Quinoline-based fluorescent probes with large Stokes shift for sequential Cu²⁺ and S^2- ions detection in bioimaging

Fluorescent probes offer a promising approach to detecting and imaging biologically essential copper (Cu²⁺) and sulfide (S^2-) ions, which play critical roles in various physiological processes. However, many existing Cu²⁺ and S^2- probes have limitations like narrow Stokes shifts. To address this, we rationally designed and synthesized three quinoline-based fluorescent probes (CuQP-1, CuQP-2, and CuQP-3), each incorporating a unique Cu²⁺ ion recognition group. Notably, CuQP-1 exhibited a substantial Stokes shift of 178 nm. Furthermore, CuQP-1 displayed selective fluorescence quenching upon interaction with Cu²⁺ ions, which was uniquely restored upon the subsequent addition of S^2- ions. Subsequent investigations revealed that CuQP-1 can effectively image Cu²⁺ and S^2- ions in HT22 cells and zebrafish, underscoring its potential as a versatile tool for studying these analytes in biological systems. In addition, the [CuQP-1 + Cu²⁺] complex is suitable for S^2- detection in real samples.