Ratiometric fluorescence detection of captopril using folic acid-assisted β-cyclodextrin‑copper nanoclusters with smartphone-based visualization

The development of sensitive and selective detection methods for captopril (CAP), a widely used antihypertensive drug with potential environmental and health risks, remains an important challenge. In this work, we present a novel ratiometric fluorescence sensor based on folic acid (FA)-assisted β-cyclodextrin-coated copper nanoclusters (FA-Cu NCs@β-CD) for rapid CAP detection. The fluorescence of the Cu NCs capped with 2-mercaptobenzimidazole-5-sulfonic acid sodium salt (MBZS) was weak, but its intensity increased significantly upon encapsulation by β-CD, which is consistent with the mechanism of aggregation-induced emission (AIE). The addition of blue-emitting FA yielded a dual-emission fluorescent probe. CAP detection was achieved through its specific affinity for copper, which disrupted the structure of the Cu NCs, leading to quenching of the orange emission (605 nm) while maintaining the stability of the blue fluorescence (460 nm) of FA. The method exhibited a wide linear detection range (0.25–40 μg/mL) and a low limit of detection (61 ng/mL). The system demonstrated excellent selectivity against interfering substances and was successfully applied to detect CAP in river water and human urine samples, with good recoveries (97.5–107.0 %). Notably, the distinct color change from pink to blue after adding CAP allowed for smartphone-based visual quantification, demonstrating significant potential for onsite monitoring. This work provides a simple, cost-effective, and reliable approach for CAP detection that combines the advantages of ratiometric fluorescence with portable visualization.