PRINCIPLES AND SENSITIVITIES OF INTEGRATED OPTICAL AND SURFACE-PLASMON SENSORS FOR DIRECT AFFINITY SENSING AND IMMUNOSENSING

The analogy between guided modes in planar optical waveguides and surface plasmons is worked out. It explains that integrated optical (IO) and surface plasmon (SP) affinity sensors and immunosensors are based on the same physical effect: changes in the effective refractive index of the guided waves are induced by the interactions of their evanescent field with the analyte molecules binding specifically to reaction partners immobilized on the sensor surface. The sensitivities of IO and SP affinity sensors are derived - as analytical expressions - by perturbation theory; also their sensitivities to refractive index changes, i.e. as differential refractometers. The sensitivities of IO sensors at lambda = 632.8 nm are compared with those of SP sensors with gold films at the same wavelength and silver films at lambda = 632.8 and 780 nm. The highest sensitivities are predicted for IO interferometric sensors.