Construction of a Near-Infrared Viscosity Fluorescent Probe Targeting Mitochondria and Study on Its pH-Coordinated Effect

In this study, a mitochondria-targeting near-infrared (NIR) fluorescent probe, Mito-V, based on an oxanthrene-like hybrid structure was designed and synthesized, for detecting viscosity with pH-cooperative response characteristics. Upon increasing viscosity, Mito-V exhibits a significant NIR fluorescence enhancement with a high signal-to-noise ratio and excellent selectivity. Under weakly acidic conditions, the viscosity response is further enhanced, demonstrating a pH-cooperative effect that improves detection sensitivity. Cellular imaging experiments confirmed that Mito-V can effectively monitor fluctuations in intracellular viscosity, and co-localization studies revealed its high specificity for mitochondria, with a Pearson's coefficient of 0.89. Furthermore, the pH-cooperative effect on viscosity detection was verified at the cellular level. In vivo imaging in zebrafish successfully visualized viscosity variations, demonstrating the probe's applicability and biosafety for monitoring viscosity in biological systems. These findings indicate that Mito-V holds great potential for studying viscosity-related processes in live cells and organisms.