Boron Nitride Nanomesh

Supramolecular Binding of Cationic Porphyrins on a Filamentous Bacteriophage Template: Toward a Noncovalent Antenna System

Engineered viruses act as scaffolds to bind porphyrins on their surfaces, exploiting mainly electrostatic interactions. The close proximity between porphyrins and tryptophan residues, exposed on the solvent-accessible surface, leads to an efficient resonant energy transfer, which makes these systems suitable for developing noncovalent antenna systems.

Surface self-organization caused by dislocation networks

We report a new mechanism of self-organization that can lead to robust surface ordering. We have quantitatively analyzed the thermal motion of holes created by sulfur atoms in a silver monolayer on a ruthenium surface, which we observed in real time with scanning tunneling microscopy. We find that the stability of the array of holes is determined by the arrangement and structure of misfit dislocations in the film.

Nucleotide-directed growth of semiconductor nanocrystals

We engineer colloidal quantum dot nanocrystals through the choice of biomolecular ligands responsible for nanoparticle nucleation, growth, stabilization, and passivation. We systematically vary the presence of, and thereby elucidate the role of, phosphate groups and a multiplicity of functionalities on the mononucleotides used as ligands. The results provide the basis for synthesis of nanoparticles using precisely controlled synthetic oligonucleotide sequences.

Utilization of the Pleiotropy of a Peptidic Aptamer To Fabricate Heterogeneous Nanodot-Containing Multilayer Nanostructures

Peptide aptamers (=binders) against inorganic materials often show a capacity for mineralization of their target atoms; thus they are able to function both as binding molecules and as mediators for mineralization. Although the mechanisms underlying these two properties of peptide aptamers are not yet fully understood, they have been used separately to fabricate various nanostructures. Here, we present a novel method of nanofabrication, in which binding and mineralization by a peptide aptamer are alternately utilized to assemble multilayered nanostructures comprised of metal loaded cage proteins ornamented with Ti-binding peptides.

Engineering atomic and molecular nanostructures at surfaces

The fabrication methods of the microelectronics industry have been refined to produce ever smaller devices, but will soon reach their fundamental limits. A promising alternative route to even smaller functional systems with nanometre dimensions is the autonomous ordering and assembly of atoms and molecules on atomically well-defined surfaces. This approach combines ease of fabrication with exquisite control over the shape, composition and mesoscale organization of the surface structures formed. Once the mechanisms controlling the self-ordering phenomena are fully understood, the self-assembly and growth processes can be steered to create a wide range of surface nanostructures from metallic, semiconducting and molecular materials.

Stable planar six-pi-electron six-membered N-heterocyclic carbenes with tunable electronic properties

Carbene analogues of borazines are highly thermally stable. Keeping quasi-identical steric demands, the electronic properties of the carbene can be precisely tuned by varying the nature of the substituents at the boron centers.

Charged Polypeptide Vesicles with Controllable Diameter

We report the preparation and characterization of charged, amphiphilic block copolypeptides that form stable vesicles and micelles in aqueous solution. Specifically, we prepared and studied the aqueous self-assembly of a series of poly(L-lysine)-b-poly(L-leucine) block copolypeptides, KxLy, where x ranged from 20 to 80 and y ranged from 10 to 30 residues, as well as the poly(L-glutamatic acid)-b-poly(L-leucine) block copolypeptide, E60L20. Furthermore, the vesicular assemblies show dynamic properties, indicating a high degree of membrane fluidity. This characteristic provides stimuli-responsive properties to the vesicles and allows fine adjustment of vesicle size using liposome-based extrusion techniques. Vesicle extrusion also provides a straightforward means to trap solutes, making the vesicles promising biomimetic encapsulants.

Design criteria for engineering inorganic material-specific peptides

Development of a fundamental understanding of how peptides specifically interact with inorganic material surfaces is crucial to furthering many applications in the field of nanobiotechnology. Herein, we report systematic study of peptide sequence-activity relationships for binding to II-VI semiconductors (CdS, CdSe, ZnS, ZnSe) and Au using a yeast surface display system, and we define criteria for tuning peptide affinity and specificity for these material surfaces. First, homohexapeptides of the 20 naturally occurring amino acids were engineered, expressed on yeast surface, and assayed for the ability to bind each material surface in order to define functional groups sufficient for binding. Histidine (H6) was able to mediate binding of yeast to the five materials studied, while tryptophan (W6), cysteine (C6), and methionine (M6) exhibited different levels of binding to single-crystalline ZnS and ZnSe and polycrystalline Au surfaces. The ability of neighboring amino acids to up- and down-modulate histidine binding was then evaluated by use of interdigitated peptides (XHXHXHX). While the 20 amino acids exhibited a unique fingerprint of modulation for each material, some general trends emerged. With neutral defined by alanine, up-modulation occurred with glycine, basic amino acids, and the previously defined binding amino acids histidine, tryptophan, cysteine, and methionine, and down-modulation generally occurred with acidic, polar, and hydrophobic residues. We conclude that certain amino acids directly bind the material surface while neighboring amino acids locally modulate the binding environment for the materials we studied. Therefore, by the specific placement of up- and down-modulating amino acids, material specificity can be controlled. Finally, by employing the compositional and spatial criteria developed herein, it was possible to predictively design peptide sequences with material specificity, including a multimaterial binder, a Au-specific binder, and a ZnS-specific binder, that were verified as such in the context of yeast display.

