Self-assembled multilayers composed of alternated layers of glucose oxidase (GOx) and poly(allylamine) covalently attached to [Os(bpy)2ClPyCOH]+ (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 Au, 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−Os) 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.

Ellipsometric parameters of layer-by-layer self-assembled osmium complex-derivatized poly(allylamine) and glucose oxidase multilayers, (PAH-Os) n (GOx) n , were measured at different wavelengths during oxidation−reduction cycles. Data were analyzed using an isotropic single layer model for the enzyme films. The changes in film thickness and refractive index during cyclic voltammetry and potential square wave experiments arise from redox modulation causing film swelling due to the exchange of anions and solvent with the bathing electrolyte. These changes correlate well with the fraction of oxidized PAH-Os(III) in the film.

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Construction and characterization of structural and charge transport properties of electrostatically LbL self-assembled multilayers of gold nanoparticles and a viologen-based redox-active polyelectrolyte is reported.