Research On The Electrochemistry Biosensor Based On The Magnetic Chitosan Microspheres/Thionine Modified Electrode

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 magnetic microspheres and thionine in the electrocatalytical analysis of dihydronicotinamide adenine dinucleotide, dopamine, uric acid and their biosensing. The main content of this paper is listed as follows:1. A novel magnetic chitosan microsphere (MCMS) was prepared using carbon-coated iron magnetic nanoparticals and chitosan. An amperometric dihydronicotinamide adenine dinucleotide (NADH) sensor was presented based on immobilize MCMS on the surface of a polythionine (PTH) modified glassy carbon electrode (GCE). The fabrication of MCMS/PTH film and its electrocatalytic effect for electrochemical oxidation of NADH were investigated by electrochemical impedance spectroscopy (EIS) and voltammetric methods. It was found that the resulting integrated films of PTH and MCMS exhibit high electrocatalytic response with the significant decrease of high overpotential. The effects of the experimental variables such as the solution pH and the working potential were investigated for optimum analytical performance. This biosensor had a fast response of NADH less than 10 s and excellent linear relationships were obtained in the concentration range of 2-10μmol/L and 10-100 umol/L with the detection limit of 0.51μmol/L (S/N=3) under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor were evaluated with satisfactory results.2. A novel magnetic chitosan microsphere(MCMS) was prepared using magnetic CCINPs and chitosan. Thionine were successfully dispersed in MCMS solution to obtain an MCMS-TH dispersion, and a drop of this homogeneous dispersion was cast onto the surface of a glassy carbon electrode (GCE) to fabricate an MCMS-TH modified GCE. The properties and electrochemical behavior of DA were characterized using CV and EIS at this modified electrode. 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 2.63×10-5 cm2/s using cyclic voltammetry. The effects of the amount of the dispersion, solution pH, scan rate and working potential were studied to obtain the optimum experimental conditions. Under the optimum conditions, the anodic peak currents (ipa) are proportional to the concentration of DA in the range of 0.5μmol/L to 8.8μmol/L with the correlation of 0.9991, and a detection limit of 0.12μmol/L. In addition, this modified electrode showed high sensitivity, selectivity and stability, which can effectively be used to determine DA in the presence of AA and UA with good selectivity. It had been applied to the determination of DA in an injection samples with a satisfactory result.3. A novel magnetic chitosan microsphere (MCMS) was prepared using carbon-coated iron magnetic nanoparticles and chitosan. A two-electron redox mediator thionine (TH) has been deliberately incorporated into the MCMS, the resulting MCMS-TH composite film modified glassy carbon electrode (MCMS-TH/GCE) exhibited excellent electrochemical catalytic activities towards the oxidation of dopamine (DA) and uric acid (UA) with obviously reduction of overpotentials. Differential pulse voltammetry was used for the simultaneous determination of DA, UA in their duplicate mixture. The peak separation between UA and DA was 140 mV. The calibration curves for DA and UA were obtained in the range of 2-30μmol/L and 9-100μmol/L, respectively. The lowest detection limits (S/N=3) were 1.0μmol/L and 4.3μmol/L for DA and UA, respectively. In addition, ascorbic acid (AA) and some other possible interferences did not interfere with the determination under the present experimental conditions. With good selectively and sensitivity, the proposed method can be applied to detect DA and UA in real samples with satisfactory results.