Preparation Of Graphene-based Composites As SERS Substrate And Its Application In Enzyme-like Catalytic Reaction And Detection

Surface-enhanced Raman scattering(SERS)is a phenomenon in which Raman signals are greatly enhanced due to the adsorption of probe molecules on the surface of rough metal nanoparticles.This technique can not only sensitively detect the analytes with low concentration adsorbed on nanostructures but also give the molecular structure information.Therefore,it has been widely used in chemical synthesis,biology,environmental protection and other fields.It has been reported that gold,silver nanoparticles and graphene oxide sheets not only possess the enzyme but also show a high SERS activity.Since the first report on Fe3O4 nanozymes,it has attracted more attention in various fields including materials,physics,chemistry,biology,medicine and environmental science.Compared with natural bio-enzymes,nanozymes show high stability and high catalytic activity,as well as low-cost.In particular,they can avoid the disadvantages of instability in biological enzyme.The advantages of nanozymes offer them broad application prospects in catalytic and enzymatic kinetics.Therefore,these catalytically active nanoparticles are of great significance in analytical chemistry.Currently,based on the analysis of colorimetric reactions catalyzed by nanozymes,the sensitive detection of heavy metal ions and biomolecules can be achieved.In this thesis,we constructed two kinds of reduced graphene oxide-based composites as SERS substrates with enzyme-like activity,which have been used for the sensing of glucose and mercury ions,respectively.The main research content is as follows:a)Fabrication of Ag-Cu2O/reduced graphene oxide nanocomposites as surfaceenhanced raman scattering substrates for in situ monitoring of peroxidaselike catalytic reaction and biosensingHighly sensitive biosensors are essential in medical diagnostics,especially for monitoring the state of an individual's disease.An ideal way to achieve this objective is to analyze human sweat secretions by noninvasive monitoring.Due to low concentrations of target analytes in human secretions,fabrication of ultrasensitive detection devices is a great challenge.In this work,Ag-Cu2O/reduced graphene oxide(r GO)nanocomposites were prepared by a facile two-step in situ reduction procedure at room temperature.Ag-Cu2O/r GO nanocomposites possess intrinsic peroxidase-like activity and rapidly catalyze oxidation of the peroxidase substrate 3,3?,5,5?-tetramethylbenzidine(TMB)in the presence of H2O2.On the basis of the excellent SERS properties and high peroxidase-like activity of the Ag-Cu2O/r GO nanocomposites,the catalytic oxidation of TMB can be monitored by SERS.This approach can detect H2O2 and glucose with high sensitivity and distinguish between diabetic and normal individuals using glucose levels in fingerprints.Our work provides direction for designing other SERS substrates with high catalytic activity and the potential for application in biosensing,forensic investigation,and medical diagnostics.b)A dual colorimetric and SERS detection of Hg2+ based on the stimulus of intrinsic oxidase-like catalytic activity of Ag-Co Fe2O4/reduced graphene oxide nanocompositesMercuric ion(Hg2+)is a toxic metal ion in the environment,which will seriously damage the people's health.Therefore,the simple sensitive detection of Hg2+ is of great significance.In this work,Ag-Co Fe2O4/reduced graphene oxide(r GO)nanocomposites were synthesized via a one-pot microwave-assisted reaction,which can directly oxidize 3,3?,5,5?-tetramethylbenzidine(TMB)to produce a light blue.Then we have developed a dual colorimetric and SERS detection of Hg2+based on the stimulus of intrinsic oxidase-like catalytic activity of Ag-Co Fe2O4/r GO nanocomposites.It is demonstrated that the interaction between Hg2+ and Ag nanoparticles can occur in a short time,which includes the formation of Ag-Hg alloy due to the reduction of Hg2+.In addition,the formation of such alloy can enhance the oxide-like activity,which makes the detection of Hg2+ more sensitive.By using the SERS detection approach,the assay can detect Hg2+ as low as 0.67 n M.This detection ability is much better than previous reports based on the enzyme-like catalytic reaction,which is also lower than the maximum value of Hg2+ permitted in drinking water by the World Health Organization(WHO)(30 n M)and United States Environmental Protection Agency(EPA)(10 n M).In addition,this detection system also shows an excellent selectivity toward Hg2+ due to the affinity of Hg to AgCo Fe2O4/r GO nanocomposites.Therefore,this approach is potentially applicable for the sensitive determination of Hg2+ in real environmental conditions.