A mitochondrial-targeted fluorescent probe to sense pH and HOCl in living cells

A series of rosamine dyes were designed and synthesized through one-step reaction. Among them, bifunctional fluorescent probe RosPO(OH)2 showed excellent water solubility and large molar extinction coefficient. RosPO(OH)2 underwent a two-step ionization process as the pH value of the HEPES buffer increased, accompanied a blue shift of UV absorption and an enhancement of fluorescence intensity. This means it can be used as a pH sensor. After the addition of HOCl, the fluorescence of RosPO(OH)2 was quenched and the color of the solution changed from pink to colorless which permitted "naked eye" detection. RosPO(OH)2 could be used as a sensor for detecting HOCl with high selectivity, rapid response, low detection limit (52 nM) and a wide range of pH application (pH 1–10). Colocalization results showed that RosPO(OH)2 could specifically stain in mitochondria. Due to the low toxicity and the excellent water solubility of RosPO(OH)2, it had been successfully applied to image pH and HOCl in living cells.