Graphene-based Electrochemical Sensors

Graphene, emerging as a true2-dimensional material, has unique physicochemicalproperties (high specific surface area, excellent conductivity, high mechanical strength, andease of functionalization and mass production). In this paper, graphene oxide (GO), grapheneoxide/terephthalic acid copper metal organic frameworks (Cu(tpa)-GO),graphene/β-cyclodextrin (GR-CD) composites were prepared and characterized by scanningelectron microscopy (SEM), transmission electron microscopy (TEM), fourier-transforminfrared (FT-IR) spectroscopy, UV-vis spectroscopy and X-ray diffraction (XRD) methods. Aseries of highly sensitive and selective electrochemical sensor were constructed bymodifiction these materials on the surface of glassy carbon electrode (GCE) and used forelectrochemical determination of luteolin, dopamine (DA), acetaminophen (ACOP) and Pb2+.The main contents are as follows:(1) A graphene oxide (GO) nanoparticle modified glassy carbon electrode (GO/GCE)was fabricated by covalent coupling method; and a graphene-modified glassy carbonelectrode (EGR/GCE) was also obtained by direct electrochemical reduction of GO/GCE.Using [Fe(CN)/4-6]3-as a probe, GO/GCE and EGR/GCE were characterized by cyclicvoltammetry (CV) and electrochemical impedance spectra (EIS). The results show that theEGR/GCE not only has great surface area but also has excellent conductivity. The modifiedelectrode (EGR/GCE) was further utilized as a sensor model to detect luteolin, and a pair ofwell-defined redox peaks appeared.Through pH impact and scan rate experiment, theelectrochemical reaction mechanism was investigated on the modified electrode. Under thebest conditions, the reduction peak currents of luteolin present a good linear relationship withthe concentrations of luteolin in the range from1.0×10-8mol/L to1.0×10-6mol/L and2.0×10-6mol/L to1.0×10-5mol/L, with a detection limit of4.6×10-9mol/L based on S/N=3.(2) A novel nanocomposite consisted of graphene oxide (GO) and copper terephthalate(Cu(tpa)) metal-organic frameworks (MOF) was synthesized through a simple ultrasonication,which shows excellent water dispersibility and stability. The binding mechanism of the twospecies was investigated by SEM, FT-IR, XRD and UV-vis. Then the nanocomposite was caston a glassy carbon electrode and conducted an electro-reduction treatment to transfer the GO component in the composite film to the reduced form (EGR), from which the electricalconductivity and the accessible surface area of the modified electrode were greatly improved.The modified electrode was further utilized as a sensor model for simultaneous detection ofacetaminophen (ACOP) and dopamine (DA). Under the optimum conditions, the oxidationpeak currents of ACOP and DA were linearly correlated to their concentrations in the rangesof1×10-6mol/L to1×10-4mol/L and1×10-6mol/L to5×10-5mol/L, respectively. Based onS/N=3, the detection limits for ACOP and DA were estimated to be3.6×10-7mol/L and2.1×10-7mol/L, respectively.(3) GR-CD composite was obtained by one-pot reduction methods, and characterized bySEM, TEM and FT-IR methods. Then the nanocomposite was cast on a glassy carbonelectrode to get a modified electrode (GR-CD/GCE). The differential pulse anodic strippingvoltammetric was used for determination of trace amounts of Pb2+ions. GR-CD/GCE showexcellent selectivity and high sensitivity for electrochemical detection of Pb2+. Under theoptimum conditions, the oxidation peak currents of Pb2+were linearly correlated to theconcentration of Pb2+in the range of1×10-9mol/L to1×10-7mol/L, and the limit of detectionis5.01×10-10mol/L based on S/N=3. The modified electrode is simple and has goodsensitivity and selectivity.