ndex changes (for example, due to chemical binding events on a bio-functionalized gold surface) as small as 10-6 RIU (refractive index units). For example, the commercial sensiQ detector from Nomadics is capable of measuring binding events of just one picogram of protein/mm2.
More recently, there has been an explosion of interest in surface plasmons on nanoscale patterned surfaces. Using modern nanofabrication facilities, it is possible to make structures with feature sizes much smaller than the wavelength of visible light (&sim 500nm). For example, enhanced transmission through arrays of sub-wavelength slits has been experimentally demonstrated and has promising applications in photolithography and high-density optical data storage. Because surface plasmons can be launched at optical frequencies with much smaller wavelengths, it is possible to manipulate the flow of light on the scale of tens of nanometers. This has led to the coining of the term "plasmonics", where surface plasmons are used to manipulate and transport information, analogous to electronics and photonics. Photonics has nearly unlimited bandwidth and almost no loss or dispersion, making it invaluable for high-throughput long-haul information networks. However, photonics components are diffraction-limited to micron-scale sizes, ruling out dense integration with nanoscale electronics. Plasmonics is potentially poised to bridge the tens of nanometer scale of modern electronics to the micron scale world of photonics. Many interesting devices, such as a 50nm metal-insulator-metal (MIM) surface plasmon waveguide capable of guiding 1.5um light even around 90o corners, have been proposed and are being actively investigated. Such devices have great promise, but also must overcome the limits imposed by the lossy propagation of surface plasmons in metals. The propagation lengths of surface plasmon waves in the visible and near infrared regimes are typically on the order of hundreds of microns on unpatterned surfaces, but drop to under thirty microns in sub-w