A reversible two-photon fluorescence probe for Cu(II) based on Schiff-base in HEPES buffer and in vivo imaging

Abstract

Developing novel probe for Copper (Cu2+) in living system is still of great importance and challenge work for researchers. However, it is rarely reported that a probe for Cu2+ with remarkable two-photon absorption properties, well biocompatibility and excellent water solubility. Herein, a novel water-soluble Schiff-base compound (HL) was confirmed by single crystal X-ray diffraction analysis, which can specifically coordinates with Cu2+，giving an obvious fluorescence quenching and a significant change of the absorption band in HEPES buffer. The mechanism of HL for sensing Cu2+ was proposed relying on 1H NMR titration, mass spectra and theoretical calculations. Furthermore, the UV-vis absorption and emission spectra exhibit a multi-recovery by the subsequent addition of histidine (His). Importantly, the copper complex (L-Cu-L) formed from the probe was still water-soluble and biocompatible. Then the probe was successfully applied to two-photon fluorescent imaging in cellular mitochondria as well as in the intestine and liver of a larval zebrafish. These results imply promising applications of using such probe in physiological systems.