Fluorogenic sensing of amorphous aggregates, amyloid fibers, and chaperone activity via a near‐infrared aggregation‐induced emission‐active probe

Abstract The presence of protein aggregates in numerous human diseases underscores the significance of detecting these aggregates to comprehend disease mechanisms and develop novel therapeutic approaches for combating these disorders. Despite the development of various biosensors and fluorescent probes that selectively target amyloid fibers or amorphous aggregates, there is still a lack of tools capable of simultaneously detecting both types of aggregates. Herein, we demonstrate the quantitative discernment of amorphous aggregates by QM‐FN‐SO 3 , an aggregation‐induced emission (AIE) probe initially designed for detecting amyloid fibers. This probe easily penetrates the membranes of the widely‐used prokaryotic model organism Escherichia coli , enabling the visualization of both amorphous aggregates and amyloid fibers through near‐infrared fluorescence. Notably, the probe exhibits sensitivity in distinguishing the varying aggregation propensities of proteins, regardless of whether they form amorphous aggregates or amyloid fibers in vivo. These properties contribute to the successful application of the QM‐FN‐SO 3 probe in the subsequent investigation of the antiaggregation activities of two outer membrane protein (OMP) chaperones, both in vitro and in their physiological environment. Overall, our work introduces a near‐infrared fluorescent chemical probe that can quantitatively detect amyloid fibers and amorphous aggregates with high sensitivity in vitro and in vivo. Furthermore, it demonstrates the applicability of the probe in chaperone biology and its potential as a high‐throughput screening tool for protein aggregation inhibitors and folding factors.