Turn-on fluorescent sensing of glutathione S-transferase at near-infrared region based on FRET between gold nanoclusters and gold nanorods.

A fluorescence resonance energy transfer (FRET) method based on gold nanoclusters capped glutathione (AuNCs@GSH) and amine-terminated gold nanorods (AuNRs) is designed for turn-on and near-infrared region (NIR) sensing of glutathione S-transferase (GST). The absorption band of AuNRs is tuned carefully to maximize the spectra overlap and enhance the efficiency of FRET. The FRET from multiple AuNCs to single AuNR quenches about 70% fluorescence emission of AuNCs. After GST is added, the strong specific interaction of GSH-GST can replace the AuNCs@GSH from AuNRs, FRET based on electrostatic interaction between AuNCs@GSH and AuNRs is switched off. Thus, emission enhancement of AuNCs@GSH is observed. The fluorescent enhancement is linearly with the increasing GST concentration over the range of 2-100 nM GST and the limit of detection for GST is about 1.5 nM.