Electrochemical recognition of single-methylene difference between cysteine and homocysteine

Both cysteine (Cys) and homocysteine (Hcy) are important aminothiols, and their molecular structure difference is a single methylene. Here, we describe the differentiation of the anodic oxidation signals of Cys and Hcy at a fluorosurfactant (i.e. Zonyl® FSO)-modified gold electrode (FSO-Au). Two separated anodic waves have been observed in neutral solutions containing both Cys and Hcy. By using differential pulse voltammetry, quantitative analysis of these aminothiol species could be achieved. The detection selectivity has been greatly improved by a Nafion film cast on the FSO-Au electrode. The method could be employed for the simultaneous determination of Cys and Hcy in a human plasma sample.