Construction of viscosity-sensitive RNA fluorescent probes and their application in inflammtation imaging

Abnormal structure or function of the nucleolus can lead to dynamic imbalances in intracellular viscosity, which is a core pathological feature of major diseases, including inflammation and cancer. However, existing fluorescent probes face challenges in synchronously and accurately detecting nucleolar RNA dynamics and viscosity changes. Therefore, in this study, probes NK-1 and NK-2, which specifically target the nucleolus, were developed and synthesized. Both probes incorporate a donor-π-acceptor (D-π-A) structure with a positively charged quinolinium salt as the core, enabling specific RNA recognition through electrostatic interactions and responding to viscosity changes based on the molecular rotor mechanism. Experiments demonstrated that the two probes exhibit a rapid response, high sensitivity, robust stability, and excellent biocompatibility. They can penetrate cell membranes and nuclear membranes without a permeabilizing agent, specifically target the nucleolus, and effectively monitor nucleolar number loss in HepG2 cells. In inflammation models induced by lipopolysaccharide (LPS) and rapamycin (Rap), inflammation-induced viscosity elevation led to a marked increase in the probes' fluorescence intensity, enabling synchronous visual monitoring of nucleolar RNA dynamics and viscosity changes in living cells. The two probes provide an effective tool for identifying nucleolar abnormalities under inflammatory conditions and offer new molecular tools for early research on RNA and inflammation-related diseases, with potential to advance in-depth analysis of nucleolar functions and disease mechanisms.