AIE nanocrystals: Emerging nanolights with ultra-high brightness for biological application

Aggregation-induced emission (AIE) dots and nanoparticles have been widely applied in biological research recently due to their high brightness, large Stokes' shift, good photo-stability and excellent biocompatibility. However, most AIE dots contain amorphous features. In these cases, although the intramolecular motions can be restricted to some degree, amorphous AIE nanoparticles still suffer from loose molecular packing, leading to the limited brightness. To solve this problem and further restrict intramolecular motion, nano-crystallization has been recently reported to produce highly emissive AIE nanocrystals (NCs), which display great potential for biological applications. Although there have been some reviews on AIE dots in recent years, research on AIE NCs has not been reviewed yet. Based on these considerations, the recent progress on AIE NCs, including their working mechanism, materials, preparation, characterization and also applications, have been summarized in this work, thus, providing a full picture and deep understanding of AIE NCs. This review also aims to offer guidelines to develop high-performance AIE NCs for material science and biological applications.