Naked-eye-visible electrochemiluminescence from Ag-In-Zn-S quantum dots via core doping and surface copassivation

Colloidal quantum dots (QDs) have emerged as promising electrochemiluminophores (ECLphores), however the intrinsic toxicity of Cd-/Pb-based QDs and their inferior performance in aqueous media severely limit their advanced analytical applications, particularly in biological systems. Herein, we report a dual-enhancement strategy that integrates surface copassivation and core doping to construct high-performance Ag-In-S-based QDs synthesized directly in the aqueous phase. Dual-ligand copassivation with glutathione (GSH) and polyethyleneimine (PEI) effectively suppresses surface defect-mediated nonradiative recombination and improves interfacial charge-transfer efficiency, while subsequent Zn²⁺ incorporation into the QDs core regulates the internal electronic structure by relieving lattice strain and promoting uniform shell growth, resulting in a photoluminescence quantum yield (PLQY) of up to 71.5%, accompanied by a pronounced enhancement in electrochemiluminescence (ECL) efficiency. Using tri-n-propylamine (TPrA) as a coreactant, the resulting Ag-In-Zn-S (AIZS) QDs exhibit intense near-infrared ECL emission centered at 710 nm, with an approximately 130-fold enhancement compared to pristine Ag-In-S (AIS) QDs, enabling naked-eye-visible ECL in aqueous solution. As a proof-of-concept analytical application, the enhanced ECL response is successfully applied to sensitive and selective iodide (I^-) detection with a detection limit of 3.2 nM. This work provides a viable strategy for constructing environmentally friendly water-soluble QDs as a promising class of ECLphores for analytical sensing applications.