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

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 (ABTS 2− ). 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 ABTS 2− to green ABTS − by H 2 O 2 , 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 ABTS 2− 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   +   0.0256 C ( C : μM, R   =   0.998) and a detection limit of 0.10   μM (3 σ /slope). Moreover, the practicability of the assay in the detection of cholesterol in human serum was studied as well.