Specific bio-recognition reactions observed with an integrated Mach-Zehnder interferometer

The combination of an integrated Mach-Zehnder-interferometer (iMZI) at the bottom of a fluidic microchannel system with supramolecular interfacial bin ding layers optimized for biosensing purposes is described. The model syste m used is based on the highly specific interaction of streptavidin to its ' ligand' biotin: a single monolayer of a correspondingly derivatized silane- compound is formed by a self-assembly procedure on top of the channel rib g uiding the light through the channels. Injection of a streptavidin solution which leads to the formation of a protein monolayer of d = 2.8 nm in effec tive thickness results in a phase shift of the sample light relative to the reference channel of Delta Phi = 6 pi, in good agreement with the theoreti cal sensitivity of Delta Phi/Delta d(r) = 2.9 pi/nm for a protein layer (n = 1.45) calculated for the device. (C) 1999 Elsevier Science S.A. All right s reserved.