Glutathione-Capped CuInS₂/ZnS Quantum Dots for the Determination of Pb²⁺ in Drinking Water and Multicolor Cellular Imaging

The widespread presence of lead in our environment necessitates the development of reliable methods for its detection and quantification, particularly in drinking water. Herein, we synthesized highly biocompatible copper indium sulfide/zinc sulfide core/shell quantum dots via an aqueous route to develop a rapid, sensitive, and pH-tolerant fluorescence-based nanoprobe for the quantification of lead ions in drinking water. The synthesized quantum dots displayed bright yellowish-orange emission with excellent stability in aqueous solutions, long photoluminescence lifetime decay, and an average particle size of approximately 4.5 nm. Interestingly, the synthesized quantum dots have excellent selectivity and sensitivity toward lead ions with a linear detection range of 0.05–6 μM and a limit of detection of 33 nM. This limit of detection value, which is below the World Health Organization’s regulatory level for lead contamination, along with excellent pH resistivity and a very short response time, elevates the promising practical application of this sensing system in water quality monitoring. The detection mechanism was investigated in detail and attributed to photoinduced electron transfer from the quantum dots to lead ions. The practical use of synthesized quantum dots for the detection of lead ions has been successfully demonstrated in real water samples with a recovery percentage of 96–105%. Furthermore, the less toxic, biocompatible nature of the prepared quantum dots was employed for the multicolor imaging and time-lapse imaging of N2a cells, confirming their applicability in biolabeling.