Output grating couplers on planar optical waveguides as direct immunosensors.

We demonstrated the feasibility of using integrated optical output grating couplers in direct immunosensing. We monitored as functions of time, first the adsorption of an antigen (Ag) on the waveguide's surface, and subsequently, the binding of the corresponding antibody (Ab), i.e. the formation of the immuno-complex Ag-Ab. The Ag was human immunoglobulin G (h-IgG), and the Ab was rabbit anti-h-IgG. We also studied the adsorption of avidin. The refractive indices nF', thicknesses dF', and surface coverages gamma of the adsorbed adlayers and of the immuno-complex Ag-Ab, respectively, were determined.