Performance Enhancement Study Of Carbon Electrode By UV/ozone Treatment And Its Application In Microfluidic Chip

Carbon is a typical non-metallic element,which has many advantages such as good stability,high chemical inertia,convenient material acquisition and low price,so it has extensive application requirement in electrode production field.Screen-printed carbon electrode has advantages of low background current.wide electrochemical window,good chemical stability,fast preparation,mass production and easy integration with microfluidic chips,which has wide application prospect in electrochemical detect areas of biomedical,environmental monitoring and food supervision.However,screen-printed carbon electrode is easily adsorbed by electroactive substances during electrochemical test,resulting in a decrease of detection sensitivity.Also,the adsorption between conductive layer and substrate of screen-printed carbon electrode is physical adsorption,so the adhesion between the conductive layer and the substrate is poor.Besides,organic binder existed in screen-printed carbon electrode can also increase electrical resistance of electrode,so the electronic transmission rate of SPCE is relatively low for above reasons,which limit rapid and efficient detection to micro-trace quantities of material by screen-printed carbon electrode.Aim at above problems,this paper researches on pollution repair and electron transfer performance enhancement of screen-printed carbon electrodes,and main research contents are as follows:(1)Combined with electrode dynamics and fluid mechanics theory,the effect of flow mass transfer on electrochemical detection in microscale was studied.The main factors affecting the sensitivity of electrochemical detection in microfluidic chip and improved methods were discussed.The feasibility of characterize status of contaminated electrode with electrochemical impedance spectroscopy by theoretical demonstration and simulation analysis.The results show that the higher of chemical reaction rate constant of the electrode,the smaller of the electrochemical impedance,and the more favorable of the electrochemical reaction on the electrode.(2)Oxidation mechanism of UV/ozone to contaminated screen-printed carbon electrodes was revealed.Combined with the characterization methods such as scanning electron microscopy and X-ray photoelectron spectroscopy,it is found that UV/ozone can not only react with organic pollutants existed on carbon electrode surface to generate volatile substances,but also the content of oxygen-containing functional groups can be increased on the electrode surface,then the electrochemical performance of contaminated carbon electrode was renewed.Screen-printed carbon electrode was selected as research object,the rationalization time of UV/ozone treatment on contaminated electrode was measured using electrochemical detection,then repairing effect of UV/ozone on contaminated carbon electrode and electrochemical repeatability of repaired electrode were examined.Finally,electrochemical response of new SPCE,contaminated SPCE and repaired SPCE to different concentration of NADH was determined.The results show that the detection sensitivity of contaminated SPCE increased from 13.31 ?A·mM-1 to 19.11 ?A·mM-1 by UV/ozone treatment.(3)A new method of UV/ozone modification for enhancing the electron transport performance of carbon electrode is proposed.The electrochemical performance of unmodified and CNT-modified screen-printed carbon electrodes before and after UV/ozone modification were determined by electrodynamic polarization and electrochemical impedance spectroscopy,the cyclic voltammetric responses of unmodified and CNT-modified SPCEs to different types of electroactive substances were determined by electrochemical analysis with macromolecular NADH and small molecule potassium ferricyanide.The results show that the current and potential responses of unmodified and CNT-modified SPCEs to potassium ferricyanide and NADH were both improved by UV/ozone modification.The increase amplitude of interfacial impedance was 12.53%and 30.33%respectively for unmodified and CNT-modified SPCEs after adsorbing NADH oxidation product,it can be seen that the CNT-modified SPCE has a strong adsorption for NADH.and which makes the unmodified SPCE is more suitable for electrochemical determination of NADH.(4)A new method of detecting glutamate pyruvate transaminase(GPT)in microfluidic chip with screen-printed carbon electrode based on transamination was developed.A microfluidic chip with passive ribbed mixer was designed and manufactured,the bio enzymes was mixed rapidly in the chip by using the chaotic convection effect produced by the mixer.The electrochemical detection time of GPT was shortened from 2 hours to 30 minutes.and the detection sensitivity of enzyme was improved,which provides a possibility for POCT detection of GPT.Due to excessive enzymatic reaction products NADH could contaminate screen-printed carbon electrode inside the chip,so repairing of contaminated carbon electrode in microfluidic chip by UV/ozone treatment was further studied in this paper.Quartz with high transmittance at 185 nm and 254 nm ultraviolet band was integrated in the microfluidic chip,the in-chip repair and enhancement of the contaminated carbon electrode is effectively realized in the chip by introducing the outside air into the microfluidic chip continuously.