Carbon quantum dots in spectrofluorimetric analysis: A comprehensive review of synthesis, mechanisms and multifunctional applications.

Carbon quantum dots (CQDs), as a representative nanomaterial, have demonstrated promising applications in fluorescence analysis owing to their unique optical properties, low cytotoxicity and exceptional biocompatibility. This review systematically summarizes recent advances in synthesis strategies, detection mechanisms and applications of CQDs for sensing metal ions (e.g., Hg, Fe, Cu), small molecules (e.g., biomolecules, pharmaceuticals, azo dyes) and proteins. Hybridization of CQDs with functional materials has been shown to significantly enhance their photoluminescence properties while optimizing detection sensitivity and selectivity. The article critically examines fundamental detection mechanisms, especially fluorescence quenching and further outlines design strategies for fluorescence probes based on "on-off" switching or ratio signaling. Moreover, current challenges are analyzed, such as the need for synthetic protocol standardization, in-depth exploration of heteroatom-doped CQDs, expansion of detectable analytes and rational design of fluorescence turn-on probes. Future prospects in environmental monitoring, biomedical diagnostics and pharmaceutical analysis are also highlighted. This comprehensive review offers critical insights to guide the rational design and application of advanced CQD-based hybrid systems.