Monitoring viscosity in live cells based on the excited-state absorption signal in transient absorption spectroscopy

Transient absorption (TA) signals have the features of real-time multi-signals and high sensitivity for biological monitoring, and they are less disturbed by the biological environment compared to single fluorescence signals. Two intelligently regulated probes (1-VBM and 1-VBH) are designed and synthesized with time-resolved excited-state absorption (ESA) and stimulated emission (SE) signals in TA spectroscopy. In mixed solutions of glycerol and DMSO, the ESA lifetimes of the 1-VBM probe linearly increase (y = 4.5419x + 303.98) with an increase in solvent viscosity (2.79–190.35 cP), showing similar sensitivity as SE lifetimes (y = 4.6342x + 311.06). Therefore, these TA signals can be used to monitor the viscosity of live cells. As serum changes in viscosity, 1-VBM has a sensitive and specific time-resolved ESA signal. Interestingly, the ESA signal is several times stronger than the SE signal in the serum of both healthy mice and mice with hepatoma. The lifetime of ESA signal in hepatoma serum (958.6 ps) is longer than that in normal serum (632.8 ps), which is induced by the higher blood viscosity in hepatoma mice. This indicates that the ESA signals in TA spectroscopy are a reliable marker for detecting viscosity in biological samples, and can be a potential tool for clinical diagnosis.