Aqueous phase transfer of AgInGaS(2)/ZnS quantum dots with intrinsic narrow band emission for multimodal visual metal ion sensing in hydrogel platforms.

Despite the potential of AgInGaS (AIGS) quantum dots (QDs) as eco-friendly alternatives to cadmium-based emitters, achieving narrow intrinsic luminescence in aqueous phases remains a tough challenge, due to their surface vulnerability and the prevalence of broad defect-related emissions. This limitation significantly impedes their application in high-precision, multi-channel sensing where spectral resolution is critical. We report AIGS/ZnS QDs synthesized via oil-phase thermal injection, which were successfully transferred into water phase through DSPE-PEG-N self-assembly. The resulting AIGS-PEG nanospheres represent the first aqueous sensing application of intrinsic AIGS QD luminescence, featuring an exceptionally narrow full-width at half maximum (FWHM) of 34 nm. These nanospheres exhibit excellent selectivity and sensitivity towards Cu and Ag ions. To realize portable applications, the probe was further integrated into a polyacrylamide hydrogel (AIGS-PAM). This integration lowered the limit of detection (LOD) for Cu sensing to 88 nM, and LOD for Ag remained comparable to that of the AIGS-PEG nanospheres aqueous solution (446 nM). Notably, the system enables multimodal visual differentiation of Cu and Ag through distinct fluorescence quenching and spectral shift patterns. By reconciling high spectral purity with aqueous stability, this work provides a robust surface engineering strategy for non-toxic QDs and establishes a promising, solid-state platform for advanced point-of-care testing (POCT).