BIOSENSORS USING INTEGRATED OPTICAL-DEVICES

A label-free, homogeneous immunoassay can be realised using surface single-mode wave guide structures. The evanescent field of the guided mode penetrates the adjacent vicinity of the wave guide, the biochemical layer. Thus, changes in its thickness and refractive index during an antigen-antibody interaction cause a change in the effective refractive index of the wave guide itself. Such small changes can be transformed into intensity modulations using an interferometric set-up. Investigations are described using an integrated optical Mach-Zehnder interferometer (IO-MZ-chip) and the experimental results are compared with model calculations. The theoretical sensitivity of the IO-MZ-chips used was determined applying Maxwell's equations to the propagation of light in stripe wave guides. For the experimental formation of a protein adlayer a three-step biotin-avidin protocol for the immobilisation of biotinylated immunoglobulins was employed.