Revisiting Carbon Quantum Dots for Malachite Green: Mechanistic Insights, Functional Integration, and Translational Barriers.

Carbon quantum dots (CQDs) have emerged as promising nanomaterials for addressing the environmental and biological challenges associated with malachite green (MG), a persistent and toxic dye. This review revisits the role of CQDs by integrating advances in rational design, photophysical interaction mechanisms, and multifunctional applications. Emphasis is placed on how precursor engineering, heteroatom doping, and surface functionalization govern CQD performance, while highlighting persistent limitations in reproducibility and structural control. Mechanistic insights into CQD-dye interactions-including Förster resonance energy transfer, photoinduced electron transfer, and inner filter effects-are examined to reveal common misinterpretations and methodological gaps. Reported applications in sensing, bioimaging, and toxicity assessment are evaluated with a critical lens, demonstrating that while CQDs offer notable sensitivity and imaging capability, challenges in selectivity, quantitative reliability, and biological specificity remain. Furthermore, the lack of integration between sensing and imaging functionalities underscores a key limitation in current research paradigms. Translational barriers, including scalability, standardization, long-term safety, and regulatory uncertainty, are identified as major obstacles to real-world deployment. This review provides a cohesive perspective aimed at bridging fundamental understanding with application-driven innovation in CQD-based platforms for MG monitoring.