Patterned and switchable surfaces for biomaterial applications

Chapter 3 – Comparison of the binding mode of plasmid DNA to allylamine plasma polymer and poly(ethyleneglycol) surfacesconcentration of the adsorbed species, K is the equilibrium constant, s is thesurface concentration of the adsorbed species at saturation and C is the concentrationof the adsorbing species in the bulk solution. s KC s1 KC(3.3)Equation 3.3 was used to model the system and for the determination of values ofK and s using KaleidaGraph 4.0. Equation 3.3 can be rearranged to equation 3.4 byplotting the reciprocal of s against the reciprocal of C, whereupon a linear resultsuggests compliance with the Langmuir model [22].1 1 sK sC 1(3.4) s3.2.6. ElectrostimulatedDNA adsorption and desorptionQuantitative studies of DNA adsorption were conducted in a custom-builtelectrochemical cell as described previously [124]. ALAPP or PEG samples wereclamped into the cell and 2.4 ml of 100 ng/ml pEGFP-N1 solution in 0.01 Mphosphate buffer containing 1.0 M NaCl, pH = 7.4 was added over the sample. After24 hr incubation at room temperature, a voltage was applied in a stepwise fashion(+1.50 V, 0.00 V, -0.75 V) over consecutive 2 min intervals with the substrate as theworking electrode, an Ag/AgCl/saturated KCl reference electrode and a platinumauxiliary electrode. The voltages used were optimised previously on ALAPP films[34]. The DNA concentration of the solution was determined using the fluorescentPicogreen ® probe according to the manufacturer’s specifications before and aftereach voltage application. Solution removed for DNA concentration analysis wasreplaced with fresh PBS. Fluorescence measurements were performed using a LS 55Luminescence Spectrometer (Perkin Elmer Instruments).3-106