Fluorometric determination and intracellular imaging of cysteine by using glutathione capped gold nanoclusters and cerium(III) induced aggregation.

A turn-on fluorometric method is described for selective and sensitive detection of cysteine (Cys). Gold nanoclusters (Au NCs) capped with glutathione (GSH) are used as a fluorescent probe. If Ce ion are present, they will bind to the carboxy groups of the GSH-capped Au NC. This results in aggregation-induced emission enhancement (AIEE), best measured at excitation/emission wavelengths of 360/575 nm. On addition of Cys, which has less steric hindrance compared with GSH and higher affinity for Ce, it will bind to Ce through the carboxyl group and link with Au NCs via Au-S bond. Hence, the AIEE is increased and Cys can be quantified via this effect with a linear response in the 0.4-120 μmol L Cys concentration range and a detection limit of 0.15 μmol L. Graphical abstract Schematic presentation of cysteine detection via the Ce-triggered aggregation of glutathione capped gold nanoclusters which leads to increased yellow fluorescence.