0D/2D Graphene Quantum Dot-MXene Heterostructures: Luminescence, Sensing, and Electrochemical Applications.

0D/2D graphene quantum dot (GQD)-MXene heterostructures have recently emerged as a versatile class of luminescent hybrid nanomaterials that combine the quantum confinement-induced photoluminescence of zero-dimensional GQDs with the metallic conductivity, surface functionality, and two-dimensional architecture of MXene nanosheets. The synergistic integration of these components enables tunable emission behavior, efficient interfacial charge transfer, enhanced fluorescence response, and improved physicochemical stability. This review systematically discusses the fundamental photophysical mechanisms governing luminescence modulation, including surface-state emission, defect engineering, energy transfer pathways, and electronic coupling at the GQD-MXene interface. Controlled synthesis strategies and structural tunability are highlighted with emphasis on their influence on optical performance and sensing characteristics. Recent applications in fluorescence sensing, electrochemical biosensing, photothermal-assisted systems, and multifunctional energy devices are critically analyzed. Particular attention is given to dopamine detection, optical signal amplification, and structure-property relationships relevant to analytical performance. Finally, current challenges and future perspectives for developing next-generation luminescent GQD-MXene platforms for sensing, imaging, and integrated optoelectronic systems are outlined.