The difference interferometer: a highly sensitive optical probe for quantification of molecular surface concentration

Abstract

A sensitive probe for label-free intermolcular affinity analysis, based on a two-mode interferometric thin-film optical waveguide sensor, is presented. The detectability of small changes in molecular surface coverage at the sensor surface is assessed. Measurements carried out with proteins as analyte molecules demonstrate the quantification of surface 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 sensors system was found to be limited by material properties of the waveguiding film.