Rapid Bioenabled Formation of Ferroelectric BaTiO3 at Room Temperature from an Aqueous Salt Solution at Near Neutral pH

Solution-Based Synthesis Routes for the Preparation of Noncentrosymmetric 0-D Oxide Nanocrystals with Perovskite and Nonperovskite Structures

With the miniaturization of electronic-based devices, the foreseen potential of new optical nanoprobes and the assessment of eventual size and shape effects, elaboration of multifunctional noncentrosymmetric nanocrystals with ferroelectric, pyroelectric, piezoelectric, and nonlinear optical properties are the subject of an increasing research interest. Here, the recent achievements from the solution-based methods (coprecipitation in homogeneous and nanostructured media, sol-gel processes including various chemistries and hydro/solvothermal techniques) to prepare 0-D perovskite and nonperovskite oxides in the 5-500 nm size range are critically reviewed. To cover a representative list of covalent- and ionic-type materials, BaTiO₃ and its derivatives, niobate compounds (i.e., K/Na/LiNbO₃ ), multiferroic BiFeO_3, and crystals of lower symmetry including KTiOPO₄ and some iodate compounds such as Fe(IO₃ )₃ and La(IO₃ )₃ are systematically in focus. The resulting size, morphology, and aggregation state are discussed in light of the proposed formation mechanisms. Because of a higher complexity related to their chemical composition and crystalline structures, improving the rational design of these multifunctional oxides in terms of finely-tuned compositions, crystalline hosts and structure-property relationships still need in the future a special attention of the research community to the detailed understanding of the reaction pathways and crystallization mechanisms.

Structure-guided identification of a peptide for bio-enabled gold nanoparticle synthesis

In this study, we show that maltose-binding protein (MBP) is capable of facilitating stable gold nanoparticle synthesis, and a structure of MBP in the presence of gold ions was determined by X-ray crystallography. Using this high-resolution structure of gold ion bound MBP, a peptide (AT1) was selected and synthesized and was shown to also aid in the synthesis of stable gold nanoparticles under similar experimental conditions to those used for protein facilitated synthesis. This structure-based approach represents a new potential method for the selection of peptides capable of facilitating stable nanoparticle synthesis.

Structural Details of BaTiO3 Nano-Powders Deduced from the Anisotropic XRD Peak Broadening

In this study, nano-BaTiO₃ (BTO) powders were obtained via the solvothermal method at different reaction times and were investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results were compared with those obtained for a larger crystallite size BTO powder (BTO-m). The sizes of the cuboid crystallites (as determined by XRD and TEM) ranged from about 18 to 24 nm, depending on the reaction time. The evolution with temperature of the structure parameters of nano-BTO was monitored by means of X-ray diffraction and Raman spectroscopy and no signs of phase transition were found up to 170 °C. Careful monitoring of the dependence of the XRD peak widths on the hkl indices showed that the effect of the cubic crystallite shape upon the XRD peak widths was buried by the effect of hidden tetragonal line splits and by anisotropic microstrain. The good correlation of the line widths with the tetragonal split amplitudes, observed especially for BTO-m above the transition temperature, indicates tetragonal deformations, as also revealed by Raman spectroscopy. The large anisotropic microstrain shown by the nano-powders, which had a maximum value in the <100> directions, was considered evidence of the phenomenon of surface relaxation of cubic crystallites edged by {100} faces. The observed behavior of the nano-BTO structures with increasing temperature may suggest a correlation between the surface relaxation and tetragonal deformation in the nano-cubes. The experimental results for both nano-BTO and mezoscale-BTO are in agreement with the core-shell model.

Metalloid Reductase Activity Modified by a Fused Se0 Binding Peptide

A selenium nanoparticle binding peptide was isolated from a phage display library and genetically fused to a metalloid reductase that reduces selenite (SeO₃^2-) to a Se⁰ nanoparticle (SeNP) form. The fusion of the Se binding peptide to the metalloid reductase regulates the size of the resulting SeNP to ∼35 nm average diameter, where without the peptide, SeNPs grow to micron sized polydisperse precipitates. The SeNP product remains associated with the enzyme/peptide fusion. The Se binding peptide fusion to the enzyme increases the enzyme's SeO₃^2- reductase activity. Size control of particles was diminished if the Se binding peptide was only added exogenously to the reaction mixture. The enzyme-peptide construct shows preference for binding smaller SeNPs. The peptide-SeNP interaction is attributed to His based ligation that results in a peptide conformational change on the basis of Raman spectroscopy.

