One of the fundamental properties of nanophotonics research is the electromagnetic interaction of different systems at the nanoscale. When the excitation frequencies of two independent energy modes overlap, the modes will interfere constructively and destructively to create an asymmetric lineshape in the absorption spectrum. This interaction is known as a Fano resonance, and it can exist between several different interacting systems, including plasmonic nanostructures, excitonic particles, electronic transitions, and molecular vibrations. In the first part of this presentation, I will discuss the basic properties of plasmonic heterodimers consisting of gold nanoparticles of different sizes . Longitudinal excitation of these structures results in a Fano resonance between hybridized plasmonic modes, whereas transverse excitation results in a unique scattering profile that depends on the direction of the k-vector.In the second part of this presentation, I will introduce a gold nanoantenna that is capable of detecting zeptomole quantities of molecules with infrared spectroscopy . The antenna is tunable across the infrared spectrum, and the detection mechanism occurs through a Fano resonance between the antenna plasmon mode and the molecular vibration of interest. With these antennas, we have demonstrated the enhanced detection of several classes of analytes, including alkanethiols, proteins, and bulk materials. I will also discuss recent variations of our antenna design that demonstrate increased sensitivity, where our ultimate goal is to analyze a single molecule with infrared spectroscopy.
 Heterodimers: plasmonic properties of mismatched nanoparticle pairs, L. V. Brown, H. Sobhani, J. B. Lassiter, P. Nordlander, and N. J. Halas, ACS Nano 4, 819–832 (2010).
 Surface-enhanced infrared absorption using individual cross antennas tailored to chemical moieties, L. V. Brown, K. Zhao, N. King, H. Sobhani, P. Nordlander, and N. J. Halas, Journal of the American Chemical Society 135, 3688–3695 (2013).
andrea.centrone [at] nist.gov (Andrea Centrone), 301-975-8225