Adsorption of polyethylenimine and its interaction with a genomic DNA on a silicon oxynitride surface characterized by dual polarization interferometry

Abstract

Dual polarization interferometry was used to investigate the adsorption of polyethylenimine (PEI) on a silicon oxynitride chip surface, as well as to study the subsequent interaction between PEI and a genomic DNA. A compact homogeneous PEI layer formed initially as a result of their strong electrostatic attraction to the negatively charged chip surface. With the adsorption going on, a short time adsorption process with constant speed was observed and the subsequent PEI molecules loosely attached on the chip surface because of the electrostatic repulsion and crowded surface conditions. A loose and thick DNA layer formed on the PEI surface due to its rigidity. Further PEI deposition induced DNA conformation changes and the swelling of the PEI–DNA complex layer, which resulted in a dramatic layer thickness increase. Under high PEI concentration, the layer mass and thickness increments were partially lost as DNA was stripped off by PEI molecules. This result was interpreted in terms of overcharged DNA–PEI complex formation and the strong electrostatic repulsion between the first PEI layer and the newly formed overcharged DNA–PEI complexes. The explanation was proved by the case of the assembly process in PBS. No stripping effect was found even at a high PEI concentration in PBS because of the salt screening effect and the low charge density of PEI.