Unique Redox Reaction between CuO Photocathode and Cysteine: Insight into the Mechanism for Cathodic Photoelectrochemical Bioanalysis.

Previously reported copper oxide-based cathodic photoelectrochemical bioanalysis of cysteine had attributed the decrease of the photocurrents to the binding of cysteine onto the CuO surface. However, our latest investigation found that the previous explanation was not correct. This Letter presents the in-depth study of such phenomena and a new insight into the underlying mechanism. Specifically, the unique redox reaction between the CuO photocathode and cysteine produced [Cys-Cu(I)] and cystine, and the insoluble complex blocked the partial contact between the photoelectrode and the dissolved O 2 -containing electrolyte and reduced the effective working area of the photocathode, leading to the decrease of photocurrent.