Butterfly Wing Scales Research Articles

Smart strategy of butterfly wing scales to control the light diffusion and absorption

The sparkling colors on the wing scales of butterflies are one of the most fascinating light–matter interactions in nature and have been an intense area of research in recent times. Controlling the light diffusion and absorption due to multiple scattering induced by the inherent disorder in the wing scales is required for applications in imaging, light trapping, and localization using such bio-inspired photonic structures. Here, we study the selective anisotropic light diffusion and absorption in the nanoarchitectures of Pieris rapae and Graphium sarpedon butterfly wing scales in the visible range. We have measured broadband spatially independent low values of specular reflectivity and ballistic transmission from the ventral and the dorsal sides of the wing scales, which are supported with finite-difference time-domain simulations. The specular reflectivity value as small as 3% indicates strong diffuse scattering within the scales, probed using total transmission and reflection measurements. We have found finite wavelength-dependent absorption < 100 % in these wing scales. Further, we have obtained negative scattering anisotropy ( g ) values from the dorsal side, whereas it is positive from the ventral side for both butterflies. The negative g value originating due to the inherent structural correlation is differentiated from that arising due to pigment absorption. The results are useful for generating the optimized light scattering in bio-inspired photonic devices.

Surface-Enhanced Raman Spectroscopy for Molecule Characterization: HIM Investigation into Sources of SERS Activity of Silver-Coated Butterfly Scales

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for obtaining structural information of molecules in solution at low concentrations. While commercial SERS substrates are available, high costs prevent their wide-spread use in the medical field. One solution is to prepare requisite noble metal nanostructures exploiting natural nanostructures. As an example of biomimetic approaches, butterfly wing scales with their intricate nanostructures have been found to exhibit exquisite SERS activity when coated with silver. Selecting appropriate scales from particular butterfly species and depositing silver of certain thicknesses leads to significant SERS activity. For morphological observations we used scanning electron microscopes as well as a helium ion microscope, highly suitable for morphological characterization of poorly conducting samples. In this paper, we describe a protocol for carrying out SERS measurements based on butterfly wing scales and demonstrate its LOD with a common Raman reporter, rhodamine 6 G. We also emphasize what special care is necessary in such measurements. We also try to shed light on what makes scales work as SERS substrates by carefully modifying the original nanostructures. Such a study allows us to either use scales directly as a raw material for SERS substrate or provides an insight as to what nanostructures need to be recreated for synthetic SERS substrates.

Broader-Band and Flexible Antireflective Films with the Window-like Structures Inspired by the Backside of Butterfly Wing Scales.

Antireflective performance is critical for most optical devices, such as the efficient solar energy utilization in photovoltaic cells of an aerospace craft and optical displays of scientific precise equipment. Therein, outstanding broad-band antireflection is one of the most crucial properties for antireflection films (ARFs). Unfortunately, it is still a challenging work to realize perfect "broader-band" antireflection because both the low refractive indices materials and time-consuming nanotexturing technologies are required in the fabricating process. Even in this case, a broader-band and flexible ARF with hierarchical structures is successfully developed, which is inspired by butterfly wing scales. First, the butterfly wings surface is treated with acid and stuck on a clean glass. Now, all the scales on the wings will form a strong adhesion with the glass substrate. Then, the wings are removed and the scales are left on the glass slide. Now the backside of scales is facing outward, the backside structures of the scales are coincidentally used as the template. Finally, the structure is replicated and the ARF with a controllable thickness is successfully fabricated by rotating PDMS on the biological template. In this work, the bionic ARFs realize the transmission of nearly 90% and more than 90% in the visible light and infrared region. It enhanced transmission to 13% under standard illumination compared with flat PDMS films of the same thickness. Furthermore, the ARF is flexible enough that it could bend nearly 180° to meet the special antireflection requirements in some extreme conditions. It is expected that this bioinspired AR film could revolutionize the technologies of broader-band antireflective materials and impact numerous applications from glass displays to optoelectronic devices.

