Aptamer-Structure Switch Coupled with Horseradish Peroxidase Labeling on a Microplate for the Sensitive Detection of Small Molecules.

Detection of small molecules with good sensitivity, high throughput, simplicity, and generality using aptamers is desired but still remains challenging. We described an aptamer-structure-switch assay coupled with horseradish peroxidase (HRP) labeling on microplates for sensitive absorbance and chemiluminescence detection of small molecules. This assay relies on competition for affinity binding to a limited HRP-labeled aptamer between small-molecule targets and immobilized short DNA strands complementary to the aptamer (cDNA) on a microplate. In the absence of targets, the HRP-labeled aptamer hybridizes with the cDNA on the microplate, and HRP catalyzes substrate into product, generating absorbance or chemiluminescence signals. The binding of small-molecule targets to aptamers causes displacement of HRP-labeled aptamers from the cDNA and signal decrease. In chemiluminescence-analysis mode, the assay achieved detection of aflatoxin B1 (AFB1), ochratoxin A (OTA), and adenosine triphosphate (ATP) with detection limits of 10 pM, 20 pM, and 20 nM, respectively. This assay does not require enzyme-labeled small molecules or the conjugation of small molecules on solid phase. HRP, as an enzyme label, here allows for easily obtainable and highly active signal amplification. This microplate assay is rapid and promising for high-throughput analysis. It shows potential for wide applications in the detection of small molecules.