A novel ratiometric two-photon fluorescent probe for imaging of Pd2 + ions in living cells and tissues

• A new ratiometric two-photon fluorescent probe was developed for the detection of Pd2 +.
• The probe displayed a more than 25-fold ratiometric enhancement for Pd2 +.
• The probe shows high ratiometric imaging resolution and deep-tissue imaging depth of 180 μm.

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 Pd2 + 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 Pd2 + 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.

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