A Surface Plasmon Resonance (SPR) biosensor that operates deep into the infrared (3-11 μm wavelengths) is potentially capable of biomolecule recognition based both on selective binding and on characteristic vibrational modes. A goal is to operate specifically at wavelengths where biological analytes are strongly differentiated by their IR absorption spectra and where the refractive index is increased by dispersion. This will provide enhanced sensitivity and selectivity, when biological analytes bind reversibly to biomolecular recognition elements attached to the sensor surface. This paper describes work on the optical and materials aspects of IR surface plasmon resonances. First, three possible coupling schemes are considered: hemicylindrical prisms, triangular prisms, and gratings. Second, materials with plasma frequencies one order of magnitude smaller than for noble metals are considered, including doped semiconductors and semimetals.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.