A facilely synthesized near-infrared fluorescent probe for selective lysosomal viscosity imaging

Lysosomal viscosity is critical for cellular homeostasis, but real-time monitoring of its fluctuations remains challenging. We developed TCF-V-Lyso, a photostable and pH-tolerant fluorescent probe, via a concise one-step procedure for selective lysosomal viscosity imaging. The probe exhibits a 480-fold fluorescence turn-on enhancement at 755 nm upon viscosity increase, with good linearity, high selectivity, and low cytotoxicity. It successfully tracked viscosity changes induced by nystatin, monensin, and H₂O₂ in living cells, and also visualized elevated lysosomal viscosity in tumor-bearing mice, demonstrating its potential for investigating lysosome-associated pathology.