Defect-engineered CdSe quantum dots for ultrasensitive heavy metal ion sensing: Surface defects and interfacial charge transfer mechanisms

Defect-engineered CdSe quantum dots (QDs) represent a rapidly evolving class of nanoscale sensing platforms in which intrinsic and surface defect states govern both electronic structure and interfacial reactivity. This review examines the role of defect-mediated energy level reconstruction in modulating excitonic recombination pathways and photoluminescence responses during heavy metal ion interactions. Emphasis is placed on the transformation of surface imperfections into functional charge trapping centers that dictate adsorption selectivity and signal transduction efficiency. Recent advances reveal that sensing performance is not solely determined by quantum confinement effects, but arises from a coupled interplay between surface chemistry, defect-induced mid-gap states, and interfacial charge transfer processes. These coupled mechanisms regulate radiative and non-radiative decay channels, enabling amplified optical responses upon heavy metal ion binding. Furthermore, ion-induced perturbations in ligand coordination and surface electronic density significantly influence carrier dynamics, providing a mechanistic basis for ultrasensitive detection. Overall, this review consolidates emerging insights into defect–interface coupling in CdSe QDs, establishing a unified mechanistic framework for rational design of next-generation nanophotonic sensors for environmental monitoring applications.