Additive and subtractive modification of butterfly wing structural colors

The modification of photonic nanoarchitectures occurring in butterfly wing scales with different nanostructures was investigated experimentally and by modeling. Single crystalline, polycrystalline, simple thin film, and pepper-pot-type photonic nanoarchitectures in the wing scales of different butterflies were investigated. By atomic layer deposition (ALD) (additive) the color of all nanoarchitectures was red shifted and by plasma etching (subtractive) the color of all nanoarchitectures was blue shifted in a controllable way. Langmuir-Blodgett multilayers of silica nanospheres were used as physical models. ALD produced color shifts similar to those for butterfly wings. In the case of a simple thin film, a theoretical calculation reproduced the spectral alterations well. For the more complex photonic nanoarchitectures, the general trends of the modifications were well reproduced by more sophisticated models, but differences in the magnitude of the alterations were found, attributed to the complex, random porous structures of the pepper-pot-type structures.

Light guidance in photonic structures of Morpho butterfly wing scales

In this paper, we investigate the impact of the periodicity along three orthogonal axes of the blue wing scales of Morpho butterflies, whereas most of the previous studies modeled the scale structure only considering one or two photonic crystal dimensions. Moreover, the previous optical studies of these scales focused on the light reflected by the wing, whereas we investigate the light propagation along the lamellae, this direction corresponding to the third dimension of the photonic crystal structure. Simulation results obtained using the finite-element method are compared with measurements and/or literature. These calculations, performed for different scale models and orientations, show that a significant part of the non-reflected light, essentially red and infrared, is guided by the lamellae towards the base of the scales where it can be more easily absorbed and the heat more quickly transferred to the hemolymph. This new phenomenon could contribute to the thermal balance of the insect and further illustrates the multifunctionality of the wings of Lepidoptera.

Highly Sensitive and Selective VOC Vapor Optical Fiber Sensor Using Hierarchical Nanostructures of Butterfly Wing Scales

Volatile organic compound (VOC) is one of the most widely spread and hazardous environmental pollutants. In this work, a VOC vapor optical fiber sensor is proposed and demonstrated based on the multilayer interference and diffraction of Morpho Didius butterfly wing scales. The sensing wing is fabricated and sheathed on the end of the optical fiber probe with a sleeve, while the sensing element could be easily renewed by replacing the sleeve part. It is found that the reflectance spectrum of the butterfly wings changes with varied VOC vapors. By tracing the spectral changes, the categories and concentrations of VOC vapors are investigated experimentally, while the differential reflectance spectrum ΔR is introduced to magnify the subtle differences of the original spectrum. Here, the dichloromethane, acetone, and ethanol vapors are tested, and the maximum sensitivity of the sensor is measured as 3.303E-5%/ppm, 7.762E-5%/ppm, and 2.881E-4%/ppm, respectively. The principal components analysis method is employed to further analyze the ΔR spectrum, and the concentration of varied VOC vapors could be discriminated and identified according to the distribution of the projected points. Considering its advantages including low-cost, easy fabrication, good repeatability, high sensitivity, and selectivity, this wing-based vapor optical fiber sensor has great application potential in the field of air monitoring.

Discovery of single gyroid structure in self-assembly of block copolymer with inorganic precursors

Triply periodic hyperbolic surfaces have attracted great attention due to their unique geometries and physical properties. Among them, the single gyroid (SG) is of significant interest due to its inherent chirality as well as the potential applications in energy and environmental science. However, the formation of the thermodynamically unstable structure is still unclear. In this work, we show the formation of SG structure in the structural transformation from the cylindrical to shifted double diamond (SDD) scaffold in a self-assembly system of diblock copolymer and silica precursors in solution. It has been found that the cylindrical tubes with zero Gaussian curvature were split and curved into hyperbolic surfaces and extruded to form SG structures and further evolved into the SDD networks. This growth or extrusion process suggests the SG structure is an intermediate phase of the cylindrical and SDD, and this transformation is found similar to the formation of butterfly wing scales (Thecla opisena), which has not been observed in neither the theoretical calculation nor the experimental self-assembly of amphiphilic molecules. We hope the structural relationship may bring new insights in understanding the formation of single networks in the biological system and the creation of new functional materials.

