Insights into Molecular Lanthanide Complexes: Construction, Properties and Bioimaging and Biosensing Applications

The lanthanide complex, characterized by narrow emission bands, large Stokes shifts, long luminescence lifetime, robust resistance to photobleaching, and magnetic properties, affords significant promise for molecular imaging and biosensing applications. While most lanthanide complexes emitting visible light are extensively studied for cellular-level detection and bioimaging, near-infrared-emitted (700-1700 nm) lanthanide compounds exhibit more favorable properties for bioimaging and biosensing, ascribed from deeper penetration and reduced bleaching effects. Besides, the magnetic lanthanide complex with higher magnetic resonance signals can enhance image resolution and sensitivity, offering more precise bioimaging analysis. However, the widespread use of high-efficiency luminescence lanthanide complexes is currently impeded by the lack of design approaches for improving magnetic properties and sensitization chromophores with extended excitation and emission wavelengths. In this review, some fundamental theories and design strategies of lanthanide complexes are summarized for luminescence imaging, lifetime-engineered imaging, magnetic resonance imaging, and dual-modal imaging, and now highlight a selection of bioimaging and biosensing applications. The review addresses the existing gap in the literature by proposing some feasible approaches for improving the fluorescent and magnetic properties. Concurrently, future challenges and opportunities in the field of lanthanide complex probes are discussed. This review briefly introduces the luminescent and magnetic properties of lanthanide complexes, highlights the approaches of lanthanide complexes for enhancing NIR-II luminescent emission, maximizing luminescence lifetime, and improving MR signals, summarizes some representative biological applications of lanthanide complex in bioimaging and biosensing, and proposes the potential directions for lanthanide complexes as next-generation imaging and therapeutic agents. image