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Title: Towards the development of one dimensional zinc oxide nanostructures as biosensor
Author: Tan, Michelle Tien Tien
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2009
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The ability to detect biomarkers at a molecular level is crucial to ensure high survival rates for patients with debilitating or life threatening diseases, for example cancer. The limitation associated with existing detection technologies call for more sensitive, selective, faster, cheaper and smaller biosensors for molecular analysis. Recent material advances made in One-dimensional (1-D) ZnO nanostructures hold great promise for fabricating the next generation of biosensors. Due to very high surface- to-volume ratios, they demonstrate high sensitivity to surface charge transfer and changes in the surrounding electrostatic environment, resulting in the significant modification of conductivity upon adsorption of certain molecules. By combining nature's bio-recognition functionalities with the nanostructure's novel electronic properties, an ultra-sensitive and selective biosensor can be developed. The first part of the work compares the electrical behaviour of 1-D ZnO nanostructures grown via hydrothermal and chemical vapour deposition (CVD) techniques, using the scanning conductance microscopy (SCM). For the first time, the polarisability of CVD grown 1-D ZnO nanostructures was observed. By using polarisability as a qualitative measure of the carriers' mobility, CVD nanostructures are shown to exhibit better carrier mobility and thus are more electrically active than hydrothermal ZnO nanorods. Hydrothermal synthesised ZnO nanostructures have higher defect density, generally oxygen vacancies, due to low oxygen concentration in the water and low temperature growth. The oxygen vacancies, known to be deep level traps, are believed to be the reason why the ZnO hydrothermal sample is less 'electrically active'. The successful implementation of biosensors is strongly related to the interface between the biological recognition system and the nanostructure. A surface plasmon resonance technique (Biacore X) is used to identify functional groups that show strong surface binding to ZnO. The respective binding of hexahistidine and zinc finger moieties to ZnO surface was investigated. For the first time, ZnO nanoparticles were discovered to bind directly to nitrilotriacetic acid (NTA), an aminotricarboxylic acid, pre-immobilised on a sensor chip. Subsequently, beta-cyclodextrin (betaCD) was modified with an NTA-like moiety to form a NTA-linked bioreceptor mimic. Analysis results revealed that NTA-like moiety significantly increased the ability of the native cyclodextrin to bind to the surface of ZnO nanoparticles. Following that, polyglutamic acid was shown to be an excellent intermediate between biological molecules (antibody) and ZnO surface. Employing polyglutamic acid as the intermediate linker between antibody and ZnO surface is novel and is recommended for the fabrication of future generation biosensor.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available