G-quadruplex DNAzyme-based microcystin-LR (toxin) determination by a novel immunosensor

In this paper, we demonstrate the application of versatile G-quadruplex–hemin DNAzymes in an immunoassay for detecting Microcystin-LR (MC-LR). Taking advantage of the high peroxidase activity of G-quadruplex–hemin complexes and the enhancement effect of gold nanoparticles (AuNPs), the method showed simple, high sensitive and selectivity detection of target toxin residues in water samples. The coated antigen, MC-LR–ovalbumin (OVA) coated on a plate, competed for MC-LR antibody with added target analyte to form antibody–antigen immune complexes. Subsequently, the immune complex reacted with G-quadruplex-labeled secondary antibodies for colorimetric detection of MC-LR. This assay specifically determined MC-LR in the linear range of 0.1–10 ng/ml, with a limit of detection (LOD) of 0.05 ng/mL for MC-LR. The results indicated that the novel immunoassay was an alternative to traditional plate-based immunoassay for MC-LR residue screening due to this method met the standard of World Health Organization (WHO) requirements for MC-LR content in drinking water (1 ng/mL).