Abstract
Two-dimensional transition-metal carbides and nitrides (MXenes) have evolved from conductive layered solids into chemically programmable platforms for theranostics, wherein function is dictated by surface coordination rather than morphology alone. Their metal-rich basal planes and termination groups (–O, –OH, –F) establish dynamic coordination environments that govern ligand binding, redox activity, and interfacial charge transfer. This review positions coordination chemistry as the central framework linking MXene synthesis, defect structure, and surface functionalisation to biological performance. We examine how etching chemistry, oxidation state, and vacancy distributions define coordination sites that control drug adsorption pathways, binding strength, and stimulus-responsive release. Particular attention is given to interfacial complexes formed with polymers, metal ions, and biomolecules, which regulate colloidal stability, protein corona formation, pharmacokinetics, and immune interactions. The mechanistic origins of imaging contrast are analysed across modalities, including magnetic relaxation, X-ray attenuation, and photoacoustic response, with explicit correlations to metal identity, electronic structure, and ligand field effects. Recent advances in fluorine-free synthesis, Lewis acidic etching, and electrochemical routes are assessed in terms of their ability to produce stable, defect-controlled coordination landscapes. Strategies for oxidation control and surface passivation are evaluated against degradation kinetics and off-target reactivity in physiological environments. Emerging data-driven approaches for predicting coordination motifs and structure–property relationships are also discussed. By mapping coordination environments to measurable therapeutic and diagnostic outputs, this review defines design rules for MXene-based systems with controlled reactivity, predictable biological interactions, and improved translational viability in precision nanomedicine.