Fluorogenic toolbox for visualizing protein aggregation: From designing principles to biological application

Protein aggregation is a process wherein misfolded proteins accumulate to assemble various forms of oligomeric or aggregated structures. This process has been closely related to a variety of human diseases, primarily represented by neurodegenerative diseases. This review provides an overview of fluorescent methods, in particular fluorogenic approaches, that can detect and follow the multiple steps of protein aggregation both in vitro and in vivo. To emphasize the advantage of these approaches, they are compared with other non-fluorescent methods, including western blotting, spectroscopy, and dynamic light scattering. Furthermore, chemical mechanisms that enable the development of these fluorogenic probes are discussed, with a focus on design principles and physical mechanisms underlying fluorescent signal changes that are induced by the process of protein aggregation. In the end, a perspective of challenges and opportunities are discussed to potentiate future method development to study protein aggregation, as well as related biological and biomedical questions.