Thiol reactive probe based on fluorescence resonance energy transfer between fluorescein and Au nanoparticles

Sensitive and selective fluorescent probe of thiols with lower limit of detection based on fluorescence resonance energy transfer (FRET) between fluorescein and Au nanoparticles (AuNPs) is presented. The fluorescein-AuNPs complex emits weak fluorescence. Upon chemically binding to organosulfur compound that contains a carbon-bonded sulfhydryl (-C-SH or R-SH) thiols, a stable enhancement of fluorescence is observed due to the competitive binding on AuNPs between thiols and fluorescein. The magnitude of fluorescence enhancement is linearly proportional to the logarithm of the thiols concentration. We use cysteine as an example to show how this useful analytical assay works selectively, which is closely nonresponsive to 20 other amino acids even though they are in solution at a concentration 10 times greater than the thiols. The detection limit for cysteine is 7.27 × 10-9 mol L-1. The possible mechanism of this assay is discussed in details. The proposed method was successfully applied for the determination of Cys in urine.