Programmable assembly of nanoarchitectures using genetically engineered viruses

Connecting the nanodots: programmable nanofabrication of fused metal shapes on DNA templates

We present a novel method for producing complex metallic nanostructures of programmable design. DNA origami templates, modified to have DNA binding sites with a uniquely coded sequence, were adsorbed onto silicon dioxide substrates. Gold nanoparticles functionalized with the cDNA sequence were then attached. These seed nanoparticles were later enlarged, and even fused, by electroless deposition of silver. Using this method, we constructed a variety of metallic structures, including rings, pairs of bars, and H shapes.

Biosynthesis and characterization of CdS quantum dots in genetically engineered Escherichia coli

Quantum dots (QDs) were prepared in genetically engineered Escherichia coli (E. coli) through the introduction of foreign genes encoding a CdS binding peptide. The CdS QDs were successfully separated from the bacteria through two methods, lysis and freezing-thawing of cells, and purified with an anion-exchange resin. High-resolution transmission electron microscopy, X-ray diffraction, luminescence spectroscopy, and energy dispersive X-ray spectroscopy were applied to characterize the as-prepared CdS QDs. The effects of reactant concentrations, bacteria incubation times, and reaction times on QD growth were systematically investigated. Our work demonstrates that genetically engineered bacteria can be used to synthesize QDs. The biologically synthesized QDs are expected to be more biocompatible probes in bio-labeling and imaging.

Spatially selective assembly of quantum dot light emitters in an LED using engineered peptides

Semiconductor nanocrystal quantum dots are utilized in numerous applications in nano- and biotechnology. In device applications, where several different material components are involved, quantum dots typically need to be assembled at explicit locations for enhanced functionality. Conventional approaches cannot meet these requirements where assembly of nanocrystals is usually material-nonspecific, thereby limiting the control of their spatial distribution. Here we demonstrate directed self-assembly of quantum dot emitters at material-specific locations in a color-conversion LED containing several material components including a metal, a dielectric, and a semiconductor. We achieve a spatially selective immobilization of quantum dot emitters by using the unique material selectivity characteristics provided by the engineered solid-binding peptides as smart linkers. Peptide-decorated quantum dots exhibited several orders of magnitude higher photoluminescence compared to the control groups, thus, potentially opening up novel ways to advance these photonic platforms in applications ranging from chemical to biodetection.

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.

The art of engineering viral nanoparticles

Viral nanotechnology is an emerging and highly interdisciplinary field in which viral nanoparticles (VNPs) are applied in diverse areas such as electronics, energy and next-generation medical devices. VNPs have been developed as candidates for novel materials, and are often described as "programmable" because they can be modified and functionalized using a number of techniques. In this review, we discuss the concepts and methods that allow VNPs to be engineered, including (i) bioconjugation chemistries, (ii) encapsulation techniques, (iii) mineralization strategies, and (iv) film and hydrogel development. With all these techniques in hand, the potential applications of VNPs are limited only by the imagination.

In vitro labeling of hydroxyapatite minerals by an engineered protein

Biological and biomimetic synthesis of inorganics have been a major focus in hard tissue engineering as well as in green processing of advanced materials. Among the minerals formed by organisms, calcium phosphate mineralization is studied extensively to understand the formation of mineral-rich tissues. Herein, we report an engineered fusion protein that not only targets calcium phosphate minerals but also allows monitoring of biomineralization. To produce the bi-functional fusion protein, nucleotide sequence encoding combinatorially selected hydroxyapatite-binding peptides (HABP) was genetically linked to the 3' end of the open reading frame of green fluorescence protein (GFPuv) and successfully expressed in Escherichia coli. The fluorescence and binding activities of the bi-functional proteins were characterized by, respectively, using fluorescence microscopy and quartz crystal microbalance spectroscopy. The utility of GFPuv-HABP fusion protein was assessed for both time-wise monitoring of mineralization and the visualization of the mineralized tissues. We used an alkaline phosphatase-based reaction to control phosphate release, thereby mimicking biological processes, to monitor calcium phosphate mineralization. The increase in mineral amount was observed using the fusion protein at different time points. GFPuv-HABP1 was also used for efficient fluorescence labeling of mineralized regions on the extracted human incisors. Our results demonstrate a simple and versatile application of inorganic-binding peptides conjugated with bioluminescence proteins as bi-functional bioimaging molecular probes that target mineralization, and which can be employed to a wide range of biomimetic processing and cell-free tissue engineering.

