Immunobiosensors based on grating couplers

Immunosensors based on grating couplers belong to the group of direct optical affinity sensors (1 ). They allow label-free monitoring not only of lmmunoaffinity reactions, i.e., of antigen (hapten)-antibody-binding (2 –8 ), but also of receptor—ligand-(9 ), protein—lipid (10 , 11 ), and protein—DNA (12 , 13 ) interactions, and DNA hybridization (13 ). In each case one of the binding partners is immobilized on the surface of the optical waveguide and binding of the other partner, present in solution, is monitored. Thus, grating coupler systems allow real-time monitoring of the binding reaction and consequently evaluation of kinetic (14 –16 ) and thermodynamic data (4 , 12 ). These are common features with other direct affinity sensor systems, such as surface plasmon resonance sensors (15 ), resonant mirrors (17 ), and piezoacoustic transducers (18 ), which all can be summarized as devices for biomolecular interaction analysis.