Reusable Structural Colored Nanostructure for Powerless Temperature and Humidity Sensing

摘要

Nanostructured materials have enabled new ways of controlling thelight–matter interaction, opening new routes for exciting applications, indisplay technologies and colorimetric sensing, among others. In particular,metallic nanoparticles permit the production of color structures out ofcolorless materials. These plasmonic structural colors are sensitive to theenvironment and thus offer an interesting platform for sensing. Here, aself-assembly of aluminum nanoparticles in close proximity of a mirror isspaced by an ultrathin poly(N-isopropylacrylamide) (PNIPAM) layer.Hybridizing the plasmonic system with the active polymer layer, athermoresponsive gap-plasmon architecture is formed that transduceschanges in the temperature and relative humidity of the environment intocolor changes. By harnessing the environmentally induced structural changesof PNIPAM, it was estimated from the finite difference time domainsimulation that the resonance can be tuned 7 nm per every 1 nm change inthickness, resulting in color variation. Importantly, these fully reversiblechanges can be used for reusable powerless humidity and temperaturecolorimetric sensing. Crucially if condensation on the structure happens, thepolymer layer is deformed beyond recovery and the colors are washedaway. We leverage this effect to produce tamper-proof dew labels that astraightforward smartphone app can read by taking a picture.