Nanotechnology's growing applications are fueled by the synthesis and engineering of myriad nanostructures, yet there is no systematic naming or classification scheme for such materials. This lack of a coherent nomenclature is confusing the interpretation of data sets and threatens to hamper the pace of progress and risk assessment. A systematic nomenclature that encodes the overall composition, size, shape, core and ligand chemistry, and solubility of nanostructures is presented. A typographic string of minimalist field codes facilitates digital archiving and searches for desired properties. This nomenclature system could also be used for nanomaterial hazard labeling.
Strong polymer fibers have a broad range of applications andplay a very important role in modern technology and everydaylife. Therefore, the development of new ultra-strong polymeror composite fibers is of great interest both scientifically andfor industry. Carbon nanotubes have been envisaged as one ofthe most promising additives for the fabrication of ultra-strongpolymer composite materials1] due to their superior mechanicalproperties. It is well-known that carbon nanotubes haveYoung’s modulus and tensile strength above 1 TPa2] and60 GPa,3,4] respectively, while their densities can be as low asSOH1.3 g cmSTX1.3,5] For these reasons, various polymer–nanotubecomposites have become a subject of intensive research andtechnological development over the last decade.1] The mostcommon approaches for the fabrication of polymer–nanotubecomposite fibers have been melt processing6–9] and solutioncoagulation spinning.10–15] In these techniques, nanotubesmust either be incorporated into a polymer solution or moltenpolymer before the formation of corresponding polymer–nanotube composite fibers. However, these methods cannot beapplied in the case of insoluble or temperature-sensitivepolymers, which decompose without melting. Kevlar is a wellknownhigh-strength polymer with a variety of importantapplications including bullet-proof vests, protective clothing,and high-performance composites for aircraft and automotiveindustries.16–18] However, Kevlar is not soluble in anycommon solvent and has no melting point, decomposingabove 400 8C.17] As a result, Kevlar fibers must be producedby wet-spinning from sulfuric acid solutions.19,20] Whilesingle-walled nanotube (SWNT) fibers can be produced byacid-spinning,21] to the authors knowledge, no reports ofKevlar–nanotube fibers have appeared in the literature(however, it should be noted that poly(paraphenylene-2,6-benzobisoxazole) (PBO, also known as Zylon)–nanotubecomposite fibers have been produced by acid dry-jet wet-wetspinning).22,23] Although it is probably possible to produceKevlar–SWNT fibers by acid-spinning, an alternative method,which would allow proof-of-concept, would be to incorporatenanotubes in commercially available, pre-existing Kevlarfibers by a post-production method. Such a method is describedin this paper, where we report the preparation of new,reinforced Kevlar–nanotube composites. These are preparedby swelling commercially available Kevlar 129TM fibers insuspensions of nanotubes in the solvent N-methylpyrrolidone(NMP). Nanotube uptake of up to 4wt% has been observed,resulting in significant mechanical enhancement of thefibers.
A versatile technique for producing monodisperse microspheresfrom both hydrophobic and hydrophilic polymersusing a simple fluidic device fabricated with a poly(vinylchloride) (PVC) tube, a syringe needle, and a glass capillarytube is described. The technique is successfully applied to avariety of different materials, including poly(e-caprolactone)(PCL) as an example of a hydrophobic polymer, ethyl-2-cyanoacrylate (ECA) as an example of organic monomer, andgelatin as an example of a hydrophilic, natural polymer. Fromthe calculated capillary number (Ca) and Weber number (We),the system is confirmed to work in the dripping regime. Precisecontrol over particle size can be achieved by varying thepolymer concentration and/or the flow rate for the continuousphase. An increase in flow rate for the continuous phase or adecrease in polymer concentration results in the reduction ofparticle size. The production of raspberry-like microsphereswith a mixture of PCL and ECA is also demonstrated. Inaddition, we have developed a tapping method based onsolvent evaporation on a concave glass for crystallizing thesemicrospheres into close-packed lattices.
