Selective characterization of proteins on nanoscale concave surfaces.

Nanoscale curvature plays a critical role in nanostructure-biomolecule interactions, yet the understanding of such effects in concave nanostructures is still very limited. Because concave nanostructures usually possess convex surface curvatures as well, it is challenging to selectively study the proteins on concave surfaces alone. In this work, we have developed a novel and facile method to address this issue by desorbing proteins on the external surfaces of hollow gold nanocages (AuNG), allowing the selective characterization of retained proteins immobilized on their internal concave surfaces. The selective desorption of proteins was achieved via varying the solution ionic strength, and was demonstrated by both calculation and experimental comparison with non-hollow nanoparticles. This method has created a new platform for the discrete observation of proteins adsorbed inside AuNG hollow cores, and this work suggests an expanded biomedical application space for hollow nanomaterials.

Stem cell behavior on tailored porous oxide surface coatings.

Nanoscale surface topographies are known to have a profound influence on cell behavior, including cell guidance, migration, morphology, proliferation, and differentiation. In this study, we have observed the behavior of human mesenchymal stem cells cultured on a range of tailored porous SiO2 and TiO2 nanostructured surface coatings fabricated via glancing angle electron-beam deposition. By controlling the physical vapor deposition angle during fabrication, we could control systematically the deposited coating porosity, along with associated topographic features. Immunocytochemistry and image analysis quantitatively revealed the number of adherent cells, as well as their basic cellular morphology, on these surfaces. Signaling pathway studies showed that even with subtle changes in nanoscale surface structures, the behavior of mesenchymal stem cells was strongly influenced by the precise surface structures of these porous coatings.

Protein immobilization in hollow nanostructures and investigation of the adsorbed protein behavior.

Understanding nanomaterial-biomolecule interactions is critical to develop broad applications in sensors, devices, and therapeutics. During the past decade, in-depth studies have been performed on the effect of nanoscale surface topography on adsorbed protein structure and function. However, a fundamental understanding of nanobio interactions at concave surfaces is limited; the greatest challenge is to create a nanostructure that allows such interactions to occur and to be characterized. We have synthesized hollow nanocages (AuNG) through careful control of morphology and surface chemistry. Lysozyme was used as a model to probe interactions between a protein and these nanostructures. Solid Au nanoparticles with a similar morphology and surface chemistry were also used as a reference. Through a series of quantitative analyses of protein adsorption profiles and enzymatic activity assays of both nanobioconjugates, we discovered that a significant amount of protein could be delivered into the core of AuNG, while maintaining a substantial fraction of native activity.

Identifying specific protein residues that guide surface interactions and orientation on silica nanoparticles.

We identify specific acylphosphatase (AcP) residues that interact with silica nanoparticles (SNPs) using a combined NMR spectroscopy and proteomics-mass spectrometry approach. AcP associated with 4- and 15-nm diameter SNPs through a common and specific interaction surface formed by amino acids from the two α-helices of the protein. Greater retention of native protein structure was obtained on 4-nm SNPs than on 15-nm particles, presumably due to greater surface curvature-induced protein stabilization with the smaller SNPs. These results demonstrate that proteins may undergo specific and size-dependent orientation on nanoparticle surfaces. Our approach can be broadly applied to various protein-material systems to help understand in much greater detail the protein-nanomaterial interface; it would also encourage better modeling, and thus prediction and design, of the behavior of functional proteins adsorbed onto different surfaces.

Tailored nanoporous coatings fabricated on conformable polymer substrates.

