Abstract <p>This study proposes a rapid approach for determining heavy metal cation content in natural and wastewater solutions by monitoring changes in the optical properties of multilayer chalcogenide quantum dots (QDs) with various stabilizing coatings. CdTe/CdS/ZnS QDs were synthesized via an aqueous colloidal method using 3-mercaptopropionic acid, L-cysteine, and cysteamine as stabilizers. Investigation of the influence of stabilizing shells on QD fluorescence revealed selective quenching in the presence of Hg²⁺, Cu²⁺, Ag⁺, and Zn²⁺ cations, enabling the development of sensors for multiple metal ions. Detection at concentrations as low as 1 × 10^–5 M was achieved within 5–6 s using a sample volume of only 3 μL. The resulting sensor systems are low-cost, simple to operate, and suitable for rapid, on-site analysis.</p>