Fluorogenic Chemical Probe Strategy for Precise Tracking\nof Mitochondrial Polarity

Mitochondrial polarity is a critical\nindicator of numerous pathological\nand biological processes; thus, the development of fluorescent probes\ncapable of targeting mitochondria and visually monitoring its polarity\nis of great significance. In this study, fluorescent probes were designed\nwith a N, N-dialkylamino rhodol scaffold as the fluorophore sensitive\nto polarity environments, in which the alkyl chain length was adjusted\nrationally to obtain distinct polarity recognition modes. By integrating\nmitochondria targeting groups, three fluorogenic chemical probes <b>ROML-1</b>, <b>ROML-2</b>, and <b>ROML-3</b> have\nbeen obtained, featuring the capability to target mitochondria and\nmonitor its polarity precisely, dynamically and visually. The probes\ndisplayed a distinctive response to the alterations in polarity. <b>ROML-1</b> and <b>ROML-2</b> followed a turn-on pattern\nwhile <b>ROML-3</b> was ratiometric. It has been demonstrated\nthat the hypersensitivity to polarity and ratio fluorescence property\nof <b>ROML-3</b> was attributed to methyl groups rather than\nethyl or butyl groups. The introduction of short methyl chains made\nthe dihedral angle between the dialkylamino substituent and fluorophore\nof <b>ROML-3</b> (spirocyclic form) rotatable and enlarged the\nenergy gap between the ground state and excited state, which has been\nvalidated by the results of density functional theory (DFT) calculations.\nFurthermore, <b>ROML-3</b> was used to monitor mitochondrial\npolarity via confocal microscopy imaging, which revealed that compared\nto healthy cells the polarity of mitochondria in cancer cells was\nenhanced; meanwhile, the polarity of mitochondria in senescent cells\nwas higher in contrast with young cells. The present probe <b>ROML-3</b> has been proven to be an efficient tool to monitor mitochondrial\npolarity dynamics, which demonstrated potential significance in biomedical\nresearch and disease diagnosis.