[Show abstract][Hide abstract] ABSTRACT: Reversible changes in phosphorylation of the reflectin proteins have been shown to drive the tunability of color and brightness of light reflected from specialized cells in the skin of squids and related cephalopods. We show here, using dynamic light scattering, electron microscopy, and fluorescence analyses, that reversible titration of the excess positive charges of the reflectins, comparable to that produced by phosphorylation, is sufficient to drive the reversible condensation and hierarchical assembly of these proteins. Results suggest a two-stage process in which charge neutralization first triggers condensation, resulting in the emergence of previously cryptic structures that subsequently mediate reversible, hierarchical assembly. The extent to which cyclability is seen in the in vitro formation and disassembly of complexes estimated to contain several thousand reflectin molecules suggests that intrinsic sequence- and structure-determined specificity governs the reversible condensation and assembly of the reflectins, and that these processes are thus sufficient to produce the reversible changes in refractive index, thickness and spacing of the reflectin-containing subcellular Bragg lamellae to change the brightness and color of reflected light. This molecular mechanism points to the metastability of the reflectins as the centrally important design principle governing biophotonic tunability in this system.
Preview · Article · Dec 2015 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Amorphous carbon is widely used as a support for Pt nanoparticle catalysts. We show here that catalytic performance can be greatly improved by functionalizing the carbon support with a nitrogen-containing molecule, in conjunction with a new method for the in situ synthesis of nanocrystalline Pt. Vulcan® carbon black is covalently functionalized with 4-aminomethylpyridine (4AMP) via formation of an acid chloride on the surface followed by amidation. The resulting 4AMP-functionalized Vulcan® (4AMP-VC) was thoroughly characterized and shown to contain N at the surface of the Vulcan® carbon support. Pt nanoparticles grown on the 4AMP-VC have a smaller average size and much narrower size distribution than Pt nanoparticles grown on bare Vulcan® (VC). In addition, the Pt/4AMP-VC catalysts show higher catalytic activity and are more durable than their Pt/VC counterparts. We infer through careful analysis of X-ray photoelectron spectra that the Pt nanoparticles bind preferentially to the pyridinic nitrogen of the 4AMP.
[Show abstract][Hide abstract] ABSTRACT: In nature, biomolecules guide the formation of hierarchically-ordered, lightweight, inorganic-organic composites such as corals, shells, teeth and bones. M13 bacteriophage has been used to mimic bio-inspired material development due to its rigid, nanoscale rod-like morphology. Liquid-crystalline monolayers of genetically engineered phage have been used to template crystallization of thin layers of inorganic and metallic materials. We have created thin films composed of engineered M13 phage capable of binding inorganic components. We employed both a dip-cast and a drop-cast film fabrication method on both smooth and rough gold, silica and glass casting surfaces to create thin films and 3D structures of various degrees of hierarchical order. We have found the engineered M13 phage and the inorganic mineral significantly affected both film morphology and the mechanical properties of the film. Similarly, film fabrication parameters such as solution chemistry, temperature, and pulling speed affected film properties. Using a calcium phosphate biomineralized 4E phage, film thickness increased linearly with the number of layers/dips in the phage solution. The stiffness of these composites (Young's modulus) were >80 GPa for mineralized, multilayer films. These materials are an order of magnitude stiffer than the biological equivalent collagen. Stiffness, however, does not appear to increase in a multilayer film beyond a saturation point. Ultimately, we have developed a platform for phage-based bio-composites for developing high performance materials.
No preview · Article · Jan 2015 · MRS Online Proceeding Library
[Show abstract][Hide abstract] ABSTRACT: 'Giant' tridacnid clams have evolved a three-dimensional, spatially efficient, photodamage-preventing system for photosymbiosis. We discovered that the mantle tissue of giant clams, which harbours symbiotic nutrition-providing microalgae, contains a layer of iridescent cells called iridocytes that serve to distribute photosynthetically productive wavelengths by lateral and forward-scattering of light into the tissue while back-reflecting non-productive wavelengths with a Bragg mirror. The wavelength- and angle-dependent scattering from the iridocytes is geometrically coupled to the vertically pillared microalgae, resulting in an even re-distribution of the incoming light along the sides of the pillars, thus enabling photosynthesis deep in the tissue. There is a physical analogy between the evolved function of the clam system and an electric transformer, which changes energy flux per area in a system while conserving total energy. At incident light levels found on shallow coral reefs, this arrangement may allow algae within the clam system to both efficiently use all incident solar energy and avoid the photodamage and efficiency losses due to non-photochemical quenching that occur in the reef-building coral photosymbiosis. Both intra-tissue radiometry and multiscale optical modelling support our interpretation of the system's photophysics. This highly evolved 'three-dimensional' biophotonic system suggests a strategy for more efficient, damage-resistant photovoltaic materials and more spatially efficient solar production of algal biofuels, foods and chemicals.
