The Structure of Layer-by-Layer Self-Assembled Glucose Oxidase and Os(Bpy)₂ClPyCH₂NH−Poly(allylamine) Multilayers:  Ellipsometric and Quartz Crystal Microbalance Studies

Abstract

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.

Form and Function in Multilayer Assembly: New Applications at the Nanoscale

“…[28,29] More recent developments include complete sensor arrays, which have been created on patterned electrodes to create high reliability detection utilizing the multilayer approach; [30] arrays were patterned onto silicon and flexible Mylar substrates. The resulting sensors, which have been designed for lactose, glucose, and pyruvate based on the use of the corresponding enzyme within the multilayer film, exhibit high sensitivity between 0 and 2 mM, beyond which saturation takes place.…”

Charge Transport in Redox Polyelectrolyte Multilayer Films: The Dramatic Effects of Outmost Layer and Solution Ionic Strength

“…The idea of z-dependent properties in polyelectrolyte multilayers has been suggested before with different properties in different regions of the polyelectrolyte multilayers. [56][57][58] Such is the case for a more dense first layer at the film/substrate interface in polymer/ enzyme multilayers [59] or the existence of an inhomogeneous proton concentration profile reported by von Klitzing and Mçhwald for LbL films. [60] The exact functionality of E 0,app (z) is unknown at present, However, we have used in the present work a very simple three-adjustable-parameter function [Eq.…”

SERS in PAH-Os and gold nanoparticle self-assembled multilayers

“…Hodak et al 5 introduced redox enzymes deposited with a polycationic redox mediator in ordered multilayers using this technique and the redox mediation of glucose oxidase in self-assembled structures formed with the enzyme and poly͑allylamine͒ modified with Os͑byp͒ 2 ClPyCHO ͑PAH-Os͒ has been studied. 6,7 The assembly of derivatized gold nanoparticles with polyelectrolyte self-assembled multilayers has been studied by Song et al,8 in particular as regard the directional electron transport. The incorporation of biomolecules with direct electrical contact to nanoparticles has been introduced by Xiao et al by wiring glucose oxidase to Au nanoparticles.…”

“…The incorporation of biomolecules with direct electrical contact to nanoparticles has been introduced by Xiao et al by wiring glucose oxidase to Au nanoparticles. 9 Different techniques have been applied for the study of these self-assembled nanostructures, including ellipsometry, 7 quartz-crystal microbalance, 7 electroacoustic admittance in thickness shear mode resonators, 6 cyclic voltammetry, 10 and infrared reflection-absorption spectroscopy. 11 In a previous work we have studied the vibrational and electronic structure of PAH-Os selfassembled multilayers with Raman spectroscopy and in situ electrochemistry.…”

“…7,11,23 The substrates consist of gold films ͑ϳ150 nm thick͒ evaporated on Si͑001͒ wafers. The adsorption time for each component, thiol, polymer, and gold nanoparticles were determined by a preliminary quartzcrystal microbalance study.…”