Diffusion kinetics of volatile organic compounds monitored by nanohole surface plasmonics

The extraordinary optical transmission, EOT, through a gold-film nanohole array was used to measure refractive index changes of a thin film of polydimethylsiloxane, PDMS, upon absorption of o-xylene gas. As o-xylene diffuses into the 10 μm thick PDMS film, the film swells slightly and its refractive index increases. The PDMS index change produces a red-shift of the EOT maximum which is observable in a simple optical transmission spectrum. Since the experiments are fast (<200 ms) and precise (<2 × 10^-4 RIU) we can follow the kinetics of the diffusion process with enough accuracy to distinguish two distinct diffusion mechanisms that occur at different time scales.