Microwave-assisted Facile Synthesized Carbon Dots as “on–off-on” Fluorescence Probes for Mercury and Iodine Ions in Bio-samples and Cell Imaging

A kind of nitrogen and sulfur co-doped CDs (N, S-CDs) was facilely synthesized using thiourea and citric acid as precursors, which established an “on–off-on” fluorescence probe to sequential detecting mercury and iodine ions inside water and biology samples. Under 360 nm excitation, CDs emit blue fluorescence with an optimal emission peak of 425 nm (on). The fluorescence of CDs experiences a significant quenching effect upon interaction with Hg²⁺ ions due to the electron transfer between CDs and Hg²⁺. This quenching effect is subsequently recovered upon the addition of I⁻ owing to the formation of complexes between Hg²⁺ and I⁻. The probe exhibits high selectivity and sensitivity toward Hg²⁺ and I⁻ with broad linearity in the range of 5–50 μM and 15–60 μM, respectively, and a low detection limit of 14.336 nM and 38.213 nM, respectively. The constructed fluorescence probe N, S-CDs has been successfully applied to the detection of Hg²⁺ and I⁻ in water and biological samples with great recoveries. More importantly, the bioimaging study demonstrated that N, S-CDs are suitable for live monitoring in biological imaging scenarios of Hg²⁺ and I⁻ in living cells.