"One stone, two birds": a mitochondria-targeted fluorescent probe for the detection of viscosity and HSO 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, as the precursor of HSO, is an endogenous signal molecule that plays a key role in information transmission. It is very important to detect viscosity and HSO in mitochondria. Here, we developed a dual-responsive fluorescent probe (named Hcy-NT) to image the changes in mitochondrial viscosity and HSO 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. Its limits of detection for HSO 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 related physiological processes and the diagnosis of potential diseases.