A wash-free red fluorescent probe for real-time monitoring of mitochondrial viscosity changes and tumor imaging

Mitochondria are important energy-producing organelles within cells, and abnormalities in the viscosity of their microenvironment are closely related to diseases such as cancer. Current methods for detecting viscosity still suffer from many limitations, whereas fluorescence imaging techniques can address these shortcomings. Therefore, there is an urgent need to develop fluorescence probes capable of detecting changes in mitochondrial viscosity. In this study, derivatives of triphenylamine were used as the core structure, and different triphenylphosphine derivatives were introduced through a condensation reaction to synthesize three red fluorescence probes with a D-π-A structure. Their photophysical properties have been systematically studied and it has been found that they are not only sensitive to viscosity but also exhibit strong anti-jamming capabilities. Among them, probe TPAP2 exhibits excellent optical properties, including large Stokes shifts and high sensitivity to viscosity. It was found that TPAP2 is mitochondria-targeted, washing-free, and fast (<10s), with the targeting process depending on the mitochondrial membrane potential. The probe has been successfully applied to tumor imaging in mice with subcutaneous tumors.