The Study On Hydrogen Peroxide And DNA Sensors Based On The Nanostructured Metal Oxides

Hydrogen peroxide (H₂O₂) will be produced in many oxidase-catalyzed reactions,including enzymes such as glucose oxidase, uric acid oxidase, cholesterol oxidase, ethanoloxidase, etc. The detection of the concentration of H₂O₂ can be employed to measure theconcentration of many target samples, which are the substrates of the oxidase s mentioned above.This makes it possible to develop biosensors for various substances such as glucose, etc. Manycells will produce H₂O₂ and it will also appear in the urine, blood and breath. The detection ofH₂O₂ could be employed to evaluate the status of the oxidative stress and to monitor the reactionin the process of therapy.On the other hand, the separation and analysis of genes have exhibited more and moreimportance in the areas of hygienic immunology, medical diagnosis, pharmaceutical research,environmental science and biological engineering. This promotes new requirements on themethods for the gene analysis and detection.In the research area of sensors, nanomaterials of different kinds and various structures havebeen applied, especially in the development of electrochemical sensors. This has resulted ingood measurement effects in the related research work, including the improvement of linearrange and detect limit.We developed electrochemical sensors for the measurement of hydrogen peroxide, basedon the ZnO nanorod arrays, to meet the requirement of this kind of sensors for the practicalapplications. Besides, the influence of surface modification of field-effect device to its functionof DNA test was studied too. TiO₂ film was deposited on the surface of thelight-addressable-potentilmetric sensor (LAPS) to simplify the surface treatment process and toimprove the efficiency, for attaining better result of DNA test.The main research contents of this work are as followings:1) The effect of the UV treatment on the properties of the hydrothermally-grown ZnOnanorod arraysThe ZnO nanorod arrays hydrothermally grown on the UV-treated area of the ZnO seedinglayer exhibit different surface morphology and photoluminescence characteristics comparedwith those grown on the non-UV-treated area. The UV treatment makes the surface of the ZnONRAs more uniform, the same as the diameter distribution of the nanorods. The nanorods on theUV-treated area were thinner than those on the non-UV treated area.2) Electrochemical characterization of gold-coated ZnO nanorod arrays electrodeGold was spurtered onto the surface of the ZnO nanorods in the arrays, which will protect them from erosion in aqueous solution and make the arrays capable of acting as electrode forelectrochemical detection. The prepared electrode was characterized by cyclic voltammetry andelectrochemical impedance spectrum, etc. With comparison to planar gold electrode, it is foundout that the diffusion property of the gold-coated ZnO NRAs electrode is nearly the same as thatof planar gold electrode, but the difffusion area enlarged and the charge transfer resistancedecreased. The decrease of the charge transfer resistance implies the increase of theelectrochemical activity of the electrode, which is in accordance with the properties ofnanostructure materials.3) Gold-coated ZnO NRAs electrode with improved electrochemical activity for thedirect detection of hydrogen peroxideThe cyclic voltammograms in H2O2 solution revealed that the cathodic potential waslowered on gold-coated ZnO NRAs electrode compared with that on the planar gold electrode.The linear range of the detection for H2O2 with this electrode is 0.088 mM to 72.6mM, and thedetection limit is 0.07M. The detect sensitivity is 30 mAcm^-2M^-1.4) Pt-modified gold-coated ZnO NRAs electrode for the detection of hydrogenperoxideWith Pt modification, the resulted gold-coated ZnO NRAs electrode exhibits differentcyclic voltammetry characteristics. The reversibility of the reduction-oxidation reaction ofH2O2 on the Pt-modified electrode was improved, indicating the improvement of theelectrochemical activity of the electrode after the Pt deposition. The linear range of the detectionfor H2O2 with this electrode is 0.044 mM to 20mM, and the detection limit is 0.03mM. Thedetect sensitivity is 50 mAcm^-2M^-1. Compared with the gold-coated ZnO NRAs electrode, afterPt modification, the detection limit and sensitivity were improved. The interference of theascorbic acid under the physiological concentration was neglected in the detection range.5) Influence of surface modification on the measurement effect of field-effect device.Two kinds of field-effect devices were studied, which could response to the change ofsurface charge by the variation of impedance of the devices.A. The influence of the surface treatment on the test characteristics of the field effectdevices (FED) has been studied. The surface treatment was carried out employing sulfuric acidand methanol-HCl solution respectively. The silanization and fluorescence-labeling of thesurface after these two kinds of treatment reveal that the treatments cause little influence on thesilanization effect of the surface. It is found that the sulfuric acid treatment makes the readout ofthe DNA sensor better.B. The non-label DNA test was conducted employing the characteristics of the LAPS responding to the surface charge. Nanocrystal titanium dioxide (TiO₂) thin film was depositedon the surface of the LAPS. The fluorescence labeling measurement indicates that the effect ofsurface silanization is improved by the UV treatment. The hybridization of 10μM target DNAwith the corresponding probe DNA immobilized on the LAPS surface can be measured by theshift of the I-V curve of LAPS.