Patterned and switchable surfaces for biomaterial applications

Chapter 1 - Introduction1.4.1. DNA microarraysVast amounts of research have been conducted with DNA microarrays and haveproven to be of paramount importance in the areas of cancer research and othergenetic based diseases. In fact, DNA microarray based research is an integral part ofmany physiological based research and has revolutionised genomic studies, whichpertains not only to oncology but also neurology, pathology, psychology,pharmacology, pharmacogenomics and toxicogenomics, to list a few.There are three methodologies utilised for DNA microarray formation. The firstmethod is contact printing, achieved by dipping an array of pins into defined samplesolutions and then, by use of high precision robotics, bringing the pins in contactwith a substrate, with the formation of spots as sample solution is transferred fromthe pin to the substrate (see section 1.2.5). DNA is typically immobilised to a surfaceby either covalent interactions, such as immobilisation of thiolated ssDNA to goldsurfaces, or non-covalent interactions such as adsorption of DNA to aminefunctionaised surfaces or interactions of biotin labelled ssDNA with surfaceimmobilised avidin. Various studies have sought to control the density ofimmobilised DNA in order to optimise DNA hybridisation whilst seeking tominimise non-specific DNA adsorption [120-122]. The surface energy of thesubstrate material is an important factor determining how the surface wets, spreadsand dries. Although microarray formation is commonly done on glass, lack ofreproducibility in spot formation has led to efforts attempting to produce variedsurfaces with desirable surface energies that produce more reproducible spots [123].One such method is the formation of a mixed SAM containing different ratios ofalcohol and methyl terminated alkanethiols. SAMs are well known for their ability toproduce regular, reproducible, defect free films [124]. Optimisation of surface energy1-42