A two-photon ratiometric ESIPT probe for fast detection and bioimaging of palladium species

A novel ratiometric ESIPT fluorescent probe, which is specific for palladium species of all the typical oxidation states (0, +2, and +4), has been designed. Notably, based on the excited state intramolecular proton transfer (ESIPT) process, the probe exhibits a ratiometric fluorescent response to palladium species with a low detection limit (9.0 nM, 0.96 ppb) in about 1.5 min at room temperature. Moreover, it has been successfully used as a two-photon ratiometric fluorescent palladium probe for in vivo and three-dimensional imaging with low cytotoxicity and autofluorescence. Compared with other reported palladium probes, the probe displays a shorter ratiometric response time and lower detection limit in milder test conditions. All of the results indicate that the probe may be favorable for environmental and biological applications.