CdTe-MSA quantum dots prepared by a green hydrothermal route as highly selective ‘turn-off’ fluorescent nanosensors for Lead(II) detection in environmental water monitoring

• Green hydrothermal synthesis of water-dispersible CdTe–MSA Quantum Dots. • Highly selective fluorescence “turn-off” response towards Pb 2+ ions. • Wide linear detection range (0.2–4 μM) with low detection limit of 72 nM. • Static quenching via Pb 2+ –carboxylate binding; adsorption fits Langmuir isotherm. • High recovery (95–109%) in real tap water confirms environmental applicability. In this study, water-dispersible CdTe quantum dots (QDs) capped with mercaptosuccinic acid (MSA) were synthesized via a green one-pot hydrothermal route and explored as efficient fluorescent probes for Pb 2+ detection in aqueous media. The obtained QDs, with an average diameter of 3.4 nm, exhibited high colloidal stability, strong fluorescence, and a narrow emission profile. Remarkably, a selective fluorescence "turn-off" response was observed exclusively in the presence of Pb 2+ ions, with no significant interference from other tested metal cations. Quantitative analysis using the Stern–Volmer model revealed a linear detection range of 0.2–4 µM (R² = 0.9948) and a low detection limit of 72 nM. Taken with the Benesi–Hildebrand analysis, results confirmed a static quenching mechanism arising from strong Pb 2+ -carboxylate binding, followed by electron transfer and formation of a non-emissive ground-state complex. Adsorption experiments demonstrated that Pb 2+ uptake follows pseudo-first-order kinetics and fits the Langmuir isotherm model, indicating monolayer adsorption on homogeneous active sites. Recovery tests in spiked real tap water samples achieved 95–109% recoveries with RSD < 5%, underscoring the probe's reliability under realistic conditions. These results highlight CdTe-MSA QDs as cost-effective, selective, and sensitive chemosensors with strong potential for environmental monitoring of lead contamination.