(16c) Diffusive Behavior of DNA Adsorbed on Lipid Bilayers Supported on a Glass Substrate

We have investigated the diffusive behavior of DNA on supported lipid bilayers with different charge densities and solution ionic strengths. In our experiments, DNA was adsorbed on positively charged lipid bilayers deposited on a glass substrate, and its conformation and diffusion were observed by a fluorescence microscope. We found that DNA conducts a simple diffusion over a long lag time but a sub-diffusion over a short lag time. The sub-diffusion behavior was highly related to the presence of some unexpected “sticky points” where DNA segments were confined for a relative long period of time. We also found that the diffusivity of DNA significantly decreases with charge density of bilayers but increases with the ionic strength of the solution. However, the diffusivity of the lipids was fairly independent from the lipid charge density and solution ionic strength. Therefore, the drastic change in DNA diffusivity is not due to the change of lipid mobility. We speculated that all these phenomena are related to the presence of the sticky points. We hypothesized that the sticky points are electrostatic potential wells resulting from the local defects of the glass substrate. In order to verify this potential well hypothesis, we employed a different positively charged lipid that is expected to reduce the potential wells and thus weaken the effect of “stick points”. The experimental data supports our hypothesis and also agrees with our own simulation results.