Inorganic binding peptide-mediated immobilization based on baculovirus surface display system

The biomolecule-mediated assembly of novel composites has been the subject of numerous investigations during the last years, providing new insights into material science and engineering. Via molecular biology technology, we were able to introduce the genetically engineered polypeptide for inorganics (GEPI) as a molecular binder into biomolecules such as phage viruses, to assemble hybrid functional nanoarchitectures. In the present work, we introduced a novel nanocomposite comprising the Autographa californica nuclear polyhedrosis virus (AcNPV) and nanoparticles bound to it. Our results show that a GEPI-encoding gene was successfully introduced by recombination into a eukaryotic expression bacmid and finally displayed outside of the AcNPV after transfection into Sf9 insect cells using the Bac-to-Bac baculovirus expression system. The recombinant baculovirus maintained both the viral infectivity and the specific binding activity of the GEPI. The construction of the gene in the recombinant plasmid was examined by polymerase chain reaction analysis and enzymatic digestion identification, and verified by gene sequencing. Surface display of the fused peptide was revealed by Western blot analysis in dissolution studies and determined by immuno- gold electron microscopy. Adherence of nanoparticles to the recombinant baculovirus was visualized by transmission electron microscopy analysis. Here, we demonstrated the possibilities of combining peptide-mediated immobilization with baculovirus surface display technology.

Virus templated metallic nanoparticles

Plant viruses are considered as nanobuilding blocks that can be used as synthons or templates for novel materials. Cowpea mosaic virus (CPMV) particles have been shown to template the fabrication of metallic nanoparticles by an electroless deposition metallization process. Palladium ions were electrostatically bound to the virus capsid and, when reduced, acted as nucleation sites for the subsequent metal deposition from solution. The method, although simple, produced highly monodisperse metallic nanoparticles with a diameter of ca. ≤35 nm. CPMV-templated particles were prepared with cobalt, nickel, iron, platinum, cobalt-platinum and nickel-iron.

Virus engineering: functionalization and stabilization

Chemically and/or genetically engineered viruses, viral capsids and viral-like particles carry the promise of important and diverse applications in biomedicine, biotechnology and nanotechnology. Potential uses include new vaccines, vectors for gene therapy and targeted drug delivery, contrast agents for molecular imaging and building blocks for the construction of nanostructured materials and electronic nanodevices. For many of the contemplated applications, the improvement of the physical stability of viral particles may be critical to adequately meet the demanding physicochemical conditions they may encounter during production, storage and/or medical or industrial use. The first part of this review attempts to provide an updated general overview of the fast-moving, interdisciplinary virus engineering field; the second part focuses specifically on the modification of the physical stability of viral particles by protein engineering, an emerging subject that has not been reviewed before.

More than just bare scaffolds: towards multi-component and decorated fibrous biomaterials