Biomolecular Material Recognition in Two Dimensions: Peptide Binding to Graphene, h-BN, and MoS2 Nanosheets as Unique Bioconjugates

Two-dimensional nanosheet-based materials such as graphene, hexagonal boron nitride, and MoS₂ represent intriguing structures for a variety of biological applications ranging from biosensing to nanomedicine. Recent advances have demonstrated that peptides can be identified with affinity for these three materials, thus generating a highly unique bioconjugate interfacial system. This Review focuses on recent advances in the formation of bioconjugates of these types, paying particular attention to the structure/function relationship of the peptide overlayer. This is achieved through the amino acid composition of the nanosheet binding peptides, thus allowing for precise control over the properties of the final materials. Such bioconjugate systems offer rapid advances via direct property control that remain difficult to achieve for biological applications using nonbiological approaches.

Space-Confined Synthesis of Core-Shell BaTiO3@Carbon Microspheres as a High-Performance Binary Dielectric System for Microwave Absorption

Binary dielectric composites are viewed as a kind of promising candidate for conventional magnetic materials in the field of microwave absorption. Herein, we demonstrate the successful fabrication of core-shell BaTiO₃@carbon microspheres through a space-confined strategy. The electromagnetic properties of BaTiO₃@carbon microspheres can be easily tailored by manipulating the relative content of carbon shells. It is confirmed that dielectric loss of these composites mainly benefits from conductivity loss, dipole orientation polarization, and interfacial polarization, and the core-shell configuration shows its positive contribution to the reinforcement of interfacial polarization. When the content of carbon shells is optimized, the as-obtained composite will display excellent microwave-absorption performance due to decent attenuation and well-matched impedance. The strongest reflection loss can reach up to -88.5 dB at 6.9 GHz with the absorber thickness of 3.0 mm, and the qualified bandwidth below -10.0 dB covers 9.0-12.0 GHz, when the thickness is designated at 2.0 mm. Such a performance in the X band is superior to those of most typical binary dielectric systems. More importantly, these BaTiO₃@carbon microspheres maintain good performance after being treated under high-temperature and acidic conditions for a long time, manifesting their promising prospect for practical application. It is believed that these results may be helpful for the development of multicomponent dielectric systems as high-performance microwave absorbing materials.

Toward Escherichia coli bacteria machine for water oxidation

Nature uses a Mn oxide-based catalyst for water oxidation in plants, algae, and cyanobacteria. Mn oxides are among major candidates to be used as water-oxidizing catalysts. Herein, we used two straightforward and promising methods to form Escherichia coli bacteria/Mn oxide compounds. In one of the methods, the bacteria template was intact after the reaction. The catalysts were characterized by X-ray photoelectron spectroscopy, visible spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, Raman spectroscopy, and X-ray diffraction spectrometry. Electrochemical properties of the catalysts were studied, and attributed redox potentials were assigned. The water oxidation of the compounds was examined under electrochemical condition. Linear sweep voltammetry showed that the onsets of water oxidation in our experimental condition for bacteria and Escherichia coli bacteria/Mn oxide were 1.68 and 1.56 V versus the normal hydrogen electrode (NHE), respectively. Thus, the presence of Mn oxide in the catalyst significantly decreased (~ 120 mV) the overpotential needed for water oxidation.

