Versatile Fabrication of Intact Three‐Dimensional Metallic Butterfly Wing Scales with Hierarchical Sub‐micrometer Structures

Abstract

Three-dimensional (3D) metallic microstructures with wellcontrolled hierarchical morphologies down to the sub-micrometer scale have attracted considerable attention.[1] These structures have broad applications owing to their unique optical, [2a] electronic, [2b] magnetic, [2c] thermal, [2d,e] and catalytic [2f] properties, which can be modulated by their intrinsic microstructures. Such structures, however, are quite difficult to prepare by traditional methods. One promising route to create these metallic structures is direct replication from hierarchical structures of various natural species. Metals have been physically deposited onto biological structures to fabricate metallic structures through physical vapor deposition (PVD).[3] However, the line-of-sight nature of PVD prevented a complete replication of the biotemplates original 3D morphologies.[4] Some groups elegantly converted natural inorganic structures such as diatom frustules into metals (Ag, Au, Pd) using wet-chemical processes, [4] but many natural species with functional structures are composed of organic materials. Versatile synthesis of metallic structures using organic-based natural species intact, 3D, and hierarchical sub-micrometer morphologies as templates is thus needed.Herein we present a versatile route (selective surface functionalization and subsequent electroless deposition) to generate metallic replicas of the intact 3D organic butterfly (Euploea mulciber) wing scales. This method can replicate the original chitin-based scales morphology in at least seven important metals, including cobalt, nickel, copper, palladium, silver, platinum, and gold ( Figure 1 and Figure 2). Significantly, using the synthetic Au scale as a surface-enhanced Raman scattering (SERS) substrate, the detectable analyte concentration (Rhodamine 6G, 10 À13 m) can be one order of magnitude lower than using commercial substrates (Klarite). To our knowledge, this work is the first demonstration of the conversion of intact hierarchical 3D butterfly structures on a sub-micrometer level into metallic replicas. It should be noted that butterflies belong to the order Lepidoptera (Latin word for "scaly wing", including butterflies and moths) that comprises an estimated 174 250 species.[5] A given species usually has more than one type of wing scale, [6] and such huge morphological diversity offers a vast structure pool for biotemplate selection (e.g., photonic crystal design).[7a] In addition, chitin, the main component of butterfly wing scales, is one of the richest natural macromolecular compounds. [8] Therefore, this approach can be extended to replicate other chitin-based biostructures, including fungi cell walls, exoskeletons of insects [9a,b] and arthropods (e.g., crabs and lobsters), [9c] radulas of mollusks (e.g., snails), and beaks of cephalopods (e.g., squids [9d] and octopuses). The fabrication route described herein consists of three steps (see Scheme S1 in the Supporting Information): 1) func- Figure 1. SEM element mapping images of seven metallic win...

Highly sensitive, reproducible and uniform SERS substrates with a high density of three-dimensionally distributed hotspots: gyroid-structured Au periodic metallic materials

“…The first two steps, amination of the biotemplate and Au nanoseed growth, were reported in our previous work. 24 In the final electroless deposition process, a moderate reductant, diethanolamine, was used to guarantee the slow and homogeneous growth of Au films. A proper concentration of halide ions (Cl − ) was also included to control the morphology of the Au films.…”

“…These results are comparable with those of many other hierarchical plasmonic substrates. 9,24,43 More importantly, the mechanism presented here can act as a guideline for the future design and selection of SPR substrates. The existence of several other bicontinuous interconnected structures has been confirmed in various biological systems and self-assembly systems, such as the diamond structure found in the brilliantly green weevil Lamprocyphus augustus 25 and the double-gyroid, 44 stripedgyroid 26 and double-diamond 45 structures in block polymer systems.…”

“…These results are comparable to those of many other SPR substrates, whereas the detection concentration is one or two orders of magnitude lower. 24,43 Meanwhile, to investigate the influence of the randomly oriented distribution of domains on the uniformity of SPR enhancement by the GAPMMs, a point-by-point SERS mapping measurement was conducted on a 20 μm × 20 μm area in zone A for the detection of CV (10 − 10 M). The step lengths in both the X and Y directions were 1 μm.…”

“…In our previous work, we proved that biotemplates, such as butterfly wings, can be used as soft templates after pretreatment and are versatile for the electroless deposition of metal films. 24 Here we use gyroid-structured photonic crystals from the wing scales of the butterfly Callophrys rubi as soft templates after activating the biomaterials on the external surface. A series of gyroid-structured Au periodic metallic materials (GAPMMs) were fabricated by properly controlling the deposition time (t d ) using an electroless deposition method, as shown in Figure 1.…”

Substrate-Independent Light Confinement in Bioinspired All-Dielectric Surface Resonators

“…Overcoming this constraint is important for many applications, such as on-chip biosensing, which relies on low optical absorption in water [24]. In light of the limitations of traditional PhC slabs and their alternatives, we introduce a new class of bioinspired, low-index surface resonators that uses periodic air gaps to support resonance modes without index contrast between the structure and the substrate.Photonic crystal structures in butterfly wings use lowindex biological materials to produce dramatic colors [25] and have been fabricated for optical devices [26,27]. We study the silver scales on the Dione juno butterfly as an inspiration for a surface resonator with low index contrast.…”