Electronic-photonic interplay in nitrogen-doped MXene quantum dots: mechanistic insights into dual-mode and multiplexed sensing.

Nitrogen-doped MXene quantum dots (N-MQDs) are emerging nanomaterials with great potential for dual-mode and multiplexed sensing owing to their tunable photoluminescence, high electrical conductivity, and chemically active surfaces. In this work, we aim to clarify the fundamental mechanisms governing the coexistence and coupling of optical and electronic responses in N-MQDs and to provide design principles for their application in sensing platforms. Specifically, the study focuses on how nitrogen doping and surface coordination modify the electronic structure, density of states, and Fermi level alignment, thereby influencing radiative emission, charge transport, and analyte interaction. The sensing behavior is interpreted through the balance between localized dopant-induced states and the delocalized MXene conduction network, which enables dual signal generation with reduced mutual interference. The phenomena are discussed in terms of photoluminescence response, carrier dynamics, surface-state effects, and charge-transfer processes, while the roles of dopant configuration and surface terminations in controlling signal orthogonality and crosstalk suppression are highlighted. Overall, this work presents a mechanistic framework for the rational design of N-MQD-based dual-mode sensing systems for environmental, chemical, and biomedical applications.