Orthogonal Self-assembly Research Articles

Fabrication of DNA Nanowires by Orthogonal Self-Assembly and DNA Intercalation on a Au Patterned Si/SiO2 Surface

A novel Ru complex bearing both an acridine group and anchoring phosphonate groups was immobilized on a surface in order to capture double-stranded DNAs (dsDNAs) from solution. At low surface coverage, the atomic force microscopy (AFM) image revealed the "molecular dot" morphology with the height of the Ru complex ( approximately 2.5 nm) on a mica surface, indicating that four phosphonate anchor groups keep the Ru complex in an upright orientation on the surface. Using a dynamic molecular combing method, the DNA capture efficiency of the Ru complex on a mica surface was examined in terms of the effects of the number of molecular dots and surface hydrophobicity. The immobilized surface could capture DNAs; however, the optimal number of molecular dots on the surface as well as the optimal pull-up speed exist to obtain the extended dsDNAs on the surface. Applying this optimal condition to a Au-patterned Si/SiO 2 (Au/SiO 2) surface, the Au electrode was selectively covered with the Ru complex by orthogonal self-assembly of 4-mercaptbutylphosphonic acid (MBPA), followed by the formation of a Zr (4+)-phosphonate layer and the Ru complex. At the same time, the remaining SiO 2 surface was covered with octylphosphonic acid (OPA) by self-assembly. The selective immobilization of the Ru complex only on the Au electrode was identified by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging on the chemically modified Au/SiO 2 surface. The construction of DNA nanowires on the Au/SiO 2 patterned surface was accomplished by the molecular combing method of the selective immobilized Ru complex on Au electrodes. These interconnected nanowires between Au electrodes were used as a scaffold for the modification of Pd nanoparticles on the DNA. Furthermore, Cu metallization was achieved by electroless plating of Cu metal on a priming of Pd nanoparticles on the Pd-covered DNA nanowires. The resulting Cu nanowires showed a metallic behavior with relatively high resistance.

Orthogonal Self-Assembly of Interconnected One-Dimensional Inorganic and Organic Nanostructures on the Si(100) Surface

Orthogonal, interconnected inorganic and organic one-dimensional nanostructures have been fabricated by parallel self-assembly on the Si(100) surface and investigated using room temperature ultrahigh vacuum scanning tunneling microscopy. In particular, bismuth nanowires were self-assembled on the clean Si(100)-2 x 1 surface perpendicular to the Si dimer rows, followed by hydrogen passivation of the surrounding Si surface. Styrene molecular chains were then self-assembled on the H-passivated Si(100)-2 x 1 surface to intersect perpendicularly with the Bi nanowires. This general approach can likely be applied to the wide range of inorganic and organic species that spontaneously form one-dimensional nanostructures on the Si(100) surface.

Nanostructured Materials through Orthogonal Self-Assembly in a Columnar Liquid Crystal

This paper describes a system in which an acid functionalized discotic molecule and poly(propylene-imine) dendrimer self-assemble into a new type of oblique columnar liquid crystalline (LC) phase that displays a well-ordered superlattice. The orthogonal combination of hydrogen bonding in the columnar direction and ionic interaction in the plane perpendicular to the columns gives rise to a structure in which the dendrimer is confined to separate columnar domains. The structure of the mesophases formed in the mixed system has been elucidated by infrared spectroscopy and X-ray diffraction. Investigation by differential scanning calorimetry and polarizing optical microscopy has shown that the LC phase is most stable in an 8:1 molar mixture but remains stable over a wide temperature and composition range. In dendrimer enriched mixtures the lattice swells to take up more dendrimer, while discotic enriched mixtures show the appearance of lamellar phases with a columnar structure that is probably closely related to the oblique superlattice. Additionally, the structure of the oblique superlattice can be covalently stabilized at elevated temperature via amidation of the ionic carboxylic acid−amine complexes. The results show the potential of orthogonal self-assembly in columnar LC phases to obtain nanostructured materials with a periodicity of 2–10 nm.

A Highly Efficient Approach to the Self-Assembly of Hexagonal Cavity-Cored Tris[2]pseudorotaxanes from Several Components via Multiple Noncovalent Interactions

A method of incorporating both metal−ligand and crown ether−dialkylammonium self-assembly techniques in the efficient synthesis of metallacyclic tris[2]pseudorotaxanes is described. These multifunctional supramolecules can be prepared by the stepwise or one-pot assembly of nine separate components on account of the orthogonality of the two noncovalent assembly strategies employed. This methodology demonstrates the power of orthogonal self-assembly and may be expanded beyond the use of two recognition motifs in hopes of mimicking the complex multifunctionality of biological systems.

