Preparation,Characterization And Electrochemical Sensing Properties Of Graphene Based Nanocomposites

Graphene?Gr?based nanocomposites have some synergistic effects compared with the single component and attract more and more attention with the scientific researchers.In this paper,a series of Gr based nanocomposites were prepared via the solvothermal method,the electroless plating method and the electrostatic attraction method.Several electrochemical sensors were fabricated by modifying them onto the screen-printed carbon electrode?SPCE?and gold electrode?GE?.The X-ray powder diffractometer?XRD?,Fourier transform infrared spectrum?FTIR?,Raman spectrum?Raman?and Transmission electron microscopy?TEM?were used to characterize the composition of nanocomposites.Scanning electron microscopy?SEM?was employed to characterize the morphologies of different electrodes.Electrochemical impedance spectroscopy?EIS?was utilized to study the interfacial properties of different electrodes.The electrochemical properties of electrochemical sensor were investigated by Cyclic voltammetry?CV?,Differential pulse voltammetry?DPV?and Chronoamperometry?i-t curve?methods.The electrochemical sensors were applied for the detection of Hydrogen peroxide?H₂O₂?,Dopamine?DA?,Clenbuterol?CLB?and Heavy metal ions(Pb²⁺ and Cd²⁺).After all experimental conditions were optimized,satisfactory results were obtained by the proposed electrochemical sensors,indicating its feasibility for routine analysis.Specific results are as follows:1.A disposable biosensor for determination of H₂O₂ based on Fe₃O₄@Au magnetic nanoparticles coated horseradish peroxidase?HRP?and Gr-Nafion film modified SPCE was fabricated.To construct the H₂O₂ biosensor,Gr-Nafion solution was first dropped onto the surface of SPCE.Subsequently,the biocomposites of Fe₃O₄@Au magnetic nanoparticles coated HRP were adsorbed on the surface with the aid of an external magnetic field to fabricate the SPCE ?Gr-Nafion/Fe₃O₄@Au-HRP electrode.The XRD,FTIR,Raman,TEM,SEM,EIS,CV and i-t curve methods were employed to study the synthesis of Gr and Fe ₃O₄@Au,the construction processes and the electrochemical properties of the biosensor.Under the optimized experimental conditions,CV demonstrated that the direct electron transfer?DET?of HRP was realized.The biosensor had an excellent performance in terms of electrocatalytic reduction toward H₂O₂.The linear response of the biosensor to H₂O₂ was in the concentration range of 2.0× 10^-5 mol/L to 2.5× 10^-3 mol/L?R=0.9994?with a detection limit of 1.2× 10^-5 mol/L?S/N=3?.The proposed electrochemical biosensor shows great promise for screen-determination of trace H₂O₂ in real samples.2.Two quick,selective and sensitive el ectrochemical sensors for nonenzymatic H₂O₂ detection based on size controllable preparation of Au and Pt loading on Gr@cerium oxide?Gr@CeO₂?nanocomposites modified GE and SPCE were fabricated.The Gr@CeO₂ nanocomposites were prepared via a facile solvothermal process.Different sizes of Au and Pt were controllably prepared and homogenously loaded on the surface of Gr@CeO₂ nanocomposites modified GE and SPCE using a simple electroless plating method.The XRD combines with FTIR were used to characterize the composition of Gr@CeO₂ nanocomposites.EIS was utilized to study the interfacial properties as well as SEM was employed to characterize the morphologies of different electrodes.The electrochemical properties of electrochemical sensor were investig ated by CV and i-t curve methods.After all experimental parameters were optimized,the Gr@CeO₂-Au modified GE?GE?Gr@CeO₂-Au?and Gr@CeO₂-Pt modified SPCE?SPCE?Gr@CeO₂-Pt?electrodes showed good performances toward the electrocatalytic reduction of H₂O₂.The linear detection range of CV and i-t peaks from 1.0× 10^-3 mmol/L to 10.0 mmol/L for both modified electrodes was achieved.The limit of detection?LOD?were 2.6× 10^-4 mmol/L and 4.3× 10^-4 mmol/L?S/N=3?,respectively.The proposed electrochemical sensors are reliable to quantitative determination of trace H₂O₂ in real contact lens care solutions.3.A highly sensitive and selective electrochemical sensor was fabricated for amperometric determination of DA at the working potential as low as +0.02 V?vs.SCE?.It was based on Gr-manganic manganous oxide?Mn₃O₄?/Nafion film supported Au composites modified GE.The prepared composites were characterized with XRD,FTIR and SEM.The electrochemical properties of the GE?Gr-Mn₃O₄/Nafion-Au electrode were investigated by CV,EIS and i-t curve methods.After all the experimental conditions were optimized,the i-t curve displayed the linear range that extended from 1.0 ?mol/L to 1.45 mmol/L?R=0.9996?with a LOD as low as 0.09 ?mol/L?S/N=3?.The GE?Gr-Mn₃O₄/Nafion-Au electrode was employed to determine DA in injection solution samples using standard addition method with satisfactory results,indicating its feasibility for routine DA analysis.4.A novel magnetic field controllable and disposable electrochemical immunosensor for rapid determination of CLB was fabricated by Gr-Nafion film dropped on the SPCE and then Fe₃O₄@Au nanoparticles coated bovine serum albumin-CLB?BSA-CLB?conjugates were absorbed on it with the aid of external magnetic field.The XRD,FTIR,Raman,TEM,SEM and EIS were employed to characterize the synthesized Gr and Fe₃O₄@Au and the construction processes of the modified electrode.The CV and DPV methods were used to study its electrochemical properties.The content of CLB was determined with a competitive immunoassay mode.When different concentrations of CLB and 2.0 ?g/m L anti-CLB were added to the phosphate buffer solution?PBS?containing 2 mmol/L K 3[Fe?CN?6],the percentage of anodic peak DPV current increase ratio?CI%?was proportional to the concentration of CLB over the range of 0.5 ng/m L to 200.0 ng/m L after incubation for 15 min at 35 ?.The detection limit was 0.22 ng/m L.The immunosensor was employed to determine CLB in pork samples and the results were consistent with high-performance liquid chromatography?HPLC?method.The proposed electrochemical immunosensor is suitable for determining trace CLB in real samples.5.An electrochemical sensor based on Gr-Nafion-Au composites modified SPCE was fabricated?SPCE?Gr-Nafion/Au?.The electrochemical analysis method for the determination of trace lead ions(Pb²⁺)and cadmium ions(Cd²⁺)in water by differential pulse stripping voltammetry?DPSV?was developed by using the proposed electrode.The XRD,FTIR,Raman and SEM were employed to characterize the Gr,Au preparation and the construction processes of SPCE?Gr-Nafion/Au electrode.The DPSV was used to study the electrochemical properties of Pb²⁺ and Cd²⁺.Under the optimum experimental conditions,the stripping peak current showed good linear relationship with Pb²⁺ and Cd²⁺ in the range of 5.0× 10^-10-6.0× 10-8 and 8.0× 10^-10-5.0× 10-8 g/m L,respectively.The detection limits were estimated to be 2.3× 10^-10 g/m L for Pb²⁺ and 3.5× 10^-10 g/m L for Cd²⁺?S/N=3?.The recovery was 94%-106% in real water samples.The analytical results were comparable with graphite furnace atomic absorption spectrometry?GF-AAS?method.The proposed SPCE?Gr-Nafion/Au electrode has high response current and enrichment ability due to the modifing with the composites.It also shows the merits of disposable design,fewer sample volume,portablity compared with other sensors.The convenient,fast and sensitive voltammetric method is suitable for analysis of Pb²⁺ and Cd²⁺ in water.