Nanoporous coatings have become the subject of intense investigation, in part because they have been shown to have unique and tailorable physical properties that can depart greatly from their dense or macroscopic counterparts. Nanoporous coatings are frequently fabricated utilizing oblique-angle or glancing-angle physical vapor-phase deposition techniques. However, a significant limitation for such coatings exists; they are almost always deposited on smooth and rigid planar substrates, such as silicon and glass. This limitation greatly constrains the applicability, tailorability, functionality and even the economic viability, of such nanoporous coatings. Here, we report our findings on nanoporous/polymer composite systems (NPCS) fabricated by utilizing oblique-angle electron-beam methodology. These unique composite systems exhibit several favorable characteristics, namely, (i) fine-tuned control over coating nanoporosity and thickness, (ii) excellent adhesion between the nanoporous coating and polymer substrate, (iii) the ability to withstand significant and repeated bending, and (iv) the ability to be molded conformably on two and three-dimensional surfaces while closely retaining the composite system's designed nanoporous film structure and, hence, properties.

Effect of gold nanoparticle structure on the conformation and function of adsorbed proteins.

Many applications of nanobiomaterials rely on or are enhanced by specific, protein-mediated interactions with biological systems. These interactions can be engineered by chemically modifying the surface of the material to affect protein adsorption, or by altering the topography of the nanoscale surface. The covalent attachment or adsorption of proteins onto materials can greatly affect their structure and function, giving rise to either beneficial effects or to unpredictable and potentially undesirable effects. Thus, it is essential to develop a detailed understanding of how nanostructured surface characteristics, such as atomic-scale topography, surface energy, and chemical structure may affect protein adsorption, structure, function, and stability. Herein we observe that nanoparticle morphology and protein surface coverage affect the structure, activity, and stability of adsorbed lysozyme (Lyz) and α-chymotrypsin (ChT) in a manner that is protein specific. Wet chemical methods were used to synthesize gold nanocubes (AuNC) with {100} facets and gold nanooctahedra (AuNO) with {111} facets. Differences in adsorption on AuNC and AuNO are observed, which may be attributed to the atomic topography of the material. Nanoparticles, as well as the final form of the resulting protein conjugates, were thoroughly characterized through various physical, microscopic, and spectroscopic techniques. As a result, additional insight into the influence of nanoscale surface properties was obtained, which will enhance our fundamental understanding of how such properties affect protein structure and function, and will hence assist us in strategically engineering protein-nanomaterial conjugates for a variety of biomedical applications.

Position-specific chemical modification and quantitative proteomics disclose protein orientation adsorbed on silica nanoparticles.

We describe a method for determining the orientation of cytochrome c, RNase A, and lysozyme on silica nanoparticles (SNPs) using chemical modification combined with proteolysis-mass spectrometry. The proteins interacted with SNPs through preferential adsorption sites, which are dependent on SNP diameter; 4 nm SNPs induce greater structural stabilization than 15 nm particles, presumably due to greater surface curvature of the former. These results suggest that nanoparticle size and protein structure influence protein orientation on SNPs.

A new class of doped nanobulk high-figure-of-merit thermoelectrics by scalable bottom-up assembly.

Obtaining thermoelectric materials with high figure of merit ZT is an exacting challenge because it requires the independent control of electrical conductivity, thermal conductivity and Seebeck coefficient, which are often unfavourably coupled. Recent works have devised strategies based on nanostructuring and alloying to address this challenge in thin films, and to obtain bulk p-type alloys with ZT>1. Here, we demonstrate a new class of both p- and n-type bulk nanomaterials with room-temperature ZT as high as 1.1 using a combination of sub-atomic-per-cent doping and nanostructuring. Our nanomaterials were fabricated by bottom-up assembly of sulphur-doped pnictogen chalcogenide nanoplates sculpted by a scalable microwave-stimulated wet-chemical method. Bulk nanomaterials from single-component assemblies or nanoplate mixtures of different materials exhibit 25-250% higher ZT than their non-nanostructured bulk counterparts and state-of-the-art alloys. Adapting our synthesis and assembly approach should enable nanobulk thermoelectrics with further increases in ZT for transforming thermoelectric refrigeration and power harvesting technologies.

Engineering Nanomaterials for Biomedical Applications Requires Understanding the Nano-Bio Interface: A Perspective.