Orthogonal Self-Assembly of Carbon Nanotube Crossbar Architectures by Simultaneous Graphoepitaxy and Field-Directed Growth

Crossbar arrays of single-wall carbon nanotubes are produced spontaneously in a single step of chemical vapor deposition by simultaneous graphoepitaxy along faceted nanosteps and field-directed growth, perpendicular to each other. The two alignment mechanisms take place selectively on miscut C-plane sapphire and patterned amorphous SiO2 islands, respectively, without mutual interference, producing dense nanotube grids, with up to 12 junctions per square micrometer. This one-step method of orthogonal self-assembly may open up new possibilities for nanotube circuit integration.

Recognition-Directed Orthogonal Self-Assembly of Polymers and Nanoparticles on Patterned Surfaces

We demonstrate the patterning of silica substrates with thymine (Thy-PS) and positively charged N-methylpyridinium (PVMP) polymers using photolithography and the subsequent orthogonal modification of these surfaces using diaminopyridine-functionalized polystyrene (DAP-PS) and carboxylate-derivatized CdSe/ZnS core-shell nanoparticles (COO-NP) through diamidopyridine-thymine three-point hydrogen bonding and pyridinium-carboxylate electrostatic interactions, respectively. This two-component orthogonal surface modification was accomplished in a self-sorting, single-step fashion, providing a versatile tool for the rapid and efficient creation of complex materials.

Self-Sorting in Polymers

Random and block copolymers containing two different classes of hydrogen-bonding side-chains have been prepared by ring-opening metathesis polymerization. The resulting copolymers can be viewed as “universal polymer backbones” based solely on two competitive hydrogen-bonding pairs. The hydrogen-bonding side chains containing thymine and cyanuric acid-based recognition motifs are shown to self-assemble with their complementary diamido pyridine and isophthalic wedge moieties, respectively, even in the presence of competitive recognition sites, i.e., selective functionalization of the copolymers can be accomplished via a one-step orthogonal self-assembly approach displaying self-sorting in a competitive environment. These results clearly demonstrate the concept of self-sorting in synthetic polymers and suggest the design of complex polymeric materials containing competitive noncovalent interactions.

Bifunctional, Conjugated Oligomers for Orthogonal Self-Assembly: Selectivity Varies from Planar Substrates to Nanoparticles

A diphenylacetylene containing two different end groups (isonitrile and thioacetate) was synthesized, showing that the chemistry used to install each end group is compatible with that of the others. The isonitrile group binds preferentially to platinum, and the thiol group binds preferentially to gold. However, the selectivity was different when nanoparticles were compared to planar substrates.

Synthesis of n-type perylene bisimide derivatives and their orthogonal self-assembly with p-type oligo(p-phenylene vinylene)s.

Four different (chiral) electron-deficient (n-type) perylene bisimides containing aliphatic, aromatic, or ethyleneoxide side chaines have been synthesized and fully characterized. All of them form supramolecular stacks in apolar methylcyclohexane (MCH) solution as demonstrated by concentration- and temperature-dependent absorption, circular dichroism, and fluorescence studies. One derivative was investigated in more detail in the solid state and proven to be liquid crystalline and capable of forming nanometer-sized fiberlike networks when drop-cast from MCH. Optical spectroscopy techniques show that perylene bisimide and an oligo(p-phenylene vinylene) (p-type) derivative orthogonally self-assemble into separate nanosized p-and n-type stacks in MCH. In contrast in toluene only molecularly dissolved species are present. In films deposited from MCH as well as from toluene photoinduced electron transfer takes place from the p-type material to the n-type material. As a result of the orthogonal self-assembly process, in films from MCH an ordered network of fibers was formed, whereas in films from toluene no ordering was observed. However, probably due to the lateral orientation on the surface and the presence of long aliphatic chains pointing toward the electrodes, efficient bulk heterojunction solar cells could not be constructed.

Cross-linked and functionalized ‘universal polymer backbones’ via simple, rapid, and orthogonal multi-site self-assembly

A novel route to cross-linked and functionalized random copolymers using a rapid, one-step, and orthogonal copolymer cross-linking/functionalization strategy has been developed. Random terpolymers possessing high concentrations of pendant alkyl chains and either (1) palladated-pincer complexes and diaminopyridine moieties (DAD hydrogen-bonding entities) or (2) palladated-pincer complexes and cyanuric wedges (ADAADA hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Non-covalent cross-linking of the resultant copolymers using a directed functionalization strategy leads to dramatic increases in solution viscosities for cross-linked polymers via metal-coordination while only minor changes in viscosity were observed when hydrogen-bonding motifs were employed for cross-linking. The cross-linked materials could be further functionalized via self-assembly by employing the second recognition motif along the polymeric backbones giving rise to highly functionalized materials with tailored cross-links. This novel non-covalent polymer cross-linking/functionalization strategy allows for rapid and tunable materials synthesis by overcoming many difficulties inherent to the preparation of covalently cross-linked polymers.