Identification of Novel Short BaTiO3-Binding/Nucleating Peptides for Phage-Templated in Situ Synthesis of BaTiO3 Polycrystalline Nanowires at Room Temperature

Ferroelectric materials, such as tetragonal barium titanate (BaTiO3), have been widely used in a variety of areas including bioimaging, biosensing, and high power switching devices. However, conventional methods for the synthesis of tetragonal phase BaTiO3 usually require toxic organic reagents and high temperature treatments, and are thus not environment-friendly and energy-efficient. Here, we took advantage of the phage display technique to develop a novel strategy for the synthesis of BaTiO3 nanowires. We identified a short BaTiO3-binding/nucleating peptide, CRGATPMSC (named RS), from a phage-displayed random peptide library by biopanning technique and then genetically fused the peptide to the major coat protein (pVIII) of filamentous M13 phages to form the pVIII-RS phages. We found that the resultant phages could not only bind with the presynthesized BaTiO3 crystals but also induce the nucleation of uniform tetragonal BaTiO3 nanocrystals at room temperature and without the use of toxic reagents to form one-dimensional polycrystalline BaTiO3 nanowires. This approach enables the green synthesis of BaTiO3 polycrystalline nanowires with potential applications in bioimaging and biosensing fields.

Synthesis of gold structures by gold-binding peptide governed by concentration of gold ion and peptide

Although biological synthesis methods for the production of gold structures by microorganisms, plant extracts, proteins, and peptide have recently been introduced, there have been few reports pertaining to controlling their size and morphology. The gold ion and peptide concentrations affected on the size and uniformity of gold plates by a gold-binding peptide Midas-11. The higher concentration of gold ions produced a larger size of gold structures reached 125.5 μm, but an increased amount of Midas-11 produced a smaller size of gold platelets and increased the yield percentage of polygonal gold particles rather than platelets. The mechanisms governing factors controlling the production of gold structures were primarily related to nucleation and growth. These results indicate that the synthesis of gold architectures can be controlled by newly isolated and substituted peptides under different reaction conditions.

Phase evolution in sonochemically synthesized Fe3+ doped BaTiO3 nanocrystallites: structural, magnetic and ferroelectric characterisation

Sonochemically synthesized Fe³⁺ doped BaTiO₃ nanostructures exhibiting phase transition and room temperature ferromagnetic and ferroelectric behaviour.

Screening of Oligopeptides that Recognize Inorganic Crystalline Facets of Metal Nanoparticles

Peptides that possess specific affinity to distinct crystal facets have been reported previously. However, their adsorption behavior in terms of the crystal sizes and shapes is less exploited. Herein, we isolate several phage clones that show the strong affinity to {100} of Pd at a neutral pH from the M13 phage library, and among them the phages that have shape selectivity to the cubic structure are identified by eliminating ones that bind randomly shaped Pd nanoparticles (NPs). Since Pd nanocube-binding phages are eluted by lowering pH values in the biopanning process, the selected phages (and their binding peptides displayed on protein pIII) can be released from Pd surfaces through pH changes. We used this feature to modulate the capping density of selected peptides on NPs. For example, when less peptides are capped on Pd nanocubes by lowering the pH values, the shape of the nanocubes is deformed and some evolve into a concave shape, indicating that Pd atoms are released from the less protected {100} facet selectively due to the higher surface energy. This type of crystalline facet-recognizing peptides can be applied for smart capping agents that not only bind target crystalline planes, but also modify their coverage on the specific surfaces with pH changes. The peptide-capping agents could be useful to fabricate NPs with characteristic shapes through etching and adsorption of atoms on specific crystalline planes of seed nanocrystals.

Perovskite ferroelectric nanomaterials

In this review, the main concept of ferroelectricity of perovskite oxides and related materials at nanometer scale and existing difficulties in the synthesis of those nanocrystals are discussed. Important effects, such as depolarization field and size effect, on the existence of ferroelectricity in perovskite nanocrystals are deliberated. In the discussion of modeling works, different theoretical calculations are pinpointed focusing on their studies of lattice dynamics, phase transitions, new origin of ferroelectricity in nanostructures, etc. As the major part of this review, recent research progress in the facile synthesis, characterization and various applications of perovskite ferroelectric nanomaterials, such as BaTiO₃, PbTiO₃, PbZrO₃, and BiFeO₃, are also scrutinized. Perspectives concerning the future direction of ferroelectric nanomaterials research and its potential applications in renewable energy, etc., are presented. This review provides an overview in this area and guidance for further studies in perovskite ferroelectric nanomaterials and their applications.

