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ABSTRACT: The fabrication of electrically conducting magnetic nanowires has been achieved using electrochemical DNA-templating of iron. In this approach, binding of the Fe(2+) cations to the DNA "template" molecules has been utilised to promote growth along the molecular axis. Formation of Fe within the product material was verified by XRD and XPS studies, which confirmed an iron/oxide "core-shell" structure. The effectiveness of the DNA duplex to direct the metal growth in one dimension was highlighted by AFM which reveals the product material to comprise high aspect ratio nanostructured architectures. These "nanowires" were observed to have morphologies consisting of densely packed linear arrangements of metal particles along the template, with wire diameters up to 26 nm. The structures were confirmed to be electrically conductive, as expected for such Fe-based materials, and to display superparamagnetic behaviour, consistent with the small size and particulate nature of the nanowires.
Nanoscale 05/2013; · 5.91 Impact Factor
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ABSTRACT: The lack of an in vitro real-time osteoclast (OC) activity assay has hampered mechanistic studies of bone resorption. Such an assay is developed, employing a hydroxyapatite matrix impregnated with alkyl-capped silicon nanocrystals, which is capable of monitoring the time-course of resorption by single osteoclasts. Resorption of the matrix by OC releases the nanocrystals, which are internalized by the cell and detected as an increase in OC luminescence. This particular choice of nanocrystals is motivated by their bright pH-independent luminescence, proportional to concentration, and by their rapid uptake without cytotoxicity. In this in vitro assay, OCs are inhibited by calcitonin (CT) and methyl-β-cyclodextrin (MCD), and stimulated by receptor activator of nuclear factor kappa-B ligand (RANKL) in the expected manner. The kinetics of the assay exhibit a lag phase representing cell attachment and commencement of resorption processes, followed by a growth of cell luminescence intensity, and the whole time-course is satisfactorily described by the logistic equation.
Small 05/2013; · 8.35 Impact Factor
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ABSTRACT: The preparation of two-component polymer composite nanoparticles encapsulating both Si quantum dots (SiQDs) and Au nanoparticles (AuNPs) by a single step miniemulsion polymerization of divinylbenzene is described. This simple and robust method affords well-defined polymer composite nanoparticles with mean diameters in a range of 100-200 nm and with narrow polydispersity indices as determined by dynamic light scattering and transmission electron microscopy. The successful encapsulation of AuNPs within poly(divinylbenzene) was confirmed by UV-visible spectroscopy and from TEM images. Plasmon-enhanced fluorescence of the luminescence of the SiQDs by AuNPs encapsulated within the polymer composite nanoparticles was evaluated by confocal microspectroscopy, and luminescence enhancements of up to 15 times were observed. These observations indicate that the luminescence of the SiQDs is enhanced by the proximity of the AuNPs. The polymer composite nanoparticles were successfully ink-jet printed onto a glass substrate, which demonstrates that these composites are processable in printing applications.
Nanoscale 03/2013; · 5.91 Impact Factor
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ABSTRACT: The thermodynamics of the templating of materials on one-dimensional templates, such as DNA, is modeled by considering two terms: the surface tension of the material (γ) and a line energy (σ = 2πr(T)γ(T)) that represents the adhesion of the material to the template (radius r(T)). We show that as long as the reaction stoichiometry does not exceed a certain limit ([Formula: see text]; v = volume of material per unit length of template) then a sample of smooth, uniform wires is the equilibrium state. If the amount of material exceeds this limit, then the material will comprise a single macroscopic particle at equilibrium. The behavior of the system is similar to a morphological wetting transition and the model can rationalize the available experimental data on the reaction conditions required to form smooth DNA-templated nanowires. Using the framework of linear non-equilibrium thermodynamics, we also show that the model can describe qualitatively the observed evolution of these nanostructures from beads-on-a-string morphologies to smooth nanowires and construct a stochastic differential equation for the process. Numerical simulations and scaling arguments suggest that the same scaling behavior as the Edwards-Wilkinson equation is observed.
Nanotechnology 12/2012; 23(50):505603. · 3.98 Impact Factor
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ABSTRACT: The synthesis of nanowires made of magnetite (Fe(3)O(4)) phase iron oxide was achieved using DNA as a template to direct formation of the metal oxide and confine its growth in two dimensions. This simple solution-based approach involves initial association of Fe(2+) and Fe(3+) to the DNA "template" molecules, and subsequent co-precipitation of the Fe(3)O(4) material, upon increasing the solution pH, to give the final metal oxide nanowires. Analysis of the DNA-templated material, using a combination of FTIR, XRD, XPS, and Raman spectroscopy, confirmed the iron oxide formed to be the Fe(3)O(4) crystal phase. Investigation of the structural character of the nanowires, carried out by AFM, revealed the metal oxide to form regular coatings of nanometre-scale thickness around the DNA templates. Statistical analysis showed the size distribution of the nanowires to follow a trimodal model, with the modal diameter values identified as 5-6 nm, 14-15 nm, and 23-24 nm. Additional scanning probe microscopy techniques (SCM, MFM) were also used to verify that the nanowire structures are electrically conducting and exhibit magnetic behaviour. Such properties, coupled with the small dimensions of these materials, make them potentially good candidates for application in a host of future nanoscale device technologies.
