The application of low dimensional nanomaterials in electrocatalysis and electrochemical biosensing

Zhu, Zanzan

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The application of low dimensional nanomaterials in electrocatalysis and electrochemical biosensing

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Electrochemistry, based on the study of an electrochemical reaction at the interface between an electrode and an electrolyte, is having a profound effect on the development of different fields of science and engineering including battery, fuel cell, electrochemical sensor, electrochromic display, electrodeposition, electroplating, electrophoresis, corrosion, and so on. The performance of the electrochemical reaction depends strongly on the nature of the employed electrode such as structure, chemical composition, and surface morphology. Nanomaterials, notable for their extremely small feature size (normally in the range of 1-100 nm), exhibit new properties which are different from those of bulk materials due to their small size effect. In past decade, nanomaterials have been widely used to develop new strategies for designing electrode and its surface morphology for electrocatalysis and electrochemical sensing applications. My work is aimed at exploring the application of low dimensional nanomaterials (nanotubes and nanoparticles) in electrocatalysis and electrochemical biosensors. Electrocatalysis plays an important role in energy and industrial applications. As one of the most attractive support materials for electrocatalyst, carbon nanotubes have been extensively reported to enhance the performance of various electrochemical catalytic reactions. In recent years, carbon nanotubes with a bamboo-like structure due to nitrogen doping have become a hot topic of increased interest in the field of electrocatalysis because of the unique bamboo shaped structure associated properties. In this work, bamboo shaped carbon nanotubes, synthesized by chemical vapor deposition method, were investigated for ethanol/methanol electro-oxidation, respectively. Small sized platinum nanoparticles (Pt NPs) were dispersed onto BCNT surface through an impregnation method. The role of nitrogen doping in the formation of bamboo shaped structure and its effect in the electrochemical performance of CNTs were discussed. The electrochemical studies showed that the as-prepared Pt/BCNTs electrocatalysts indeed exhibited a remarkable enhancement in catalytic activity for methanol/ethanol oxidation compared to that of the Pt/commercial CNT electrocatalysts. In order to further investigate the potential of using BCNTs as bioelectrocatalyst support materials, a hybrid organic-inorganic nanocomposite film of BCNTs/ploymer was constructed to immobilize an enzyme horseradish peroxidase (HRP) to examine the direct electrochemical behavior of the enzyme towards electrocatalysis process of H2O2. The results indicated that the immobilized HRP onto the film retains its good bioelectrocatalytic activity to H2O2. The defective sites on the BCNTs surface induced by nitrogen doping could help to promote the direct electron transfer between enzyme and the electrode. The BCNT/polymer film structure provides a vast array of new opportunities to use BCNTs as building units for bioelectrochemical and biomedical applications. Compared to carbon nanotubes, TiO2 nanotubes have much better biocompatibility and show greater potential as implant materials. The advantages of TiO2 nanotube array include high biocompatibility, good corrosion resistance in biological environments and highly ordered one dimensional nanotubular geometry. Herein, a well performing non-enzymatic electrochemical glucose biosensor by using CuO nanoparticle decorated TiO2 nanotube array electrode was developed. Well-aligned TiO2 nanotube arrays were successfully synthesized by electrochemical anodization. Highly uniform CuO nanoparticles were electrodeposited onto TiO2 nanotube arrays through a two-step method and used to electrocatalyze the glucose oxidation. The proposed electrode produced a high sensitivity of 239.9 ìA mM-1 cm-2 and a low detection limit of 0.78 ìM with good stability, reproducibility, selectivity and fast response time, suggesting its potential to be developed as a low-cost nano-biosensor for glucose measurements in human fluids. The final work of this thesis presents a simple sandwich-type electrochemical impedance immunosensor with antitoxin heavy-chain-only VH (VHH) antibodies labeled gold nanoparticles as the amplifying probe for detecting Clostridium difficile toxins. Gold nanoparticles (Au NPs) with diameter of ~13-15 nm were synthesized and characterized by transmission electron microscopy and UV-vis spectra. The electron transfer resistance of the working electrode surface was used as parameter in the measurement of the biosensor. With the increase of the concentration of toxins from 1pg/mL to 100 pg/mL, a linear relationship was observed between the relative electron transfer resistance and toxin concentration. In addition, the detection signal was enhanced due to the amplification effect. This proposed method achieved a limit of detection for TcdA and TcdB as 0.61 pg/mL and 0.60 pg/mL, respectively. The pilot study with spiked clinical stool samples showed promising results, indicating the designed biosensor has a great potential in clinical applications.

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