Patterned and switchable surfaces for biomaterial applications

Chapter 2 – Spatially controlled electro-stimulated DNA adsorption and desorption for biodeviceapplicationsfor the adsorption of DNA to a surface has been previously studied [20] where thedriving force for adsorption was proposed as the entropically favourable dehydrationof the surface. However, for the ALAPP surface, electrostatic interactions also needto be considered.The adsorption of DNA was enhanced by the application of a positive voltage(Figure 2.7), where an increase in DNA from 0.4 mg/m 2 for spontaneously adsorbedDNA to 1.0 mg/m 2 for the electro-stimulated adsorption of DNA was observed.Maximum DNA was typically attained at +1 V, whereupon the application of highervoltages showed no further increase in DNA adsorption, suggesting that saturationwas reached. The increase in DNA observed (0.4 mg/m 2 to 1.0 mg/m 2 ) implies that arearrangement of the adsorbed DNA has taken place in order to accommodate ahigher DNA coverage. The existence of two or more different configurations of theabsorbed DNA layer is also consistent with the observed decrease in DNA from 1mg/m 2 to 0.8 mg/m 2 once the voltage was no longer applied (Figure 2.7), suggestingthat the formed DNA layer was, at least in part, unstable, and could revert to a lowerdensity configuration. The process of DNA adsorption onto ALAPP may be drivenby the electrostatic repulsion between adjacent DNA strands. This result alsodemonstrates the DNA constraining properties of a positively biased surface. Theresulting DNA layer had a greater DNA of 0.8 mg/m 2 than after spontaneousadsorption, further suggesting that the application of the positive voltage biasrearranged the initial DNA layer to a high density configuration.A decrease in DNA as a result of the fast electro-stimulated desorption of DNAfrom the surface, where desorption occurred within 2 min, was observed with theapplication of negative voltages above -250 mV (Figure 2.7). The initial applicationof -250 mV did not alter the DNA , implying that the attractive electrostatic2-88