We are entering a new phase in biomaterials research in which rational design is being used to produce functionalised materials tailored to specific applications. As is evident from this Themed Issue, there are now a number of distinct types of designed, self-assembling, fibrous biomaterials. Many of these are ripe for development and application for example as scaffolds for 3D cell culture and tissue engineering, and in templating inorganic materials. Whilst a number of groups are making headway towards such applications, there is a general challenge to translate a wealth of excellent basic research into materials with a genuine future in real-life applications. Amongst other contemporary aspects of this evolving research area, a key issue is that of decorating or functionalising what are mostly bare scaffolds. There are a number of hurdles to overcome to achieve effective and controlled labelling of the scaffolds, for instance: maintaining biocompatibility, i.e., by minimising covalent chemistry, or using milder bioconjugation methods; attaining specified levels of decoration, and, in particular, high and stoichiometric labelling; introducing orthogonality, such that two or more functions can be appended to the same scaffold; and, in relevant cases, maintaining the possibility for recombinant peptide/protein production. In this critical review, we present an overview of the different approaches to tackling these challenges largely for self-assembled, peptide-based fibrous systems. We review the field as it stands by placing work within general routes to fibre functionalisation; give worked examples on our own specific system, the SAFs; and explore the potential for future developments in the area. Our feeling is that by tackling the challenges of designing multi-component and functional biomaterials, as a community we stand to learn a great deal about self-assembling biomolecular systems more broadly, as well as, hopefully, delivering new materials that will be truly useful in biotechnology and biomedical applications (107 references).

Biologically activated noble metal alloys at the nanoscale: for lithium ion battery anodes

We report the synthesis and electrochemical activity of gold and silver noble metals and their alloy nanowires using multiple virus clones as anode materials for lithium ion batteries. Using two clones, one for specificity (p8#9 virus) and one versatility (E4 virus), noble metal nanowires of high-aspect ratio with diameters below 50 nm were successfully synthesized with control over particle sizes, morphologies, and compositions. The biologically derived noble metal alloy nanowires showed electrochemical activities toward lithium even when the electrodes were prepared from bulk powder forms. The improvement in capacity retention was accomplished by alloy formation and surface stabilization. Although the cost of noble metals renders them a less ideal choice for lithium ion batteries, these noble metal/alloy nanowires serve as great model systems to study electrochemically induced transformation at the nanoscale. Given the demonstration of the electrochemical activity of noble metal alloy nanowires with various compositions, the M13 biological toolkit extended its utility for the study on the basic electrochemical property of materials.

On the thermal stability of surface-assembled viral-metal nanoparticle complexes

Biological supramolecules offer attractive templates for nanoparticle synthesis and nanodevice fabrication because of their precise size and shape. Viruses in particular have gained significant attention in nanodevice fabrication for applications such as nanoelectronics, batteries, catalysis, and sensing. However, the performance range of these viral-nanoparticle complexes is not well known because of the lack of fundamental studies on their properties. In this work, we employ in situ grazing incidence small-angle X-ray scattering (GISAXS) to examine the thermal stability of viral-nanoparticle complexes composed of tobacco mosaic virus (TMV) and palladium nanoparticles. Specifically, we show that the stability of the Pd nanoparticles on TMV is significantly enhanced as compared to that of particles on the solid substrate surface. Furthermore, we show that the agglomeration of Pd nanoparticles and the degradation of the TMV templates are coupled and occur simultaneously. These results demonstrate a potent methodology toward the in situ analysis of subtle changes in viral-nanoparticle complexes in dynamic environments. We envision that the results and methodology demonstrated in this study could be applied to better understand the properties and dynamic behaviors of organic-inorganic hybrid materials and nanodevices in various applications.

Baculoviral capsid display of His-tagged ZnO inorganic binding peptide

Virus-templated fabrication of compound structures can be made through incorporating the specifically inorganic-binding peptide into the viral scaffold, widely used is phage display system. Compared to prokaryotic phages, insect cell-based baculovirus has some strengths such as the adaptability to the proteins' posttranslational modification and non-replication in mammalian cells. As an attempt to explore the baculovirus-mediated bioconjugates, we show in this study that a genetically engineered baculovirus, with a hexahistidine (His(6)) tagged ZnO binding peptide fused to the N-terminus of the viral capsid protein vp39 of AcNPV, was constructed. It maintains both the viral infectivity and the fusion protein's activity. The presence of the fusion protein on the baculovirus particle was demonstrated by western blot analysis of purified budded virus. Its display on the virus capsid was revealed by virus fractionation analysis. The binding of nanosized ZnO powders to the virus capsid was visualized by transmission electron microscopy (TEM). This is the first report of the display of the inorganic-binding peptide on the capsid of eukaryotic baculovirus. Aimed at the nanomaterials' application in the biological field, this research could find useful in the biotracking of the baculovirus transduction process and the preparation of novel functional nanodevices.

