Study On Electrochemical Biosensors And Modified Electrodes Based On Magnetic Nanoparticles And Quantum Dots

Nanomaterials are the research focus in modern materials science. Considerable research efforts are being devoted toward the development of the chemical modified electrodes and electrochemical biosensors based on the nanomaterials. The main work of this paper is focus on the synthesis of magnetic nanoparticles (Fe₃O₄ nanoparticles) and quantum dots (CdS) and the fabrication of the modified electrodes based on the nanomaterials. Besides, some electrochemical biosensors have been developed. Also, the biosensors have been used to determine the real samples. The main results are listed below:(1) A new type of amperometric hydrogen peroxide biosensor was constructed based on horseradish peroxidase (HRP) immobilized on Fe₃O₄/chitosan modified glass carbon electrode. The effects of some experimental variables such as the concentration of supporting electrolyte, pH, enzyme loading, the concentration of the mediator of methylene blue (MB) and the applied potential were investigated. The linear range of the calibration curve for H₂O₂ was 2.0×10^-4～1.2×10-2 mol/L and the detection limit was 1.0×10^-4 mol/L (S/N=3). The response time was less than 12 s. The apparent Michaelis-Menten constant Km was 21.4 mmol/L and it illustrated the excellent biological activity of the fixed enzyme. In addition, the biosensor had long-time stability and good reproducibility. And this method has been used to determine H₂O₂ concentration in the real sample.(2) A novel magnetic microsphere (Fe₃O₄/chitosan) was prepared using Fe₃O₄ magnetic nanoparticles and natural macromolecule (chitosan). Then an innovative biosensor was constructed based on an easy and effective Hemoglobin (Hb) immobilization method with the"sandwich"configuration of Fe₃O₄/CS-Hb-Fe₃O₄/CS. The effects of some experimental variables such as amount of glutaraldehyde, the concentration of HQ, and the working potential were investigated in the presence of the mediator of hydroquinone (HQ). This biosensor had a fast response to H₂O₂ less than 10 s and excellent linear relationships were obtained in the concentration range of 5.0×10-5 to 1.8×10^-3 mol/L and 1.8×10^-3 to 6.8×10^-3 mol/L with the detection limit of 4.0×10^-6 mol/L (S/N=3) under the optimum conditions. The apparent Michaelis-Menten constant Km was 0.29 mmol/L and it illustrated the excellent biological activity of the fixed Hb. Moreover, the biosensor had long-time stability and good reproducibility. And this method has been used to determine H₂O₂ concentration in the real sample.(3) A novel type of Fe₃O₄ nanoparticles modified glass carbon electrode (Fe₃O₄/GCE) was constructed and the electrochemical properties of N-(4-nitro-2-phenoxyphenyl) methanesulfonamide (nimesulide) were studied on the Fe₃O₄/GCE. In 0.4 mol/L HAc-NaAc (pH 5.0) buffer solution, the electrode process of the nimesulide was irreversible at bare GCE or Fe₃O₄/GCE. The Fe₃O₄/GCE exhibited a remarkable catalytic and enhancement effect on reductin of the nimesulide. The reduction peak potential of nimesulide shifted positively from -0.707 V at bare GCE to -0.682 V at Fe₃O₄/GCE, and the sensitivity increased ca 3 times. Some experimental conditions were optimized. The linear range between the peak current and the concentration of nimesulide was 2.6×10^-6～1.0×10^-4 mol/L (R=0.993) with a detection limit of 1.3×10^-7 mol/L. This method has been used to determine the content of nimesulide in medical tablets. The recovery was determined to be 96.9%～101.9% by means of standard addition method. Compared with ultraviolet spectrometry, the method is not remarkable difference.(4) A novel type of cobalt nanoparticles modified glass carbon electrode (CoNP/GCE) was constructed and the electrochemical properties of chloramphenicol (CAP) were studied on the CoNP/GCE. In 0.3 mol/L NH3-NH4Cl (pH 10.0) buffer solution, the electrode process of CAP was irreversible at bare GCE or CoNP/GCE. The CoNP/GCE exhibited a remarkable enhancement effect on reductin of CAP. The sensitivity increased ca 6 times. Some experimental conditions were optimized. The linear range between the peak current and the concentration of CAP was 5.0×10^-6～1.2×10^-4 mol/L (R=0.997) with a detection limit of 3.0×10^-7 mol/L. This method has been used to determine the content of CAP in the real sample. The recovery was determined to be 98.7%～102.2% by means of standard addition method.(5) A novel third-generation hydrogen peroxide (H₂O₂) biosensor (Hb/CdS/MWNTs/GCE) was fabricated through hemoglobin (Hb) adsorbed onto the mercaptoacetic acid modified CdS QDs/carboxyl multiwall carbon nanotubes (MWNTs) films. Cyclic voltammogram of Hb/CdS/MWNTs/GCE showed a pair of well-defined and quasi-reversible redox peaks with the formal potential (E0') of -0.230 V (vs. Ag/AgCl) in 0.1 mol/L pH 8.0 phosphate buffer solution (PBS), which was the characteristic of the Hb heme Fe(â…¢)/Fe(â…¡) redox couples. The biosensor showed excellent electrocatalytic activity to the reduction of H₂O₂. The response time to H₂O₂ of the designed biosensor at a potential of -0.30 V was less than 2 s and linear relationships were obtained in the concentration range of 2.0×10^-6～2.7×10^-3 mol/L and 2.7×10^-3～7.7×10^-3 mol/L with the detection limit of 3.0×10^-7 mol/L (S/N=3). The apparent Michaelis-Menten constant Km was estimated to be 1.324 mmol/L and it illustrated the excellent biological activity of the fixed Hb.(6) A new method for the determination of Nimesulide was established based on the multiwalled carbon nanotubes (MWCNTs) modified glassy carbon electrode (MWCNTs/GCE). In 0.2 mol/L PBS (pH 6.6) buffer solution, the MWCNTs/GCE showed a remarkable catalytic and enhancement effect on reduction of the nimesulide. The reductoin peak potential of nimesulide shifted positively from -0.665 V at bare GCE to -0.553 V at MWCNTs/GCE, and the sensitivity increased ca 7 times. A linear dynamic range of 3.2×10^-7 mol/L to 6.5×10-5 mol/L (R=0.999) with a detection limit of 1.6×10^-7 mol/L was obtained. The electrochemical behaviors of nimesulide were studied and this method has been used to determine the content of nimesulide in medical tablets. Compared with UV-Vis spectrometry, the method was not remarkable difference.