Mid-Infrared Metaplasmonic Sensing.

The significant mismatch between the long wavelengths of the mid-infrared and the length scales of many chemical, biological, and/or material elements results in weak light-matter interaction and is a significant obstacle for molecular sensing at the nanoscale. Here we demonstrate that metaplasmonic resonators, which extend true plasmonic response from the visible/near-infrared wavelength range to the mid-infrared via geometric dilution of thin noble metal films, enable strong mode confinement at long wavelengths, commensurate with the length scale of nanovolume analytes. Metaplasmonic materials and geometries are investigated to optimize mode confinement and optical response, and we demonstrate strong resonant enhancement of absorption features in ultrathin (≈30 nm) polymer films. The metaplasmonic architectures explored show a significant improvement over wavelength-scale noble metal antenna structures, offering a scalable approach for long-wavelength molecular sensing of nanoscale material volumes.