The Development Of New Bio-nano Sensors For The Physical Detection Of 2,4 - Dichlorophenol

Application of Nano-materials and electrochemical biosensor has been a hot topic in the 21th century. Especially, carbon nanotubes and their composites, as new chemically modified materials, is a new direction in the field of chemically modified electrodes. Carbon nanotubes with excellent physical chemical characteristics have attracted people's attention because of the unique mechanical, electronic and chemical stability, and have been used as the material of sensors. Carbon nanotubes can promote the electronic transmission of certain substances in the electrochemical reaction and have specific catalytic characteristics due to the surface with more functional corps.The main work of this paper is focus on the electroanalytical chemistry of the carbon nanotubes and the preparation of novel modified electrodes based on nanomaterials (electrochemical sensors). The main points of this thesis are summarized as follows:1. Determination of rutin by a nanocomposite modified electrochemical sensorA new electrochemical sensor for the determination of rutin was prepared. A carbon nanotube/chitosan layer with positive charged was first coated on the glassy carbon electrode, then an Au nanoparticles layer charged negatively was strongly adsorbed on the surface of the electrode.This biosensor with good stability, displays the current response to rutin due to the direct electron transfer between rutin and carbon nanotube/chitosan/Au nanoparticles interface of the electrode. The biosensor can be used for the determination of rutin in the range of 4.00×10-7～1.77×10-5 mol/L with the detection limit of 1.29×10-7moL/L. Compared with the oxidation of ascorbic acid(AA) at the bare GC electrode, oxidation potential of AA at the modified electrode negatively shifted 200 mV. The interference of AA during the determination of rutin can be neglected. The method has been assessed for the determination of rutin in medicament without separation.2. Sensitive mediator-free tyrosinase biosensor for the determination of 2,4-dichlorophenol2,4-Dichlorophenol (2,4-DCP), one of the most important organic pesticides, is used extensively for herbicides, fungicides and insecticides in the agriculture. It is very meaningful for determining and degradation 2,4-DCP in the environment. A novel tyrosinase-based biosensor was developed for the determination of 2,4-DCP by immobilizing tyrosinase on multi-walled carbon nanotubes (MWNTs) and polydiallyl -dimethylammonium chloride(PDDA) modified glassy carbon electrode. The biosensor showed a sensitive electrochemical response to 2,4-DCP in the presence of O2 in solution. The effects of pH, adsorption time of PDDA, amount of tyrosinase immobilized on enzyme electrode, and volume of the MWNTs solution during the preparation of the sensor on the amperometric response of the electrode were explored for optimum analytical performance. The biosensor exhibited a fast amperometric response (less than 7 s), a high sensitivity and good storage stability for monitoring 2,4-DCP. The method showed good linearity in the range 1.99×10-6 ~ 1.01×10-4 mol/L of 2,4-DCP with a correlation coefficient of 0.997 and a detection limit of 6.58×10-7 mol/L. The response of the electrode showed Michaelis-Menten behavior at lower 2,4-DCP concentrations. The Kmapp value of immobilized tyrosinase on the modified electrode was calculated to be 6.63×10?5 mol/L using 2,4-DCP as the substrate. The performance of the electrode was verified by determination of 2,4-DCP in the environmental water.3. Direct electrochemistry of horseradish peroxidase immobilized on modified glassy carbon electrodeDirect electron transfer process of immobilized horseradish peroxidase (HRP) mixed with poly(styrenesulfonate) (PSS) on a modified glassy carbon electrode with poly(dimethyldiallylammonium chloride )(PDDA) membrane, and its application as a biosensor were investigated by using electrochemical methods. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and amperometric i-t curve. The modified process was characterized by electrochemical impedance spectroscopy (EIS) and ultraviolet-visible spectroscopy (UV-Vis). The sensor displayed an excellent electrocatalytic response to the reduction of H2O2 without the aid of an electron transfer mediator. Analytical parameters such as pH value and the ratio of HRP and PSS were also studied. Linear calibration for H2O2 was obtained in the range 1.66×10?6 to 1.14×10?4 mol/L under the optimized conditions. The sensor was highly sensitive to H2O2 with a detection limit of 9.76×10?7 mol/L (S/N= 3), and the sensor achieved 95% of the steady-state current within 10 s. The sensor exhibited high sensitivity, selectivity and stability.