Integrated optical output grating coupler as biochemical sensor

The output-grating-coupler sensor was used for real-time studies of the adsorption of the proteins avidin, NeutrAvidin, and streptavidin. The feasibility of affinity sensing with subnanomolar detection limit was demonstrated with biotin-BSA (bovine serum albumin) as analyte binding to immobilized (adsorbed) avidins on the waveguide surface. Not only the surface coverage but also both the thicknesses and refractive indices of the adsorbed and bound adlayers were determined.