Patterning and templating for nanoelectronics

The semiconductor industry will soon be launching 32 nm complementary metal oxide semiconductor (CMOS) technology node using 193 nm lithography patterning technology to fabricate microprocessors with more than 2 billion transistors. To ensure the survival of Moore's law, alternative patterning techniques that offer advantages beyond conventional top-down patterning are aggressively being explored. It is evident that most alternative patterning techniques may not offer compelling advantages to succeed conventional top-down lithography for silicon integrated circuits, but alternative approaches may well indeed offer functional advantages in realising next-generation information processing nanoarchitectures such as those based on cellular, bioinsipired, magnetic dot logic, and crossbar schemes. This paper highlights and evaluates some patterning methods from the Center on Functional Engineered Nano Architectonics in Los Angeles and discusses key benchmarking criteria with respect to CMOS scaling.

Biofabrication methods for the patterned assembly and synthesis of viral nanotemplates

This paper reports on novel methodologies for the patterning and templated synthesis of virus-structured nanomaterials in two- and three-dimensional microfabricated architectures using the Tobacco mosaic virus (TMV). The TMV is a high aspect ratio biological molecule which can be engineered to include amino acids with enhanced binding properties. These modifications facilitate self-assembly of the TMV onto various substrates and enable its use as a template for the synthesis of nanostructured materials. This work focuses on the combination of this bottom-up biologically inspired fabrication method with standard top-down micromachining processes that allow direct integration of the virus-structured materials into batch-fabricated devices. Photolithographic patterning of uncoated as well as nickel-coated TMV nanostructures has been achieved using a lift-off process in both solvent and mild basic solutions and their assembly onto three-dimensional polymer and silicon microstructures is demonstrated. In addition to these patterning techniques, in situ formation of metal oxide TMV coatings in patterned microfabricated environments is shown using atomic layer deposition directly on the nickel-coated viruses. The biofabrication 'process toolbox' presented in this work offers a simple and versatile alternative for the hierarchical patterning and incorporation of biotemplated nanomaterials into micro/nanofabrication schemes.

Self-assembled chitosan/heparin multilayer film as a novel template for in situ synthesis of silver nanoparticles

Chitosan and heparin multilayer films were successfully constructed via layer-by-layer self assembly. These films were used as a polymeric template to synthesize silver nanoparticles. The silver concentration and nanoparticle size can be simply controlled by the assembly pH and loading pH, as demonstrated by UV-visible spectroscopy, transmission electron microscopy and atomic absorbance spectroscopy. The pH tunable uncompensated charge density within the multilayer films is believed to have great effect on the loading of silver ions, and then control the size and amount of silver nanoparticles within multilayer films. The antibacterial experiment shows that the silver nanoparticle-loaded chitosan/heparin multilayer films exhibit greatly enhanced antibacterial performance compared to the chitosan/heparin multilayer films without silver nanoparticles. In addition, the strong antibacterial property of silver nanoparticle-loaded films can last more than 1 month. Our method of in situ synthesis of metal nanoparticles in biocompatible multilayer films might provide great potential to design biofunctional nanocomposite films.

The ferritin superfamily: Supramolecular templates for materials synthesis

Members of the ferritin superfamily are multi-subunit cage-like proteins with a hollow interior cavity. These proteins possess three distinct surfaces, i.e. interior and exterior surfaces of the cages and interface between subunits. The interior cavity provides a unique reaction environment in which the interior reaction is separated from the external environment. In biology the cavity is utilized for sequestration of irons and biomineralization as a mechanism to render Fe inert and sequester it from the external environment. Material scientists have been inspired by this system and exploited a range of ferritin superfamily proteins as supramolecular templates to encapsulate nanoparticles and/or as well-defined building blocks for fabrication of higher order assembly. Besides the interior cavity, the exterior surface of the protein cages can be modified without altering the interior characteristics. This allows us to deliver the protein cages to a targeted tissue in vivo or to achieve controlled assembly on a solid substrate to fabricate higher order structures. Furthermore, the interface between subunits is utilized for manipulating chimeric self-assembly of the protein cages and in the generation of symmetry-broken Janus particles. Utilizing these ideas, the ferritin superfamily has been exploited for development of a broad range of materials with applications from biomedicine to electronics.