Recently, some innovative techniques have been developedfor the fabrication of arrays of complex functional nanoscaledevicestructures, such as the layer-by-layer assembly ofnanowire (NW) building blocks,1] nanoskiving,2] a polymerdirectedselective nucleation and growth process,3] a bottomupand top-down hybrid methodology,4] and a printing-liketransfer process.5] Progress in these techniques has demonstratedthe future feasibility of three-dimensional (3D)integrated multifunctional nanoscale devices based on nanomaterialbuilding blocks. Simultaneously, suitable NWs forinterconnects and precise positioning of NWs are criticalissues. First of all, the NWs should be of long-term stability andsuperior electrical transport properties.
Ultraflat gold nanoplates were found to be very attractivesubstrates for tip-enhanced Raman scattering (TERS) measurements.The transparent flat triangular or hexagonalnanoplates were synthesized by citrate reduction of HAuCl4in aqueous solution. The obtained nanoparticles with a heightof 15–20nm had a smooth homogeneous surface with aroughness of about 100–200 pm. After spreading the goldplates on glass slides, cystine was successfully immobilized onthem and the first TERS spectra of an amino acid wererecorded. The spectra revealed a local variation of theattachment of cystine on the gold surface in two conformers.
The nanoengineering of materials for biomedical applicationssuch as drug delivery, gene therapy and tissue engineering is anarea of intense scientific research.1,2] To develop innovativematerials with tailored properties, new synthetic methods thatare highly specific and capable of delivering high yields ofpredesigned, functional building blocks, and complex molecularassemblies are required. Click chemistry meets suchstringent requirements; it has provided a set of quantitative,highly selective covalent reactions that are simple andversatile, and can be performed under mild reaction conditionsto produce high product yields.3] The most commonly usedclick reaction is the copper(I)-catalyzed variant of Huisgen’s1,3-dipolar cycloaddition of alkynes and azides to produce1,2,3-triazoles.4–6] The versatility and specificity of this clickreaction has been demonstrated through the synthesis of arange of advanced materials, including hydrogels,7] crosslinkedmicelles,8] and dendritic copolymers9] as well as for thepreparation of functionalized nanoparticles,10] nanotubes,11]and cotton and organic resin surfaces.12] This technique hasalso been popular in a number of bioapplications for thefunctionalization of DNA,13] site specific modification ofproteins,14] and selective dye labeling within cells.15]
Nanoparticles of coinage metals (Au, Ag, Cu) are known todisplay attractive optical properties, arising from localizedsurface plasmon resonances in the visible and the nearinfrared(NIR) frequencies. Such properties have stimulatedthe development of numerous synthetic (colloid chemistry)strategies for tuning the optical response through control ofgold and silver nanoparticle size and shape. However, copperis less popular, mainly because the fabrication of chemicallystable Cu colloids with intense plasmon resonance bands is farmore complicated, first because they are prone to fastoxidation, but also because of the lower ‘‘free-electroncharacter’’ of copper.1] The free-electron behavior of Auand Ag colloids in the visible range is reflected in the fairlyconstant value of the imaginary part of their dielectricfunctions, which is responsible for the sharp and prominentextinction bands displayed by colloids of these metals. For Cumetal, the real and imaginary parts of the dielectric functionvary markedly in the UV–Vis range, so that electronicinterband transitions from the valence band to the Fermi leveloverlap the plasmon resonances up to 600 nm. Since interbandtransitions can efficiently damp surface plasmon resonancesthrough dephasing of the optical polarization associated withthe electron oscillation,2] well-defined plasmon bands canonly be achieved if the resonance wavelength is shifted awayfrom the interband transitions. This can in principle beachieved for non-spherical nanoparticles, but it is still difficultfor copper because of the extended range of the interbandtransitions. Although a number of methods have beenreported for the fabrication of Cu nanoparticles, such asUV-light irradiation,3,4] pulsed sonoelectrochemical reduction,5] g-irradiation,6] chemical7–9] or polyol reduction10] ofcopper salts, and growth in reverse micelles,11–14] few of them have focused on improving the optical response from theobtained Cu nanoparticles, that is, on achieving plasmonbands located at sufficiently high wavelengths with respect tothe interband transitions and thereby minimize dampingeffects. Pileni et al. have demonstrated that by mixing reversemicelles with a large excess of reducing agent, coppernanocrystals can be prepared with a fair control of size11,12]and shape.13–15] Although tuning of the optical response wasclaimed in these reports, the experimental absorption spectrado not display sharp and well-defined plasmon peaks, asexpected from calculations.16] This is likely due to damping byinterband transitions in the case of the smaller particles or toshape polydispersity in other cases. A successful example ofvariation of the particle geometry to tune the plasmon energyaway from the onset of interband transitions in the metal wasprovided by Halas et al.17] through the synthesis of Cunanoshells via seed-catalyzed reduction of Cu2 by formaldehydein alkaline aqueous solutions at room temperature.
