An Aptamer-based Self-Catalytic Colorimetric Assay for Carcinoembryonic Antigen

We report a visualization assay for carcinoembryonic antigen (CEA). The assay was prepared based on target-specific recognition, aptamer-based DNAzyme self-catalysis, and colorimetric reaction. Aptamer of CEA was gathered at the surface of magnetic beads for sandwiched co-conjugate when CEA was added. The second aptamer (Apt2) on the beads was folded into G-quadruplex by KCl to make G-quadruplex-hemin DNAzyme with hemin. Apt2-based DNAzyme catalyzed H 2 O 2 -mediated oxidation of 3,3′,5,5′-tetramethylbenzidine, resulting in color changes and significant increase in absorption intensity at 450 nm (Δ A 450nm ). Yellow products can be observed with naked eyes when over 1.0 ng/mL CEA was added and there was a linear correlation between Δ A 450 nm and CEA concentrations in the range of 0.1–8.0 ng/mL with the detection limit of 0.06 ng/mL. The proposed method was then used to determine CEA in human serum from healthy people and tumor patients, revealing a correlation with data from the electrochemiluminescent immunoassay. Owing to its simplicity, selectivity, and low-cost, this method is a promising candidate for detecting CEA and clinical diagnosis of cancer.