ASSEMBLY OF ALTERNATING POLYELECTROLYTE AND PROTEIN MULTILAYER FILMS FOR IMMUNOSENSING .2.

Alternating polyelectrolyte films constructed by the sequential adsorp tion of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate ) (PSS) have been used as substrates for the immobilization of immunog lobulin G (IgG) and anti-IgG. Anti-IgG has also been immobilized in mu ltilayer films by the alternate deposition of PSS and anti-IgG. The as sembly process of the multilayer films was monitored using a quartz cr ystal microbalance (QCM) and surface plasmon resonance (SPR). Film gro wth was achieved up to at least nine (5 anti-IgG and 4 PSS) layers. Th e utility of these films for immunosensing has been investigated via t heir 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 dete ction. The sensitivity, determined using IgG mass uptake data from qua rtz 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 separa ted by five polyelectrolyte (PSS(PAH/PSS)(2)) layers, only the outer a nti-IgG layer is immunologically active. This is attributed to the for mation of a dense polyelectrolyte film through which antibody permeati on is restricted. The films evaluated have promise in that the sensiti vity can be tuned by fabricating the desired number of protein layers, whilst the selectivity can be modified by selecting the desired biosp ecific biomolecule.