Electrochemical immunoassay for the biomarker 8-hydroxy-2′-deoxyguanosine using a glassy carbon electrode modified with chitosan and poly(indole-5-carboxylic acid)

We describe an electrochemical immunosensor for the determination of 8-hydroxy-2′-deoxyguanine (8-OHdG), which is a marker substance indicating oxidative DNA damage. Poly(indole-5-carboxylic acid) (PICA) and chitosan were immobilized on a glassy carbon electrode (PICA/CHI/GCE) via electrochemical polymerization and self-assembly. The use of PICA/CHI results in an increased effective surface area for immunoresponse and promotes electron transfer kinetics. The electrode surface was further modified by dropping protein A (PA) onto it in order to bind antibody Fc fragments. Next, anti-8-OHdG was covalently immobilized on the electrode. Finally, bovine serum albumin was applied to block any remaining active sites in order to prevent nonspecific adsorption. The modified electrode was characterized by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry, respectively. Under optimized conditions, the electron transfer between 8-OHdG and the PICA/CHI/PA was quasi-reversible with a formal potential of 0.16 V vs Ag/AgCl. The peak currents of differential pulse voltammetry are linearly related to the 8-OH-dG concentration in the 0.1 to 10,000 ng · mL range, with a detection limit of 30 pg · mL (at an S/N ratio of 3). The immunosensor displays excellent reproducibility and stability and represents a sensitive method for the specific determination of 8-OHdG in human urine. [Figure not available: see fulltext.]