An endoplasmic reticulum-targeted fluorescent probe for detecting polarity and viscosity and its bioimaging in vitro and vivo

Revealing the dynamics of intracellular microenvironment (viscosity and polarity) during endoplasmic reticulum (ER) stress is crucial for the diagnosis of related diseases. Herein, we developed an ER-targeted dual-response fluorescent probe (XHXA) for simultaneously detecting polarity and viscosity with large emission spectral separation (>180 nm). By leveraging intramolecular charge transfer (ICT) and twisted intramolecular charge transfer (TICT) mechanisms, XHXA exhibited excellent responsiveness to polarity and viscosity at emission wavelengths of 482 nm and 665 nm, respectively. Moreover, XHXA enabled real-time imaging of ER microenvironment in living cells, and tracking ER stress and autophagy. Meanwhile, reduced polarity and increased viscosity were observed in non-alcoholic fatty liver disease (NAFLD) models via XHXA. Notably, XHXA was first applied to diagnose liver cirrhosis in vivo through monitoring ER viscosity. Thus, this work established a powerful platform for early diagnostics and investigating the physiological and pathological of disease related with ER stress.