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(center 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 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 mu M, with a linear regression equation of A= 0.362 + 0.0256C (C: mu M, R = 0.998) and a detection limit of 0.101 mu M (3 sigma/slope). Moreover, the practicability of the assay in the detection of cholesterol in human serum was studied as well. (C) 2012 Elsevier B.V. All rights reserved.