Model experiments with integrated optical input grating couplers as direct immunosensors.

Using an input grating coupler instrument and monomode optical waveguides, we studied the adsorption of various proteins (e.g. human immunoglobulins G and A (h-IgG and h-IgA), and avidin) on the waveguide surface. In model experiments for immunoassays, we also monitored as a function of time the formation of time formation of the immuno-complex Ag-Ab between antigen (Ag) molecules absorbed on the waveguide surface and antibody (Ab) molecules, for example, of adsorbed h-IgG vs anti-h-IgG, anti-goat-IgG (cross-reaction) and anti-h-IgA (negative test). We also studied the affinity reaction between adsorbed protein A and h-IgG. From the measured changes in the effective refractive indices N(TE0) and N(TM0) of the TE0 and TM0 modes, we determined the thickness dF, the refractive index nF, and the surface coverage gamma of the absorbed protein adlayers and of the immuno-complexes.