Surface desensitization of polarimetric waveguide interferometers

Nonspecific surface binding of small protein molecules presents a major obstacle to surface biosensing techniques attempting to detect very low concentrations (< 1 pg/mm/sup 2/) of large biological objects such as cells and bacteria. A new method for selective desensitization of a polarimetric waveguide interferometer eliminates the background noise from nonspecific surface binding. We demonstrate the ability to tune the phase sensitivity of a waveguide interferometer as a function of the distance of the biological or chemical analyte from the waveguide surface. This makes possible a sensor that has zero sensitivity at a particular distance where nonspecific surface binding occurs without significantly reducing the sensitivity to target larger biological species.