A red-emission and viscosity-ultrasensitive probe for identifying non-alcoholic fatty liver via imaging lysosomal viscosity

Elucidating the intrinsic correlation between non-alcoholic fatty liver (NAFL) and lysosomal viscosity is a challenging work owing to the disadvantages of state-of-the-art technologies for NAFL identification. Herein, we constructed a red emission imaging fluorophore L-TPQ based on D-π-A (donor–π–bridge-acceptor) structure for identifying NAFL tissues by tracking the change in lysosomal viscosity. Specifically, L-TPQ is ultrasensitive to viscosity with a remarkable enhancement in fluorescence intensity (about 910 fold) and fluorescence quantum yield (about 221 fold) through a twisted intra-molecular charge transfer (TICT) mechanism. In addition, L-TPQ shows a single selectivity toward viscosity with an excellent pH stability and insignificant interference from environmental polarity or biomolecules. Moreover, probe L-TPQ is lysosome-specific, which is capable of monitoring the lysosome movement, lysosomal viscosity change, and mitophagy. Importantly, by means of this probe, we have successfully observed an increased viscosity in the pathological model of NAFL mice. Given the comprehensive property of probe L-TPQ, it is expected to serve as a convenient and effective tool for better understanding the pathophysiology of NAFL and the early diagnosis of this disease.