We present measurements on biomolecular surface multilayers using an integrated optical sensor based on the Mach-Zehnder interferometer (MZI). The sensor design is unique in that it incorporates a three-waveguide coupler structure at the interferometer output which gives advantages in terms of signal referencing and in establishing and maintaining a sensitive operating point. The sensor performance is characterized with respect to bulk superstrate index and by the formation of multiple protein adlayers using a biotin-avidin-based biochemical system. The detection limit for protein loading is estimated as 5 pg/mm2.
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