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Direct and reversible electron transfer of myoglobin (Mb), for the first time, is achieved at nanopyramidal gold surface, which was fabricated by one-step electrodeposition, with redox formal potential of 0.21+/-0.01 V (vs. Ag/AgCl) and an apparent heterogeneous electron-transfer rate constant (k(s)) of 1.6+/-0.2 s(-1). Electrochemical investigation indicates that Mb is stably confined on the nanopyramidal gold surface and maintains electrocatalytic activity toward hydrogen peroxide (H(2)O(2)). The facilitated electron transfer combined with the intrinsic catalytical activity of Mb substantially construct the third-generation biosensor for H(2)O(2). The positive redox potential of Mb at the nanostructured gold electrode gives a strong basis for determination of H(2)O(2) with high selectivity. Besides this advantage, the present biosensor also exhibits quick response time, broad linear range, and good sensitivity. The dynamic detection linear range is from 1 microM to 1.4 mM with a detection limit of 0.5 microM at 3sigma. The striking analytical performance of the present biosensor, as well as the biocompatibility of gold nanostructures provided a potential for continuous, on-line detection of H(2)O(2) in the biological system.

It is the first time that direct electron transfer of copper, zinc-superoxide dismutase (Cu, Zn-SOD) is realized at nanospherical, nanorodlike, and nanopyramidal gold nanostructures, without any mediators or promoters. Thermodynamic and kinetic parameters of the electron transfer vary with the morphology of the electrodeposited gold nanostructures, suggesting the morphology-dependent electrochemistry of SOD. Experimental results reveal that SOD is strongly confined onto the nanostructured gold surfaces and processes its inherent enzymatic activity after being adsorbed on all three kinds of gold nanostructures, which also enable the direct electron transfer of SOD itself. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SOD substantially offers a dual electrochemical approach to determination of O2(*-), in which O2(*-) could be detected both anodically and cathodically. In both the oxidation and reduction regions, the present O2(*-) biosensors display excellent analytical performance, such as wide linear range, low detection limit, quick response time, and good stability and reproducibility, while not being limited by interferences, for instance, uric acid, ascorbic acid, and hydrogen peroxide.