Selective sensing of cysteine on manganese dioxide nanowires and chitosan modified glassy carbon electrodes.

We report a simple approach for the selectively electrochemical sensing of cysteine (CySH) using beta-MnO(2) nanowires modified glassy carbon (GC) electrode via a direct and facile electrochemical co-deposition process with chitosan hydrogel. The electrode showed excellent electrocatalytic effect toward cysteine oxidation. A possible reaction mechanism related to the formation of surface complexes was proposed: the -SH group is the reacting group in the reaction between cysteine and MnO(2), while the -NH(2) group acts as an anchor to stabilize the surface complexes. The electrocatalytic behavior is further developed as a sensitive detection scheme for cysteine by amperometric measurement, which shows a large determination range of 0.5-630 microM and a low detection limit of 70 nM. Other nineteen amino acids in a 20-fold concentration do not interfere in the detection of cysteine. Furthermore, other biological species containing -SH group or S-S bonds, such as glutathione, cystine, and bovine serum albumin (BSA), show no interferences because of steric hindrance and inactive S-S bonds.