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Sequence analyses show that deletions of 10 and 12 bp occur at homologous sites in a domain that is rich in alternating purines and pyrimidines (Pu/Py) in B42 and EXT, two cloned variants of a complex satellite DNA. A 3-bp deletion occurs 27 bp upstream from the site of the specific deletions in B42 and RU, a third cloned satellite variant that has not suffered the 10-bp deletion. Under torsional stress, the Pu/Py-rich domain adopts a Z-conformation as shown by (i) inhibition of cutting at a BssHII site that accounts for built2 5 of a 15-bp tract of pure Pu/Py in the domain; (ii) binding of polyclonal and monoclonal anti-Z-DNA antibodies to the domain; and (iii) antibody stabilization and subsequent relaxation of the Z-region.

Pregnancy tests and related immunoassays are heavily dependent on specific and non-specific protein adsorption. These interfacial processes are affected by many factors that influence the in situ conformations of interfacially immobilised antibodies. This thesis examines a number of representative features with dual polarisation interferometry (DPI) and neutron reflection (NR), thus combining real-time dynamic monitoring with high interfacial structural resolution. Bovine serum albumin (BSA) was initially used as a model system to compare the surface coverage and thickness measurements of DPI and NR. The results show that DPI and NR provided similar surface coverage data but the measured thicknesses differed at BSA concentrations above 0.1 mg/ml. This discrepancy arose from the adoption of the uniform-layer model used by DPI for data analysis and the greater thickness sensitivity of NR. A model pregnancy immunoassay was built in steps on a silica surface so that the adsorption of each protein could be accurately monitored. Both DPI and NR provided evidence of BSA insertion into the gaps on the surface between the antibody molecules. This suggests that BSA adsorption is an excellent method to block the non-specific adsorption of target antigens to the immunoassay test surface. A magnetic tweezer system was designed and built in order to measure the specific antibody/antigen binding force. The antibodies and antigens were used to immuno-link magnetic beads to the experimental surface before the immuno-links were broken by increasing the attractive force between the magnetic tweezers and beads. The force per antibody/antigen immuno-link was estimated to lie between the values of 13.6 pN and 43.8 pN.Immuno-link detachment as a function of time was investigated. It was found that the immuno-link comprised both a strong and a weak interaction. The dissociation constant of the strong antibody/antigen interaction was found to equal 3E-4 /s and had an interaction length of 0.06 nm. The low population of beads bound by the second, weaker interaction meant that it was not possible to obtain accurate values of the dissociation constant and bond length of the second weaker interaction.

Existing methods for pathogen/pollutant detection or wound infection monitoring employ high-cost instruments that could only be operated by trained personnel, and costly device-based detection requires a time-consuming field-to-lab process. This expensive process with multiple prerequisites prolongs the time that patients must wait for a diagnosis. Therefore, improved methods for point-of-care biosensing are necessary. In this study, we aimed to develop a direct, easy-to-use, portable, low cost, highly sensitive and selective sensor platform with the goal of pollutant detection and wound infection/cancer migration monitoring. This study has two main parts, including microfluidic, electrical, and optical sensing platforms. The first part, including chapters 2, 3, and 4, focuses on Bisphenol A (BPA) lateral flow assay (LFA) detection; the second part, including chapter 5 focuses on the electrical sensing platform fabrication for one of the markers of inflammation, matrix metalloproteinases-9 (MMP-9), monitoring/detection. In chapters 2, 3, and 4, we found that the few lateral flow assays (LFAs) established for detecting the endocrine-disrupting chemical BPA have employed citrate-stabilized gold nanoparticles (GNPs), which have inevitable limitations and instability issues. To address these limitations, in chapter 2, a more stable and more sensitive biosensor is developed by designing strategies for modifying the surfaces of GNPs with polyethylene glycol and then testing their effectiveness and sensitivity toward BPA in an LFA. In chapter 3, we describe the development of a new range-extended bisphenol A (BPA) detection method that uses a surface enhanced Raman scattering lateral flow assay (SERS-LFA) binary system. In chapter 4, we examine advanced bisphenol A (BPA) lateral flow assays (LFAs) that use multiple nanosystems. The assays include three nanosystems, namely, gold nanostars, gold nanocubes, and gold nanorods, which are rarely applied in LFAs, compared with general gold nanoparticles. The developed LFAs show different performances in the detection of BPA. In chapter 5, a stable electrical sensing platform is developed for MMP-9 detection.