Poly(ethyleneimine) cross-linked multilayers deposited onto solid surfaces and enzyme immobilization as a function of the film properties

Single polycation cross-linked multilayers, based on poly(ethyleneimine) (PEI), have been prepared using a method of 3,3′,4,4′-benzophenonetetracarboxylic-dianhydride (BTCDA)-mediated electrostatics and hydrogen bonds layer-by-layer assembly. Linear PEI [PEI(L)] and branched PEI [PEI(B)] were adsorbed from salt-free aqueous solutions, either onto silica microparticles with particle diameter of 40–60 μm (Daisogel type) and 9–11 μm (Davisil type) or silicon wafers. The BTCDA cross-linking of the polycation adsorbed onto the solid surface results in a surface covered with carboxylic groups. The cross-linked polycation layers, which are negatively charged over a wide range of pH, can adsorb a new positively charged polyelectrolyte layer. A regular increase of the single polycation multilayers onto silica microparticles was observed by zeta potential measurements and X-ray photoelectron spectroscopy. The immobilization of two enzymes (pepsin and lysozyme) onto the functionalized silica surface, via glutaraldehyde (GA), has been tested. The amount of the attached enzyme significantly depended on the isoelectric point of the enzyme. Surface characteristics, average height, ha, and average roughness, Ra, slightly increased after each modification step of the organic film.