Evaluation of Fluorescent Cu²⁺ Probes: Instant Sensing, Cell Permeable Recognition and Quantitative Detection

By incorporating a rhodamine spirolactam structure as the recognition site for Cu²⁺, two novel probes were synthesized through a connection of rhodamine 6G acylhydrazine and 5-formyl-6-hydroxyl-4-methylcoumarin/2,4-dihydroxybenzaldehyde. In the recognition process of probes towards Cu²⁺, the spirolactam ring exhibited opening and closing, accompanying an instant and specific change in fluorescence and in color, which could also achieve a naked-eye and semiquantitative recognition of aqueous Cu²⁺ besides the fluorescent Cu²⁺ detection method. Fluorescent analyses and ECV304 cell imaging further revealed the probes' good optical stability, instant response, low toxicity, and membrane permeability, which offers future possibilities for the probes' instant detection and the real-time tracking of Cu²⁺ in biological systems.