Rhodol-based fluorescent probe for polarity detection in living cells and application in bioimaging

Cell polarity, a vital characteristic of the intracellular microenvironment, significantly influences various biological and pathological processes. A precise and systematic approach to monitoring polarity variations is required to elucidate its mechanistic contributions within complex pathophysiological processes. To address this critical challenge, fluorescence probe-based analytical techniques offer substantial potential due to their high sensitivity, ease of use, and adaptability. They facilitate precise polarity detection across complex biological systems, from controlled in vitro conditions to dynamic in vivo living animal modes. In this study, we developed a novel fluorescent probe based on rhodol, designed to be sensitive to changes in polarity. We compared it with reported fluorophores, coumarin, 2-formyl rhodol (ROA), and coumarin derivative CSS. The novel probe was achieved by incorporating dithiolane, a flexible, rotatable ring, into the rhodol core, resulting in our novel investigation, which we named RSS. RSS remained in a spirocyclic, colourless, and non-fluorescent form in least-polarity environments but shifted to a fluorescent open ring state as polarity increases, resulting in a fluorescent response that positively correlates with polarity levels. RSS has especially proved effective in tracking polarity variations within living cells, including cancerous, young, and senescent cells. Our results indicate that cancer cells exhibited reduced polarity relative to young cells, whereas senescent cells display enhanced polarity.