Studies Of Electrochemical Biosensors Based On Iron Magnetic Nanomaterials

Nanomaterials have been applied extensively in electrochemical biosensing because of their excellent physical and chemical properties.As one kind of novel nanomaterial, magnetic nanomaterials have been used successfully in many research fields including enzyme immobilization and electrocatalytical analysis because they not only have the common nano-characters but also have some other excellent properties including superparamagnetism and abundant functional groups on the surface.The fundamental purpose of this paper is to study the application of the iron magnetic nanoparticles and magnetic microspheres in the electrocatalytical analysis of dopamine, the immobilization of redox enzymes such as hemoglobin and horseradish peroxidase and their biosensing.The main content of this paper is listed as follows:1.A drop of homogeneous carbon-coated iron nanoparticles(CCINPs)dispersion and Nafion were successively cast on the surface of a glassy carbon electrode(GCE)to fabricate a Nafion/CCINPs modified GCE.The modified electrode exhibited good electrocatalytic activity for electrochemical oxidation of dopamine(DA)which was controlled by diffusion in the pH 5.5 phosphate buffer solution(PBS),and the diffusion coefficient was determined as 3.0×10^-5cm²/s using chronocoulometry.The oxidation peak currents determined by differential pulse voltammetry(DPV)showed a linear dependence on the DA concentration and a linear analytical curve was obtained in the range from 2.0 to 60μmol/L with a correlation coefficient of 0.9992.The detection limit was estimated to be 0.83μmol/L.This method was also examined for the detection of DA in an injection sample which was good consistent with the pharmacopeial method.In addition,ascorbic acid(AA)and some other possible interferents didn't interfere with the determination of DA under the present experimental conditions.Due to its good linear relationship,stability and reproducibility,the CCINPs/Nafion modified GCE can be effectively used for voltammetric detection of DA.2.Iron nanoparticles(INPs)were successfully dispersed in Nafion solution to obtain an INPs-Nafion dispersion,and a drop of this homogeneous dispersion was cast onto the surface of a carbon paste electrode(CPE)to fabricate an INPs-Nafion modified CPE. The electrochemical behavior of DA has been studied by cyclic voltammetry at this modified electrode in a pH 7.0 B-R buffer solution.By comparing with a bare CPE,the anodic and cathodic peak potentials shifted negatively and positively respectively,and a pair of good defined redox peaks were observed with great enhance of the peak currents. The effects of the constitute of carbon paste,amount of the dispersion,pH and scan rate were studied to obtain the optimum experimental conditions.The peak currents determined by DPV showed an excellent linear relationship with the DA concentration in the range from 0.01 to 0.11mmol/L with the detection limit of 3.3μmol/L.In addition, this modified electrode also has good stability,reproducibility and selectivity.3.A novel magnetic chitosan microsphere(MCMS)was prepared using magnetic CCINPs and chitosan.Hemoglobin(Hb)was successfully immobilized on the surface of MCMS modified GCE with the cross-linking of glutaraldehyde,and the immobilized Hb displayed an excellent electrocatalytic property to the reduction of H₂O₂ in the presence of the mediator of methylene blue(MB).The effects of the experimental variables such as the concentration of MB,solution pH and the working potential were investigated using steady-state amperometry.This biosensor had a fast response of H₂O₂ less than 10s and excellent linear relationships were obtained in the concentration range of 0.069-0.29 mmol/L and 0.29-3.0mmol/L with the-detection limit of 0.021mmol/L under the optimum conditions.Moreover,this biosensor has good selectivity,stability and reproducibility, which can be used successfully for H₂O₂ determination.4.A new kind of magnetic dextran microsphere(MDMS)with uniform shape and narrow diameter distribution was prepared using magnetic INPs and dextran.Horseradish peroxidase(HRP)was successfully immobilized on the surface of MDMS modified GCE, and the immobilized HRP displayed an excellent electrocatalytic property to the reduction of H₂O₂ in the presence of the mediator of hydroquinone(HQ).The effects of the experimental variables such as the concentration of HQ,solution pH and the working potential were investigated.This biosensor had a fast response of H₂O₂ less than 10s and an excellent linear relationship was obtained in the concentration range of 0.20μmol/L-0.68mmol/L with the detection limit of 0.078μmol/L(S/N=3)under the optimum conditions.The amperometric response showed a Michaelis-Menten behavior at larger H₂O₂ concentrations,and the apparent Michaelis-Menten constant K_M^appwas estimated to be 1.38mmol/L.Moreover,the selectivity,stability and reproducibility of this biosensor were evaluated with satisfactory results.