Multichanneled hierarchical porous nanocomposite CuO/carbonized butterfly wing and its excellent catalytic performance for thermal decomposition of ammonium perchlorate

To meet the requirement of generating more apparent specific heat release at lower temperatures for ammonium perchlorate (AP)‐based composite solid propellants, the development of high‐performance catalysts for improving the thermal decomposition properties of AP still remains essential and challenging. Herein, a novel catalyst, multichanneled hierarchical porous nanocomposite of CuO and carbonized butterfly wing (CuO/CBW), has been prepared through an in‐situ reaction on original butterfly wing scales. Owing to the high active surface area and the good electrical and thermal conductivity, as well as the synergistic effect of CuO nanoparticles (20–25 nm) and CBW, CuO/CBW nanocomposite exhibits excellent catalytic activity for AP thermal decomposition in reducing the high‐temperature decomposition temperature by 88.3°C, lowering the apparent activation energy from 190.0 to 103.1 kJ mol−1 and increasing the heat release from 255 to 1841 J g−1.

Butterfly wing architectures inspire sensor and energy applications.

Natural biological systems are constantly developing efficient mechanisms to counter adverse effects of increasing human population and depleting energy resources. Their intelligent mechanisms are characterized by the ability to detect changes in the environment, store and evaluate information, and respond to external stimuli. Bio-inspired replication into man-made functional materials guarantees enhancement of characteristics and performance. Specifically, butterfly architectures have inspired the fabrication of sensor and energy materials by replicating their unique micro/nanostructures, light-trapping mechanisms and selective responses to external stimuli. These bio-inspired sensor and energy materials have shown improved performance in harnessing renewable energy, environmental remediation and health monitoring. Therefore, this review highlights recent progress reported on the classification of butterfly wing scale architectures and explores several bio-inspired sensor and energy applications.

(Invited) Enhancing Reliability of Gas Sensors with New Design Rules for Sensing Materials and Transducers

