flavin-adenine-dinucleotide and titanium-dioxide

A light-controlled multiplexing platform has been developed on the basis of a quantum dot-sensitized inverse opal TiO

Topics: Biocatalysis; Biosensing Techniques; Electrochemical Techniques; Electrodes; Flavin-Adenine Dinucleotide; Glucose; Glucose 1-Dehydrogenase; Lactic Acid; Light; Mixed Function Oxygenases; Optical Imaging; Particle Size; Photochemical Processes; Quantum Dots; Surface Properties; Titanium

Redox processes in nano-TiO(2)-flavin adenine dinucleotide (TiO(2)-FAD) layer-by-layer assembled films on ITO substrate electrodes are investigated and compared in contact to aqueous electrolyte media (for dilute and saturated electrolyte) and in contact to solid humidified salt electrolyte (for extreme salt levels and different types of salts). Under these unusual conditions an aqueous microphase present at the gas | salt | electrode interface allows voltammograms to be obtained and redox processes to be analysed. It is demonstrated that the 2-electron 2-proton reduction of FAD can be used as reporter redox system to determine local pH at the electrode | gas | salt interface as pH 15, 12, 7 for contacts to K(3)PO(4), K(2)HPO(4), and KH(2)PO(4), respectively. Exposure to gases such as carbon dioxide is shown to lead to unexpected changes in surface pH. In the future, bio-electrochemical microphase processes under halophilic conditions could be useful for air-quality and rapid gas sensing devices.

Topics: Carbon Dioxide; Electrochemical Techniques; Electrodes; Electrolytes; Flavin-Adenine Dinucleotide; Gases; Hydrogen-Ion Concentration; Nanocomposites; Oxidation-Reduction; Phosphates; Potassium Compounds; Protons; Salts; Titanium

Thin films of TiO2 (anatase) nanoparticles are assembled at an electrode surface via a layer-by-layer deposition process employing phytic acid, pyromellitic acid, or flavin adenine dinucleotide (FAD) as molecular binders. With all three types of binders, layers of typically 30 nm thickness are formed each deposition cycle. FAD as an electrochemically active component immobilized at the surface of the TiO2 particles is reduced to FADH2 and reoxidized in a chemically reversible two electron-two proton redox process. Two distinct voltammetric signals are observed for the immobilized FAD redox system associated with (i) hopping of electrons at the TiO2 surface (reversible) and (ii) conduction of electrons through the TiO2 assembly (irreversible). The conduction of electrons through the TiO2 assembly is possible by diffusion over considerable distances as well as through a "spacer" layer of TiO2 phytate. An order of magnitude (upper limit) estimate for the diffusion coefficient of electrons through TiO2 phytate, D(electron) approximately 10(-6) m(2) s(-1), is obtained from voltammetric data. Finally, it is demonstrated that the calcination of TiO2 assemblies causes dramatic changes in the electron transfer kinetics for the immobilized FAD/FADH2 redox system.

Topics: Adsorption; Biophysical Phenomena; Biophysics; Flavin-Adenine Dinucleotide; Indicators and Reagents; Kinetics; Membranes, Artificial; Oxidation-Reduction; Titanium