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

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.