Ligand-Based Surface Engineering of Lanthanide Nanoparticles for Bioapplications

The rapid development of biomedicine in recent decades has benefited from optical imaging with high temporal and spatial resolution. In particular, lanthanide nanoparticles (LnNPs) are one of the most impressive signal providers for optical imaging due to their unique optical properties, such as abundant emission peaks, long luminescence lifetimes, and ultrastable luminescence intensity. However, to become better optical labels that are more suitable for biological applications, LnNPs must overcome their inherent flaws, including original hydrophobic surface, insufficient luminescence intensity, as well as the low environmental responsiveness. Recently, researchers have achieved extraordinary results in ameliorating these defects through ligand-based surface engineering. In this Review, we discussed several representative methods for the hydrophilic modification of LnNPs. Then, the significant attempts for luminescence amplification of LnNPs were concluded. Subsequently, attentions were paid to the methods that helped to fabricate responsive LnNPs systems, as well as the potential biomedical applications. Finally, we considered the current limitations and prospects of the surface engineering strategies for LnNPs. We hope this timely Review can exhibit the outstanding achievement in manipulating the surface properties of LnNPs and promote a broader development of LnNPs in the field of biomedical applications.