Inorganic nanofluidic devices, such as nanopores,1–3] nanochannels,4–10] and nanotubes (NTs)8,11–17] have been activelystudied in bioseparation, bioanalysis, fluidic transistors, powergeneration, and fast mass transport. Compared to biologicalnanopores, inorganic nanofluidic devices have been demonstratedto be robust, to have easily tuned surfaces and to beintegrable into arrays. One of the most powerful nanofluidicdevice fabrication methods is templating against a porousmembrane16,17] or chemically synthesized or lithographicallypatterned nanowires (NWs).11,14] NTs or nanochannels madein this way have controllable dimensions, with diameters downto several nm and lengths up to tens of mm. Herein, we exploithyperbranched PbSe NWs18,19] as templates to produce 3Dinterconnected hyperbranched silicon dioxide (silica) NTs bysimple coating and etching steps. The obtained NTs with athick enough shell retain the orientation of the originalhyperbranched arrays and are either parallel or perpendicularto each other. These hyperbranched NTs afford interestingopportunities for constructing new 3D nanofludic devices.
Surfaces exhibiting ordered nanopillars have a wide range ofpotential biomedical applications based on the alteredadhesivity of living cells on nanopatterned surfaces comparedto planar ones. Examples include scaffolding for tissueengineering, designer bandages for wound dressing, andantifouling surfaces for implants. Although numerous experimentsperformed over the last decade have confirmed thatcells respond to the chemistry (biochemical 2D imprint) andgeometry (topographical 3D relief) of their surroundings atthe nanoscale, the fundamental processes by which cellsrecognize nanostructures is a subject of on-going research.1–6]In this context, there is a need to ensure that thenanostructured surfaces have large-scale coverage and arecompatible with quantitative optical microscopy (QOM), animportant tool for studying living cells, especially the dynamicsthereof.7,8] While biochemical patterning is not expected topose a special challenge for QOM, topographical patterningmay do so. Well-known techniques for topographicalpatterning are nanoimprint lithography (NIL, includingthermal embossing and UV curing) and self-assembly basedon colloidal beads or phase separation of polymers, all ofwhich achieve large coverage.9–15,16] NIL is relatively resourceintensive and usually depends on conventional techniques likeelectron-beam lithography for the initial stamp. Self-assembly,although increasingly refined, has limited flexibility for thechoice of motif.16] Transparent substrates made using these techniques have been used in pioneering microscopic studiesof cells, however, these studies were usually confined totechniques that are not sensitive to the details of the optics ofthe substrate.2,3,6,17,18] Techniques like reflection interferencecontrast microscopy (RICM) or total internal reflectionfluorescence (TIRF) microscopy that allow the determinationof nanometric distances in the vertical direction, or differentialinterference contrast (DIC) that detects very the thintransparent lamellipodia, have stringent requirements onrefractive index and thickness of the substrates. So far,topographical patterning has invariably led to drastic changesin the optical properties of the substrate, thus making the useof QOM unreliable.
A long-range ordered organic/inorganic material is synthesized from a bissilane, (EtO)(3)Si-(CH2)(3)-NHCONH-C6H4-NHCONH-(CH2)(3)-Si(OEt)(3). This crosslinked so-gel solid exhibits a supramolecular organization via intermolecular hydrogen bonding interaction between urea groups (-NHCONH-) and covalent siloxane bonding, Si-O-Si . Time-resolved in situ X-ray measurements (coupling small- and wide-angle X-ray scattering techniques) are performed to follow the different steps involved in the synthetic process. A new mechanism based on the crystallization of the hydrolyzed species followed by their polycondensation in solid state is proposed.