The promise of nanobiomaterials for diagnostic and therapeutic biomedical applications has been widely reported throughout the scientific community, and great strides have been made in those directions. And yet, the translation of nanomaterial-based therapeutics to clinical applications remains an elusive target. Many challenges have blocked the usage of nanomaterials in biomedicine, including potential toxicity, immunogenicity, and decreased efficacy. In order to overcome some of these issues, detailed studies have been undertaken to understand fundamental interactions between nanomaterials and the biological environment. In particular, recent developments in nanoparticle synthesis, a better understanding and control over nanoparticle surface chemistry, as well as the organization of that chemistry on the nanoparticle surface, has allowed researchers to begin to understand how spatial arrangement of atomic and molecular species at an interface can affect protein adsorption, structure, and subsequent biological outcomes. This perspective strives to identify ways in which the nanomaterial interface can be controlled to affect interactions with biomolecules for beneficial biomedical applications.

Al-doped zinc oxide nanocomposites with enhanced thermoelectric properties.

ZnO is a promising high figure-of-merit (ZT) thermoelectric material for power harvesting from heat due to its high melting point, high electrical conductivity σ, and Seebeck coefficient α, but its practical use is limited by a high lattice thermal conductivity κ(L). Here, we report Al-containing ZnO nanocomposites with up to a factor of 20 lower κ(L) than non-nanostructured ZnO, while retaining bulklike α and σ. We show that enhanced phonon scattering promoted by Al-induced grain refinement and ZnAl(2)O(4) nanoprecipitates presages ultralow κ ∼ 2 Wm( -1) K(-1) at 1000 K. The high α∼ -300 µV K(-1) and high σ ∼ 1-10(4) Ω(-1 )m(-1) result from an offsetting of the nanostructuring-induced mobility decrease by high, and nondegenerate, carrier concentrations obtained via excitation from shallow Al donor states. The resultant ZT ∼ 0.44 at 1000 K is 50% higher than that for the best non-nanostructured counterpart material at the same temperature and holds promise for engineering advanced oxide-based high-ZT thermoelectrics for applications.

Preparation and optical properties of indium tin oxide/epoxy nanocomposites with polyglycidyl methacrylate grafted nanoparticles.

Visibly highly transparent indium tin oxide (ITO)/epoxy nanocomposites were prepared by dispersing polyglycidyl methacrylate (PGMA) grafted ITO nanoparticles into a commercial epoxy resin. The oleic acid stabilized, highly crystalline, and near monodisperse ITO nanoparticles were synthesized via a nonaqueous synthetic route with multigram batch quantities. An azido-phosphate ligand was synthesized and used to exchange with oleic acid on the ITO surface. The azide terminal group allows for the grafting of epoxy resin compatible PGMA polymer chains via Cu(I) catalyzed alkyne-azide "click" chemistry. Transmission electron microscopy (TEM) observation shows that PGMA grafted ITO particles were homogeneously dispersed within the epoxy matrix. Optical properties of ITO/epoxy nanocomposites with different ITO concentrations were studied with an ultraviolet-visible-near-infrared (UV-vis-NIR) spectrometer. All the ITO/epoxy nanocomposites show more than 90% optical transparency in the visible light range and absorption of UV light from 300 to 400 nm. In the near-infrared region, ITO/epoxy nanocomposites demonstrate low transmittance and the infrared (IR) transmission cutoff wavelength of the composites shifts toward the lower wavelength with increased ITO concentration. The ITO/epoxy nanocomposites were applied onto both glass and plastic substrates as visibly transparent and UV/IR opaque optical coatings.

Effect of gold nanoparticle morphology on adsorbed protein structure and function.

