Controllable synthesis of nitrogen-doped graphene and its effect on the simultaneous electrochemical determination of ascorbic acid, dopamine, and uric acid

A simple, low-cost method for fabricating nitrogen-doped graphene (NG) is demonstrated by combining the ultrafast thermal exfoliation and covalent transformation from the melamine (MA)–graphene oxide (GO) mixture. NGs prepared at 300, 600, and 900 °C were systematically characterized by X-ray photoelectron spectroscopy (XPS), in which pyridinic-N, pyrrolic-N and graphitic-N are the main nitrogen-doped structures in various ratios. These NGs possess large specific surface area and porous microstructures, confirmed by the N2 adsorption–desorption isotherms. The NG-modified screen-printed carbon electrodes (SPCEs) were fabricated to detect ascorbic acid (AA), dopamine (DA) and uric acid (UA) simultaneously by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Due to the large specific surface area, mesoporous structures and nitrogen-doped sites, these NGs show highly electrochemical sensitivity for AA, DA and UA. Notably, the pyrrolic-N structure makes the negative shift in the oxidation peak potential of these biomolecules, showing the better catalytic activity than pyridinic-N and graphitic-N structures. The large surface area of NGs provides more nitrogen-doped sites to oxidize bio-compounds and enhances the corresponding currents. The good sensitivity of NG-modified SPCEs makes them become effective sensors for determining AA, DA and UA simultaneously. The discrimination to peak potential and current among these NGs can be observed.