A viscosity-sensitive probe based on the structure of indole salt

It is of great importance to research intracellular viscosity as a new tumor biomarker. Herein, we synthesized a simple NIR viscosity-sensitive probe YS-3, which exhibits a good fluorescence quantum yield and a suitable Stokes shift. Molecular orbital wavefunctions elucidate its near-infrared emission and changes in electron transfer during excitation. Additionally, cell experiments demonstrated that YS-3 possesses unique viscosity responsiveness and multi-organelle staining abilities, and can also monitor intracellular viscosity fluctuations. The experiments demonstrate that the viscosity of the endoplasmic reticulum, mitochondria and lysosomes in tumor cells is abnormal compared to that in normal cells. Additionally, YS-3 achieves prolonged and high-contrast differentiation between muscle tissue and tumors in a mouse model. This study provides a new perspective for the differentiation, identification and diagnosis of tumors. Long-lasting and high-intensity fluorescence imaging of tumor cells.