An electrochemical DNA biosensor from graphene decorated with graphitic nanospheres.

Graphene decorated with graphitic nanosphere functionalized with pyrene butyric acid (PBA) is used for the first time to fabricate a DNA biosensor. The electrode was formed by attaching DNA probe onto PBA, which had been stacked onto a graphene material decorated with graphene nanospheres (GNS). The nanomaterial was drop-coated onto a carbon screen printed electrode (SPE) to afford the GNS-PBA modified electrode (GNS-PBA/SPE). A simple method was used to produce GNS via annealing graphene oxide (GO) solution at high temperature. Field emission scanning electron micrographs confirmed the presence of spherical shape of GNS with a diameter range of 40-80 nm. A stable and uniform PBA-modified GNS (GNS-PBA) was obtained by facile ultrasonication step. Thus, allowing aminated DNA probes of genetically modified (GM) soybean to be attached to the nanomaterials to form the DNA biosensor. The GNS-PBA/SPE exhibited excellent electrical conductivity via cyclic voltammetry (CV) and differential pulse voltammetry (DPV) by using potassium ferricyanide (K3[Fe(CN)6]) as the electroactive probe. By employing anthraquinone monosulfonic acid (AQMS) redox intercalator as the DNA hybridization indicator, the biosensor response was evaluated by DPV electrochemical method. A good linear relationship between AQMS oxidation peak current and target DNA concentrations from 1.0×10-16-1.0×10-8 M with a detection limit (LOD) of less than 1.0×10-16 M was obtained. Selectivity experiment revealed that the voltammetric GM DNA biosensor could discriminate complementary sequences of GM soybean from non-complementary sequences and hence good recoveries were obtained for real GM soybean sample analysis. The main advantage of using graphene nanosphere is an improvement of the DNA biosensor analytical performance.