Patterned and switchable surfaces for biomaterial applications

Chapter 1 - Introductionmorphology of adsorbed dsDNA could be changed by application of an increasedmagnitude of positive voltage.Heller et al., [92] utilised the electro-responsive nature of DNA to formswitchable checkerboard patterns of fluorescently labelled DNA on a microelectronicchip (Figure 1.6). By application of the appropriate positive and negative voltagesDNA became spatially confined and a pattern was formed (Figure 1.6B). The inversecheckerboard pattern was formed by reversing the polarity of the applied voltage,and this reorientation was complete after 7 s (Figure 1.6D). Analysis of thestringency of DNA hybridisation was also achieved by controlling the surfacediffusion of DNA oligonucleotides to move, on demand, over different regionsfunctionalised with complementary or slightly mismatched oligonucleotides. Gilleset al., [93] used this technology to study single point mutations along the encoding ahuman mannose binding protein. Point mutations on genes are stable and cancontribute to genetic disorders. Detection of a single point mutation is difficultconsidering the vast number of base pairs within any given genome. Gilles et al., [93]immobilised a number of different single stranded 123 bp oligonucleotide fragmentsof the allele of a mannose binding protein gene that differed by single pointmutations at different sites on a 5 x 5 microelectronic chip array by streptavidinbiotininteractions. Application of a positive voltage at a particular site directed theimmobilisation of each strand to a desired location. 21 or 22 bp oligonucleotideprobes specific for the wild type allele or specific for a particular single pointmutation were injected into the system and allowed to hybridise with immobilisedDNA strands. By application of a negative voltage at a specific site the mismatchedprobe DNA could be driven away, whereas complementary probes would stay1-32