Research On Synthesis And Photoresponse Property Of Metallic Functional Micro/Nano Structures Mimicking Butterfly Wing Scales

Metallic sub-micrometer structures with multi-dimensions, multi-levels, andmulti-functions have attracted great attention owing to their excellent and fascinatingproperties. One of the most important optical properties of metallic sub-micrometerstructures is surface plasmon resonance. This phenomenon is induced by collectiveoscillations of free electrons driven by the electromagnetic field of incident lights. Itcan provide light concentration, optical waveguide, optical enhancement, opticalstorage, and other optical effects and thus has many potential applications in opticalintegrate circuits, biosensors, biomarkers, bioimaging, solar cells, and surface enhancedspectroscopy, et al. Great efforts have been made on the fabrication of metallicmicro/nano structures. However, most approaches need a trade off between the highcost and the high producibility. In addition, the fabrication of complicated hierarchicalthree dimensional （3D） structures at sub-micrometer levels is still a challenge at present.Such situation limits the applications of metallic sub-micrometer structures. Therefore,it is critical to develop novel fabrication techniques for the3D metallic nanostructures.Nature has been providing us inspirations for the design of elaborated hierarchicalstructures with various functions. A butterfly wing with hierarchical sub-micrometerstructures is such a perfect example, which can provide unique photo-responseproperties.In this work, we have fabricated seven kinds of novel metallic functional materialswith butterfly scales’ sub-micrometer structures, which are difficult to imitate bytraditional methods, and explored their photo-response properties. The main results areas follows:1. A versatile route is designed for the fabrication of metallic functional materials（Co, Ni, Cu, Pd, Ag, Pt, Au） with sub-micrometer superstructures of butterfly wingscales. Through selective surface functionalization and standard electroless deposition,a homogeneous and morphology preserving replication of original scales intricate3Dmicrostructures is achieved. Since chitin, the main component of butterfly wing scales, is one of the richest natural macromolecular compounds, this approach can be extendedto replicate other chitin-based biostructures.2. Using the novel Au butterfly wings （or scales） with periodic structures asSERS substrates, a detectable lower limit (10^-13M) of R6G concentration has beenachieved. Such a detection sensitivity is one order of magnitude higher than itscommercial counterpart （Klarite）, and the SERS substrates of Au butterfly wings are10times cheaper per piece in cost than Klarite. Moreover, the Au scales exhibite goodreproducibility with a relative standard deviation （RSD）5.2%, which is comparable toKlarite. These results help bring affordable SERS substrates as consumables with highsensitivity, high reproducibility, and low cost to ordinary laboratories across the world.3. The3D sub-micrometer Cu structures replicated from butterfly wing scales aresuccessfully tuned by modifying the Cu deposition time. An optimized Cu platingprocess （10min in Cu deposition） yields replicas with the best conformal morphologiesof original wing scales and in turn the best SERS performance. Simulation results showthat the so-called “rib-structures” in Cu butterfly wing scales present naturally piled-uphotspots where electromagnetic fields are substantially amplified, giving rise to a muchhigher hotspot density than in plain2D Cu structures. Such a mechanism is furtherverified in several Cu replicas of scales from various butterfly species. This findinghelps select the best morphologies for SERS use in175,000butterfly and moth species,and can provide a theorotical guidance for designing sub-micrometer metallicstructures for photo-response applications.4. The Au metal enhanced fluorescence （MEF） substrates directly replicatedfrom natural butterfly （Morpho sulkowskyi） wing scales can greatly enhance thefluorescence of fluorophores （fluorscein isothiocyanate, FITC）. A31fold andreproducible （relative standard deviation, or RSD=6.5%） fluorescence enhancementfactor （EF） of FITC is achieved on gold M. sulkowskyi wing scales that can be preparedwith a half time-cost in an ordinary laboratory. Such results are confirmed in abioimaging process for HeLa cells （human cervical cancer cells） grown on our goldbutterfly wings. This nature inspired strategy paves the way towards3D MEFsubstrates with over175,000butterfly scale morphologies to choose from, and mayopen a new way for MEF research areas.In general, this work has proposed a new method for building sub-micrometer metallic materials with175,000morphologies. It also puts up a new concept andmethod for designing3D metals with sub-micrometer resolutions, and provides a vaststructural pool for the development of new physical phenomena and properties basedon these materials.