Contemporary gas monitoring scenarios for industrial safety, environmental surveillance, medical diagnostics, personal wellness, and other applications demand sensors with higher accuracy, enhanced stability, and often lower power; all in unobtrusive formats and at low cost [1-3]. Unfortunately, available sensors based on traditional detection principles often have not only inadequate accuracy and stability but also have relatively high power demands, pushing the limits of existing detection concepts where we are reaching their fundamental performance limits. These limitations of available sensors drive the innovative designs of new generation of sensors. We are focusing on development of new principles of gas sensing based on multiparameter signal excitation and detection resulting in a new generation of gas sensors based on the multivariable response principles. Design criteria of these individual sensors involve a sensing material with multi-response mechanisms to different gases and a multivariable transducer with independent outputs to recognize these different gas responses. In our talk, we will discuss our different sensor types that operate over the electromagnetic spectrum ranging from the radio-frequency to microwave and to optical regions. We will discuss new performance capabilities of the developed sensors using two broad examples of our recent developments. In the first example, we will discuss our multivariable sensors in the radio-frequency and microwave spectral regions [4-6]. We are implementing impedance spectroscopy and diverse types of sensing materials and transducers with the goals of improving gas-selectivity of our sensors and rejection of interferences. Examples of our sensing materials in these spectral regions include conjugated and dielectric polymers, ligand-functionalized metal nanoparticles, metal oxides, and carbon allotropes. Examples of our transducers include resonant and non-resonant structures. In the second example, we will discuss our multivariable sensors in the optical spectral region [7-11]. We are implementing our bio-inspired three-dimensional nanomaterials with the visible-light reflectance or transmittance measurements with the goals of improving gas-selectivity of our sensors and enhancing sensor stability. Examples of our sensing materials operating in the optical spectral region include polymeric and inorganic nanostructures functionalized based on our design rules for multi-gas detection using individual sensors. Our developments resulted in sensors with previously unavailable performance characteristics in wearable, stationary, airborne and other formats where our multivariable sensors independently quantify up to four individual gases in complex mixtures, reject interferences with up to 2,000,000-fold overloading in concentrations over the analytes, and enhance sensor-response stability. Such performance characteristics are attractive when selectivity advantages of classic gas chromatography, ion mobility, and mass spectrometry instruments are canceled by requirements for no consumables, low power, low cost, and unobtrusive form factors for Internet of Things, Industrial Internet, and other applications. We will conclude with a perspective for future needs in fundamental and applied aspects of gas sensing and with the 2030 roadmap for ubiquitous gas monitoring.[1] Bogue, R. Towards the trillion sensors market. Sensor Rev. 34, 137-142 (2014).[2] Alexander, M., Bernhart, W., Rossbach, C. & Nölling, K. Smart Strategies for Smart Sensors. (Roland Berger GMBH, 2017).[3] Potyrailo, R. A. Ubiquitous wearable and disposable chem-bio sensors: markets demands and innovative technology solutions. (Sensors Expo & Conference, San Jose, CA, June 26-28, 2018).[4] Potyrailo, R. A., Surman, C., Nagraj, N. N. & Burns, A. Materials and Transducers Toward Selective Wireless Gas Sensing. Chem. Rev. 111, 7315–7354 (2011).[5] Potyrailo, R. A. Multivariable sensors for ubiquitous monitoring of gases in the era of Internet of Things and Industrial Internet. Chem. Rev. 116, 11877–11923 (2016).[6] Potyrailo, R. A. Toward high value sensing: monolayer-protected metal nanoparticles in multivariable gas and vapor sensors. Chem. Soc. Rev. 46, 5311-5346 (2017).[7] Potyrailo, R. A. et al. Morpho butterfly wing scales demonstrate highly selective vapour response. Nature Photonics 1, 123-128 (2007).[8] Potyrailo, R. A. et al. Discovery of the surface polarity gradient on iridescent Morpho butterfly scales reveals a mechanism of their selective vapor response. Proc. Natl. Acad. Sci. U.S.A. 110, 15567–15572 (2013).[9] Potyrailo, R. A. et al. Towards outperforming conventional sensor arrays with fabricated individual photonic vapour sensors inspired by Morpho butterflies. Nature Commun. 6, 7959 (2015).[10] Potyrailo, R. A., Karker, N., Carpenter, M. A. & Minnick, A. Multivariable bio-inspired photonic sensors for non-condensable gases. J. Opt. 20, 024006 (2018).[11] Potyrailo, R. A. et al. Multi-gas sensors for enhanced reliability of SOFC operation. ECS Transactions 91, 319-328 (2019).

Bioinspired Structural Color Patterns Derived from 1D Photonic Crystals with High Saturation and Brightness for Double Anti-Counterfeiting Decoration

Imitating the butterfly wing scale with a layer-by-layer structure and angle-dependent property, we present a facile method for the fabrication of flexible, transferable, and multilayered one-dimen...

Orientation-Dependent Reflection of Structurally Coloured Butterflies.

The photonic structures of butterfly wing scales are widely known to cause angle-dependent colours by light interference with nanostructures present in the wing scales. Here, we quantify the relevance of the horizontal alignment of the butterfly wing scales on the wing. The orientation-dependent reflection was measured at four different azimuth angles, with a step size of 90°, for ten samples—two of different areas of the same species—of eight butterfly species of three subfamilies at constant angles of illumination and observation. For the observed species with varying optical structures, the wing typically exhibits higher orientation-dependent reflections than the individual scale. We find that the measured anisotropy is caused by the commonly observed grating structures that can be found on all butterfly wing scales, rather than the local photonic structures. Our results show that the technique employed here can be used to quickly evaluate the orientation-dependence of the reflection and hence provide important input for bio-inspired applications, e.g., to identify whether the respective structure is suitable as a template for nano-imprinting techniques.

