H2S sensing properties of nanocrystalline Sr2Fe(0.6)Ni(0.4)MoO6 thick film prepared by sol-gel citrate method.

Nanocrystalline Sr(2)FeMoO(6) (SFMO) belonging to the group of double perovskite oxides, was prepared by the sol-gel citrate method. The structural and microstructural characterization has been carried out with the help of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. XRD of Sr(2)Fe(1-x)Ni(x)MoO(6) (SFNMO) shows the formation of solid solution with average grain size of about 40nm. A comparative study of gas sensing behaviour of Sr(2)FeMoO(6) and Sr(2)Fe(1-x)Ni(x)MoO(6) with reducing gases like hydrogen sulfide (H(2)S), liquid petroleum gas (LPG), hydrogen (H(2)), ethanol (C(2)H(5)OH) and carbon monoxide (CO) were also discussed. The sensitivity is calculated by measuring the change the resistance of the sensor material in the presence of gas. Among the different composition of x (x=0.2, 0.3, 0.4, 0.5), Sr(2)Fe(0.6)Ni(0.4)MoO(6) (x=0.4) shows better response to H(2)S gas at 260 degrees C. Incorporation of palladium (Pd) improves the gas response, selectivity, response time and reduced the operating temperature from 260 to 220 degrees C for H(2)S gas.

Enzyme field effect transistor (ENFET) for estimation of triglycerides using magnetic nanoparticles.

Ion-selective field effect transistor (ISFET) is a robust platform to develop biosensors. A variety of methods are used including covalent attachment or polymer entrapment, to associate enzymes or antibodies to the gate surface of a FET. We have employed a novel method of retaining the enzyme molecules at the gate surface by immobilizing the enzyme on magnetic nickelferrite nanoparticles and applying a permanent magnet below the gate of the FET. We were able to estimate the triglyceride concentrations in the range of 0.1-1.5% by immobilizing a thermostable lipase on nanoparticles. Tributyrin, trioctanoate and triolein have given similar results. The reaction volume could be scaled down to 0.2ml without a loss in slope or sensitivity. Ionic strength (>150mM NaCl) has a strong influence on the sensitivity of the measurement. The advantages of this configuration of enzyme biosensor are reduction of mass transfer problems, increasing the amount of enzyme at the gate surface besides providing an opportunity to use a single FET device for multiple analyte detection.

Detection of liquid petroleum gas using mixed nanosized tungsten oxide-based thick-film semiconductor sensor.

The thick-film semiconductor sensor for liquid petroleum gas (LPG) detection was fabricated using a mixed WO(3)-based sensor. We present the characterization of both their structural properties by means of XRD measurements and the electrical characteristics by using gas-sensing properties. The sensing characteristics such as sensitivity, working range, cross-sensitivity and response time were studied by using nanosized WO(3)-based mixed with different metal oxides (SnO(2), TiO(2) and In(2)O(3)) and doped with noble metals (Au, Pd and Pt). The WO(3)-based mixed with 5 wt.% In(2)O(3) and 0.5 wt.% Pd showed the higher sensing characteristic at low concentration of LPG sensor at an operating temperature 225 degrees C.

Probing the association behavior of poly(ethylene glycol)-based amphiphilic comb-like polymer in NaCl solution.

The effect of salt on the associative behavior of intramolecular aggregates obtained from poly(ethylene glycol)-based amphiphilic comb-like polymers in aqueous medium at pH 6.2 has been investigated by surface tension, fluorescence probe, dynamic light-scattering, and viscometry techniques. Results reveal that the addition of salt screens the electrostatic repulsion between the charges along the polymer backbone in the aggregates and consequently (1) reduces the surface activity at the air/water interface, (2) leads to the contraction of the polymer backbone, and (3) reduces the hydrodynamic sizes of the aggregates. In contrast, the hydrophobicity of the aggregates remains unperturbed.

Aggregation and Polymerization of PEG-Based Macromonomers with Methacryloyl Group as the Only Hydrophobic Segment.

Aggregation behavior in aqueous solution of a series of poly (ethylene glycol) (PEG)-based macromonomers with methacryloyl group as the only hydrophobic segment has been investigated using surface tension, steady-state and time-resolved fluorescence spectroscopy using pyrene as a probe, and small-angle neutron scattering techniques. The general formula of these macromonomers is CH(2)&dbond;C(CH(3))-CO-O-E(m)-CH(3), where E is the ethylene glycol unit and m=8 (ME(8)), 18 (ME(18)), 49 (ME(49)), and 120 (ME(120)). The results indicate that a macromonomer with 8 ethylene glycol units forms as an aggregate above a certain critical concentration, which can be defined as critical aggregation concentration. The observed high value of I(1)/I(3) in pyrene emission spectra at the interface of these aggregates and the inability to scatter a neutron beam by these aggregates indicate that the hydrophobic cluster formed by this macromonomer is remarkably solvated. ME(18) has a tendency to aggregate but others do not form any hydrophobic cluster. The homopolymerization behaviors of these macromonomers in an aqueous medium at 70 degrees C are consistent with these possibi- lities. Copyright 2001 Academic Press.