A supramolecular fluorescence probe that simultaneously responds to viscosity and G-quadruplex for autophagy...

Autophagy, as an essential physiological process in eukaryotes, has been revealed to be closely related to aging and many major diseases. Real-time in situ imaging of autophagy processes in living cells is necessary for timely detection of autophagy defects and the development of treatment methods. Currently, many studies are dedicated to the design of autophagy probes, and various types of fluorescent probes for autophagy detection have been reported. However, most of them are single fluorescence signal outputs, which may lead to non-specific signals. Nowadays a reliable and sensitive autophagy monitoring probe is still essential.

A supramolecular fluorescent probe was prepared via the controllable self-assembly of a thiacyanine dye named PTC for tracking autophagy in living cells. PTC was very sensitive to viscosity, and its aggregates were completely converted into monomers as viscosity increased. This process led to a significant increase of over 2000 times in the fluorescence intensity ratio between monomers and aggregates. PTC also exhibited selective affinity for G-quadruplex (G4) structure, which decomposed PTC aggregates into monomers, resulting in a fluorescence ratio increase of up to tens of folds. In living cells, PTC existed as aggregates in lysosomes, maintaining sensitivity to viscosity and G4s. In confocal imaging experiments, PTC sensitively responded to the induction and inhibition of cellular autophagy, displaying opposite changes in the monomer and aggregate fluorescent channels.

This work provides a reliable fluorescent probe for autophagy detection in live cells, which has the advantages of high sensitivity, low cost, and ease of use, making it have the potential for widespread application. This study also offers a new strategy for designing autophagy probes with both high sensitivity and high specificity.