Patterning biomolecules using AFM charge-writing on polymeric and silicon dioxide substrates

Electrostatic interactions are common-place in biological processes with biomolecules typically charged in solution. In this thesis electrostatic forces were used for the spatial manipulation of biomolecules by driving their attachment to surfaces patterned with localised charges. Charge-patterns can be created on dielectric materials using Atomic Force Microscope Charge-Writing and imaged by Kelvin-probe Force Microscopy with a resolution of one hundred nanometres. There are a wide variety of materials that can be used for charge-patterning including polymers such as poly (methyl methacrylate) (PMMA) and polystyrene (PS), which are also commonly used in nanofabrication and in biological environments. Silicon dioxide is also well known for its charge storage capabilities. Since it is a key material for microfabrication and electronic devices, achieving controlled attachment of biomolecules on its surface would have far-reaching applications for the development of novel biosensors. The charge-pattern stability on PMMA, PS and Si02 was investigated regarding their preparation and the surrounding media. The charge-patterns were subsequently used to localise biomolecular attachment. The biomolecules were enclosed in water droplets dispersed in a dielectric oil to pre- vent the rapid decay of charge-patterns in an aqueous environment. The droplets were attracted electrostatically to the charge-patterns. After removing the liquid, the contents of the droplets remained localised on the surface and a resolution of approximately 1 fim was achieved. To illustrate the repeatability of the process, different types of biomolecules commonly used in immunoassays were patterned on silicon dioxide: mouse immunoglobulin G, rabbit immunoglobulin G and biotinylated bovine serum albumin. The multiprotein array thus produced wTas tested by immersing it in a solution containing three different fluorescently labelled biomolecules, each exhibiting specific, biomolecular interaction to the deposited ones. The discrimination from the mixture of these secondary biomolecules by antibody-antibody or biotin-avidin interactions confirmed the functionality and high selectivity of the patterned array