Patterned and switchable surfaces for biomaterial applications

Chapter 1 - IntroductionIn general, higher salt concentrations and lower pH increase the propensity forDNA adsorption and likewise, low salt concentration and high pH both increase thepropensity for DNA desorption [20, 23, 24]. This is a result of two effects. First,under high salt concentration or low pH the strength of the DNA-surface electrostaticinteractions can be increased by enhancing the cationic character of a surface anddampening the anionic character of DNA, which allows the DNA to proceed closeenough to the surface for hydrophobic interactions to occur. Second, and morecommonly observed with the use of cationic ions with a high valency of typically +3or more, individual DNA strands are compacted due to neutralisation of repulsiveelectrostatic forces between adjacent phosphate groups, resulting in more compactDNA molecules and, therefore, the scope for higher surface coverage of DNA ( DNA )[25, 26].Electrostatic interactions with DNA have been the primary focus in studies wherethe adsorption of DNA and its manipulation was desired. The formation of positivelycharged surfaces is often employed for DNA adsorption experiments. This iscommonly achieved by the production of amine rich surfaces, which are typicallyprotonated at neutral pH, and have been shown to increase the DNA [27]. The ease offormation of strong DNA-surface interactions using aminated surfaces wherehybridisation can still proceed [28] makes this an attractive approach for microarrayapplications as opposed to covalently immobilising DNA. A common strategy for theformation of aminated surfaces is silanisation of glass [9, 24, 28-30]. Aminatedsurfaces have also been produced by the adsorption of cationic molecules such aspoly(ethyleneimine) (PEI) [31] or poly(L-lysine) (PLL) [32] and plasmapolymerisation [33-37]. For a comprehensive review of plasma polymerisation seereference [38]. Interestingly, Saoudi et al., [27] reported the adsorption of DNA to1-8