Fabrication of ZnS nanoparticle chains on a protein template

In the present study, we have exploited the properties of a fibrillar protein for the template synthesis of zinc sulfide (ZnS) nanoparticle chains. The diameter of the ZnS nanoparticle chains was tuned in range of ~30 to ~165 nm by varying the process variables. The nanoparticle chains were characterized by field emission scanning electron microscopy, UV-Visible spectroscopy, transmission electron microscopy, electron energy loss spectroscopy, and high-resolution transmission electron microscopy. The effect of incubation temperature on the morphology of the nanoparticle chains was also studied.

Enhanced photogenerated carrier collection in hybrid films of bio-templated gold nanowires and nanocrystalline CdSe

Hybrid films of bio-templated gold nanowires and chemical bath deposited nanocrystalline CdSe were fabricated. The conductivity of the gold nanowires within the hybrid material was controlled by gold electroless deposition. Photocurrent measurements were taken on gold nanowire films, CdSe chemical bath deposited films, and hybrid films. The incorporation of gold nanowires within the hybrid material clearly increased the extraction of photogenerated carriers within the CdSe. Photocurrent showed a direct correlation with gold nanowire conductivity.

Construction of bifunctional phage display for biological analysis and immunoassay

A phage display-based bifunctional display system was developed for simple and sensitive immunoassay. The resulting bifunctional phage could simultaneously display a few single-chain variable fragment (ScFv) and many copies of the gold-binding peptide on its surface, thereby mediating antigen recognition and signal amplification. As a demonstration study, it was possible for bifunctional phage-based immunoassay to identify Bacillus anthracis spores from other Bacillus strains with detection sensitivity 10-fold higher than that of conventional phage enzyme-linked immunosorbent assay (ELISA). This protocol may be applied to build other bifunctional phage clones for broad applications (e.g., immunoassay kits, affinity biosensors, biorecognition assays).

Janus-like protein cages. Spatially controlled dual-functional surface modifications of protein cages

Protein cages have been used both as size-constrained reaction vessels for nanomaterials synthesis and as nanoscale building blocks for higher order nanostructures. We generated Janus-like protein cages, which are dual functionalized with a fluorescent and an affinity label, and demonstrated control over both the stoichiometry and spatial distribution of the functional groups. The capability to toposelectively functionalize protein cages has allowed us to manipulate hierarchical assembly using the layer-by-layer assembly process. Janus-like protein cages expand the toolkit of nanoplatforms that can be used for directed assembly of nanostructured materials.

Fabricating genetically engineered high-power lithium-ion batteries using multiple virus genes

Development of materials that deliver more energy at high rates is important for high-power applications, including portable electronic devices and hybrid electric vehicles. For lithium-ion (Li+) batteries, reducing material dimensions can boost Li+ ion and electron transfer in nanostructured electrodes. By manipulating two genes, we equipped viruses with peptide groups having affinity for single-walled carbon nanotubes (SWNTs) on one end and peptides capable of nucleating amorphous iron phosphate(a-FePO4) fused to the viral major coat protein. The virus clone with the greatest affinity toward SWNTs enabled power performance of a-FePO4 comparable to that of crystalline lithium iron phosphate (c-LiFePO4) and showed excellent capacity retention upon cycling at 1C. This environmentally benign low-temperature biological scaffold could facilitate fabrication of electrodes from materials previously excluded because of extremely low electronic conductivity.