Colorimetric aptamer-based sensors offer a simple means of on-site or point-of-care analyte detection; however, these sensors are largely incapable of achieving naked-eye detection because of the poor performance of the target-recognition and signal-reporting elements employed. The project described in this article addresses this problem. CBSAzymes consist of two fragments that remain separate in the absence of target, but effectively assemble in the presence of the target to form a complex that catalyzes the oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline)-6-sulfonic acid, developing a dark green color within 5 min. This assay enables rapid, sensitive, and visual detection of small molecules, which has not been achieved with any previously reported split-aptamer-DNAzyme conjugates. In an initial demonstration, researchers generated a cocaine-binding CBSAzyme that enables naked-eye detection of cocaine at concentrations as low as 10 micrometer Notably, CBSAzyme engineering is straightforward and generalizable. This is demonstrated by developing a methylenedioxypyrovalerone (MDPV)-binding CBSAzyme for visual detection of MDPV and 10 other synthetic cathinones at low micromolar concentrations, even in biological samples. Given that CBSAzyme-based assays are simple, label-free, rapid, robust, and instrument-free, the researchers believe that such assays should be readily applicable for on-site visual detection of various important small molecules, such as illicit drugs, medical biomarkers, and toxins in various sample matrices. (publisher abstract modified)
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