Detection and Bioimaging of Glutathione in Cells via a Turn-On Near-Infrared Fluorescent Nanoprobe Composed of Ag₂S Quantum Dots and CoOOH Nanosheets

The variations of the microenvironment in cells are always associated with changes in the concentrations of some active species. However, visual detection of these species is still a challenge. In this work, near-infrared (NIR)-emitting fluorescent Ag2S quantum dots (Ag2S QDs) were synthesized via a rapid microwave reaction under normoxic conditions, which were utilized as sensitive fluorescent nanoprobes in sensing and bioimaging of glutathione (GSH) combined with CoOOH nanosheets (CoOOH NSs). The negatively charged Ag2S QDs can easily and effectively attach to the surface of CoOOH NSs to form the Ag2S QD/CoOOH nanoprobe through electrostatic interactions, accompanied by the quenching of the fluorescence of Ag2S QDs at 685 nm via the inner-filter effect (IFE). However, upon the addition of GSH, the fluorescence of Ag2S QDs was recovered due to the reduction of CoOOH NSs into Co2+ by GSH. Meanwhile, the fluorescent emission wavelength shifts slightly, which may result from the ligand exchange reaction between GSH and d-penicillamine (DPA) to form comodified Ag2S QDs. Based on the low toxicity and high tissue penetration depth of the NIR fluorescence of the Ag2S QDs and the good biocompatibility of CoOOH NSs, the nanoprobe composed of Ag2S QDs and CoOOH NSs was successfully applied in bioimaging, which can distinguish the normal cells and cancer cells, the semiquantitative content of endogenous and exogenous GSH. The as-developed strategy not only provides a simple, convenient, cost-effective, and rapid platform for the diagnosis of clinical diseases related to GSH but shows great prospects in fluorescence-assisted surgery.