Viscosity-sensitive mitochondrial fluorescent probes and their bio-applications

As a vital index of the mitochondrial micro-environment, mitochondrial micro-viscosity plays a fundamental role in cell life activities. Normal mitochondrial viscosity is a necessary condition for the maintenance of normal life activities of mitochondria. Abnormal mitochondrial viscosity can lead to a series of mitochondria-related diseases. Therefore, it is essential to observe mitochondrial viscosity for physiological and pathological processes. Given the conventional viscosity measurement methods (viscometer, etc.) cannot monitor the changes in mitochondrial viscosity, the fluorescence method supplemented with the fluorescent probe is widely used to observe the changes in mitochondrial viscosity. In view of the booming development in this area, this review describes the applications of viscosity-responsive mitochondrial fluorescent probes in biological samples from the cellular and tissue levels. We hope that this review will deepen our understanding of mitochondrial viscosity and related fields, and promote the development of viscosity-sensitive mitochondrial probes and other organelle fluorescence probes.