The Preparation of Graphene-noble Metal Nanocomposites and Their Electrochemical Determination of Small Biomolecules

Author:Zou Cui E

Supervisor:du yu kou


Degree Year:2018





Ascorbic acid(AA),uric acid(UA)and dopamine(DA)are indispensable small biomolecules,which play an important role in human and animal health.Nitrite(NaNO2),widely applied in our daily life as a corrosion inhibitor and an additive in food industry,has been recognized as an alarming pollutant to the environment.Rutin(RT)is one of the effective components in drugs for the treatment of high blood pressure and cerebral hemorrhage.For these biomolecules,abnormal content in human body will influence our health.For instance,irregular UA content in blood may lead to some diseases such as gout,arthritis,gouty nephropathy,hyperuricemia and anemia.An excessive nitrite level in human body,not only can lead to the irreversible oxidation of hemoglobin to methemoglobin,but also can react with dietary components to form a nitrosamine,resulting in cancer and hypertension.Accordingly,it is of great significance to develop efficient methods to detect these small biomolecules.Owing to the electrochemical activity of AA,DA,UA,NaNO2 and RT,electrochemical techniques have attracted great attention due to their high sensitivity,ease of handling and electrode fabrication,low cost and short response time.However,it’s hard to get satisfying result to determine AA,DA,UA,NaNO2 and RT electrochemically on bare glassy carbon electrode(GCE)since bare GCE has poor electron transfer ability.Hence,it is extremely important to prepare an electrode with higher selectivity and sensitivity for the reliable detection of AA,DA,UA,NaNO2and RT.Recently there have been many studies on graphene–noble metal nanocomposites acting as electrochemical biosensors.Graphene(GE)has attracted particular attention due to its large specific surface area,unique electronic properties,excellent physicochemical properties,high chemical and thermal stability.In addition,noble metal nanostructures have been playing an important role in electrochemical biosensors due to their excellent catalytic capability,unique dimension property and high effective surface area.To this end,the combination of noble metal-based NPs and the special 2D carbon-based material GE at the nanoscale dimension offers great promise for improved applications.In our work,graphene-noble metal nanocomposites are used to determine AA,DA,UA,NaNO2 and RT electrochemically.The research is presented in the four sections described below:(1)The spherical Au nanoparticles and 3D flower-like structure graphene were successively deposited on glassy carbon electrode to obtain Au/f-GE/GCE via a two-step electrodeposition method for the detection of NaNO2.The morphology and elemental compositions as well as crystal structures were confirmed by scanning electron microscopy(SEM),energy dispersive X-ray spectroscopy(EDX)and X-ray diffraction measurements(XRD).Electrochemical measurements including cyclic voltammetry(CV)and differential pulse voltammetry(DPV)were used to evaluate the electrochemical behaviors of NaNO2on the as-prepared electrode.Compared with f-GE/GCE and Au/GCE,Au/f-GE/GCE showed a sharper and more obvious oxidation peak at 0.78 V.The oxidation peak current of NaNO2 on Au/f-GE/GCE was linearly proportional to its concentration in the range from 0.13 to 20375.98μM,with a detection limit of 0.01μM(at S/N=3).Furthermore,it also demonstrated that the as-prepared electrode exhibited excellent reproducibility and long-term stability,as well as good recovery when applied to the determination of NaNO2in pickled pork samples.(2)A hybrid nanostructure of Au-Ag nanorings decorated by N-doped graphene(NG)was utilized as an electrocatalyst to construct a novel electrochemical sensor.Transmission electron microscopy(TEM),Energy dispersive X-ray spectroscopy(EDX)and X-ray photoelectron spectroscopy(XPS)were used to characterize the as-prepared composites.The Au-Ag nanorings/NG modified electrode exhibited a much better electrochemical response for rutin than the Au/NG,Ag/NG and NG electrodes due to the synergestic catalytic effect between the Au-Ag nanorings and NG.Under optimal conditions,the electrochemical sensor of the Au-Ag nanorings/NG exhibited a wide linear range from0.05μM to 241.20μM with a low detection limit of 0.01μM(S/N=3).In addition,the proposed sensor also displayed good repeatability and long-term stability,all of which are essential for applications in bioassay analysis.(3)Using Pd nanocubes as the structure-directing cores,a facile method for the fabrication of PdAu core-shell(PdAu)heterostructures has been successfully developed.The as-prepared Pd@Au was further modified by reduced graphene oxide(RGO)to obtain Pd@Au/RGO.The glassy carbon electrode fabricated by Pd@Au/RGO was employed to detect ascorbic acid,dopamine and uric acid simultaneously.Owing to the synergistic effect among Au,Pd and RGO,the Pd@Au/RGO/GCE demonstrates excellent electrocatalytic activity,electron transfer capability,selectivity and sensitivity in the analysis of AA,DA and UA.CV and DPV were used to evaluate the electrochemical behaviors of AA,UA and DA on the as-fabricated electrode.Good linear calibration plots for AA,DA and UA were established by simultaneously increasing the concentration of AA,DA and AA in the ranges of 50.00-2856.63μM,1.00-400.56μM and 5.00-680.76μM,respectively.The individual DPVs for AA,DA and UA were also investigated and the detection limits were found to be 24.88μM,0.20μM and 1.25μM,respectively.(4)A facile method was employed to develop PdAu bimetallic nanocomposite(PdAu)successfully.The synthesized PdAu nanoparticles were further modified by reduced graphene oxide to obtain PdAu/RGO.The glassy carbon electrode fabricated by the as-prepared PdAu/RGO was utilized to determine ascorbic acid,dopamine,uric acid and rutin electrochemically.The synthesized PdAu/RGO nanoparticles were characterized by TEM,EDX and XRD,which revealed that the Au and Pd were alloyed and distributed evenly on the thin structured reduced graphene oxide.CV and DPV were utilized to evaluate the electrochemical performances toward AA,UA,DA and RT on the as-fabricated electrode.The individual DPV for AA,DA,UA and RT were studied and good linear relationship was observed for all the four materials in the ranges of12.50-700.00μM,1.25-73.75μM,2.50-66.25μM and 0.025-5.63μM,respectively,with individual detection limits of 12.50μM,0.75μM,2.50μM and 0.025μM,respectively.AA,DA and UA were determined simultaneously via CV and DPV.The simultaneous analysis of AA,DA and RT was also investigated using CV and DPV.Additionally,the modified electrode has fairly good performance when used in the analysis of real samples to determine the content of AA,DA,UA and RT.