Cu2+-Mediated turn-on fluorescence assay for sulfide ions using glutathione-protected gold nanoclusters: enhanced sensitivity, good reusability, and cell imaging†
Abstract
We develop a simple assay for highly selective and sensitive fluorescence detection of sulfide ions (S2−) using glutathione-protected gold nanoclusters (GSH-Au NCs). This approach was based on the much higher affinity of CuS than that of the Cu–GSH complex, which makes the fluorescence of the NCs quenched by Cu2+ recover upon addition of S2−. Importantly, the assistance of Cu2+ enables S2− detection in the “turn-on” mode, eventually enhancing detection sensitivity toward S2− about 15 times more compared to that in the “turn-off” mode. Under the optimal conditions, the linear fluorescence response toward S2− was given within the concentration range of 2 to 24 μM with a low detection limit of 0.7 μM. Also, the GSH-Au NCs show good reusability for S2− detection due to effective removal of the bridging reagent Cu2+ by S2−. This phenomenon is further exploited as an integrated logic gate and successfully employed for imaging S2− in living cells.