Elemental mercury vapor interaction with individual gold nanorods

We show that single gold nanorods can act as highly sensitive mercury vapor sensors with attogram resolution. We exposed assorted gold nanorods, with aspect ratios ranging from 2.8-4.1, to mu g m(-3) concentrations of mercury vapor in air for 1 hour. Pre- and post-exposure, the nanorods were examined with a combination of dark field spectroscopy and transmission electron microscopy. Because we isolated individual particles, we can describe the shape and size effects distinctly rather than statistically (a constraint of studying heterogeneous nanoparticle films). No measurable changes occurred to the shape and size of the nanorods due to their saturation with mercury vapor. The localized surface plasmon resonance (LSPR) of the mercury-saturated nanorods blue shifted 2.6-3.8 nm; the magnitude of the shift depended on the initial shape and size of the nanorod. Larger aspect ratios and surface-area-to-volume ratios both enhance the LSPR shift seen in saturated nanoparticles. The predictions of a core-shell model mirrors the shape and size effects observed experimentally. These results increase our understanding of mercury-adsorption by gold surfaces, and help to optimize nanoparticle-based plasmonic mercury sensing.