Colorimetric detection of cholesterol with G-quadruplex-based DNAzymes and ABTS2− Original Research Article

A novel colorimetric method for detection of cholesterol was developed with hemin-G-quadruplex DNAzyme by transducing oxidation of cholesterol into the color change of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS2−). Oligonucleotide 5′-GTGGGTAGGGCGGGTTGG-3′ (Oligo-1) formed G-quadruplex structure in the presence of K+, it acted as a horseradish peroxidase (HRP) mimicking DNAzyme when binding hemin and catalyzed the oxidation of colorless ABTS2− to green ABTSradical dot− by H2O2, which was produced by the reaction of cholesterol and oxygen that catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the color change of ABTS2− by combining these two reactions. Under the optimum conditions, the absorbance was proportional to the concentration of cholesterol over the range of 1.0–30 μM, with a linear regression equation of A = 0.362 + 0.0256C (C: μM, R = 0.998) and a detection limit of 0.10 μM (3σ/slope). Moreover, the practicability of the assay in the detection of cholesterol in human serum was studied as well.