Sensing viruses using terahertz nano-gap metamaterials.

We demonstrate highly sensitive detection of viruses using terahertz split-ring resonators with various capacitive gap widths. Two types of viruses, with sizes ranging from 60 nm (PRD1) to 30 nm (MS2), were detected at low densities on the metamaterial surface. The dielectric constants of the virus layers in the THz frequency range were first measured using thick films, and the large values found identified them as efficient target substances for dielectric sensing. We observed the resonance-frequency shift of the THz metamaterial following deposition of the viruses on the surface at low-density. The resonance shift was higher for the MS2 virus, which has a relatively large dielectric constant. The frequency shift increases with surface density until saturation and the sensitivity is then obtained from the initial slope. Significantly, the sensitivity increases by about 13 times as the gap width in the metamaterials is decreased from 3 µm to 200 nm. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization.