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We report on the development of a fluorescence turn-on "molecular beacon" probe for the detection of glutathione (GSH) and cysteine (Cys). The method is based on a competitive ligation of Hg(2+) ions by GSH/Cys and thymine-thymine (T-T) mismatches in a DNA strand of the self-hybridizing beacon strand. The assay relies on the distance-dependent optical properties of the fluorophore/quencher pair attached to the ends of the molecular beacon DNA strand. In a very selective coordination of Hg(2+) to GSH/Cys, the fluorophore/quencher distance increases concomitantly with the dehybridization and dissociation of the beacon stem T-Hg(2+)-T due to the extraction of Hg(2+) ions. This process results in switching the molecular beacon to the "on" state. The concentration range of the probe is 4-200 nM with the limit of detection (LOD) of 4.1 nM for GSH and 4.2 nM Cys. The probe tested satisfactorily against interference for a range of amino acids including sulfur-containing methionine.

A new method of the formation of composite olypyrrole films containing a highly dispersed three-dimensional array of platinum catalyst particles is presented. PtC14 anions were trapped inside the polypyrrole matrix during the electropolymerization of pyrrole. In the next step followed by solution exchange, PtCl anions were reduced to Pt° particles with an average size of 10 nm. Metallic particles were incorporated in electrically conducting polypyrrole films in order to achieve multielectron-transfer processes in a three-dimensional matrix. These films were characterized using the electrochemical quartz crystal microbalance technique. The use of this technique allowed us to evaluate the Pt° loading inside the polymer film. The electropolymerization process was controlled by measuring frequency changes of piezoelectrodes. The presence of Pt° particles in composite polypyrrole films and their uniform distribution were confirmed by energy-dispersive x-ray spectroscopy and x-ray diffraction. The size of the Pt° particles was evaluated from transmission electron microscopy experiments. The electrocatalytic effect toward the methanol oxidation was observed. Larger surface area and higher catalytic activity were found for electrodes with dispersed Pt° nanoparticles in the polymer matrix than electrodes with electrodeposited Pt' on the surface of the conductive polymer.

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This report describes new findings of an investigation of a bifunctional nanocomposite probe for the detection of cancer biomarkers, demonstrating the viability of magnetic focusing and SERS detection in a microfluidic platform. The nanocomposite probe consists of a magnetic nickel-iron core and a gold shell. Upon bioconjugation, the nanoprobes are magnetically focused on a specific spot in a microfluidic channel, enabling an enrichment of "hot spots" for surface enhanced Raman scattering detection of the targeted carcinoembryonic antigen. The detection sensitivity, with a limit of detection of ∼0.1 pM, is shown to scale with the magnetic focusing time and the nanoparticle size. The latter is also shown to exhibit an excellent agreement between the experimental data and the theoretical simulation. Implications of the findings to the development of rapid and sensitive microfluidic detection of cancer biomarkers are also discussed.

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An analysis of the capability of porous tungsten trioxide films as a material for photocurrent generation was performed. The photogeneration properties of single-component WO 3 and TiO 2 films and bicomponent WO 3 /TiO 2 films were compared. The morphology, structure, fundamental absorption edge, flatband potential, vibration spectra, and photocurrent response of the amorphous WO 3 films and nanocrystalline TiO 2 films were measured. We found that in bicomponent WO 3 /TiO 2 films, the porous films of the tungsten trioxide with a high open surface area can serve as substrates for nanocrystalline TiO 2 films to increase the efficiency of photocurrent generation at bandgap excitation.