Microstructures of responsive photonic crystals on the stimuli-responsive performance: Effects and simulation

Nature provides abundant photonic structures which give a great inspiration on the synthesis of stimuli-responsive photonic crystals (PCs) with unique structures. However, the intrinsic effects of microstructures on the responsive properties of the hierarchical PCs are still not clear. Herein, the relationship between the photonic structures and the responsive properties is investigated by choosing three natural photonic structures replicated from templates, Morpho Menelaus and Morpho peleides both with a 1D tree-like hierarchical structure while having eight and four layers, respectively and Papilio paris, with an eight layered 1D concave structure. Humidity responsive PCs were prepared by in-situ polymerizing polyacrylamide (PAAm) onto the surface of the butterfly wing scales. The 1D concave (Papilio paris) structured PCs exhibited a higher humidity sensitivity: a wavelength redshift of 92 nm when the relative humidity rose from 11 to 97 %, as compared with the Morpho menelaus PCs, which have about 70 nm redshift for the same rise of the relative humidity. The eight layer 1D tree-like structured Morpho menelaus PCs had a higher reflectance intensity. The results were also supported by a finite-difference time-domain (FDTD) simulation. This work paves a new avenue to design responsive PCs with a diversity of structures from nature and controllable responsive properties.

Naturally safe: Cellular noise for document security.

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.

Roaming of Materials Scientists in Biology: Structural Colours of Butterfly Wings

Abstract The photonic nanoarchitectures occurring in the wing scales of Lycaenid butterflies were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-VIS spectroscopy. We found that the males of all the nine investigated species possess photonic nanoarchitectures built according to the same general “plan”, but each species exhibits species-specific features which results in species-specific colours reproduced generation by generation with a high degree of accuracy.

Optical Detection of Vapor Mixtures Using Structurally Colored Butterfly and Moth Wings.

Photonic nanoarchitectures in the wing scales of butterflies and moths are capable of fast and chemically selective vapor sensing due to changing color when volatile vapors are introduced to the surrounding atmosphere. This process is based on the capillary condensation of the vapors, which results in the conformal change of the chitin-air nanoarchitectures and leads to a vapor-specific optical response. Here, we investigated the optical responses of the wing scales of several butterfly and moth species when mixtures of different volatile vapors were applied to the surrounding atmosphere. We found that the optical responses for the different vapor mixtures fell between the optical responses of the two pure solvents in all the investigated specimens. The detailed evaluation, using principal component analysis, showed that the butterfly-wing-based sensor material is capable of differentiating between vapor mixtures as the structural color response was found to be characteristic for each of them.

Absorption spectra and electric field distributions of butterfly wing scale models coated with a metal film studied by finite-difference time-domain method

Inspired by alternative hybrid-biophotonic structures and modern computational electromagnetics in plasmonics, herein, we attempted to understand the plasmonic properties of a metal film (gold or palladium) on the surface features of butterfly wing scales, as they might represent the dominant features of structure-enhanced and/or structure-attenuated optical properties. Light-harvesting plasmonic antenna was loaded on these natural substrates. We examined the plasmonic properties of three models representing the scales of three lepidoptera species. Each scale model was assumed to have a 100 nm metal coating. In addition to the electron micrograph of the lepidopterans’ wings, the optical properties of the investigated structures were numerically studied using the finite-difference time-domain technique. We first constructed the biophotonic models of butterfly structures coated with a metal film, and then they were verified by scanning electron microscopy images using Lumerical Software, which provided an accurate solution of Maxwell’s equation for the micro/nanostructures. The metal samples were palladium or gold, while the investigated scales of butterfly species were Catopsilia pomona, Danaus genutia, and Cetbosia pentbesilea. Electric field and absorption spectra were observed under broadband light irradiations at perpendicular- and parallel-polarized light illuminations. As a result of the formation of variations of metals on the different features of wing scales, we observed changes in the absorption intensities and a redshift in the main peak absorbance. The spectra further showed a close relationship with the electric field distribution. A metal film coated on the butterfly wing scales acted as an optical plasmonic sensitivity to amplify and attenuate the visible light, whereas the existence of wave propagating modes from the well-defined structural variations resulted in a reduction and enhancement of the bandwidth of absorbance. Among the three simulation models, the Cetbosia pentbesilea scale model coated with a gold film demonstrated the best plasmonic properties to the electric field, in terms of its potential application for further biophotonic structure fabrication.

