Antibody binding on LiNbO3:Zn waveguides for biosensor applications

In order to develop biochemical optosensors in LiNbO3, one first issue is to study the antibody binding process on the waveguides. Planar waveguides on LiNbO3 were fabricated by using Zn diffusion from the vapour phase following a two-step process, which produce low loss optical waveguides supporting both TE and TM propagation modes. The cleaned LiNbO3:Zn diffused waveguide surface was incubated with an aqueous solution containing 90 μg/ml anti-c-myc monoclonal antibody with an attached chromophore group and thoroughly washed several times in phosphate buffer solution. This simple functionalising procedure showed a remarkable stability over time (at least 2.5 months kept at 4 °C). Backscattered secondary electrons at 0.9 Torr water vapour atmosphere revealed that the antibody was immobilised on the surface in small spots covering roughly a 50% of the surface. After injection of light in the waveguide using an Ar+ laser at 488 nm, it was proved that the evanescent field of the waveguide mode interacted with the antibody, giving rise to the characteristic luminescence of the chromophore. These results provide evidence of the feasibility of using LiNbO3:Zn, a material with potential advantages derived from its electrooptical properties, in protein detection technologies.