THE DIFFERENCE INTERFEROMETER - A HIGHLY SENSITIVE OPTICAL PROBE FOR QUANTIFICATION OF MOLECULAR-SURFACE CONCENTRATION

A sensitive probe for label-free intermolecular affinity analysis, bas ed on a two-mode interferometric thin-film optical waveguide sensor, i s presented. The detectability of small changes in molecular surface c overage at the sensor surface is assessed. Measurements carried out wi th proteins as analyte molecules demonstrate the quantification of sur face concentration from nanograms per square millimetre down to a few picograms per square millimetre directly at the solid/liquid interface . The ultimate resolution of the sensor system was found to be limited by material properties of the waveguiding film.