University; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University ; Tailandi

Controlling the preferential orientation in sol-gel prepared CaCu3Ti4O12 thin films by LaAlO3 and NdGaO3 substrates

Researchers have paid considerable attention to CaCu3Ti4O12 (CCTO) due to the colossal dielectric constant over a wide range of frequency and temperature. Despite of the growing number of works dealing with CCTO, there have been few studies of the role played by the substrate in inducing structural and dielectric effects of this material. In this work, highly-oriented CCTO thin films have been deposited on LaAlO3(100), NdGaO3(100) and NdGaO3(110) substrates using a sol-gel method. These single crystal substrates were chosen in terms of small lattice mismatch between CCTO and the substrate. The X-ray diffraction patterns showed that the CCTO film layers grow with different orientations depending upon the substrate used. We show that the preferred orientation of CCTO thin films can be manipulated to a high degree by growing it on specific crystal planes of the substrates without the use of buffer layers. Colossal dielectric constants are observed in our films which appear to correlate with the film crystallinity and preferred orientation.Fil: Pongpaiboonkul, Suriyong. Chulalongkorn University; TailandiaFil: Kasa, Yumairah. Chulalongkorn University; TailandiaFil: Phokharatkul, Ditsayut. Nanoelectronics and MEMS laboratory; TailandiaFil: Putasaeng, Bundit. Thailand Science Park; TailandiaFil: Hodak, Jose Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Inorgánica, Analítica y Química Física; Argentina. Chulalongkorn University; TailandiaFil: Wisitsoraat, Anurat. Nanoelectronics and MEMS laboratory; TailandiaFil: Hodak, Satreerat K.. Chulalongkorn University; Tailandi

3D Graphene-Carbon Nanotubes-Polydimethyl Siloxane Flexible Electrodes for Simultaneous Electrochemical Detections of Hg, Pb and Cd

In this work, the effect of CNTs content in 3D graphene-PDMS-CNTs electrodes were systematically studied for simultaneous determination of Hg, Pb and Cd by differential pulse anodic stripping voltammetry. The composites were formed by dip coating CVD graphene on Ni foam in CNTs-dispersed PDMS solution with varying CNTs concentrations. The optimal CNTs content was found to be ~0.5 mg/mL for all analytes. The optimal graphene-PDMS-CNTs electrode showed good analytical performances with sharp well-separated peaks of Pb, Hg and Cd in the concentration range of 100–500 μg/L. Therefore, the graphene-PDMS-CNTs electrode is highly promising for multiple detections of heavy metal pollutants