A colorimetric aptasensor for the highly sensitive detection of 8-hydroxy-2′-deoxyguanosine based on G-quadruplex–hemin DNAzyme

A highly sensitive, low-cost colorimetric aptasensor was developed for the determination of 8-hydroxy-2′-deoxyguanosine (8-OHdG) in human urine. The method is based on a conformational switching of the 8-OHdG aptamer to form a G-quadruplex structure in the presence of 8-OHdG. The resulting G-quadruplex assembles into a peroxidase-like DNAzyme with hemin , which effectively catalyzes the oxidation of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS 2− ) by H 2 O 2 to ABTS + , resulting in an increase in the absorption signal at 416   nm along with a color change of the solution. The response signals linearly correlated with the concentration of 8-OHdG, ranging from 466   pM to 247   nM with a detection limit of 141   pM. The relative standard deviation and the recovery were 1.97–3.47% ( n   =   11) and 98.8–100.2%, respectively. The proposed method avoids the label and derivatization steps in common methods and allows direct analysis of the samples by the naked eye without costly instruments, which is reliable, inexpensive, and sensitive.