Platinum Nanoparticles Modified Micro Electrode In The Application Of Capillary Electrophoresis

Pt nanoparticles （PtNPs） are extensively used as electrocatalysts inelectrochemical applications, attributing to their high surface area, high reactivity,high electrocatalytic efficiency, chemical inertness and high selectivity. Capillaryelectrophoresis with electrochemical detection （CE-ECD） has already been applied toanalyse many substances in cell owing to its minute consumption of sample, inherentefficient separation capabilities, high sensitivity and simplicity of instrumentionneeded. When PtNPs-modified microelectrodes are used as detector of CE-ECD, thesensitivity will enhance largely and the kind of substance determined will increasegreatly. And this is one of the important aspects in modern analytical chemistry.In this thesis, two kinds of PtNPs-modified microelectrodes were described forthe direct identification of ascorbic acid and hydrogen peroxide by capillaryelectrophoresis with amperometric detection. And the method has been successfullyapplied to the analysis of single cells.In the first chapter, excellent physical and chemical properties of PtNPs and howto make PtNPs-modified microelectrodes were introduced in detail. And then theprinciple of CE, the detection method which was often used with CE was introduced.Finally, the application of PtNPs-modified microelectrodes used with CE-ECD, werereviewed.In the second chapter, ascorbic acid （AA）, vitamin C, is an important essentialnutrient for mammalian cells, acts as a cofactor of different enzymatic reactions, e.g.collagen synthesis. AA can mitigate the reactive oxygen species production triggeredby lipopolysaccharide and thereby prevent the induction of nitric oxide synthase andexcessive production of nitric oxide that worsens oxidative stress in hepatocytes.Additionally, it was reported that AA demonstrates a cytotoxic effect by generatinghydrogen peroxide, a reactive oxygen species involved in oxidative cell stress. So thedetermination of AA in cells is an important and significant work. In this work,platinum nanoparticles modified carbon fiber micro-disk electrode （PtNPsME） waselectrochemically prepared and exploited as an amperometric detector for capillary electrophoresis. And scanning electron microscope （SEM） was employed in order tocharacterize the morphologies and microstructures of PtNPsME. The prepared sensordisplayed rapid and sensitive response towards ascorbic acid, which was attributed tothe electrocatalytic effect of platinum nanoparticles. Compared with the bare CFME,the sensitivity enhanced nearly four times was gained, and the detection limit of0.50μmol/L （S/N=3） for ascorbic acid. Acceptable repeatability of the microanalysissystem was verified by ten consecutive injections of ascorbic acid without capillaryand electrode treatments, the RSDs for peak current and migration time were1.7%and4.8%, respectively. The developed capillary electrophoresis-electrochemistrysetup was first applied to the determination of ascorbic acid in single liver cancer cells（HepG2）.In the third chapter, H₂O₂is considered as a key metabolite because it is arelatively stable molecule with ability to cross cell membranes, and mountingevidence supports its physiological role as a second messenger in cellular signaltransduction. And hydrogen peroxide is shown to be closely related to tumor genesisand growth. Therefore, it is of critical importance for H₂O₂detection in biologicalsamples especially in cells, because of its potential to act as a diagnostic biomarker ofdiseases induced by oxidative stress and damage events. In this article, we reported anovel PtNPs/MWNTs/PtE to detect H₂O₂. SEM and transmission electron microscope（TEM） were employed in order to characterize the morphologies and microstructuresof PtNPs/MWNTs/PtE. This work demonstrated that the use of PtNPs and MWNTscan improve the performances of electrochemical measurements with CE. Thedetection conditions were optimized including detection potential, the concentrationof phosphate buffer, pH value of phosphate buffer, and separation voltage etc. Andthe electrode provides excellent stability, enhanced sensitivity and highly catalyticactivity toward H₂O₂by CE. The detection limit of0.40μmol/L （S/N=3） for H₂O₂. This method has been successfully applied to the determination of H₂O₂in neutrophilsof human beings.