A TICT mechanism-based viscosity fluorescent probe for monitoring viscosity in inflammatory cells†

Viscosity, as a fundamental biophysical parameter of cellular microenvironments, critically regulates physiological processes, including molecular transport and signal transduction. Lysosomes, functioning as pivotal organelles, orchestrate essential biological activities such as macromolecular degradation and autophagic flux. Aberrant viscosity fluctuations disrupt the substrate delivery within lysosomal enzymatic activation zones, precipitating accumulation of undegraded metabolites and subsequent release of inflammatory mediators, ultimately contributing to chronic inflammatory diseases. Consequently, developing high-performance probes capable of real-time lysosomal viscosity monitoring is imperative for the prevention, diagnosis and therapeutic intervention of inflammatory diseases. We developed a lysosome-targeted fluorescent probe, LTP-H, based on the TICT mechanism. The probe demonstrated a linear correlation between fluorescence intensity at 650 nm and medium viscosity (R² = 0.995), exhibiting a 93-fold viscosity response ratio with robust stability against solvent polarity variations, pH fluctuations, and biological interferents. Density functional theory calculations corroborated the TICT response mechanism. Based on the strong hydrophobic property of the triphenylamine group, the LTP-H probe achieved pH-independent lysosomal targeting through a hydrophobicity-mediated membrane localization mechanism (p = 0.90). Successful application in monitoring viscosity dynamics within inflammatory cellular models and pharmacologically manipulated zebrafish demonstrated its utility as a molecular tool for investigating microenvironmental viscosity in inflammatory diseases.