Patterned and switchable surfaces for biomaterial applications

Chapter 3 – Comparison of the binding mode of plasmid DNA to allylamine plasma polymer and poly(ethyleneglycol) surfacescrystal/solution system to alter the sensitive frequency of the crystal. A DNA of 1.02mg/m 2 was reached after approximately 2000 s (Figure 3.2). According to the K and s∞ values for DNA adsorption to ALAPP determined under equivalent pH, saltconcentration and DNA concentration (200 ng/ml) by measurements of the depletionof solution fluorescence, a DNA of 1.20 mg/m 2 is predicted, which is slightly greaterthan the DNA measured by QCM. The reason for this difference could be the resultof a second slow step in the adsorption of DNA not measured over the time course ofthe QCM experiment.The QCM measurements also enable the analysis of the kinetics of DNAadsorption onto the ALAPP surface. The adsorption trace shown in Figure 3.2display simple Langmuir kinetics with an initial exponential increase in DNAadsorption, plateauing off to a maximum value that is achieved after about 2000 s. Asimilar result has been previously reported by Zhang et al., for DNA adsorption toALAPP achieved by surface plasmon resonance studies [36]. For comparison, kineticmeasurements of DNA adsorption were also undertaken by measurements of thedepletion of solution fluorescence. The results are shown in Figure 3.3. The shape ofthe adsorption time curve is similar to the time curve obtained from QCMmeasurements for low concentrations of DNA. An initial sharp increase in DNA wasobserved followed by a much slower rise. These results suggest a two-step DNAadsorption process; an initial fast DNA uptake followed by a slower rearrangementof surface bound DNA allowing for further, but kinetically much slower, DNAadsorption. The negative charge of DNA would mean that once a DNA strand hadadsorbed, further DNA adsorption on this site would be unfavourable due toelectrostatic repulsion. A two-step process would fit with this model. Such a processhas been previously reported [22].3-112