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Many studies on the use of enzymatic activity in nonaqueous solutions have been carried out after Dastoli and Price's report of their investigation of the catalytic activity of xanthine oxidase suspended in several organic media. 1 Updike and Hicks published the results of their experiment involving an enzyme electrode with cross-linked polyacrylamide (PAA) membrane as matrix for use in aqueous solutions.2 Enzymes have been found to have numerous applications as practical and specific catalysts in chemical and pharmaceutical syntheses and as recognition elements in biosensors. The discovery that they are catalytically active in organic solvents containing little or no water has expanded their repertoire of use still further. 3,4 Some of the benefits in utilizing enzymes in nonaqueous solvents over the use of conventional aqueous reaction media include the high solubility of many hydrophobic substrates in such solvents, the suppression of various side reactions promoted by water, altered enzymatic selectivity and the ability to control it with the solvent, and the comparative simplicity of immobilization procedures due to the insolubility of enzymes in organic solvents. Many studies have been conducted in order to gain an understanding of so-called solvent effects due to organic solvent properties. Factors such as solvent hydrophobicity, 5 solvent polarity, water content, 6 and substrate hydrophobicity 7 can affect the enzymatic reaction. It remains important to continue the search for new enzymatic reaction systems because of the use which might be made of such systems in both pure and applied research.Many enzyme-based electrochemical biosensors have been described for use in both aqueous and nonaqueous solutions. A tyrosinase-immobilized polyacrylamide membrane platinum electrode has been prepared and the electrochemical behavior of o-hydroxybenzene derivatives in acetonitrile 8 and dimethylacetamide 9 has been studied. Because of unique properties of nanoparticles, recent investigations have focused on the development of enzyme-modified nanoparticle-based electrochemical biosensors. [10][11][12] The ability of nanoparticles to stabilize enzymes, and to improve the efficiency of immobilized enzymes is extremely useful when preparing biosensors. Moreover, other characteristics of nanoparticles, such as their high surface-to-volume ratio, their high surface energy, and their ability to decrease the distance between enzyme and metal particles, may facilitate electron transfer between redox sites and the electrode surfaces.In our laboratory, a gold nanoparticle self-assembled electrode has been constructed by using 4,4′-bis(methanethiol)biphenyl (MTP), rigid rod dithiols, as a binder between a gold disk and gold nanoparticles. The effect of gold nanoparticles on the interaction of Co(phen)3 3+ with DNA, and the characteristics of the electrode in a nonaqueous solution were described in a recent report. 13 We have also devised a method of preparing density-controlled gold nano-particle self-assembled monolayer (SAM...

The voltammetric detection of copper(II) was carried out at a carbon paste electrode (CPE) modified with tetraphenylporphyrin (TPP). The analysis procedure consisted of an open circuit preconcentration step in stirred sample solution. This was followed by medium exchange to a pure electrolyte solution (Britton-Robinson buffer pH ¼ 6) where the accumulated copper(II) was reduced at À0.8 V vs. Hg/Hg 2 SO 4 and subsequently an anodic potential scan was effect to obtain the voltammetric peak. The parameters and conditions such as pH of the analyte solution and supporting electrolyte, preconcentration time, CPE composition, its activation and regeneration, and others, were studied in detail. The detection limit of the proposed procedure was found to be 2.0 Â 10 À9 mol l À1 of 369 ORDER REPRINTS Cu(II) in the analyte solution for a preconcentration time of 12 min. Applying suitable preconcentration times, a linear calibration graph from 9.0 Â 10 À8 to 5.0 Â 10 À5 mol l À1 of Cu(II) was established. Multiple determinations (n ¼ 8), following a preconcentration-measurement-regeneration cycle, gave a relative standard deviation of 4.5% at Cu(II) concentration of 1.0 Â 10 À7 mol l À1 . The proposed method was applied to the determination of Cu(II) in a real sample of residue solution after extraction and a mineral sample of Jinchuan Corporation.

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