Many biomedical applications of gold nanoparticles (NPs) rely on proteins that are covalently attached or adsorbed on the NP surface. The biological functionality of the protein-NP conjugate depends on the protein's ability to interact with target molecules, which is affected by NP characteristics such as size, curvature, aspect ratio, morphology, crystal structure, and surface chemistry. In the present study, the effect of gold nanoparticle morphology on the structure and function of adsorbed enzymes, lysozyme (Lyz) and α-chymotrypsin (ChT), has been investigated. Gold nanospheres (AuNS) were synthesized with diameters 10.6 ± 1 nm, and gold nanorods (AuNR) were synthesized with dimensions of (10.3 ± 2) × (36.4 ± 9) nm. Under saturating conditions, proteins adsorb with a higher surface density on AuNR when compared to AuNS. In the case of Lyz, adsorption on AuNS and AuNR resulted in a 10% and 15% loss of secondary structure, respectively, leading to conjugate aggregation and greatly reduced enzymatic activity. ChT retained most of its secondary structure and activity on AuNS and AuNR at low surface coverages; however, as protein loading approached monolayer conditions on AuNR, a 40% loss in secondary structure and 86% loss of activity was observed. Subsequent adsorption of ChT in multilayers on the AuNR surface allowed the conjugates to recover activity and remain stable. It is clear that AuNP morphology does affect adsorbed protein structure; a better understanding of these differences will be essential to engineer fully functional nanobioconjugates.

High electrical conductivity antimony selenide nanocrystals and assemblies.

Antimony selenide is a promising thermoelectric material with a high Seebeck coefficient, but its figure of merit is limited by its low electrical conductivity. Here, we report a rapid and scalable (gram-a-minute) microwave synthesis of one-dimensional nanocrystals of sulfurized antimony selenide that exhibit 10(4)-10(10) times higher electrical conductivity than non-nanostructured bulk or thin film forms of this material. As the nanocrystal diameter increases, the nanowires transform into nanotubes through void formation and coalescence driven by axial rejection of sulfur incorporated into the nanowires from the surfactant used in our synthesis. Individual nanowires and nanotubes exhibit a charge carrier transport activation-energy of <60 meV arising from surface sulfur donor states. Nanocrystal assemblies also show high electrical conductivity, making the nanocrystals attractive building blocks to realize nanostructured thin film and bulk forms of this material for thermoelectric device applications.

Nanostructure-biomolecule interactions: implications for tissue regeneration and nanomedicine.

Great strides are being made worldwide in our ability to synthesize and assemble nanoscale building blocks to create advanced materials with novel properties and functionalities. The novel properties of nanostructures are derived from their confined sizes and their very large surface-to-volume ratios. Nanostructured surfaces have also been shown to elicit more favorable and selective biomolecule and cellular responses than surfaces at coarser length scales. In the case of nanoscale ceramics and osteoblasts, for example, the benefit results from protein (vitronectin) unfolding at the nanostructured surface. These nanoscale attributes are enabling a variety of nanostructures to form the bases for a new field--nanomedicine. A fundamental issue in much of nanomedicine, and especially tissue regeneration, is to understand and to eventually control nanostructure-biomolecule interactions. To elucidate the fundamental bases for changes of protein conformation and function on nanostructured surfaces, and hence select responses including those of stem cells, a number of model experiments have been carried out. The results of these studies are presented and discussed in the context of the fundamental driving forces for protein conformation changes associated with nanostructures, their relationship to modified cell responses and tissue engineering, and our present knowledge regarding nanostructure properties.

Translational nanomedicine: status assessment and opportunities.

Nano-enabled technologies hold great promise for medicine and health. The rapid progress by the physical sciences/engineering communities in synthesizing nanostructures and characterizing their properties must be rapidly exploited in medicine and health toward reducing mortality rate, morbidity an illness imposes on a patient, disease prevalence, and general societal burden. A National Science Foundation-funded workshop, "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience," was held 16-19 March 2008 at the University of Southern California. Based on that workshop and literature review, this article briefly explores scientific, economic, and societal drivers for nanomedicine initiatives; examines the science, engineering, and medical research needs; succinctly reviews the US federal investment directly germane to medicine and health, with brief mention of the European Union (EU) effort; and presents recommendations to accelerate the translation of nano-enabled technologies from laboratory discovery into clinical practice. FROM THE CLINICAL EDITOR: An excellent review paper based on the NSF funded workshop "Re-Engineering Basic and Clinical Research to Catalyze Translational Nanoscience" (16-19 March 2008) and extensive literature search, this paper briefly explores the current state and future perspectives of nanomedicine.

