Carbon quantum dot-based sensors for detecting emerging contaminants: synthesis, functionalization, sensing...

In recent years, carbon quantum dots (CQDs) have emerged as promising nanomaterials for environmental sensing due to their excellent optical properties, tunable surface chemistry, high sensitivity, and low toxicity. CQD-based sensors have attracted increasing attention for detecting various pollutants due to their low cost, sustainability, and potential for practical applications. This review provides a critical overview of recent advances in CQD-based sensing platforms for emerging contaminants (ECs), with particular emphasis on the relationship between CQD structure, surface chemistry, sensing mechanisms, and detection performance. First, different CQD synthesis methods are discussed, highlighting their advantages, limitations, and effects on CQD properties. Then, strategies for improving sensing performance through metal and non-metal doping, co-doping, and hybridization with other materials, including metal-organic frameworks (MOFs), are evaluated. The review further examines the detection of major classes of ECs, considering not only sensitivity and detection limits but also selectivity, stability, and performance in real samples. In addition, the roles of key sensing mechanisms, including the inner filter effect, fluorescence resonance energy transfer, photoinduced electron transfer, and surface interaction-induced fluorescence changes, are analyzed to provide deeper insight into pollutant recognition processes. Current challenges related to surface heterogeneity, reproducibility, interference from complex matrices, large-scale production, and practical implementation are critically discussed. Finally, future opportunities involving multifunctional CQDs, portable sensing devices, artificial intelligence-assisted analysis, smartphone-based platforms, and sustainable synthesis strategies are highlighted. This review provides insights into the rational design of CQD-based sensors and supports their future development for reliable environmental monitoring and public health protection.