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The authors describe an electrochemical DNA biosensor based on a glassy carbon electrode modified with gold nanoparticles (AuNPs) and reduced graphene oxide that was functionalized with hemin (hemin-rGO). Capture DNA (a 21-mer) is immobilized on the AuNPs via gold-thiol chemistry. The detection scheme relies on the measurement of the differential pulse voltammetric current change of the oxidation-reduction reaction of hemin before and after DNA hybridization has occurred. The decrease in the voltammetric currents of iron (III) (best measured at −0.3 V vs. Ag/AgCl) is linearly related to the concentration of complementary DNA. The calibration plot covers the 1.0 aM to 0.1 pM concentration range, and the detection limit is as low as 0.14 aM (at a signal-to-noise ratio of 3). The biosensor was successfully applied to the direct determination of complementary DNA in self-prepared samples by using the standard addition method.

This work describes a new approach for rapid detection of sulfide using a glassy carbon electrode (GCE) modified with hemin functionalized reduced graphene oxide (hemin-rGO). The modified GCE was applied to the selective amperometric detection of sulfide at a working potential of 0.05 V (vs. Ag/AgCl) at pH 7.5, which gave a linear range of 0.002–0.212 mM, a sensitivity of 246.5 µA mM−1 cm−2, and a detection limit of 1.3 µM. The proposed method was applied in determination of sulfide-spiked water, and the method was verified with recovery percentage of standard samples with an acceptable satisfaction.