Highly sensitive and visual dual-mode quinine sensor based on small molecule-templated split aptamer click ligation reaction

Quinine, a cinchona alkaloid, is utilized as an antimalarial agent or a preservative in aquatic products. Owing to its resistance to biodegradation, quinine readily persists in human body fluids and environmental water systems, posing risks of harmful side effects to human health. Here, we developed a highly sensitive and specific detection strategy for quinine based on a small molecule-templated split aptazyme click ligation reaction (SMT-SpAzyme-CLR). This strategy constructs a highly sensitive fluorescent biosensor by integrating a quinine-specific split aptamer with a Mg 2 + -dependent DNAzyme catalytic core, which undergoes quinine-induced click ligation and activates enzymatic cleavage activity. The recycling of the ligated SpAzyme facilitates a one-to-many signal amplification cascade, substantially enhancing the detection sensitivity. The proposed sensor exhibits a wide linear response range from 0.02 to 50 μM and achieves an impressively low detection limit of 5 nM, outperforming most existing aptasensors. It was successfully applied to the determination of quinine in tonic water samples, with recoveries ranging from 96.9 % to 104.9 %. Furthermore, a lateral flow immunoassay strip was implemented for visual semi-quantitative detection, demonstrating high specificity and strong anti-interference capability even in complex matrices. This work provides a sensing platform that combines the strengths of highly sensitive laboratory quantification and rapid on-site screening for quinine.