Functionalization of luminescent lanthanide complexes for biomedical applications

Luminescent lanthanide complexes (LLC) have been gaining popularity for use in the field of biomedicine, owing to their unique optical properties and tunable coordination behaviors. In recent years, functionalization of LLC with bioactive molecules, other bioimaging entities, or nanoarchitectures has attracted tremendous attentions, which has significantly increased the likelihood of applications of LLC at a broader range of biomedical scopes. In this review, we summarize the major strategies that have been used to functionalize LLC by introducing multifunctional pendant or chelating antennas into the complexes, and constructing multifunctional coordination polymers through assembly between lanthanide ions and ligands. Representative examples of functional LLC are classified into three categories based on their biomedical applications, including multimodal imaging-guided diagnosis, therapeutics, and theranostics. Their structures, functionalization rationales, and working mechanisms in the applications are discussed in detail. In the end, the future perspectives and challenges of functional LLC for clinical translations are also proposed.