Surface Enhanced Infrared Absorption (SEIRA) on volatile organic compounds is enabled by the concerted action of resonant nano-antennas and nanosize zeolites.

The ability to detect trace amount (ppb) of volatile organic compounds, such as benzene, in real-time is of paramount importance to assess the long-term impact of pollution, to verify whether industries comply with imposed standards, and ultimately to support regulatory authorities to define new guidelines.
Although infrared spectroscopy can readily identify chemical species without prior knowledge, portable systems are not suitable to detect trace amount, due to the small absorption cross-section of molecular vibrations, requiring long optical paths. Attempts to boost light-matter interaction by means of optical resonances have been successful in amplifying the molecular fingerprint via the so called Surface Enhanced Infrared Absorption (SEIRA) mechanism. Despite the tremendous potential, SEIRA has been mostly limited to solid-state monolayers adsorbed from the liquid phase onto the resonant nano-antennas, while the detection of gas traces still remains elusive, due to the evanescent nature of such resonances.
In this work, we establish a new strategy that combines in an ultra-thin functional layer the benefits of SEIRA with those of sorbent materials that can adsorb volatile compounds at very low partial pressures.
Resonant nano-antennas are coated at room temperature by a layer of nanosized zeolites, that traps molecules in the near vicinity of the nano-antennas to take full advantage of the amplified electromagnetic field. Performance equivalent to a ~120 m long optical path is achieved with such a functional layer that is only ~200 nm thin (8 orders of magnitude thinner).
We demonstrate the potential of our strategy by detecting benzene at a concentration of 25 ppb in less than 10 minutes with a standard FTIR spectrometer. This sets a new record for the real-time detection of benzene from its vibrational fingerprint.