Carbon quantum dot fluorescent sensors for tetracycline detection: Quenching mechanisms, signal strategies, and analytical reliability in complex matrices

Turn-off fluorescent carbon quantum dot (CQD)-based sensors have emerged as highly efficient analytical platforms for tetracycline detection in complex food and environmental matrices. This review examines recent advances in CQD design and their fluorescence quenching behaviors, with a particular focus on mechanistic pathways governing signal attenuation. The dominant quenching processes, including the inner filter effect, static and dynamic quenching, charge transfer interactions, and aggregation-induced effects, are systematically analyzed in relation to their analytical implications. Special attention is given to how heteroatom doping, surface functionalization and structural heterogeneity influence emission properties and sensing performance. The review further evaluates the analytical performance of CQD-based turn-off systems in real sample environments such as milk, serum, honey, and environmental water, highlighting both their strengths in sensitivity and rapid response, as well as their limitations in terms of matrix interference, reproducibility, and calibration reliability. Despite significant progress, inconsistencies in mechanistic interpretation and lack of standardization remain key barriers to quantitative robustness. Overall, this work provides an integrated perspective on the relationship between photophysical quenching mechanisms and analytical outcomes, emphasizing the need for more rigorously designed CQD systems to achieve reliable tetracycline monitoring in complex matrices.

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