Design and Fabrication of Glucose Biosensors Based on Immobilization of Glucose Oxidase on Titanium Oxide Nanotube Arrays.

An electrochemical biosensor for the detection of glucose is realized by immobilizing glucose oxidase (GOx) enzyme onto titanium dioxide nanotube arrays by a coupling encapsulation process. We present details of a robust fabrication technique that results in a durable and reproducible sensor characteristics. The TiO2 nanotube arrays are grown directly on a titanium substrate by a potentiostatic anodization process in a water and ethylene-glycol mixture solution, which contains ammonium fluoride. An electropolymerization process was also performed to enhance interfacial adhesion between GOx and TiO2 nanotubes. Detection of glucose concentrations was achieved with a linear response in the range of 0.01 to 0.2 mM. Investigation of enhanced sensitivity by increasing the count, the length, and the cross-section of the nanotubes was also carried out. Surface morphologies of Ti substrate were examined by scanning electron microscopy to optimize the anodization process and thus the TiO2/Ti nanotube dimensions. We utilized a time-based amperometric response for the quantitative determination of hydrogen peroxide concentration through electro-reduction reaction with a bare TiO2/Ti nanotube-array electrodes, thus providing a reference for the determination of glucose levels with a GOx-coated TiO2/Ti nanotube array electrodes. Detection levels down to 5.2 µM were recorded.

Reactive Conjugated Polymers: Synthesis, Modification, and Electrochemical Properties of Polypentafluorophenylacetylene (Co)Polymers.

(Co)Polymers containing pentafluorophenylacetylene (F5 PA) have been prepared for the first time mediated by [Rh(nbd)Cl]2 /NEt3 to give materials with properties typical of poly(phenylacetylene)s prepared with this catalyst/co-catalyst combination. It is demonstrated that the F5 PA repeat units in these new (co)polymers serve as convenient reactive species for post-polymerization modification with thiols via para-fluoro aromatic nucleophilic substitution reactions to give an entirely new family of novel thioether-functional polyene materials accompanied by absorption maxima shifts of up to 130 nm. Finally, the electrochemical properties of these new fluorinated polyene materials are briefly examined and the distinct difference in behavior of the F5 PA homopolymer versus polyphenylacetylene, copolymers, and functional derivatives is highlighted.

Void-Assisted Ion-Paired Proton Transfer at Water-Ionic Liquid Interfaces.

At the water-trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P14,6,6,6][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H(+)) and deuterium ions (D(+)) was identified. Alkali metal cations (such as Li(+), Na(+), K(+)) did not undergo this transfer. H(+)/D(+) transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP](-), resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton-coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents.

Ion-transfer electrochemistry of rat amylin at the water-organogel microinterface array and its selective detection in a protein mixture.

The behavior of proteins and polypeptides at electrified aqueous-organic interfaces is of benefit in label-free detection strategies. In this work, rat amylin (or islet amyloid polypeptide) was studied at the interface formed between aqueous liquid and gelled organic phases. Amylin is a polypeptide that is co-secreted with insulin from islet beta-cells and is implicated in fibril formation. In this study, rat amylin was used, which does not undergo aggregation. The polypeptide underwent an interfacial transfer process, from water to the gelled organic phase, under applied potential stimulation. Cyclic voltammetry revealed steady-state forward and peak-shaped reverse voltammograms, which were consistent with diffusion-controlled water-to-organic transfer and thin-film stripping or desorptive back-transfer. The diffusion-controlled forward current was greater when amylin was present in an acidic aqueous phase than when it was present in an aqueous phase at physiological pH; this reflects the greater charge on the polypeptide under acidic conditions. The amylin transfer current was concentration dependent over the range 2-10 µM, at both acidic and physiological pH. At physiological pH, amylin was selectively detected in the presence of a protein mixture, which illustrated the bioanalytical possibilities for this electrochemical behavior.