The carbon nanotubes provide large surface that can enhance the gas adsorption properties and increase the conductivity at a lower temperature for gas sensing. The gas sensing properties of the hybrid TiO2/CNTs material are examined in this study. The sol-gel technique is used to prepare a thin layer of nano-TiO2 coated on CNTs. The structure of TiO2/CNTs hybrid materials is identified by X-ray diffraction (XRD) and Raman spectrum. The granules and surface morphology are analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrical properties of the hybrid TiO2/CNTs indicate that the operation temperature can be lowered to ambient temperature and this will enhance the gas sensitivity for detecting CO gas. The n-type or p-type behavior of hybrid TiO2/CNTs can be controlled by the coating thickness of hybrid TiO2. According to the image results, the mechanisms of the n-type and p-type behavior of hybrid TiO2/CNTs system are proposed.

We report a study of pulse shapes of a radiation detector with a sandwich structure fabricated from chemical vapor deposited (CVD) polycrystalline diamond. The pulse shapes were recorded at room temperature using 5.486 MeV alpha particles from 241Am source. Only “fast” component was observed in the electron predominated pulses, whereas both “fast” and “slow” components were obtained in the hole predominated pulses, suggesting that electron charge drift is prompt and no detrapping occurred. In contrast, hole charge drift is slower than expected and trapping-detrapping took place during hole travel process.

Differential adherent surfaces were used to induce attachment of C2C12 myoblasts that later would form engineered muscle organoids. Narrow channels, 60–400 μm wide, were micromachined in a 2% agarose gel using an ArF laser, and subsequently filled with extracellular matrix. Upon addition of 1 mL of a 2×104 cells/mL myoblast suspension, cells selectively adhered to the ECM lined channels in a non-confluent manner and we monitored their growth at various time points. The adherent myoblasts were flourescently imaged with a propidium iodide live/dead assay, which revealed that the cells were alive within the channels. After 72 hours growth, the myoblasts grew, proliferated and differentiated into myotubes. Myoblasts residing in the narrow channels (60–150 μm wide) aligned parallel to the channel, while myoblasts adhered to the wide channel (400 μm) were randomly aligned within the channel. The fully-grown 1 cm long organoids maintained an aspect ratio on the order of 100:1. These results provide the foundation for future three-dimensional tissue growth using differential adherent

Dispenser technique was employed to integrate the Pt loaded on alumina (Pt/alumina) micro-catalysts on thin membrane of micro-thermoelectric hydrogen sensor (μ-THS). The μ-THS with Pt loaded alumina showed higher sensing performance than bulk-type THS with Pt thin film prepared by RF sputtering method. For the μ-THS with Pt/alumina catalyst, its voltage signal was 7.3 mV for hydrogen concentration of 1 % in dry air at catalyst temperature of 100 °C. In the case of the bulk-type THS with Pt thin film catalysts, the voltage signal was 0.33 mV under the same condition.

This paper presents the use of Floating-Gate Ion Sensitive Field-Effect Transistor (FGISFET) as a real-time chemical and biological sensor. The structure of FGISFET is similar to that of an electrically erasable programmable read-only memory (EEPROM). The floating-gate of a FGISFET is connected to an exposed metallic structure, which serves as a probe for detecting ionic activities. By applying ion-sensitive chemical and biological materials to the floating gate, its threshold voltage can be modulated in the presence of selective chemical or biological targets. As a demonstration, FGISFETs have been fabricated in 1.2 μm process technology available through MOSIS [1]. Our preliminary measurements confirmed the basic design and operation of FGISFET, and using doped aniline trimer (TANI) as a sensing material, we were able to sense 70ppm of ammonium gas.

The chemical reactions occurring at the surface of tin oxide nanoparticles under NOx adsorption have been investigated by Fourier transform infrared spectroscopy and correlated with the variations of the electrical conductivity of tin oxide. These surface reactions have been found dependent on the particle size and on the presence of oxygen. The strong coordination of the newly formed chemical species onto the nanoparticle surface may result in a poor reversibility of the sensor response.

Polycrystalline samples of GdCo1−xCuxO3 (x=0, 0.15, 0.3), were prepared by two different routes: solution and ultrasonic-assisted aerosol decomposition. For both procedures, aqueous solutions containing stoichiometric amounts of Gd(NO3)36H2O, Co(NO3)26H2O and Cu(NO3)22.5H2O were used. In the solution method, the aqueous solutions were heat-dried at 76°C obtaining precursor powders, these were calcined from 80 to 950°C, in air. In the aerosol method, very small droplets were produced by an ultrasonic generator, then a flow of oxygen transported the mist through a tubular furnace, previously heated at 950°C. Solvent evaporation and chemical reaction takes place at that temperature, and the resulting powder was collected by filtration. X-ray powder diffraction was used to identify the formation of target phases. Surface microstructure of powders was analyzed by SEM, and showed that solution method produced sub-micron particles with irregular shape, whereas the aerosol method yield micron-sized hollow spherical particles. In order to determine gas sensitivity vs. temperature, electrical measurements were made in air, O2 and CO2, from room temperature to 650°C. The results showed a semiconductor behavior and a moderate gas sensitivity for samples prepared by solution method. However, unreliable data were registered for samples made by the aerosol route, caused by short connectivity between particles.

