Date of Award


Document Type

Master Thesis

Degree Name

Masters of Science (Research)


Department of Applied Physics and Instrumentation

First Advisor

Dr. Liam McDonnell


The overall aim of this thesis was twofold. Firstly, to evaluate how scanning force microscopy (SFM) could be used to characterise the surfaces of immunosensors. Four aspects of immunosensor characteristics where SFM has particular application potential have been identified: (a) immobilisation chemistry and (b) the surface density, (c) orientation and (d) specificity of the immobilised antibodies. Secondly, to examine experimentally how the Explorer SFM instrument could be used for such characterisation.

The Explorer SFM instrument is of an open-loop actuator design that is exposed to the intrinsic inadequacies of piezoelectric actuators. In this regard, careful calibration has shown that achieving high accuracy long-range height measurements with the Explorer is particularly problematic when the actuator involved is used away from its mid-range position. However, data has been obtained that enables these effects to be quantified.

The Explorer has been used to image different immunosensor surfaces and the solid supports on which they were built. The topographies of evaporated gold supports and the immobilised antibodies were similar and nanogold conjugates were needed to validate the presence of the antibodies. When immunosensors were built on smooth silicon wafers the antibodies could be unambiguously imaged. The Explorer was able to provide information on the surface density and a real distribution of antibodies. In agreement with the literature, the Explorer could not directly identify by imaging antibody orientations within immunosensors. However, indirect information on antibody orientation could be inferred by imaging nanogold conjugates that had been bound to the antibodies. Another method to determine orientation, that can also be used to determine specificity, uses force spectroscopy with biospecific SFM tips. Whilst the Explorer was shown to be very capable of force spectroscopy it was found to suffer from a level of drift that prevented the crucial correlation between force spectroscopy data and image topography.

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