Equipment-free detection of saccharin based on the confined space enhanced AIE effect of a novel ratiometric fluorescent Zn-MOF: Probe design, sensing performance, and practical applications

Saccharin (SAC) is a widely used low-calorie sweetener, which is also classified as a Group 2B carcinogen. However, fluorescent probes for SAC sensing are rarely reported. Herein, we reveal the first equipment-free method for the highly selective detection of saccharin based on a novel ratiometric fluorescent probe, MOF-1@RhB. MOF-1@RhB was obtained by physically encapsulating RhB in MOF-1 as an internal self-calibration through the one-pot solvothermal synthesis. A naked-eye distinguishable color change from orange to green could be observed for MOF-1@RhB in the presence of SAC. MOF-1@RhB exhibits a fast response speed (30 seconds), a wide linear range (0–160 μM), and a good limit of detection (LOD = 109 nM) in the detection of SAC. Taking advantage of MOF-1@RhB, paper-based sensors were prepared and used for on-site detection. A portable device integrating a smartphone and paper sensors for point-of-care testing has been developed. In real-sample detection, the photograph of the paper sensors could be taken using a smartphone and then analyzed with a dedicated smartphone app to derive the SAC concentration. Moreover, the proposed method has been successfully applied to monitor SAC in food samples and its accuracy has been verified with the HPLC method.