A facile and highly sensitive impedimetric DNA biosensor with ultralow background response based on in situ reduced graphene oxide

Abstract

A novel electrochemical impedimetric DNA sensor was constructed based on in situ chemical reduction of graphene oxide (GO) that had been attached at a DNA modified electrode. First, the mercapto-modified probe DNA was anchored on a gold electrode surface through the Au–S bond. Then the GO was adsorbed on the probe DNA through the unique π–π stacking, which was followed by incubation in sodium borohydride (NaBH₄) solution to in situ reduce the GO to the reduced form (rGO). Thus, a highly conductive biointerface with ultralow charge-transfer resistance was obtained. When the biosensor was hybridized with the target DNA to form the rigid double-stranded DNA, the rGO was released from the electrode surface and the charge-transfer resistance increased again. Compared with the analogous sensing interface without pre-accumulation of GO, the signal variation ratio was found to increase by 8-fold upon hybridization as determined by electrochemical impedance spectra, suggesting a higher signal-to-noise of the constructed biosensor. Quantitative analysis experiments showed that the impedance change values exhibited a good linear relationship with the logarithmic values of target DNA concentration over a wide range from 1.0 × 10⁻¹⁵ M to 1.0 × 10⁻⁹ M. The detection limit was estimated to be as low as 2.9 × 10⁻¹⁶ M. The biosensor also presented excellent selectivity, good regeneration ability and outstanding stability.