A LABEL-FREE AFFINITY SENSOR WITH COMPENSATION OF UNSPECIFIC PROTEIN-INTERACTION BY A HIGHLY SENSITIVE INTEGRATED OPTICAL MACH-ZEHNDER INTERFEROMETER ON SILICON

An integrated optical Mach-Zehnder interferometer (IO-MZI) on silicon was specially designed and tested for application as an affinity senso r. In order to obtain the necessary sensitivity, an optimisation of th e refractive index and the thickness of the waveguiding layer was carr ied out. Refractive measurements with ethanol/water mixtures show a se nsitivity of about one order of magnitude higher than the IO-MZIs prev iously described. The compensation oi unspecific protein interaction i n an affinity sensor set-up was demonstrated by using both branches of the IO-MZI. One branch was coated with a antigenic structure and bloc ked with a protein mixture whereas the other was only blocked. A sampl e with a high background of serum proteins was applied and only the sa mple containing the specific antibody gave a measurable signal. (C) 19 97 Elsevier Science S.A.