Organic–Inorganic Copassivation Enables Environmentally Benign Water-Soluble InP Quantum Dots for Pb ²⁺ Ion Detection

Heavy-metal pollution, particularly from lead ions, threatens environmental and human health, necessitating sensitive detection methods. Fluorescent probes based on colloidal quantum dots (QDs) offer a promising solution, yet toxicity concerns of the state-of-the-art Cd/Pb-based QDs and achieving high-quality water-soluble eco-friendly QDs remain challenging due to ineffective surface passivation during phase transfer. Here, we demonstrate an organic–inorganic surface copassivation strategy to obtain eco-friendly water-soluble InP-based QDs with excellent optical properties. By employing organic mercaptopropionic acid together with inorganic zinc salts during ligand exchange, both surface cationic and anionic sites are effectively passivated, yielding water-soluble InP/ZnSe/ZnS QDs with a high photoluminescence quantum yield of up to 91%, monoexponential decay dynamics, and outstanding stability. Utilizing these bright QDs as fluorescent probes, ultrasensitive and selective detection of Pb 2+ ions with a 0.3 nM detection limit is achieved, comparable to conventional probes. This work establishes a general design principle for high-quality water-soluble QDs and highlights the potential use of eco-friendly QDs for aqueous-based applications.