Development of a Pd⁰ fluorescent probe based on coumarin derivatives and its detection applications in biological and...

With the expanding application of palladium in various fields, its environmental release has significantly increased. The detection of residual Pd⁰ in catalytic wastes is often overlooked, while Pd²⁺ poses significant toxicity risks. Consequently, fluorescent probes that can distinguish between palladium species-particularly those selectively detecting Pd⁰ in complex biological systems-are of great importance. In this study, two novel fluorescent probes based on modified coumarin fluorophores were designed and synthesized, utilizing allyl formate as the recognition moiety for Pd⁰: Dcou-1, Dcou-2, Dcou-3, and Cou-1. Probe Dcou-1 demonstrates excellent selectivity for Pd⁰, effectively differentiating it from Pd²⁺, and enables highly sensitive detection of trace amounts of Pd⁰ in aqueous samples and pharmaceutical matrices, with a detection limit as low as 55 nM. Probe Cou-1 exhibits a large Stokes shift (173 nm) and near-infrared emission at a maximum wavelength of 661 nm, which effectively minimizes background interference and enhances tissue penetration. Furthermore, Cou-1 demonstrates mitochondrial targeting capability, providing a valuable tool for investigating the relationship between mitochondrial function and Pd⁰ intoxication. This study further validated the probes' biocompatibility and dynamic monitoring capabilities in live-cell and zebrafish models co-incubated with Pd⁰, where distinct spatiotemporal dynamic variations of fluorescent signals triggered by Pd⁰ were systematically observed. This work not only provides a superior Pd⁰-specific detection tool, solving the problem of valence state discrimination and compatibility with biological applications, but also opens up new avenues for the design of coumarin-based Pd⁰ probes and their application in environmental safety assessment and life science research.