Ultra-sensitive detection of cysteine by gold nanorod assembly.

In this paper, we have developed a simple, rapid, selective, and ultra-sensitive assay to detect cysteine by means of gold nanorods assembly. This methodology is based on the end-to-end assembly of gold nanorods and it is very sensitive due to the useful formation of the gold nanorods chain in the presence of cysteine under acidic aqueous solution. The sharp absorption peak changes observed from the assembly formed by the gold nanorods allow one to monitor very subtle differences induced by cysteine in an acidic medium and therefore, it can provide a quantitative measure of the cysteine concentration. On the other hand, the high extinction coefficients of gold nanorods allow one to monitor the changes at lower concentrations compared to that accomplished by conventional absorbance-based chromophores. Therefore, one of the significant features is the ability to detect cysteine in the presence of other essential alpha-amino acids at concentrations as low as 10 pM, which to the best of our knowledge is the lowest reported for a colorimetric cysteine detection system. More importantly, this assay is particularly attractive because it does not rely on organic cosolvents, enzymatic reactions, light-sensitive dye molecules, lengthy protocols, and sophisticated instrumentation.