Full-text · Article · Oct 2014 · Journal of The Royal Society Interface
[Show abstract][Hide abstract] ABSTRACT: A two-step colloidal lithography process (Langmuir-Blodgett dip coating + reactive ion etching) was developed to fabricate single and double-sided moth-eye structures in Si, Ge, and GaAs for antireflection applications in the IR. Large increases in transmittance were obtained in all three material platforms (up to 97% single-side and 91% absolute transmittance) over the lambda = 4-20+ mu m region. Effective medium theory and the transfer matrix method were used to predict IR optical response of moth-eye substrates as well as investigate the effect of protuberance shape on antireflectance behavior. Overall, it is demonstrated that colloidal lithography and etching provide an easy and generic way to synthesize moth-eyes in different IR material platforms. (C) 2014 American Vacuum Society.
No preview · Article · Sep 2014 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
[Show abstract][Hide abstract] ABSTRACT: Organisms of the phylum Porifera, that is, sponges, utilize enzymatic hydrolysis to concatenate bioavailable inorganic silicon to produce lightweight, strong, and often flexible skeletal elements called spicules. In their optical transparency, these remarkable biomaterials resemble fused silica, despite having been formed under ambient marine biological conditions. Although previous studies have elucidated the chemical mechanisms of spicule formation and revealed the extensive hydration of these glasses, their precise composition and local and medium-range structures had not been determined. We have employed a combination of compositional analysis, 1H and 29Si solid-state nuclear magnetic resonance spectroscopy, and synchrotron X-ray total scattering to characterize spicule-derived silica produced by the demosponge Tethya aurantia. These studies indicate that the materials are highly hydrated, but in an inhomogeneous manner. The spicule-derived silica is, on average, perfectly dense for the given extent of hydration and regions of fully condensed and unstrained SiO networks persist throughout each monolithic spicule. To accommodate chemical strain and defects, the extensive hydration is concentrated in distinct regions that give rise to mesostructural features. The chemistry responsible for producing spicule silica resembles hydrolytic sol-gel processing, which offers exceptional control over the precise local atomic arrangement of materials. However, the specific processing involved in forming the sponge spicule silica further results in regions of fully condensed silica coexisting with regions of incomplete condensation. This mesostructure suggests a mechanism for atomistic defect tolerance and strain relief that may account for the unusual mechanical properties of the biogenic spicules.
Full-text · Article · Apr 2014 · Chemistry - A European Journal
[Show abstract][Hide abstract] ABSTRACT: Loliginid squid dynamically tune the structural iridescence of cells in their skin for active camouflage and communication. Bragg reflectors in these cells consist of membrane-bound lamellae periodically alternating with low refractive index extracellular spaces; neuronal signalling induces condensation of the reflectin proteins that fill the lamellae, consequently triggering the expulsion of water. This causes an increase in refractive index within the lamellae, activating reflectance, with the change in lamellar thickness and spacing progressively shifting the wavelength of reflected light. We used micro-spectrophotometry to measure the functionally relevant refractive index of the high-index lamellae of the Bragg reflectors containing the condensed reflectins in chemically fixed dermal iridocytes of the squid, Doryteuthis opalescens. Our high-magnification imaging spectrometer allowed us to obtain normalized spectra of optically distinct sections of the individual, subcellular, multi-layer Bragg stacks. Replacement of the extracellular fluid with liquids of increasing refractive index allowed us to measure the reflectivity of the Bragg stacks as it decreased progressively to 0 when the refractive index of the extracellular medium exactly matched that of the reflectin-filled lamellae, thus allowing us to directly measure the refractive index of the reflectin-filled lamellae as ncondensed lamellae ≈ 1.44. The measured value of the physiologically relevant ncondensed lamellae from these bright iridocytes falls within the range of values that we recently determined by an independent optical method and is significantly lower than values previously reported for dehydrated and air-dried reflectin films. We propose that this directly measured value for the refractive index of the squid's Bragg lamellae containing the condensed reflectins is most appropriate for calculations of reflectivity in similar reflectin-based high-index layers in other molluscs.
