Surface modification for direct immunoprobes

The modification of glass-type surfaces by several hydrophilic polymers of different molecular masses and functional properties [chitosan, dextran, poly(oxyethylene), poly(ethyleneimine) and poply(acrylamide)] with respect to the application for direct immunoprobes was investigated. Activation of the surface was carried out by silanisation and the polymers were coupled to the surface via amide bonds. The carboxyl derivative of a hapten was attached to the functional groups of the polymers by carbodiimide-activated coupling. As a reference system, the ligand was directly coupled to the silanised surface. Non-specific protein adsorption, specific binding of antibodies and regeneration were monitored by evaluation of reflectance spectra obtained by white light interference at a thin silica layer (RifS). All polymer modified layers showed improved properties compared to those with direct attachment of the hapten. The non-specific adsorption was reduced to 5-50%. Binding of a specific antibody was significantly increased by the polymer modification: Mass transport limited binding of the specific antibody in low concentrations (30 nM) up to a surface coverage value of 2 ng/mm2 and a maximum surface coverage in the range of a monolayer of IgG (5-6 ng/mm2) was observed for most of the polymers. The surface coverage found for IgG bound specifically to the dextran-modified surface exceeded a protein monolayer.