Lysosome-targeted high resolution near-infrared fluorescent probe for low physiological pH imaging in vivo

Abstract

Low physiological pH have an essential role in keeping the digestive function of stomach, avoiding infection and affecting the absorption effect of oral drugs, monitoring the minor fluctuations of low physiological pH is of great concern. An imidazopyridine-based ratiometric near-infrared (NIR) fluorescent probe SPO is rationally designed and synthesized for low physiological pH imaging. SPO exhibits high-resolution characteristics, including large Stokes shift (237 nm), remarkable emission shift (110 nm) and good fluorescence quantum yield (Φ = 0.68). It also possesses good reversibility, high selectivity and excellent photostability, and profits to monitoring of continuous pH changes. Moreover, ratiometric fluorescence imaging showed that the probe could conveniently and sensitively track the lysosomal pH fluctuation in living cells. The pKa value of SPO (pKa = 3.0) permits the accurate monitoring of the minor fluctuations of low physiological pH, and SPO was used for noninvasive monitoring gastric pH in living mice successfully.