Sub-micrometer insights into the cytoskeletal dynamics and ultrastructural diversity of butterfly wing scales.

The color patterns that adorn lepidopteran wings are ideal for studying cell type diversity using a phenomics approach. Color patterns are made of chitinous scales that are each the product of a single precursor cell, offering a 2D system where phenotypic diversity can be studied cell by cell, both within and between species. Those scales reveal complex ultrastructures in the sub-micrometer range that are often connected to a photonic function, including iridescent blues and greens, highly reflective whites, or light-trapping blacks. We found that during scale development, Fascin immunostainings reveal punctate distributions consistent with a role in the control of actin patterning. We quantified the cytoskeleton regularity as well as its relationship to chitin deposition sites, and confirmed a role in the patterning of the ultrastructures of the adults scales. Then, in an attempt to characterize the range and variation in lepidopteran scale ultrastructures, we devised a high-throughput method to quickly derive multiple morphological measurements from fluorescence images and scanning electron micrographs. We imaged a multicolor eyespot element from the butterfly Vanessa cardui (V. cardui), taking approximately 200 000 individual measurements from 1161 scales. Principal component analyses revealed that scale structural features cluster by color type, and detected the divergence of non-reflective scales characterized by tighter cross-rib distances and increased orderedness. We developed descriptive methods that advance the potential of butterfly wing scales as a model system for studying how a single cell type can differentiate into a multifaceted spectrum of complex morphologies. Our data suggest that specific color scales undergo a tight regulation of their ultrastructures, and that this involves cytoskeletal dynamics during scale growth.

Modeling the Reflectance Changes Induced by Vapor Condensation in Lycaenid Butterfly Wing Scales Colored by Photonic Nanoarchitectures.

Gas/vapor sensors based on photonic band gap-type materials are attractive as they allow a quick optical readout. The photonic nanoarchitectures responsible for the coloration of the wing scales of many butterfly species possessing structural color exhibit chemical selectivity, i.e., give vapor-specific optical response signals. Modeling this complex physical-chemical process is very important to be able to exploit the possibilities of these photonic nanoarchitectures. We performed measurements of the ethanol vapor concentration-dependent reflectance spectra of the Albulina metallica butterfly, which exhibits structural color on both the dorsal (blue) and ventral (gold-green) wing sides. Using a numerical analysis of transmission electron microscopy (TEM) images, we revealed the details of the photonic nanoarchitecture inside the wing scales. On both sides, it is a 1D + 2D structure, a stack of layers, where the layers contain a quasi-ordered arrangement of air voids embedded in chitin. Next, we built a parametric simulation model that matched the measured spectra. The reflectance spectra were calculated by ab-initio methods by assuming variable amounts of vapor condensed to liquid in the air voids, as well as vapor concentration-dependent swelling of the chitin. From fitting the simulated results to the measured spectra, we found a similar swelling on both wing surfaces, but more liquid was found to concentrate in the smaller air voids for each vapor concentration value measured.

In situ printing of liquid superlenses for subdiffraction-limited color imaging of nanobiostructures in nature

The nanostructures and patterns that exist in nature have inspired researchers to develop revolutionary components for use in modern technologies and our daily lives. The nanoscale imaging of biological samples with sophisticated analytical tools, such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), has afforded a precise understanding of structures and has helped reveal the mechanisms contributing to the behaviors of the samples but has done so with the loss of photonic properties. Here, we present a new method for printing biocompatible “superlenses” directly on biological objects to observe subdiffraction-limited features under an optical microscope in color. We demonstrate the nanoscale imaging of butterfly wing scales with a super-resolution and larger field-of-view (FOV) than those of previous dielectric microsphere techniques. Our approach creates a fast and flexible path for the direct color observation of nanoscale biological features in the visible range and enables potential optical measurements at the subdiffraction-limited scale.