Using centrosome fragments in the directed assembly of microtubules.

In animal cells, microtubules are organized by centrosomes, which are 1-2 microm diameter organelles. The generation of functional centrosome fragments in-vitro through ultrasonication is presented along with microtubule assembly directed by the patterned centrosome fragments. While centrosome fragments are smaller than the fully constituted centrosomes, their microtubule organization function is retained. The centrosome fragment templates offer greater flexibility and better coverage in both patterning and assembly of microtubules when compared with intact centrosomes. This work provides the rationale and potential for the large-area assembly of microtubules and should expand the application of centrosomes and centrosome components for the creation of microtubule-based nanoscale devices.

Cytochrome C on silica nanoparticles: influence of nanoparticle size on protein structure, stability, and activity.

The structure, thermodynamic and kinetic stability, and activity of cytochrome c (cyt c) on silica nanoparticles (SNPs) of different sizes have been studied. Adsorption of cyt c onto larger SNPs results in both greater disruption of the cyt c global structure and more significant changes of the local heme microenvironment than upon adsorption onto smaller SNPs. The disruption of the heme microenvironment leads to a more solvent-accessible protein active site, as suggested by Soret circular dichroism spectroscopy and through an increase in peroxidase activity as a function of increased SNP size. Similarly, the stability of cyt c decreases more dramatically upon adsorption onto larger SNPs. These results are consistent with changes in protein-nanoparticle interactions that depend on the size or surface curvature of the supporting nanostructure. This study provides further fundamental insights into the effects of nanoscale surfaces on adsorbed protein structure and function.

New rules for the old game of porous micro- and nanoparticle synthesis.

The field of research focused on the synthesis of micro- and nanoparticles has not yet conclusively addressed the challenges presented by the hierarchical control of surface topography. An established approach to hierarchical multicomposite nanostructured particles is based on template-directed synthesis, while spectacular advances have been reached in nanoparticle fabrication based on a variety of physicochemical processes. These results exemplify an additive route to hierarchical control, where multiple layers are stacked onto each other or where discretely identifiable particles are assembled into a larger spherical conglomerate. We present here a new strategy for the synthesis of micro- and nanoparticles, which we refer to as "textured isomorphic synthesis", that uses only the toolbox of inorganic chemistry coupled to the physics of cavitation, viscous fingering, and bubble nucleation. The results illustrate a topological route to hierarchical control of particle topography where dimples or holes are deterministically introduced on a planar substrate later transformed into isomorphic hollow spherical micro- and nanostructures.

The generation of domain boundaries in catalytically-grown carbon nanotubes.

Arrays of catalytically-grown multi-wall carbon nanotubes were grown using identical conditions in a chemical vapor deposition environment, but cooled at different cooling rates, to identify the influence of cooling rate on the structural properties of the nanotube at the catalyst-wall interface. Ex-situ transmission electron microscopy led to the identification of twist, twin, and tilt domain boundaries in all samples irrespective of cooling rate. In addition, the relative position of twist, twin, and tilt domain boundaries in nanotubes cooled at different rates was maintained uniformly across all samples cooled at different rates. The results are interpreted in light of the concurrence of base- and tip-growth for the catalytic synthesis of nanotubes, suggesting a rather steady position occupied by the domain boundaries coupled to the catalytic particles.

Unfolding of ribonuclease A on silica nanoparticle surfaces.

This paper reports on the unfolding behavior of ribonuclease A (RNase A) on silica nanoparticle surfaces and quantitively demonstrates that nanoscale size and surface curvature play key roles in influencing the stability of adsorbed proteins. Urea denaturation analyses showed that the thermodynamic stability of RNase A decreased upon adsorption onto the nanoparticles, with greater decrease on larger nanoparticles. The stability changes of RNase A correlate well with the changes in the protein-nanoparticle interactions, which increase as the surface contact area and surface charge interaction increases. This study, therefore, provides fundamental information on the effect of nanoscale surfaces on protein structure and function.