Shining natural flavonols in sensing and bioimaging

Abstract Widely distributed natural flavonols with broad-spectrum pharmacological activities are unique dual emission fluorescence dyes. The excited state intramolecular proton transfer (ESIPT) characteristics for flavonols makes them sensitive to microenvironment. Notably, flavonols exhibit aggregation-induced emission (AIE), large Stokes shift, high photostability, excellent biocompatibility, and low cytotoxicity. Therefore, natural flavonols are ideal and valuable fluorescent probes in sensing metal ions, anions, small biomolecules, and biomacromolecules, as well as bioimaging, even to theranostics. This review describes the sources and structures of natural flavonols, dual emission fluorescent mechanism and AIE characteristic of flavonols, and then summarizes the advances of natural flavonols as fluorescent probes in sensing and bioimaging. Finally, challenges and development trends of flavonol-based fluorescent sensors are discussed. We believe this review will provide comprehensive and systematic reference for researchers to fabricate flavonol-based fluorescent sensors.