Integrated optical difference interferometer as immunosensor

We have used an integrated optical difference (or polarimetric) interferometer as an immunosensor. The goat anti-rabbit IgG antibodies are immobilized on a planar SiO2-TiO2 waveguide as receptor layer. The corresponding ligand, the antigen rabbit IgG in the sample solution, is selectively detected in sub-nanomolar concentrations in less than 10 min. The following technique for immobilizing the antibody leads to a stable receptor layer: the waveguide is first coated with avidin by adsorption, as avidin adheres well on it; in a second step, the biotinylated antibodies are bound irreversibly to the avidin layer by the strong avidin-biotin affinity binding.