One-step multifunctionalization of random copolymers via self-assembly.

A novel methodology for random copolymer functionalization based on a noncovalent, one-step, multifunctionalization strategy has been developed. Random copolymers possessing both palladated-pincer complexes and diaminopyridine moieties (hydrogen-bonding entities) have been synthesized using ring-opening metathesis polymerization. Noncovalent functionalization of the resultant copolymers is accomplished via (1) directed self-assembly, (2) multistep self-assembly, and (3) one-step orthogonal self-assembly. This system shows complete specificity of each recognition motif for its complementary unit, with no observable changes in the association constants regardless of the degree of functionalization.

Orthogonal self-assembly of low molecular weight hydrogelators and surfactants.

The concurrent self-assembly of new 1,3,5-trisamide-cyclohexane-based low molecular weight hydrogelators and various surfactants in water leads to the formation of self-assembled fibrillar networks with encapsulated micelles. This prototype system presents an example of orthogonal self-assembly, that is, the independent formation of two different supramolecular structures, each with their own characteristics that coexist within a single system.

Orthogonal Self-Aligned Electroless Metallization by Molecular Self-Assembly

A strategy for achieving orthogonal electroless metallization (i.e., formation of a metal pattern not overlapping and self-aligned with a first metal pattern) is described. The approach comprises molecular passivation of a first gold pattern with 1-hexadecanethiol (HDT), followed by priming of the SiO2 substrate with (3-aminopropyl)triethoxysilane (APS) and activation with Pd(II) complexation to spatially direct electroless nickel metallization. Scanning electron microscopy indicates that the nickel nucleates on the gold sidewall and grows laterally over the dielectric but not over the gold surface. This confirms successful deactivation of the intrinsic catalytic activity of gold. Using this two-step orthogonal self-assembly of the molecular resist and primer, a lateral nickel metal pattern orthogonal and self-aligned to the first gold pattern with line width down to 10 μm has been demonstrated. The process can also be applied to curved and flexible substrates.

Meniscus Force Nanografting: Nanoscopic Patterning of DNA

Thiol-modified DNA is patterned with an atomic force microscope (AFM) on a resist-covered gold surface with line widths as small as 15 nm at speeds as high as 320 μm/s. In meniscus force nanografting, a drop of patterning solution simultaneously wets a hydrophilic resist on gold and an AFM tip. The surface tension supplies enough normal force for the tip to selectively remove the resist molecules and allow the DNA to attach to the gold surface. Different DNA-derivatized nanostructures can then hybridize to the complementary, surface-bound DNA in a demonstration of surface initiated orthogonal self-assembly.

Electrochemical Synthesis of Multi-Material Nanowires as Building Blocks for Functional Nanostructures

AbstractNanostructures are electrochemically deposited into alumina or polycarbonate templates resulting in monodisperse, anisotropic particles with a range of tunable sizes. These particles have been synthesized with diameters of 20–250 nm and with lengths of 1–10 μm. Currently, structures have been made with stripes of Au, Ag, CdSe, Co, Cu, Ni, Pd, and Pt. These materials offer a variety of different properties. In particular, many of the metals in this group are excellent conductors, meaning these particles can actually be used as nanowires. Co and Ni are ferromagnetic and may be used for separation or assembly. CdSe is a semiconductor, possibly allowing for the synthesis of electronic devices such as transistors. Furthermore, many of these materials have different surface chemistries, making the orthogonal functionalization and assembly of these nanowires more accessible. This research focuses on increasing the number of materials available, especially semiconductors, incorporating these potentially useful materials into multilayered nanowires and evaluating their electrical properties, either individually or in small bundles. In addition, the surface chemistry of the various materials in the nanowires is being compared to aid in orthogonal self-assembly of functional nanostructures such as memory devices. The work presented will demonstrate the effects of rod composition on electrical properties. In particular, the effects of changing the work function of the materials on either side of a semiconductor to form Schottky junctions or ohmic contacts will be shown.

Systems for orthogonal self-assembly of electroactive monolayers on Au and ITO: an approach to molecular electronics

Systems for orthogonal self-assembly of electroactive monolayers on Au and ITO: an approach to molecular electronics

Toward orthogonal self-assembly of redox active molecules on platinum and gold: selective reaction of disulfide with gold and isocyanide with platinum

Toward orthogonal self-assembly of redox active molecules on platinum and gold: selective reaction of disulfide with gold and isocyanide with platinum