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Abstract: The catalytic activity of a membrane-bound enzyme, d-fructose dehydrogenase (FDH), at the polarized oil/water (O/W) interface was studied. Multisweep cyclic voltammetry and ac voltammetry were carried out to show the irreversible adsorption of FDH at the interface. Using the thusly prepared FDH-adsorbed O/W interface, clear steady-state catalytic current was observed in amperometry and cyclic voltammetry, where 1,1′-dimethylferrocenium ion (DiMFc+, electron acceptor) and d-fructose (substrate) were added to the O and W phases, respectively. The observed catalytic current was then analyzed by using two mechanisms. In mechanism (A), the heme c site of FDH, where DiMFc+ is reduced, was assumed to be located in the O-phase side of the interface. The intramolecular electron transfer in FDH should be affected by the Galvani potential difference of the interface (). However, the theoretical equations derived for the catalytic current could not reproduce the experimental data. In mechanism (B), the heme c site was assumed to be in the W-phase side. In this case, should affect the interfacial distribution of DiMFc+. This mechanism could reproduce well the observed potential dependence of the catalytic current. [Copyright &y& Elsevier]

A new mediated carbon nanotube paste (CNTP) amperometric biosensor for fructose is described. The biosensor is formed by a CNTP electrode modified with an electropolymerized film of 3,4-dihydroxybenzaldehyde (3,4-DHB) and is based on the activity of a commercial available D-fructose dehydrogenase (FDH) immobilized on an immobilon membrane placed on the top of the electrode surface. Analytical parameters such as enzyme immobilization, pH, temperature, and probe lifetime were studied and optimized. The biosensor response current was directly proportional to D-fructose concentration from 5 × 10−6 to 2 × 10−3 mol/L with a detection limit of 1 × 10−6 mol/L and a good reproducibility (RSD = 1.8%, n = 5). The biosensor was used for the determination of fructose content in three honey samples and validated with a commercial spectrophotometric enzymatic kit. [ABSTRACT FROM AUTHOR]