Sensing light and sound velocities of fluids in phoxonic crystal

We discuss theoretically the new concept of dual phononic and photonic (phoxonic) crystal for sensing the light and sound velocities of fluidic analytes. We show that such a structure can support cavity modes with well confinement of both electromagnetic and acoustic fields with high quality factors. These modes give rise to peaks or dips in the transmission spectrum that are sensitive to both the acoustic velocity of sound and the optical index of refraction. Such an ultra compact structure is shown to be a label-free, affinity-based acoustic and optical nanosensor, useful for sensing applications in which the amount of analyte is often limited.