The electrical properties of alpha,omega-mercaptoalkyl ferrocenes with different alkyl chain lengths embedded in a self-assembled host matrix of alkanethiols on Au(111) are studied by scanning tunneling microscopy and spectroscopy. Based on current-distance spectroscopy, as well as on the evaluation of Fowler-Nordheim tunneling current oscillations, the apparent barrier height of ferrocene is determined independently by two methods. The electronic coupling of the ferrocene moiety to the Au(111) substrate is shown to depend on the length of the alkane-spacer chain. In a double tunnel junction model our experimental findings are explained, addressing the role of the different molecular moieties of the mercaptoalkyl ferrocenes.
The effects of exposure of human dermal fibroblasts of rutile and anatase TiO2 nanoparticles are reported. These particles can impair cell function, with the latter being more potent at producing damage. The exposure to nanoparticles decreases cell area, cell proliferation, mobility, and ability to contract collagen. Individual particles are shown to penetrate easily through the cell membrane in the absence of endocytosis, while some endocytosis is observed for larger particles clusters. Once inside, the particles are sequestered in vesicles, which continue to fill up with increasing incubation time till they rupture. Particles coated with a dense grafted polymer brush are also tested, and using flow cytometry, are shown to prevent adherence to the cell membrane and hence penetration of the cell, which effectively decreasexs reactive oxygen species (ROS) formation and protects cells, even in the absence of light exposure. Considering the broad applications of these nonoparticles in personal health care products, the functionalized polymer coating can potentially play an important role in protecting cells and tissue from damage.
Interactions between proteins and DNA are essential for the regulation of cellular processes in all living organisms. In this context, it is of special interest to investigate the sequence-specific molecular recognition between transcription factors and their cognate DNA sequences. As a model system, peptide and protein epitopes of the DNA-binding domain (DBD) of the transcription factor PhoB from Escherichia coli are analyzed with respect to DNA binding at the single-molecule level. Peptides representing the amphiphilic recognition helix of the PhoB DBD (amino acids 190-209) are chemically synthesized and C-terminally modified with a linker for atomic force microscopy-dynamic force spectroscopy experiments (AFM-DFS), For comparison, the entire PhoB DBD is overexpressed in E. coli and purified using an intein-mediated protein purification method. To facilitate immobilization for AFM-DFS experiments, an additional cysteine residue is ligated to the protein. Quantitative AFM-DFS analysis proves the specificity of the interaction and yields force-related properties and kinetic data, such as thermal dissociation rate constants. An alanine scan for strategic residues in both peptide and protein sequences is performed to reveal the contributions of single amino acid residues to the molecular-recognition process. Additionally, DNA binding is substantiated by electrophoretic mobility-shift experiments. Structural differences of the peptides, proteins, and DNA upon complex formation are analyzed by circular dichroism spectroscopy. This combination of techniques eventually provides a concise picture of the contribution of epitopes or single amino acids in PhoB to DNA binding.
A simple and facile procedure to synthesize a novel hybrid nanoelectrocatalyst based on polyaniline (PANI) nanofiber-supported supra-high density Pt nanoparticles (NPs) or Pt/Pd hybrid NPs without prior PANI nanofiber functionalization at room temperature is demonstrated. This represents a new type of ID hybrid nanoelectrocatalyst with several important benefits. First, the procedure is very simple and can be performed at room temperature using commercially available reagents without the need for templates and surfactants. Second, ultra-high density small "bare" Pt NPs or Pt/Pd hybrid NPs are grown directly onto the surface of the PANI nanofiber, without using any additional linker. Most importantly, the present PANI nanofiber-supported supra-high density Pt NPs or Pt/Pd hybrid NPs can be used as a signal enhancement element for constructing electrochemical devices with high performance.