A versatile fluorescent probe for visualizing microenvironment polarity across environmental and biological systems.

Microenvironment polarity, a key parameter governing intermolecular interactions, plays a critical role in both ecological environments and living systems. In environmental contexts, the surface polarity of microplastics dictates their adsorption behavior and subsequent migration and transformation, whereas in living systems, aberrant cell polarity, exemplified by alterations in the lipid droplet microenvironment, is intimately associated with the pathogenesis of various diseases. Current methods for polarity detection, however, rely heavily on bulky instrumentation, which hinders rapid in situ characterization. Despite the advantages of fluorescent probes, including high sensitivity, fast response, and visual signal output, those that integrate environmental robustness with biocompatibility remain scarce. To address this gap, this study designed and synthesized a novel polarity-sensitive fluorescent probe, SSF. Experimental results demonstrate that SSF possesses excellent anti-interference capability and photostability, with its fluorescence intensity exhibiting a linear response to medium polarity over a wide range. The probe was successfully applied in two typical scenarios. In environmental monitoring, it enabled naked-eye identification under 365 nm UV illumination and dual-modal fluorescence detection of 14 types of microplastics in both seawater and ultrapure water systems. Not only that, in bioimaging, it specifically targeted lipid droplets in living cells and allowed real-time monitoring of polarity changes within the lipid droplet microenvironment during apoptosis. This work presents a versatile molecular tool for visualizing microenvironment polarity across diverse scenarios, highlighting considerable potential for applications in environmental monitoring and biomedical fields.