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The fabrication of ultrathin-ring electrodes with a diameter of 2 mm and a thickness of 100 nm is established. The ultrathin-ring electrodes provide a large density of pseudo-steady-state currents, and realize pseudo-steady-state amperometry under quiescent conditions without a Faraday cage. Under the limiting current conditions, the current response at the ultrathin-ring electrode can be well explained by the theory of the microband electrode response. Cyclic voltammograms at the ultrathin-ring electrode show sigmoidal characteristics with some hysteresis. Numerical simulation reveals that the hysteresis can be ascribed to the time-dependence of pseudo-steady-state current. The performance of amperometry with the ultrathin-ring electrode has been verified in its application to redox enzyme kinetic measurements.

Highly reproducible bioelectrocatalytic endpoint assays are described. The method is based on a complete redox conversion of a substrate to a redox mediator with a corresponding redox enzyme and an amperometric detection of the reduced mediator on a diffusionally independent microelectrode array. The current reaches a steady state within a few seconds and is proportional to the number of the integrated microelectrodes. The method has successfully been applied to histamine detection at micro-molar level and glucose detection at milli-molar level.

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