Dual‐Coded Plasmene Nanosheets as Next‐Generation Anticounterfeit Security Labels

Abstract

COMMUNICATIONtable" of plasmonic atoms. [ 9 ] Under the guidance of plasmon hybridization theory, [ 12 ] these artifi cial plasmonic atoms can be assembled into periodic nanostructure arrays with unparalleled optical signatures, opening unlimited possibilities for engineering Raman hot spots and their distribution. Consequently, this platform of combining plasmonic nanoparticle assemblies and their tunable SERS signatures allows selective coding encryption capabilities, which hold a great promise as an advanced suite of next-generation anticounterfeit security labels.We have previously developed a robust self-assembly strategy to synthesize a new class of 2D plasmonic nanomaterialssoft plasmene nanosheets. [13][14][15] Despite the exciting advances achieved for designing of such plasmonic nanosheets, successful self-assembly mechanisms are generally limited to simple nanoparticle shapes such as nanospheres, nanorods, and nanocubes. [ 13,14,16,17 ] In comparison, complex anisotropic shapes such as nanostars may exhibit unique novel properties. [ 18,19 ] Herein, we demonstrate that two new plasmonic elements-gold rhombic dodecahedrals (RD) and gold nanostars (NStr)-could self-assemble to form high-quality plasmene nanosheets. More importantly, we show that these nanosheets could be dual-coded with plasmonic signatures and SERS fi ngerprints, enabling them to serve as a unique anticounterfeit security label for banknotes. Nine different plasmonic codes were created using gold nanospheres, gold rhombic dodecahedrals, and gold nanostars as building blocks, each with three different sizes. With the same plasmonic code, fi ve additional SERS fi ngerprint barcodes were demonstrated. The facile adjustment of plasmonic codes by fi ne-tuning size and shapes in conjunction with choices of Raman dyes makes our system an ideal dual-coded currency label with virtually unlimited coding capacity.Free-standing RD-based plasmene nanosheets were fabricated using a previously developed two-step polymer-mediated self-assembly strategy. [13][14][15] High-quality and monodispersed RD nanoparticles with a nominal edge length of ≈26.3 ± 2.1 nm were fi rst functionalized with thiolated-polystyrene, followed by an evaporation induced self-assembly process at air-water interface into plasmene nanosheets. TEM characterization revealed the assembled nanosheet to be monolayered, with the RDs lying fl at into an elongated hexagon-like shape ( Figure 1 a) and exhibiting a 2D hexagonally close-packed (hcp) ordering (Figure 1 b). As a proof of our dual coding concept, a droplet (5 µL, 1 × 10 −3 M ) of 4-aminothiophenol (4-ATP) solution, which is a model Raman dye with well-established characteristic vibrational fi ngerprints, was deposited on a banknote surface, followed by stamping of nanosheets on the deposited region and spin-coated (3000 rpm,

Flexible Plasmonic Metasurfaces with User‐Designed Patterns for Molecular Sensing and Cryptography

“…The SERS performance of our FPPM material is comparable to other reported flexible plasmonic metamaterials (enhancement factor (EF) ca. 10 7 ), as shown in Table S1 (Supporting Information). Although, a higher EF value can be achieved by employing a sophisticated lithography‐based approach to fabricate deliberately designed metal nanostructures as SERS‐active substrates, our FPPM has an obvious advantage in fabrication cost.…”

“…Counterfeiting and forgery are pervasive worldwide; thus, there is a pressing need for novel security measures. Our FPPM could be developed into a “layered” security label, when combined with already developed coding techniques, as shown in Figure . The iridescent plasmonic pattern served as the first layer, which is easy for members of the public to verify.…”

Graphene‐Enhanced 3D Chemical Mapping of Biological Specimens at Near‐Atomic Resolution

“…Au NPs Preparing and Resin Embedding : Gold chloride trihydrate (HAuCl 4 ·3H 2 O, ≥99.9%), hexadecyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride solution (CTAC, 25 wt% in water), silver nitrate (AgNO 3 ), sodium borohydride (NABH 4 ), and l ‐ascorbic acid (AA) were purchased from Sigma Aldrich and without further purification were used to synthesize the Au NPs based on a repeated seeded growth approach, as detailed elsewhere . After preparing a high concentration Au NPs solution, it was spun down at 14 500 rpm for 10 min and rinsed with Milli‐Q water three times in a 1.5 mL Eppendorf tube.…”

Versatile design and synthesis of nano-barcodes

“…134 Furthermore, the portable Raman spectrometer has been proposed to decode the SERS code from dual-coded nanosheets for anti-counterfeiting purposes. 286 Another emerging portable decoder is smartphones which have high resolution camera and computing power, allowing for detection of optical based barcodes, including colour and graphics. Several smartphone based decoders have been developed, such as for scanning the Raman codes, upconversion nanoparticle ink-based 2D barcodes, photonic crystal barcodes and also detecting the optical density of lateral immuno-assay based SERS barcodes, as shown in Fig.…”