Oligopyrenotides: chiral nanoscale templates for chromophore assembly

Getting organized: DNA-like supramolecular polymers formed of short oligopyrenotides serve as a helical scaffold for the molecular assembly of ligands. The cationic porphyrin meso-tetrakis(1-methylpyridin-4-yl)porphyrin interacts with the helical polymers in a similar way as with poly(dA:dT).     

Molecular dynamics simulation of DNA‐directed assembly of nanoparticle superlattices using patterned templates

DNA‐directed assembly is a well developed approach in constructing desired nano‐architectures. On the other hand, E‐beam lithography is widely utilized for high resolution nano‐scale patterning. Recently, a new technique combining these two methods was developed to epitaxially grow DNA‐mediated nanoparticle superlattices on patterned substrates. However, defects are observed in epitaxial layers which restricts this technique from building large‐scale superlattices for real applications. Here we use molecular dynamics simulations to study and predict defect formation on adsorbed superlattice monolayers. We demonstrate that this epitaxial growth is energetically driven by maximizing DNA hybridization between the epitaxial layer and the substrate and that the shape anisotropy of the DNA‐mediated template posts leads to structural defects. We also develop design rules to dramatically reduce defects on epitaxial layers. Ultimately, with the assist of the computational study, this technique will open the door to constructing well‐ordered, three‐dimensional novel nanomaterials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1687–1692     

A chemical circular communication network at the nanoscale

In nature, coordinated communication between different entities enables a group to accomplish sophisticated functionalities that go beyond those carried out by individual agents. The possibility of programming and developing coordinated communication networks at the nanoscale—based on the exchange of chemical messengers—may open new approaches in biomedical and communication areas. Here, a stimulus-responsive circular model of communication between three nanodevices based on enzyme-functionalized Janus Au–mesoporous silica capped nanoparticles is presented. The output in the community of nanoparticles is only observed after a hierarchically programmed flow of chemical information between the members.

A community of three nanodevices communicates through a hierarchically programmed circular flow of chemical information between members.     

Activity study of self-assembled proteins on nanoscale diblock copolymer templates

Novel methods for affixing functional proteins on surfaces with high areal density have the potential to promote basic biological research as well as various bioarray applications. The use of polymeric templates under carefully balanced thermodynamic conditions enables spontaneous, self-assembled protein immobilization on surfaces with spatial control on the nanometer scale. To assess the full potential of such nanometer-scale protein platforms in biosensing applications, we report for the first time the biological activity of proteins on diblock copolymer platforms. We utilized horseradish peroxidase, mushroom tyrosinase, enhanced green fluorescent protein, bovine immunoglobulin G, fluorescein isothiocyanate conjugated anti-bovine IgG, and protein G as model systems in our protein activity studies. When specific catalytic functions of HRP and MT, immobilized on selective domains of microphase-separated PS-b-PMMA, are evaluated over a long period of time, these enzymes retain their catalytic activity and stability for well over 3 months. By performing confocal fluorescence measurements of self-fluorescing proteins and interacting protein/protein systems, we have also demonstrated that the binding behavior of these proteins is unaffected by surface immobilization onto PS-b-PMMA diblock copolymer microdomains. Our polymer platforms provide highly periodic, high-density, functional, stable surface-bound proteins with spatial control on the nanometer scale. Therefore, our diblock copolymer-guided protein assembly method can be extremely beneficial for high-throughput proteomic applications.     

Site-directed molecular assembly on templates structured with electron-beam lithography

We describe a simple method for patterning biomolecular films on surfaces with high resolution. A conventional polymeric resist is structured by electron-beam lithography. The exposed and developed patterns are then used for the directed self-assembly (SA) of a first molecule from solution. Removal of the remaining resist allows the SA of a second species. We illustrate the potential of the approach by assembling on gold (Au) substrates two alkanethiols of contrasting terminal functionality. The patterns have dimensions from the micrometer range down to 40 nm and an edge resolution of 3.5 nm.     