No preview · Article · Mar 2014 · Journal of The Royal Society Interface
[Show abstract][Hide abstract] ABSTRACT: A high-rate, continuous synthesis of functional nanomaterials using a home engineered reactor is reported. The reactor is able to produce low-cost, kilogram-scale BaTiO3 nanopowders with a nanocrystalline particle size less than 30 nm at mild temperatures (<100 °C) and ambient pressure. Nebulization and collision of warm microdroplets (60–80 °C) of Ba(OH)2 and Ti(O-nBu)4 very quickly result in total hydrolysis and subsequent conversion to BaTiO3, yielding 1.3 kg/day of high purity, highly crystalline nanoparticles (25–30 nm). This synthesis procedure also enables high-rate production of TiO2 anatase (2.9 kg/day). It therefore provides a general platform for processing and scaling up of functional inorganic nanomaterials under very mild conditions.
No preview · Article · Mar 2014 · Advanced Functional Materials
[Show abstract][Hide abstract] ABSTRACT: Moth-eye (ME) arrays with varying aspect ratios and profile heights were fabricated in Si using a general colloidal lithography and reactive ion etching technique. Antireflective (AR) properties of the arrays were rigorously assessed from the near to far infrared (λ=2-50 μm) using transmission and reflection measurements via dispersive and Fourier transform infrared spectroscopy and modeled using an effective medium approximation (EMA). Infrared transmission of low aspect ratio structures (∼2) matched the EMA model, indicating that the most important factor for AR at higher wavelengths is structure height. High aspect ratio structures (>6) were highly transmissive (>90% of theoretical maximum) over a large bandwidth in the mid-infrared (20-50 μm). Specular reflectance, total transmission, and diffuse reflectance (DR) measurements indicate that ME structures do not reach the theoretical maximum at near-infrared wavelengths due to DR and forward scattering phenomena. Ultimately, correlating optical performance with feature geometry (pitch, profile, height, etc.) over multiple length scales allows intelligent design of ME structures for broadband applications.
[Show abstract][Hide abstract] ABSTRACT: DNA-based information systems drive the combinatorial optimization processes of natural evolution, including the evolution of biominerals. Advances in high-throughput DNA sequencing expand the power of DNA as a potential information platform for combinatorial engineering, but many applications remain to be developed due in part to the challenge of handling large amounts of sequence data. Here we employ high-throughput sequencing and a recently developed clustering method (AutoSOME) to identify single-stranded DNA sequence families that bind specifically to ZnO semiconductor mineral surfaces. These sequences were enriched from a diverse DNA library after a single round of screening, whereas previous screening approaches typically require 5-15 rounds of enrichment for effective sequence identification. The consensus sequence of the largest cluster was poly-d(T)30. This consensus sequence exhibited clear aptamer behavior and was shown to promote the synthesis of crystalline ZnO from aqueous solution at near-neutral pH. This activity is significant, as the crystalline form of this wide-bandgap semiconductor is not typically amenable to solution synthesis in this pH range. High-resolution TEM revealed that this DNA synthesis route yields ZnO nanoparticles with an amorphous-crystalline core-shell structure, suggesting that the mechanism of mineralization involves nanoscale coacervation around the DNA template. We thus demonstrate that our new method, termed Single round Enrichment of Ligands by deep Sequencing (SEL-Seq), can facilitate biomimetic synthesis of technological nanomaterials by accelerating combinatorial selection of biomolecular-mineral interactions. Moreover, by enabling direct characterization of sequence family demographics, we anticipate that SEL-Seq will enhance aptamer discovery in applications employing additional rounds of screening.
