A sensor scheme combining nano-photonics and nano-fluidics on a single platform through the use of free-standing photonic crystals is described. By harnessing nano-scale openings, both fluidics and light can be manipulated at sub-wavelength scales. The convective flow is actively steered through the nanohole openings for effective delivery of the analytes to the sensor surface, and refractive index changes are detected in aqueous solutions. Systems and methods using cross-polarization measurements to further improve the detection limit by increasing the signal-to-noise ratio are also described.