Silica-Coated S^2–-Enriched Manganese-Doped ZnS Quantum Dots as a Photoluminescence Probe for Imaging Intracellular Zn²⁺ Ions

Detection of intracellular Zn²⁺ has gained great attention because of its biological significances. Here we show the fabrication of silica-coated S^2–-enriched Mn-doped ZnS quantum dots (SiO₂–S–Mn–ZnS QDs) by enriching S^2– with a silica shell on the surface of Mn-doped ZnS QDs via a sol–gel process for imaging intracellular Zn²⁺ ions. The developed probe gave a good linearity for the calibration plot (the recovered PL intensity of the SiO₂–S–Mn–ZnS QDs against the concentration of Zn²⁺ from 0.3 to 15.0 μM), excellent reproducibility (1.2% relative standard deviation for 11 replicate measurements of Zn²⁺ at 3 μM), and low detection limit (3s; 80 nM Zn²⁺). The SiO₂–S–Mn–ZnS QDs showed negligible cytotoxicity, good sensitivity, and selectivity for Zn²⁺ in a photoluminescence turn-on mode, being a promising probe for photoluminescence imaging of intracellular Zn²⁺.