The versatile world of MXene nanohybrids: designed synthesis, functional diversity, and promising theranostics.

MXenes, a rapidly expanding class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides (Mₙ₊₁XₙTₓ), have emerged as transformative platforms for advanced analytical and biosensing technologies because of their metallic conductivity, tunable surface terminations, and high interfacial reactivity. This review establishes a mechanistic framework linking MXene surface chemistry and hybridization strategies to analytical performance across emerging biomedical applications. Particular emphasis is placed on MXene-enabled electrochemiluminescence (ECL) and surface-enhanced Raman spectroscopy (SERS) systems, where integration with plasmonic nanostructures, catalytic nanozymes, and semiconductor interfaces enables ultrasensitive detection of cancer biomarkers, nucleic acids, and exosomes, with detection limits reaching sub picomolar to femtomolar levels. In parallel, MXene-based platforms are advancing toward integrated theranostics systems that combine real-time sensing with photothermal, photodynamic, and catalytic therapeutic functionalities, enabling closed-loop diagnostic-treatment strategies. Despite these advances, critical barriers to practical deployment remain, including rapid oxidative degradation, restacking-induced loss of active surface area, batch-to-batch variability in surface terminations, and insufficient in vivo validation. These challenges are analyzed from a structural, property and performance perspective. Finally, key translational priorities are identified, including fluorine-free scalable synthesis, long-term stability engineering, standardized biocompatibility evaluation, and integration with AI-assisted analytical platforms. By bridging materials chemistry with analytical functions and translational requirements, this review positions MXenes as a central enabling platform for next-generation biosensing and precision diagnostic technologies.