Nanocavity plasmonic device for ultrabroadband single molecule sensing.

We present a new structure that combines a metal-dielectric-metal sandwich with a periodic structure to form a plasmon polariton photonic crystal. Three-dimensional finite-difference time-domain simulations show a clear bandgap in the terahertz regime. We exploited this property by adding a defect to the crystal, which produces a cavity with a quality factor of 23.3 at a wavelength of 3.45 microm. Despite the small Q factor, the ultrasmall sensing volume of 15 zeptoliters produces an extremely large Purcell constant of 4.8x10(6). Compared to photonic crystals with similar Purcell constant, the bandwidth is several orders of magnitude larger, or about 7 THz, ensuring high tolerances to manufacturing parameters, and environmental changes, as well as a high specificity owing to the possibility of broadband spectral fingerprint detection.