Two-Photon Ratiometric Fluorescence Probe with Enhanced Absorption Cross Section for Imaging and Biosensing of Zinc Ions in Hippocampal Tissue and Zebrafish.

Zinc ion (Zn2+) not only plays an important function in the structural, catalytic, transcription, and regulatory of proteins, but is also an essential ionic signal to regulate brain neurotransmitters pass process. In this work, we designed and synthesized an intramolecular charge transfer-based ratiometric two-photon fluorescence probe, P-Zn, for imaging and biosensing of Zn2+ in live cell, hippocampal tissue, and zebrafish. The developed probe demonstrated high two-photon absorption cross section (δ) of 516 ± 77 GM, which increased to 958 ± 144 GM after the probe was coordinated with Zn2+. Furthermore, this P-Zn probe quickly recognized Zn2+ with high selectivity, over other metal ions, amino acids, and reactive oxygen species. More interestingly, the initial emission peak of the present probe at 465 nm decreased with a new peak increased at 550 nm, leading to the ratiometric determination of Zn2+ with high accuracy. Finally, this two-photon fluorescence probe with high temporal resolution and remarkable analytical performance, as well as low-cytotoxicity, was successfully applied in imaging of live cells, hippocampal tissues, and zebrafishes. The present P-Zn probe combined with FLIM provided accurate mapping of Zn2+ distribution at single-cell level. More interestingly, the two-photon spectroscopic results demonstrated that the level of Zn2+ in hippocampal tissue of mouse with AD was higher than that in normal mouse brain.