Electrochemical Detection Platform Based on RGO Functionalized with Diazonium Salt for DNA Hybridization

In this paper, we propose an improved electrochemical platform based on graphene for the detection of DNA hybridization. Commercial screen-printed carbon electrodes (SPCEs) were used for this purpose due to their ease of functionalization and miniaturization opportunities. SPCEs were modified with reduced graphene oxide (RGO), offering a suitable surface for further functionalization. Therefore, aryl-carboxyl groups were integrated onto RGO-modified electrodes by electrochemical reduction of the corresponding diazonium salt to provide enough reaction sites for the covalent immobilization of amino-modified DNA probes. Our final goal was to determine the optimum conditions needed to fabricate a simple, label-free RGO-based electrochemical platform to detect the hybridization between two complementary single-stranded DNA molecules. Each modification step in the fabrication process was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3-/4- as a redox reporter. Although, the diazonium electrografted layer displayed the expected blocking effect of the charge transfer, the next steps in the modification procedure resulted in enhanced electron transfer properties of the electrode interface. We suggest that the improvement in the charge transfer after the DNA hybridization process could be exploited as a prospective sensing feature. The morphological and structural characterization of the modified electrodes performed by scanning electron microscopy (SEM) and Raman spectroscopy, respectively, were used to validate different modification steps in the platform fabrication process.

Surface-passivated, soluble and non-toxic graphene nano-sheets for the selective sensing of toxic Cr(vi) and Hg(ii) metal ions and as a blue fluorescent ink

Non-toxic amine-functionalized soluble graphene nano-sheets (f-GNS) were synthesized by using an old and well-known simple organic procedure. The f-GNS exhibited enhanced optical properties, such as strong blue fluorescence emission with a high value of quantum yield (∼13%). The O,O'-bis-(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol 800 as block polymeric amine (BPA)-passivized surface of f-GNS exhibited high aqueous solubility and excitation-dependent fluorescence emission behavior with a strong photo-stability performance. These f-GNS were tested for the significant selective sensing of toxic metal ions Cr(vi) and Hg(ii) from various tested toxic metal ions. The sensing experiment was supported by cyclic voltammetry analysis. The dual metal ion sensing method based on fluorescence showed the limit of detection (LOD) of ∼56 nM for Cr(vi) and ∼45 nM for Hg(ii) through a fluorescence quenching process. f-GNS were found to be non-toxic when tested over Escherichia coli (E.coli) cells. Additionally, the strong blue emission properties of f-GNS enabled their use as a suitable blue fluorescent ink under UV light illumination.