Abstract
Quartz Crystal Microbalance (QCM) was used in monitoring the DNA adsorption kinetics by cationic lipid nano-disc bicelles supported by silicon dioxide substrate. Atomic Force Microscope (AFM) was also used in examining the surface morphology of the substrate with adsorbed DNA. The nano-disc bicelles were formed by mixing long-chain lipid DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) with the short-chain lipid diC7PC (1,2-diheptanoyl-sn-glycero-3-phosphocholine), and doped with different amounts of cationic lipid DC-Cholesterol. By doping cationic lipids from 15% to 50% of the long chain lipids, only single layer of bicelles are adsorbed on the silicon dioxide surface with a surface coverage of from 71% to 77% as estimated from the adsorbed mass. As for the DNA adsorption by bicelles, it is found the adsorption process can be divided into three distinctive stages. In the beginning, there is a very fast adsorption stage lasting for about 30 seconds to reach about 15% to 50% of the equilibrium values for 15% to 50% DC-Cholesterol doped bicelles. This fast adsorption stage is followed by a much slower adsorption stage for a few minutes. It is likely that the DNA adsorbed in the fast adsorption stage need to rearrange their distribution on the surface to form more ordered and compact structure. Finally a slow adsorption stage will lead to the equilibrium state in about 30 minutes. For the fast adsorption stage, the DNA adsorption rate constant is higher for higher charge doping percentage bicelles and also for longer DNA. For the second and third adsorption stages, the DNA adsorption rate constants may differ from each other but are all similar.