An electrochemical quinine detection approach based on small molecule promoted split aptamer click ligation reaction

Quinine is a natural antimalarial drug that also serves as a food additive; however, excessive consumption can result in harmful side effects. Here, we propose a simple and cost-effective electrochemical strategy for quinine detection based on the small molecule-templated split aptamer click ligation (SMT-SpA-CLR), where the integrity of the aptamer is restored through the template-promoted proximity effect. We first investigate the effects of two splitting sites on the affinity of quinine aptamer and find that the loop of the stem with more Watson-Crick base pairs is more suitable for splitting, which can maintain the affinity to a great extent. The affinity of the Split 1 design (K_d = 48 μM) is slightly reduced compared to the affinity of the parent aptamer. The stable quinine recognition and its sensitive detection are achieved by integrating the SMT-SpA-CLR with an electrochemical signal output. The linear response range for quinine detection is from 0.05 μM to 10 μM with a low detection limit of 25 nM (at S/N = 3). This strategy provides a novel ideal for the design of small molecule-templated split aptamer reaction and can potentially be expanded for detecting other small molecules and proteins.