Spectroscopic studies on the spontaneous assembly of phenosafranin on glycosaminoglycans templates

Spectroscopic studies showed that binding of phenosafranin (PSF) molecules to glycosaminoglycans (GAGs) resulted in the following observations: (i) appearance of a 52.6 nm hypsochromic shift of the visible absorption band; (ii) static quenching of fluorescence from PSF; (iii) induction of strong circular dichroism (CD) signal of PSF. Stoichiometry of the PSF-GAGs complex was determined by spectrophotometric titration, spectrofluorimetric titration and MacIntosh extraction method. These studies demonstrated the formation of the extended helical PSF array aligned on the helical backbone of GAGs templates by electrostatic force, and the dimeric binding mode of PSF to each anionic site was proposed. The comparative studies between PSF-heparin (Hep) and PSF-chondroitin 4-sulfate (CS) complexes revealed that: (i) stoichiometry of PSF-Hep complex was 1.8 times of PSF-CS complex; (ii) Hep was more effective than CS (1.8 times) in decreasing the absorbance of PSF; and (iii) Stern-Volmer constants of the Hep-PSF system were greater than that of the CS-PSF system. These differences were attributed to the different charge density on the Hep and CS molecules, which in turn suggested that the electrostatic force was dominant in the interaction between PSF and GAGs.     

Directed assembly of carbon nanotubes at liquid-liquid interfaces: nanoscale conveyors for interfacial biocatalysis

We report that single-walled carbon nanotubes (SWNTs) can be directed to aqueous-organic interfaces with the aid of surfactants. This phenomenon can also be used to transport enzymes to the interface to effect biphasic biotransformations. Consequently, SWNT-enzyme conjugates enhance the rate of catalysis by up to 3 orders of magnitude relative to the rates obtained with native enzymes in similar biphasic systems. Furthermore, we demonstrate that this concept can be extended to other nanomaterials and other enzymes, thereby providing a general strategy for efficient interfacial biocatalysis. The ability to direct the assembly of nanotubes at the interface also provides an attractive route to organizing these nanomaterials into 2D architectures.     

Chain-like assembly of gold nanoparticles on artificial DNA templates via 'click chemistry'

We present a new type of azide-functionalized gold nanoparticle and their coupling to an alkyne-modified DNA duplex using the copper(I)-catalyzed Huisgen cycloaddition ('click chemistry'), resulting in a chain-like assembly of nanoparticles on the DNA template.     

Welding of gold nanoparticles on graphitic templates for chemical sensing

Controlled self-assembly of zero-dimensional gold nanoparticles and construction of complex gold nanostructures from these building blocks could significantly extend their applications in many fields. Carbon nanotubes are one of the most promising inorganic templates for this strategy because of their unique physical, chemical, and mechanical properties, which translate into numerous potential applications. Here we report the bottom-up synthesis of gold nanowires in aqueous solution through self-assembly of gold nanoparticles on single-walled carbon nanotubes followed by thermal-heating-induced nanowelding. We investigate the mechanism of this process by exploring different graphitic templates. The experimental work is assisted by computational studies that provide additional insight into the self-assembly and nanowelding mechanism. We also demonstrate the chemical sensitivity of the nanomaterial to parts-per-billion concentrations of hydrogen sulfide with potential applications in industrial safety and personal healthcare.     

Highly selective directed assembly of functional actomyosin on Au surfaces

The capability of assembling biomotors onto specific locations of solid substrates is a key for development of biomotor-based nanomechanical systems. We developed a method to direct the assembly of the heavy meromyosin fragment from rabbit skeletal muscle myosin onto specific locations of Au substrates utilizing surface molecular patterns. In this strategy, chemically directed patterns of streptavidin were achieved to direct highly specific assembly of biotinylated heavy meromyosin on the substrates--a strategy applicable for patterning a variety of biotinylated molecules--while BSA was utilized to avoid nonspecific adsorption. In vitro motility assays of filament sliding were used to confirm functionality of assembled actomyosin.     

