Recent Advances in Lanthanide Complexes in Biological Systems: Coordination Principles and Interactions with Biomolecules

: Lanthanide ions and their complexes have emerged as versatile tools in biology and medicine owing to their unique photophysical, magnetic, and coordination properties. Their applications span bioimaging, sensing, therapy and diagnostics, underpinned by their strong preference for oxygen-donor ligands, kinetic stability, and tunable luminescence. This review integrates current developments in lanthanide coordination chemistry, focusing on the mechanistic basis of their interactions with biomolecules such as nucleic acids, proteins, and peptides. Moreover, this work highlights the design principles governing complex stability and biological compatibility, summarizing key biomedical uses of lanthanides ranging from imaging and drug delivery to anticancer and antioxidant effects, and discusses their toxicity and biodistribution, and their potential for clinical translation. In particular, this review offers a mechanistically oriented synthesis of recent advances, emphasizing the interplay between coordination behavior and biological function, and identifying emerging trends that define the current landscape of lanthanide-based bioinorganic research. By correlating molecular coordination features with biological performance, the review identifies the main trends shaping lanthanide-based bioinorganic research, also including a brief discussion of complexes formed between lanthanides and naturally occurring molecules, such as amino acids.