Integrated-optical and surface-plasmon sensors for direct affinity sensing .2. Anisotropy of adsorbed or bound protein adlayers

The theory of sensitivities of integrated-optical (IO) and of surface-plasmon resonance sensors used for real-time analysis of adsorption processes or of binding reactions in affinity sensing given previously for an optically isotropic adlayer formed by the adsorbed or bound molecules (Lukosz, 1991) is extended to anisotropic adlayers. The anisotropy of a (sub-)monomolecular adlayer of (protein) molecules on the sensor surface, caused by their nonspherical (e.g., ellipsoidal) shape and preferential orientation, is described by Maxwell-Garnett theory. The analyses of adsorption or binding processes monitored with IO grating-coupler sensors, not only yield results for the thickness and refractive indices and the surface mass density of the adlayer, but can also give some information about the shape and orientation of the adsorbed or bound molecules. (C) 1997 Elsevier Science Limited.