"One stone, two birds": a mitochondria-targeted fluorescent probe for the detection of viscosity and HSO 3 - in living cells.

The material transport and physiological events of mitochondria need to be supported by a suitable microenvironment. For example, high viscosity will seriously hinder material exchange, and SO 2 , as the precursor of HSO 3 - , is an endogenous signal molecule that plays a key role in information transmission. It is very important to detect viscosity and HSO 3 - in mitochondria. Here, we developed a dual-responsive fluorescent probe (named Hcy-NT) to image the changes in mitochondrial viscosity and HSO 3 - in a "killing two birds with one stone" manner. Hcy-NT showed an OFF-ON fluorescence signal for the increase in cell viscosity induced by nystatin, while an ON-OFF fluorescence signal for intracellular and endogenous HSO 3 - . Its limits of detection for HSO 3 - were calculated by both absorption and fluorescence methods, which were 1.200 and 1.291 μM, respectively. This work provides a valuable tool for the study of viscosity and HSO 3 - related physiological processes and the diagnosis of potential diseases.