Alternating polyelectrolyte films constructed by the sequential adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) have been used as substrates for the immobilization of immunoglobulin G (IgG) and anti-IgG. Anti-IgG has also been immobilized in multilayer films by the alternate deposition of PSS and anti-IgG. The assembly process of the multilayer films was monitored using a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). Film growth was achieved up to at least nine (5 anti-IgG and 4 PSS) layers. The utility of these films for immunosensing has been investigated via their subsequent interaction with IgG. The alternating polyelectrolyte/protein layers were constructed in order to increase the binding layer capacity (i.e. sensitivity) of the thin film with respect to IgG detection. The sensitivity, determined using IgG mass uptake data from quartz crystal microgravimetry, was found to be linearly dependent on the number of anti-IgG layers (and hence the amount of IgG incorporated) in the polyelectrolyte film when the anti-IgG layers are separated by one PSS layer. In contrast, for films where anti-IgG layers are separated by five polyelectrolyte (PSS(PAH/PSS) 2) layers, only the outer anti-IgG layer is immunologically active. This is attributed to the formation of a dense polyelectrolyte film through which antibody permeation is restricted. The films evaluated have promise in that the sensitivity can be tuned by fabricating the desired number of protein layers, whilst the selectivity can be modified by selecting the desired biospecific biomolecule.

Thin organic films fabricated by the successive deposition of the polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) have been successfully grown up to 24 layers on gold surfaces. These films are formed via electrostatic attraction between adjacent layers of opposite charge. Their construction has been examined using a quartz crystal microbalance (QCM), reflection spectroscopy (RS), surface plasmon resonance (SPR), and X-ray photoelectron spectroscopy (XPS). The thickness of the multilayer assemblies increases with the number of adsorbed layers, although a linear increase is observed only after the deposition of four polyelectrolyte layers ((PAH/PSS) 2). The (PAH/PSS)2 film facilitates regular, stepwise deposition of subsequent PAH and PSS layers. The thickness of (PAH/ PSS)2 on gold was determined independently by QCM, SPR, and XPS to be 7.9 ( 0.6 nm. The PAH/PSS layer pair thickness after regular film growth was calculated to be 10.0 ( 0.8 nm. The formation of these thin films on gold surfaces opens the possibility of constructing supramolecular assemblies for use in the areas of biological and chemical sensing.

Protein-containing polyelectrolyte multilayer films of poly(styrenesulfonate) and poly(allylamine hydrochloride), fabricated by the sequential adsorption of polyelectrolyte and anti-immunoglobulin G (anti-IgG) on solid substrates, have been characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), and Fourier transform infrared reflection-absorption spectroscopy (FTIR-RAS). Visualization of the film structure on the nanometer scale, by AFM and SEM, showed that either layered or disordered films were formed depending on the number of polyelectrolyte layers separating each protein layer. For films where each anti-IgG layer was separated by one polyelectrolyte layer, an open, disordered film structure was observed and significant protein aggregation occurred. In contrast, for films in which the anti-IgG layers were separated by five polyelectrolyte layers, a layered structure with uniform protein layers was formed. Film thicknesses determined by SEM measurements were consistent with those calculated from quartz crystal microbalance measurements. FTIR-RAS confirmed the presence of anti-IgG in the multilayer films, with the amide I and II bands due to anti-IgG clearly visible in the spectra, and provided direct evidence that anti-IgG was not denatured. Both types of films fabricated are interesting for biosensing applications: the first provides ordered, functional protein layers within a polyelectrolyte matrix for sensing investigations, and the second serves as a useful functional film for applications where an increased binding capacity of the film is sought.