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J Biophotonics ; 12(12): e201900218, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31452335


Modern document protection relies on the simultaneous combination of many optical features with micron and submicron structures, whose complexity is the main obstacle for unauthorized copying. In that sense, documents are best protected by the diffractive optical elements generated lithographically and mass-produced by embossing. The problem is that the resulting security elements are identical, facilitating mass-production of both original and counterfeited documents. Here, we prove that each butterfly wing-scale is structurally and optically unique and can be used as an inimitable optical memory tag and applied for document security. Wing-scales, exhibiting angular variability of their color, were laser-cut and bleached to imprint cryptographic information of an authorized issuer. The resulting optical memory tag is extremely durable, as verified by several century-old insect specimens still retaining their coloration. The described technique is simple, amenable to mass-production, low cost and easy to integrate within the existing security infrastructure.

Soft Matter ; 14(27): 5595-5603, 2018 Jul 11.
Artigo em Inglês | MEDLINE | ID: mdl-29911714


We describe a new type of photonic material inspired by a Diachrysia chrysitis moth, whose nano-structured wings exhibit a prominent golden color. This is a layered photonic structure with a large refractive index contrast, whose alternating layers are rough at the nanoscale level. Theoretical analysis shows that the scattering and interference interact to enhance the local field within the layers and increase the absorption of the material, particularly in the UV-blue part of the spectrum. Theory is experimentally verified using holographically manufactured Bragg gratings in the dichromated-pullulan (DCP). Alternating air-pullulan layers are produced and held in place by sparsely separated nano-pillars. Air voids are filled with 20-100 nm diameter spherical nanoparticles which act as scatterers. Such materials, with a high refractive index contrast and nano-scale scatterers, are important for achieving large reflectance and a broad spectrum, with scattering as an additional mechanism for spectral control.

Absorção Fisiológica , Materiais Biomiméticos , Mariposas , Nanotecnologia , Animais , Modelos Teóricos , Fenômenos Ópticos , Asas de Animais
Phys Rev E ; 95(3-1): 032405, 2017 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-28415223


Here we report how interference and scattering-enhanced absorption act together to produce the golden wing patches of the burnished brass moth. The key mechanism is scattering on rough internal surfaces of the wing scales, accompanied by a large increase of absorption in the UV-blue spectral range. Unscattered light interferes and efficiently reflects from the multilayer composed of the scales and the wing membranes. The resulting spectrum is remarkably similar to the spectrum of metallic gold. Subwavelength morphology and spectral and absorptive properties of the wings are described. Theories of subwavelength surface scattering and local intensity enhancement are used to quantitatively explain the observed reflectance spectrum.

Cor , Mariposas , Asas de Animais , Animais , Microscopia , Microscopia Eletrônica de Varredura , Modelos Biológicos , Mariposas/anatomia & histologia , Mariposas/efeitos da radiação , Espalhamento de Radiação , Asas de Animais/anatomia & histologia , Asas de Animais/efeitos da radiação
Microsc Res Tech ; 75(7): 968-76, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-22392855


Apatura ilia (Denis and Schiffermüller, 1775) and A. iris (Linnaeus, 1758) are fascinating butterflies found in the Palaearctic ecozone (excepting the north of Africa). The wings of these insects are covered with a great number of two types of scales positioned like roof tiles. Type I scales are on the surface, while type II scales are situated below them. The structural color of the type I scales is recognized only on the dorsal side of both the fore and hind wings of the males of the aforementioned species. Both types of scales are responsible for pigment color of the wings, but iridescence is observed only in the type I scales. The brilliant structural color is due to a multilayer structure. The features of the scales, their dimensions and fine structure were obtained using scanning electron microscopy. Cross sections of the scales were then analyzed by transmission electron microscopy. The scales of the "normal" and clytie forms of A. ilia have a different nanostructure, but are of the same type. A similar type of structure, but with a different morphology, was also noticed in A. iris. The scales of the analyzed species resemble the scales of tropical Morpho butterflies.

Borboletas/ultraestrutura , Asas de Animais/ultraestrutura , África , Animais , Feminino , Masculino , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Nanoestruturas/ultraestrutura