A novel ratiometric two-photon fluorescent probe for imaging of Pd^{2 +} ions in living cells and tissues

Ratiometric two-photon fluorescent probes can not only eliminate interferences from environmental factors but also achieve deep-tissue imaging with improved spatial localization. To quantitatively track Pd^{2 +} in biosystems, herein, we reported a ratiometric two-photon fluorescent probe, termed as Np-Pd, which based on a D-π-A-structure two-photon fluorophore of the naphthalimide derivative and deprotection of aryl propargyl ethers by palladium species. The probe Np-Pd displayed a more than 25-fold enhancement towards palladium species with high sensitivity and selectivity. Additionally, the probe Np-Pd was further used for fluorescence imaging of Pd^{2 +} ions in living cells and tissues under two-photon excitation (820 nm), which showed large tissue-imaging depth (19.6-184.6 μm), and a high resolution for ratiometric imaging.