Model experiments with integrated optical input grating couplers as direct immunosensors

Abstract

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 the immuno-complex Ag-Ab between antigen (Ag) molecules adsorbed 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(TE 0) and N(TM 0) of the TE 0 and TM 0 modes, we determined the thickness d F′, the refractive index n F′, and the surface coverage Γ of the adsorbed protein adlayers and of the immuno-complexes.