Bioengineered MXene–Polymer–Metal Composites: From Synthesis and Structure to Multimodal Diagnostic and Therapeutic Applications

MXenes are an emerging class of 2D nanomaterials known for their exceptional electronic conductivity, hydrophilicity, surface reactivity, and mechanical robustness. Despite the growing body of research, a unified understanding of their structure-property relationships, functionalization strategies, and translational potential remain incomplete. This review presents a comprehensive overview of recent advances in the synthesis and surface engineering of MXene nanostructures, emphasizing biocompatible and biologically relevant fabrication methods. We explore MXene composites integrated with polymers and metal/metal oxide heterostructures, highlighting their functional versatility and synergetic effects. Special attention is given to stimuli-responsive MXene platforms, including MXenzymes, and their application as multifunctional theranostic agents in bioimaging, biosensing, drug delivery, and tumor therapy. We also examine how atomic configuration, surface terminations, and responsive properties impact biomedical performance. Finally, the review outlines key challenges limiting clinical translation and suggests future directions to overcome these barriers. By consolidating recent findings and identifying knowledge gaps, this review aims to provide a roadmap for the rational design of next-generation MXene-based nanoconjugates tailored for multimodal diagnostics and targeted therapeutics.