title: Plasmonic Nanogels for Unclonable Optical Tagging.
abstract: We demonstrate the fabrication of novel functional gel coatings with randomized physical and chemical patterns that enable dual encoding ability to realize unclonable optical tags. This design is based on swelling-mediated massive reconstruction of an ultrathin responsive gelatinous polymer film uniformly adsorbed with plasmonic nanostructures into a randomized network of interacting folds, resulting in bright electromagnetic hotspots within the folds. We reveal a strong correlation between the topology and near-field electromagnetic field enhancement due to the intimate contact between two plasmonic surfaces within the folds, each of them representing a unique combination of local topography and chemical distribution caused by the formation of electromagnetic hotspots. Because of the efficient trapping of the Raman reporters within the uniquely distributed electromagnetic hotspots, the surface enhanced Raman scattering enhancement from the morphed plasmonic gel was found to be nearly 40 times higher compared to that from the pristine plasmonic gel. Harnessing the nondeterministic nature of the folds, the folded plasmonic gel can be employed as a multidimensional (with dual topo-chemical encoding) optical taggant for prospective anticounterfeiting applications. Such novel optical tags based on the spontaneous folding process are virtually impossible to replicate because of the combination of nondeterministic physical patterns and chemical encoding.
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Limei
authors.initials: L
authors.lastname: Tian
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Keng-Ku
authors.initials: KK
authors.lastname: Liu
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Max
authors.initials: M
authors.lastname: Fei
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Sirimuvva
authors.initials: S
authors.lastname: Tadepalli
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Sisi
authors.initials: S
authors.lastname: Cao
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Geldmeier
authors.affiliation: School of Materials Science and Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Tsukruk
authors.affiliation: Department of Mechanical Engineering and Materials Science, Institute of Materials Science and Engineering, Washington University in St. Louis , St. Louis, Missouri 63130, United States.
authors.forename: Srikanth
authors.initials: S
authors.lastname: Singamaneni
keywords: anticounterfeiting; electromagnetic hotspot; optical tag; plasmonic gel; responsive polymer