Anisotropic nanocrystal arrays organized on protein lattices formed by recombinant clathrin fragments

Recombinant clathrin protein fragments form assemblies that template gold nanocrystals in an array across the latticed surface. The nanocrystals exhibit unusual anisotropic morphologies with long range ordering, both of which are dependent upon the presence of a hexahistidine tag on the clathrin heavy chain fragments.

Novel ZnO-binding peptides obtained by the screening of a phage display peptide library

Zinc oxide (ZnO) is a semiconductor compound with a potential for wide use in various applications, including biomaterials and biosensors, particularly as nanoparticles (the size range of ZnO nanoparticles is from 2 to 100 nm, with an average of about 35 nm). Here, we report isolation of novel ZnO-binding peptides, by screening of a phage display library. Interestingly, amino acid sequences of the ZnO-binding peptides reported in this paper and those described previously are significantly different. This suggests that there is a high variability in sequences of peptides which can bind particular inorganic molecules, indicating that different approaches may lead to discovery of different peptides of generally the same activity (e.g., binding of ZnO) but having various detailed properties, perhaps crucial under specific conditions of different applications.

Design and synthesis of binding growth factors

Growth factors play important roles in tissue regeneration. However, because of their instability and diffusible nature, improvements in their performance would be desirable for therapeutic applications. Conferring binding affinities would be one way to improve their applicability. Here we review techniques for conjugating growth factors to polypeptides with particular affinities. Conjugation has been designed at the level of gene fusion and of polypeptide ligation. We summarize and discuss the designs and applications of binding growth factors prepared by such conjugation approaches.

Nanotechnology Meets Biology: Peptide-based Methods for the Fabrication of Functional Materials

Nature exploits sustainable methods for the creation of inorganic materials on the nanoscale for a variety of applications. To achieve such capabilities, biomolecules such as peptides and proteins have been developed that recognize and bind the different compositions of materials. While a diverse set of materials binding sequences are present in the biosphere, biocombinatorial techniques have been used to rapidly identify peptides that facilitate the formation of new materials of technological importance. Interestingly, the binding motif of the peptides at the inorganic surface is likely to control the size, structure, composition, shape, and functionality of the final materials. In order to advance these intriguing new biomimetic approaches, a complete understanding of this biotic/abiotic interface is required. In this Perspective, we highlight recent advances in the biofunctionalization of nanoparticles with potential applications ranging from catalysis and energy storage to plasmonics and biosensing. We specifically focus on the physical characterization of the peptide-based surface from which specificity and activity are likely embedded.

Material binding peptides for nanotechnology

Remarkable progress has been made to date in the discovery of material binding peptides and their utilization in nanotechnology, which has brought new challenges and opportunities. Nowadays phage display is a versatile tool, important for the selection of ligands for proteins and peptides. This combinatorial approach has also been adapted over the past decade to select material-specific peptides. Screening and selection of such phage displayed material binding peptides has attracted great interest, in particular because of their use in nanotechnology. Phage display selected peptides are either synthesized independently or expressed on phage coat protein. Selected phage particles are subsequently utilized in the synthesis of nanoparticles, in the assembly of nanostructures on inorganic surfaces, and oriented protein immobilization as fusion partners of proteins. In this paper, we present an overview on the research conducted on this area. In this review we not only focus on the selection process, but also on molecular binding characterization and utilization of peptides as molecular linkers, molecular assemblers and material synthesizers.