Cerium oxide nanosized powder was synthesized by modified precipitation method. The precipitate, which was formed from the addition of NH4OH to Ce(NO3)3 aqueous solution, and was filtered. The obtained gel was mixed with carbon powder with a particle size of about 20 nm by a mechanically rotating mixer. The mixture was dried at 343 K in air. The carbon powder was burned out by heat treatment at 1173 K in air for 4 h, resulting in the formation of CeO2 powder with a size of 50 nm. A thick film was formed on an alumina substrate by screen printing, and was fired at 1373 K. The thick film had porous structure and the grain size was about 120 nm. The resistance of the thick film was almost proportional to P (O2)1/6, where P (O2) is oxygen partial pressure, in the P (O2) range from 10−13 to 105 Pa at 1073 and 1173 K. The response time (t90) was 23 and 7 ms at 1023 K when P(O2) changed from 65 to 25 kPa and 25 to 65 kPa, respectively. The reason for this result was explained on the basis of surface reaction of cerium oxide grain.

Organically hybridized In2O3 thin films have been prepared. The surface of In2O3 thin films was hybridized by organic components with various kinds of functional groups. Upon exposure to CO gas, the electrical resistance of the hybrid sensor with amino group in the organic components increased (R-increasing response), whereas H2 gas caused the decreasing in the sensor resistance. No response was obtained to CH4 gas. For the n-type metal oxide semiconductors, the R-increasing response cannot be explained by the ordinary combustion mechanism. The response of R-increasing or R-decreasing to CO was controlled by functional groups of organic components as in the case of SnO2-based hybrid thin films. The approach of organic-inorganic hybridization is effective to realize the selective detection of reducing gas molecules.

Currently, systems for the detection of nucleic acid sequences, known as DNA-chips, are getting lots of attention. Such systems usually involve either an enzymatic or chemical labelling reaction as part of the detection process. The next generation of DNA-chips aims at a labelfree, fully electronic readout system. Several new approaches to signal generation that avoid a labelling step have been developed in recent years. Besides other surface sensitive measurements the possibility of electrochemical impedance and field-effect measurements for the detection of biomolecules have been discussed. The fully electronic detection of charged biomolecules based on the field-effect principle offers a labelfree method, which combines the unique sensitivity and selectivity of biomolecular recognition reactions with an electronic chip-based readout. In this approach one type of molecules is fixed at a surface and the biomolecular reaction with complementary molecules is detected by change in the drain-source current of the transistor. This change can occur by a change of the interface capacitance of the transistor gate or by change of the surface potential during adsorption of the molecules. At the moment a complete theoretical description of the detection principle is still under discussion. However, the fully electronic readout of biomolecular reactions offers a unique principle for the construction of many different sensors for bioassays. We are working on an approach to detect the hybridization of DNA sequences using electrolyte-oxide-semiconductor field-effect transistor (EOSFET) arrays. This method allows direct and in situ detection of specific DNA sequences without any labelling.

The goal of our research is to combine porous silicon and enzymes in order to build hybrid platforms for extremely selective chemical sensing applications. For this, a new synthetic route to covalently anchor bio-molecules on photo-luminescent porous silicon (PL PSi) while preserving the optical properties of the matrix was developed. The hydride terminated porous silicon surface was covalently functionalized with t-butyloxycarbonyl protected amine by light-assisted hydrosysilation. Protein cross-linker chemistry was then used to extend the linker and immobilize various enzymes. The glu-coronidase enzyme/p-nitro-phenyl-beta-glucoronide substrate test system provided a proof of concept for an enzyme-based porous silicon detector. The enzymatic activity and the luminescence of the porous silicon platform were both retained after the functionali-zation procedure and, charge transfer between the products of the enzymatic breakdown and the silicon quantum dots was demonstrated. The organophosphorous hydrolase enzyme OPAA was then immobilized and tested on p-nitrophenyl-soman, a surrogate substrate for soman. The production of the hydrolysis product, p-nitrophenol, correlated with the reversible luminescence quenching of the porous silicon matrix demonstrating the relevance of the enzyme-based platform for detection applications. This detection scheme, although indirect, takes advantage of the extreme specificity of enzymes. The approach is general and can be implemented for a series of target molecules.

A new constitutive equation for the gas sensitivity of n-type semiconductor oxide thin film gas sensor has been proposed here based on a single-crystal model. The derived constitutive equation shows the dependence of the gas sensitivity on various critical parameters such as nanocrystallite size, space-charge-layer thickness, reducing gas concentration, bulk charge-carrier-concentration, surface-density of states, oxygen-ion-vacancy concentration, operating temperature, and film thickness. The present theoretical model is applicable to all n-type semiconductor oxides gas sensors.

This paper documents the study of thickness effects of ion beam deposited molybdenum trioxide thin films on their gas sensing properties. For processing the films, the primary plasma beam source was used to sputter material from the target, while the secondary beam was used as an ion assist source. The deposited material was annealed at 500°C for 8 hours. The microstructural characterization of the films was done using Scanning Electron Microscopy and X-ray diffraction. Sensing tests were performed in the temperature range of 350–500°C under varying and constant concentration levels of ammonia. The recorded data have been qualitatively and quantitatively analyzed and significant trends according to different parameters (thickness, sensing temperature, gas concentration) have been identified. These suggest a relation existing between processing conditions, the microstructure of the material and its response to gases at different concentration, and the optimum working temperature regime.