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.