A guided mode resonance (GMR) sensor assembly and system are provided. The GMR sensor includes a waveguide structure configured for operation at or near one or more leaky modes, a receiver for input light from a source of light onto the waveguide structure to cause one or more leaky TE and TM resonant modes and a detector for changes in one or more of the phase, waveshape and/or magnitude of each of a TE resonance and a TM resonance to permit distinguishing between first and second physical states of said waveguide structure or its immediate environment.