Programmable assembly of nanoarchitectures using genetically engineered viruses

Biological systems possess inherent molecular recognition and self-assembly capabilities and are attractive templates for constructing complex material structures with molecular precision. Here we report the assembly of various nanoachitectures including nanoparticle arrays, hetero-nanoparticle architectures, and nanowires utilizing highly engineered M13 bacteriophage as templates. The genome of M13 phage can be rationally engineered to produce viral particles with distinct substrate-specific peptides expressed on the filamentous capsid and the ends, providing a generic template for programmable assembly of complex nanostructures. Phage clones with gold-binding motifs on the capsid and streptavidin-binding motifs at one end are created and used to assemble Au and CdSe nanocrytals into ordered one-dimensional arrays and more complex geometries. Initial studies show such nanoparticle arrays can further function as templates to nucleate highly conductive nanowires that are important for addressing/interconnecting individual nanostructures.

Virus crystals as nanocomposite scaffolds

The generation of long-range three-dimensional nanoscopic patterns is a major goal in materials chemistry. Here we report a strategy for creating such systems using virus crystals as scaffolds which can be infiltrated with metal specifically palladium and platinum. The inorganic component effectively packs within the porous macromolecular crystal architecture, providing a route for patterning these materials on the nanometer length scale. To verify the quality of the metal infiltration, SEM-EDX was used to determine the homogeneous distribution of metal across the crystal, and TEM was used to confirm that the metal was confined within the porous structure of the crystal.

Engineered protein cages for nanomaterial synthesis

Self-assembled particles of genetically engineered human L subunit ferritin expressing a silver-binding peptide were used as nanocontainers for the synthesis of silver nanoparticles. The inner cavity of the self-assembled protein cage displays a dodecapeptide that is capable of reducing silver ions to metallic silver. This chimeric protein cage when incubated in the presence of silver nitrate exhibits the growth of a silver nanocrystal within its cavity. Our studies indicate that it is possible to design chimeric cages, using specific peptide templates, for the growth of other inorganic nanoparticles.

Chitosan-mediated and spatially selective electrodeposition of nanoscale particles

Nanoscale particles offer a variety of interesting properties, and there is growing interest in their assembly into higher ordered structures. We report that the pH-responsive aminopolysaccharide chitosan can mediate the electrodeposition of model nanoparticles. Chitosan is known to electrodeposit at the cathode surface in response to a high localized pH. To demonstrate that chitosan can mediate nanoparticle deposition, we suspended fluorescently labeled latex nanoparticles (100 nm diameter spheres) in a chitosan solution (1%) and performed electrodeposition (0.05 mA/cm2 for several minutes). Results demonstrate that chitosan is required for nanoparticle electrodeposition; chitosan confers spatial selectivity to electrodeposition; and nanoparticles distribute throughout the electrodeposited chitosan film. Additionally, we observed that the deposited films reversibly swell upon rehydration. This work indicates that chitosan provides a simple means to assemble nanoparticles at addressable locations and provides further evidence that stimuli-responsive biological materials may facilitate fabrication at the microscale.

A virus-based nanoblock with tunable electrostatic properties

Five different "HIS tag" mutants of cowpea mosaic virus were made by genetically introducing six contiguous histidine residues at various locations on the virus capsid. The mutant particles showed differential affinity for binding nickel, and their electrostatic properties could be controlled as a function of the protonation state of the exposed histidine sequence. The specific addressability of the HIS tag was corroborated by the selective modification of the histidine sequence with nanogold cross-linked to the Ni-NTA moiety.

Growth induced reordering of fullerene clusters trapped in a two-dimensional supramolecular network

We have investigated the growth of molecular clusters in confined geometries defined by a bimolecular supramolecular network. This framework provides a regular array of identical nanoscale traps in which further deposited molecules nucleate cluster growth. For the higher fullerene, C84, molecules aggregate into close packed assemblies with an orientation which switches when the cluster size increases by one molecule. This change is controlled by the interactions between the molecules and the confining boundaries of the network pore. We show that, following nucleation of small clusters, further growth requires a reconfiguration of previously captured molecules resulting in a transition between nanoscale phases with different ordering.

Nanoparticle dispersion on reconstructed carbon nanomeshes

A nanoporous template which can be used for the preparation of monodispersed metal nanoparticles can have wide-ranging applications in the catalyzed growth of single-walled nanotubes, as well as the preparation of energetic, nanostructured ferromagnetic particle arrays. Here, we found that a honeycomb-like carbon nanomesh with periodically arranged pores of approximately 2-nm dimension could be fabricated on the reconstructed 6H-SiC(0001) surface. The carbon nanomesh arises from the periodic arrangement of segregated carbon clusters on the 6H-SiC surface to form a highly regular, nanoporous film. The carbon nanomesh can be dynamically structured to control the periodicity and depth of the pores by annealing in a vacuum. We evaporated cobalt on the surface of the nanomesh and investigated the diffusion and agglomeration behavior of cobalt clusters using in situ scanning tunneling microscopy. It is found that monodispersed Co nanoclusters that resist aggregation up to a temperature of 500 degrees C can be fabricated on this template.

Bottom-up Assembly of RNA Arrays and Superstructures as Potential Parts in Nanotechnology

DNA and protein have been extensively scrutinized for feasibility as parts in nanotechnology, but another natural building block, RNA, has been largely ignored. RNA can be manipulated to form versatile shapes, thus providing an element of adaptability to DNA nanotechnology, which is predominantly based upon a double-helical structure. The DNA-packaging motor of bacterial virus phi29 contains six DNA-packaging RNAs (pRNA), which together form a hexameric ring via loop/loop interaction. Here we report that this pRNA can be redesigned to form a variety of structures and shapes, including twins, tetramers, rods, triangles, and 3D arrays several microns in size via interaction of programmed helical regions and loops. Three dimensional RNA array formation required a defined nucleotide number for twisting of the interactive helix and a palindromic sequence. Such arrays are unusually stable and resistant to a wide range of temperatures, salt concentrations, and pH.