A label-free ultrasensitive assay of 8-hydroxy-2'-deoxyguanosine in human serum and urine samples via polyaniline deposition and tetrahedral DNA nanostructure.

Oxidative damage is an important factor in causing various human disease and injury. As an oxidative DNA damage product, 8-hydroxy-2'-deoxyguanosine (8-OHdG) is a key marker, which is widely used to study oxidative damage mechanism in diseases. Most reported electrochemical methods were based on oxidation current of 8-OHdG. In this work, a simple electrochemical biosensor for ultrasensitive detection of 8-OHdG was proposed based on it triggered polyaniline (PANI) deposition on tetrahedral DNA nanostructure (TDN). TDN was immobilized onto a gold electrode surface based on self-assembly between three thiolated nucleotide sequences. 8-OHdG-aptamer on the top of TDN formed a hemin/G-quadruplex structure in the presence of 8-OHdG and hemin, which have high catalytic activity to trigger PANI deposition. Numerous negative charges on the duplex DNAs contained in hemin/G-quadruplex and TDN supplied exquisite environment for PANI deposition, which improved the detection sensitivity greatly by increasing the DPV current to10-fold (∼3 μA) compared to our previously reported method without TDN. The response signals correlated linearly with the concentration of 8-OHdG ranging from 10 pM to 2 nM, with a detection limit of 1 pM (S/N = 3). The sensitivity was improved to almost 300-fold when compared with most of previously reported electrochemical methods. The method was also simple and reliable, avoiding complex, expensive label procedures and nanomaterial synthesized procedures. The method had been successfully applied to quantify 8-OHdG in urine and human serum samples with satisfactory results.