The Use of Nanostructures in Bioelectronics

Casey, Brendan George (1999) The Use of Nanostructures in Bioelectronics. PhD thesis, University of Glasgow.

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This thesis describes research performed to investigate the use of nano and microstructures in bioelectronics. The nanofabrication techniques and developed processes are presented first in conjunction with the application design ideas at each stage. The results obtained by the application of these devices in bioelectronics are then described. The two application areas for nanotextured devices presented in this thesis are biological cell adhesion and DNA sequencing. The nanostructure fabrication processes used throughout this project were electron beam lithography, reactive ion etching, electroplating and anodic bonding. These techniques have been used either to directly fabricate a working device or as donor processes for mechanical pattern transfer technology. The mechanical pattern transfer fabrication process developed for biological applications was based on polymer substrates and embossing to produce working devices from a nanofabricated master die. Three other novel polymer patterning procedures are presented in this thesis. It is shown that it is possible to pattern cellulose acetate using deep ultra violet exposure and that when applied to a previously embossed plastic substrate, it is possible to produce multilevel polymer devices. It is also shown that using electron beam lithography, solid sheets of polymethylmethacrylate can be patterned thus producing working devices in a single step. Following on from this, such perspex samples have been used as soft embossing masters for the fabrication of polystyrene devices. Using the nanofabrication techniques developed during the course of this work, fractionating chambers for the direct, real time observation of migrating DNA molecules have been fabricated. The driving force behind this work was the Human Genome Project which is concerned with the mapping of all the genes in the human nuclear genome. The benefits of knowing this information are extensive, from applications in cloning to the discovery of which genes are responsible for hereditary illnesses and traits. However, the current method for sequencing the genetic code contained within DNA of gel electrophoresis is far from optimal and is very slow. Therefore, we have designed and fabricated a system on a chip which should be capable of rapid, high resolution DNA sequencing. The device works by passing the DNA molecules through an environment which presents different levels of retardation to molecules depending on their size. The genetic code contained within the DNA strands can then be calculated by comparing molecular migration rates. The DNA is moved through the device by an electric field using a process known as electrophoresis. The devices used to analyse DNA motion under electrically induced migration were initially fabricated in SiO2 using e-beam lithography and C2F6 reactive ion etching. They were then sealed using anodic bonding to produce a hermetic flow chamber for molecular observation. These samples consisted of 500nm diameter pillars on a 1mum pitch in arrays of 7,840,000 structures. The function of the pillar elements was to act as a retarding environment to DNA molecules which were passed through the chamber using electrophoresis. The migrating DNA was stained with ethidium bromide and observed using fluorescence microscopy. The conformational changes that the migrating molecules exhibited were compared to those predicted by the biophysical theory of DNA migration and a suitable geometry capable of producing highly dispersive mobilities was mathematically and electrostatically modelled. The geometry which produced the desired response was found to be an array of 'U' shaped elements. Devices consisting of such features were fabricated using our embossing technique with the polymer cellulose acetate as the substrate. The DNA migration was again visualised using fluorescence microscopy and the results obtained with these devices are presented. Biological cell adhesion to surfaces is an extremely important phenomenon in tissue and vascular repair. It is critical that platelet cells do not adhere to the inside of a plastic tube used to replace a diseased vascular section. The mechanisms for cell adhesion have been studied for many years, however the influence of topographical cues on adhesion is still uncertain. Cell adhesion to a surface is strongly affected by the roughness of that surface. However, studies into the effect of rugosity are inconclusive, mainly due to the difficulty in characterising such surfaces. In this work, the embossing technique utilising perspex and silicon master samples was used for the fabrication of substrates to examine biological cell adhesion to rough surfaces. We fabricated large areas of 15nm and 60nm pillars which presented cells with a quantifiable surface roughness. These devices were made in cell culture grade polystyrene and cell adhesion to nanotextured areas was compared with that for smooth unpattemed areas. The results for such devices are presented and a mechanism for the cellular reaction is suggested.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Chris Wilkinsons
Keywords: Electrical engineering, Nanotechnology
Date of Award: 1999
Depositing User: Enlighten Team
Unique ID: glathesis:1999-76203
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 16:29
Last Modified: 19 Nov 2019 16:29

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