Efficient plasmonic gas sensing based on cavity-coupled metallic nanoparticles

Here, we demonstrate the gas sensing ability of cavitycoupled metallic nanoparticle systems, comprising gold nanoparticles separated from a gold mirror with a polymer spacer. An increase in relative humidity (RH) causes the spacer to expand, which induces a significant reduction of nanoparticle scattering intensity, as the scattering is highly dependent on the cavity-nanoparticle coupling that closely relates to the nanoparticle-mirror distance. With high structural tolerance, i.e., no requirement for high-precision nanoparticle geometry, this lithography-free system enables a remarkable average sensitivity at 0.12 dB/% RH and 0.25 dB/% RH over a wide RH range (45-75%) and full reversibility with much faster response time than the commercial electrochemical sensors, possessing the characteristics to be used for notable gas sensing.