Understanding the mechanism of amino acid-based Au nanoparticle chain formation

Understanding the surface orientation and interactions between biomolecules and nanoparticles is important in order to determine their effects on the final structure and activity. At present, limited analytical techniques are available to probe these interactions, especially for materials dispersed in solution. We recently demonstrated that arginine, a simple amino acid, is able to bind to the surface of Au nanoparticles in a segregated pattern, which produces an electronic dipole across the structure. As a result, the formation of linear chains of Au nanoparticles occurred that was dependent upon of the concentration of arginine. Here, we present new information concerning the mechanism of assembly and demonstrate unique reaction conditions that can be used to directly control the assembly rate, and thus the size of the final superstructure that is produced. The assembly process was modulated by the arginine/Au nanoparticle ratio, the temperature of the system, the dielectric of the solvent, and the solution ionic strength, all of which can be used in combination to control the process. These effects were monitored using UV-vis spectroscopy, transmission electron microscopy, and dynamic light scattering. From these results, it is suggested that the second step of the assembly process, which is the formation of nanoparticle chains mediated by Brownian motion, controls the overall assembly rate and thus the size and orientation of the final superstructure produced. Furthermore, the reaction kinetics of the system have been studied from which rate constants and activity energies have been extracted for electrostatic-based nanoparticle assembly. This analysis indicates that the assembly/organization step is likely broken into two substeps with the formation of nanoparticle dimers occurring in solution first, followed by the oligomerization of the dimers to form the linear and branched chains. The dimerization step follows traditional second-order kinetics and is relatively fast, while the oligomerization process is quite complex and is anticipated to be slower than the dimerization step. These results are important, as they lay the basis for the subsequent use of this technique for the possible fabrication of electronic device components or as sensitive assays to probe the surface structure of nanomaterials.

Experimental studies on the interactions between Au nanoparticles and amino acids: bio-based formation of branched linear chains

Biomacromolecules represent new structures employed for the fabrication, assembly, and subsequent use of nanomaterials for a variety of applications. By genetically selecting for the binding abilities of these bio-based molecules, the generation of materials with enhanced and environmentally sound properties is possible. Unfortunately, the level of understanding as to how the biomolecules bind and arrange on the nanomaterial surface is incomplete. Recent experimental and theoretical results suggest that the binding is dependent upon the peptide composition, sequence, and structure; however, these results were obtained for two-dimensional surfaces of the targeted inorganic material. Changing of the sample from two-dimensional targets to in solution three-dimensional nanomaterials presents a challenge because the level of analytical characterization for the latter system is minimal. Here we present our recent studies on the interactions between Au nanoparticles and the amino acid arginine. In our experimental design, the introduction of increasing concentrations of arginine to citrate-capped Au nanoparticles resulted in the formation of branched linear chains of the spherical nanomaterials. This assembly process was able to be monitored using UV-vis spectroscopy, transmission electron microscopy, and dynamic light scattering. The final results suggest that incomplete substitution of the original citrate surface passivant with the amino acid occurs, resulting in surface segregation of the two species. The segregation effect produces a dipole across the Au nanoparticle surface to drive the linear assembly of the materials in solution. Such results can possibly be exploited in understanding binding motifs and modes for biomolecules on the surface of functional nanomaterials.

Biomimetic synthesis of Pd nanocatalysts for the Stille coupling reaction

Here we report on the biomimetic synthesis of Pd nanoparticles for use as models of green catalytic systems. The nanomaterials are synthesized using peptides isolated via phage-display techniques that are specific to Pd surfaces. Using this synthetic strategy, peptide-functionalized Pd nanoparticles of 1.9 +/- 0.3 nm in diameter are produced, which are soluble and stable in aqueous solutions. Once characterized, these biobased materials were then used as catalysts to drive the formation of C-C bonds using the Stille coupling reaction. Under the conditions of an aqueous solvent at room temperature, quantitative product yields were achieved within 24.0 h employing catalyst loadings of > or = 0.005 mol % of Pd. Additionally, high TOF values of 3207 +/- 269 mol product x (mol Pd x h)(-1) have been determined for these materials. The catalytic reactivity was then examined over a set of substrates with substitutions for both functional group and halide substituents, demonstrating that the peptide-based Pd nanoparticles are reactive toward a variety of functionalities. Taken together, these bioinspired materials represent unique model systems for catalytic studies to elucidate ecologically friendly reactive species and conditions.

Room-temperature synthetic pathways to barium titanate nanocrystals

Novel room-temperature pathways to BaTiO(3) nanocrystals have been recently developed, which stand in contrast to traditional high-temperature methods. Peptide-assisted, bio-facilitated routes have been developed for low-temperature nanocrystal growth, in addition to two low-temperature routes completely independent of biomolecules. These innovative methods lay the groundwork for the facile production of nanoscale BaTiO(3) in economical and energy-efficient ways.