[Show abstract][Hide abstract] ABSTRACT: Loliginid squid use tunable multilayer reflectors to modulate the optical properties of their skin for camouflage and communication. Contained inside specialized cells called iridocytes, these photonic structures have been a model for investigations into bio-inspired adaptive optics. Here, we describe two distinct sexually dimorphic tunable biophotonic features in the commercially important species Doryteuthis opalescens: bright stripes of rainbow iridescence on the mantle just beneath each fin attachment and a bright white stripe centered on the dorsal surface of the mantle between the fins. Both of these cellular features are unique to the female; positioned in the same location as the conspicuously bright white testis in the male, they are completely switchable, transitioning between transparency and high reflectivity. The sexual dimorphism, location and tunability of these features suggest that they may function in mating or reproduction. These features provide advantageous new models for investigation of adaptive biophotonics. The intensely reflective cells of the iridescent stripes provide a greater signal-to-noise ratio than the adaptive iridocytes studied thus far, while the cells constituting the white stripe are adaptive leucophores - unique biological tunable broadband scatterers containing Mie-scattering organelles activated by acetylcholine, and a unique complement of reflectin proteins.
No preview · Article · Oct 2013 · Journal of Experimental Biology
[Show abstract][Hide abstract] ABSTRACT: A biologically inspired synthesis method is presented as a new tool for the design of novel electrochemically active materials, focusing on the advantages for fuel cell development. The need for cost-effective, high-performance materials is driving contemporary fuel cell research, with the expectation that advances in synthetic methods will be necessary for commercialization of this energy technology. Highly active electrocatalysts for proton-exchange-membrane (PEM) fuel cells are being developed, by combining a kinetically controlled synthesis method of the nanocrystalline metal catalyst with the mesoscale assembly of two morphologically different carbon building blocks of the supporting matrix. These methods provide access to new combinations of porosity, conductivity and electrochemical hydrogen oxidation. The relationships between the porous morphologies of the carbon matrices, the sizes of the platinum nanocrystals and their resulting electrochemical activities are discussed, correlating these with the relevant fuel cell principles.
[Show abstract][Hide abstract] ABSTRACT: Detailed examinations of an algal-microherbivore symbiosis have revealed mutualistic components of such herbivore-plant interactions. High-resolution photomicroscopy and experimental analyses in the field and laboratory were used to evaluate effects of foraging by Haliotis rufescens (red abalone) postlarvae ˜ 200 μm in length, on their encrusting red algal hosts, Lithothamnion (=Lithothamnium) californicum, Lithophyllum lichenare, and Hildenbrandia rubra (=H. prototypus). We have quantified the microscopic food availability, postlarval foraging behaviour, changes in stomach and faecal contents, growth, and mutualistic effects of grazing. Host algae were found to benefit both from a reduction in coverage by epiphytic algae, and from enhancement of vegetative growth.
No preview · Article · Jun 2013 · Molluscan Research
[Show abstract][Hide abstract] ABSTRACT: Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack-the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures.
No preview · Article · May 2013 · Journal of The Royal Society Interface
[Show abstract][Hide abstract] ABSTRACT: Squids have used their tunable iridescence for camouflage and communication for millions of years; materials scientists have more recently looked to them for inspiration to develop new "biologically inspired" adaptive optics. Iridocyte cells produce iridescence through constructive interference of light with intracellular Bragg reflectors. The cell's dynamic control over the apparent lattice constant and dielectric contrast of these multilayer stacks yields the corresponding optical control of brightness and color across the visible spectrum. Here, we resolve remaining uncertainties in iridocyte cell structure and determine how this unusual morphology enables the cell's tunable reflectance. We show that the plasma membrane periodically invaginates deep into the iridocyte to form a potential Bragg reflector consisting of an array of narrow, parallel channels that segregate the resulting high refractive index, cytoplasmic protein-containing lamellae from the low-index channels that are continuous with the extracellular space. In response to control by a neurotransmitter, the iridocytes reversibly imbibe or expel water commensurate with changes in reflection intensity and wavelength. These results allow us to propose a comprehensive mechanism of adaptive iridescence in these cells from stimulation to color production. Applications of these findings may contribute to the development of unique classes of tunable photonic materials.
Preview · Article · Jan 2013 · Proceedings of the National Academy of Sciences