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.