The structure of layer-by-layer self-assembled glucose oxidase and Os(Bpy)2CIPyCH2NH-Poly(allylamine) multilayers:: Ellipsometric and quartz crystal microbalance studies

Self-assembled multilayers composed of alternated layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)(2)ClPyCOH](+) (PAH-Os), deposited on a 3-mercaptopropanesulfonic acid (MPS)-modified gold surface were studied ''ex situ'' and ''in situ'' (with the films in contact with water) by ellipsometry and quartz crystal microbalance (QCM). The ellipsometric parameters of the thiol film on gold in the first layer were analyzed in terms of an anisotropic single-layer model. For the subsequent (PAH-Os)(n)(GOx)(n) multilayers on An, a two-layer model with the anisotropic thiol film and the isotropic enzyme/ polyelectrolyte film yielded identical results with an isotropic one-layer model with the substrate parameters measured after thiol adsorption to offset any effect due to the Au-S bond. Film thickness and complex refractive index for each adsorbed layer in Au/MPS/(PAH-O-s)(n)(GOx)(n) multilayers were determined for dry films and for films in contact with water. Quartz crystal impedance analysis showed that the self-assembled multilayers behave as acoustically thin films (rigid), and therefore the observed shifts in the resonance frequency were interpreted in gravimetric terms. The mass of enzyme in each adsorption step was determined by the quartz crystal microbalance for both dry films and films exposed to water. From comparison of the ellipsometric thickness and acoustic mass, the average apparent film density (1.7 +/- 0.2 g cm(-3)) was estimated. A model for the enzyme and redox polyelectrolyte distribution in the (PAH-Os)(n-)(GOx)(n) multilayer structure is presented on the basis of combined ellipsometric and QCM results. A comparison of the QCM mass and the ellipsometric mass based on the de Feijter equation fails to sense the layer near the film/water interface while the acoustic method senses the coupled water and open polymer-enzyme structure at the polymer/liquid interface.