Computational screening of biomolecular adsorption and self‐assembly on nanoscale surfaces

The quantification of binding properties of ions, surfactants, biopolymers, and other macromolecules to nanometer‐scale surfaces is often difficult experimentally and a recurring challenge in molecular simulation. A simple and computationally efficient method is introduced to compute quantitatively the energy of adsorption of solute molecules on a given surface. Highly accurate summation of Coulomb energies as well as precise control of temperature and pressure is required to extract the small energy differences in complex environments characterized by a large total energy. The method involves the simulation of four systems, the surface‐solute–solvent system, the solute–solvent system, the solvent system, and the surface‐solvent system under consideration of equal molecular volumes of each component under NVT conditions using standard molecular dynamics or Monte Carlo algorithms. Particularly in chemically detailed systems including thousands of explicit solvent molecules and specific concentrations of ions and organic solutes, the method takes into account the effect of complex nonbond interactions and rotational isomeric states on the adsorption behavior on surfaces. As a numerical example, the adsorption of a dodecapeptide on the Au {111} and mica {001} surfaces is described in aqueous solution. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Micro- and nanopatterned copper structures using directed self-assembly on templates fabricated from phase-separated mixed Langmuir-Blodgett films

We report a versatile method to confine metal thin films in micro- and nanopatterns using directed self-assembly on the templates fabricated from phase-separated mixed Langmuir-Blodgett (LB) films. The pattern of the mixed LB films can be tuned by adjusting intermolecular interaction between the film-forming molecules in the LB films and by varying the fabrication conditions of the films such as the mixing ratio, subphase temperature, and surface pressure. We use the patterned LB films for templates to confine metal in patterned regions, taking advantage of the difference between the surface free energy of the patterned regions and that of the self-assembled monolayer of the silane coupling agent. Au nanoparticles are confined onto the patterned films as a catalyst for the succeeding Cu electroless deposition. The atomic force microscopic images, Auger electron spectra, and scanning Auger electron maps of a Cu-deposited film show that Cu is selectively deposited on the patterns of phase separation of the original mixed LB films.     

"Lens" effect in directed assembly of nanowires on gradient molecular patterns

We report a new phenomenon, named here as the "lens" effect, in the directed-assembly process of nanowires (NWs) on self-assembled monolayer (SAM) patterns. In this process, the adsorption of NWs is focused in the nanoscale regions at the center of microscale SAM patterns with gradient surface molecular density just like an optical lens focuses light. As a proof of concepts, we successfully demonstrated the massive assembly of V2O5 NWs and single-walled carbon nanotubes (swCNTs) with a nanoscale resolution using only microscale molecular patterning methods. This work provides us with important insights about the directed-assembly process, and from a practical point of view, it allows us to generate nanoscale patterns of NWs over a large area for mass fabrication of NW-based devices.     

Size selective assembly of colloidal particles on a template by directed self-assembly technique

We report a simple and effective approach to organize micron- and submicron-sized particles in a size selective manner. This approach utilizes the template assisted directed self-assembly technique. A topographically patterned photoresist surface is fabricated and used to create an ordered array of colloidal particles from their aqueous suspensions. Assembly of particles on this template is then achieved by using a conventional spin coating technique. Feasibility of this technique to form a large area of patterned particle assemblies has been investigated. To arrange the particles on the template, the physical confinement offered by the surface topography must overcome a joint effect of centrifugal force and the hydrophobic nature of the photoresist surface. This concept has been extended to the size selective sorting of colloidal particles. The capability of this technique for sorting and organizing colloidal particles of a particular diameter from a mixture of microspheres is demonstrated.     

基于分子间相互作用的纳米尺度分子传递

纳米尺度下的分子传递是以纳米先进材料为导向的材料化学工程学科所面临的关键科学问题之一.借鉴分子热力学的建模研究思路研究分子传递,从分子之间相互作用出发,结合分子模拟技术,有望最终建立理论模型,实现分子传递的定量预测.本文通过几个研究实例初步探索了如何从分子间相互作用出发开展纳米尺度下分子传递的研究,利用分子模拟手段解析纳米尺度下特殊的微结构,并以此为基础进而实现对分子传递行为的调控和预测,指导具有丰富纳米结构的膜材料以及催化材料的设计和应用.     

Controlled assembly of bacteria on chemical patterns using soft lithography

Highly ordered arrays of single living bacteria were obtained by selective adsorption of bacteria onto chemical patterns with micrometric resolution. The chemically engineered template surfaces were prepared with the combination of microcontact printing process and a simple incubation technique. This methodology can be used for fundamental studies of bacterium's inner mechanisms and sub-cellular organization as well as for interfacing living bacteria with artificial microsystems.