Au nanoparticle decorated reduced graphene oxide and its electroanalytical characterization for label free dopamine detection

A facile and cost-effective in situ colloidal procedure has been optimized for the synthesis of a novel colloidal hybrid nanocomposite based on 1-aminopyrene (AP) functionalized reduced graphene oxide (RGO) sheets, decorated with oleylamine (OLEAM)-coated Au nanoparticles (NPs). The effect of relevant experimental parameters, such as the OLEAM:Au precursor molar ratio and AP-RGO:Au precursor w/w, on the morphological features and spectroscopic characteristics of the nanocomposites has been explored to elucidate their formation mechanism. Au NPs, 9-20 nm in mean size, were grown on the -NH2 groups of the 1-aminopyrene molecules that are anchored at the RGO basal plane via aromatic π-π stacking interactions. The OLEAM ligand coordinating the Au NPs has been found to endow the nanocomposites with dispersibility in organic solvents, thus enabling their solution processability, essential for their fabrication as films onto screen printed carbon electrodes (SPCEs). Cyclic voltammetry and electrochemical impedance spectroscopy were performed to investigate the effect of the AP linker, the OLEAM capping ligand and surface chemistry and morphology of the hybrid nanocomposites on electrical conductivity, heterogeneous charge transfer capability and sensitivity of the nanocomposite modified SPCEs for label-free detection of dopamine (DA), an known biomarker of human neurodegenerative disorders. The AP linker has been found to establish an effective NP-RGO electron coupling, endowing the nanostructured platforms with high electrical conductivity and high electroanalytical activity, which have been found to be dependent on the size of Au NPs. The possibility of easily displacing OLEAM from the Au NP surface by ligand exchange allows modifying the nanoplatform surface chemistry and morphology, which are found to influence the electrochemical reactivity and sensitivity. The hybrid nanoplatforms show superior electroactivity for the determination of DA and viability for the effective detection of H2O2, another relevant biomarker of physiological alterations. The developed platform holds a great promise for innovative point-of-care technological solutions, that, enabling rapid and sensitive monitoring of biomarkers of human diseases, may represent valuable tools in modern medicine.