Construction of a pH- and viscosity-switchable near-infrared fluorescent probe and its imaging application.

Viscosity is a parameter used to measure the fluidity of liquids and a key indicator in evaluating the states of body fluid in biological tissues and lesions. Most traditional detection methods have many drawbacks such as a short emission wavelength and interference by background fluorescence. Inspired by the multiple double bond structure of retinal, a novel pH and viscosity dual-response fluorescent probe (Rh-TR) was constructed in this study. Rh-TR exhibited two emission signals centered at 510 and 660 nm. As the pH of the phosphate-buffered saline increased, the fluorescence at 510 nm increased by about 124-fold, while the change in fluorescence at 660 nm was not obvious. When detecting the change in viscosity using the probe, the fluorescence at 510 nm decreased by about 85 %, while the fluorescence at 660 nm increased by over 20-fold. The probe also showed high selectivity and little toxicity. As demonstrated by the biological imaging experiment, the probe successfully imaged changes in the pH and viscosity of cells and in a live animal model of zebrafish. Considering the unique structure of Rh-TR with retinal and its pH- and viscosity-switchable spectral property, the probe may find further application in detecting viscosity-related diseases and industrial detection.