Nanoscale 08/2012; 4(19):5936-45. · 5.91 Impact Factor
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ABSTRACT: Supramolecular polymer nanowires have been prepared by using DNA-templating of 2,5-(bis-2-thienyl)-pyrrole (TPT) by oxidation with FeCl(3) in a mixed aqueous/organic solvent system. Despite the reduced capacity for strong hydrogen bonding in polyTPT compared to other systems, such as polypyrrole, the templating proceeds well. FTIR spectroscopic studies confirm that the resulting material is not a simple mixture and that the two types of polymer interact. This is indicated by shifts in bands associated with both the phosphodiester backbone and the nucleobases. XPS studies further confirm the presence of DNA and TPT, as well as dopant Cl(-) ions. Molecular dynamics simulations on a [{dA(24) :dT(24) }/{TPT}(4) ] model support these findings and indicate a non-coplanar conformation for oligoTPT over much of the trajectory. AFM studies show that the resulting nanowires typically lie in the 7-8 nm diameter range and exhibit a smooth, continuous, morphology. Studies on the electrical properties of the prepared nanowires by using a combination of scanned conductance microscopy, conductive AFM and variable temperature two-terminal I-V measurements show, that in contrast to similar DNA/polymer systems, the conductivity is markedly reduced compared to bulk material. The temperature dependence of the conductivity shows a simple Arrhenius behaviour consistent with the hopping models developed for redox polymers.
Chemistry 08/2012; 18(38):12008-19. · 5.93 Impact Factor
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ABSTRACT: In this article, we have studied and developed two approaches for organizing metallic nanoparticles into one-dimensional assemblies.
The first uses DNA as a ‘template’ and allows the preparation of various silver nanostructures (‘beads-on-a-string’ or rod-like
wires). The conductance of such nanostructures was demonstrated by employing a powerful technique, Electrostatic Force Microscopy
(EFM). This technique gave us ‘contactless’ information about the electrical properties of silver nanostructures, aligned
on a SiO2/Si surface. Additionally, I–V characteristics of a single silver nanowire crossing two microelectrodes were recorded. The nanowire resistivity was estimated
at 1.46×10−7Ωm (at 300K), which is one order of magnitude higher than that of bulk silver (1.6×10−8Ωm). The second approach is a ‘template-free’ one, and exploits the binding ability of l-arginine, which favours the self-assembling of capped gold nanoparticles into gold nanochains. The results suggest that gold
nanochains were formed due to dipole–dipole interaction between adjacent nanoparticles, which fuse together through an oriented
attachment mechanism. Atomic force microscopy, TEM, UV–vis spectroscopy and X-ray diffraction were used to characterize the
morphological, optical and structural properties of these metallic nanostructures.
Journal of Materials Science 04/2012; 45(12):3151-3159. · 2.02 Impact Factor
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ABSTRACT: DNA strands have been used as templates for the self-assembly of smooth and conductive cuprous oxide (Cu₂O) nanowires of diameter 12-23 nm and whose length is determined by the template (16 μm for λ-DNA). A combination of spectroscopic, diffraction and probe microscopy techniques showed that these nanowires comprise single crystallites of Cu₂O bound to the DNA molecules which fused together over time in a process analogous to Ostwald ripening, but driven by the free energy of interaction with the template as well as the surface tension. Electrical characterization of the nanowires by a non-contact method, scanned conductance microscopy and by contact mode conductive AFM showed the wires are electrically conductive. The conductivity estimated from the AFM cross section and the zero-bias conductance in conductive AFM experiments was 2.2-3.3 S cm⁻¹. These Cu₂O nanowires are amongst the thinnest reported and show evidence of strong quantum confinement in electronic spectra.
Nanotechnology 02/2012; 23(7):075601. · 3.98 Impact Factor
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ABSTRACT: DNA strands have been used as templates for the self-assembly of smooth and conductive cuprous oxide (Cu2O) nanowires of diameter 12–23 nm and whose length is determined by the template (16 μm for λ-DNA). A combination of spectroscopic, diffraction and probe microscopy techniques showed that these nanowires comprise single crystallites of Cu2O bound to the DNA molecules which fused together over time in a process analogous to Ostwald ripening, but driven by the free energy of interaction with the template as well as the surface tension. Electrical characterization of the nanowires by a non-contact method, scanned conductance microscopy and by contact mode conductive AFM showed the wires are electrically conductive. The conductivity estimated from the AFM cross section and the zero-bias conductance in conductive AFM experiments was 2.2–3.3 S cm−1. These Cu2O nanowires are amongst the thinnest reported and show evidence of strong quantum confinement in electronic spectra.
Nanotechnology 01/2012; 23(7):075601. · 3.98 Impact Factor
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ABSTRACT: Miniemulsion polymerization techniques were used to encapsulate luminescent alkylated silicon quantum dots (Si-QDs) within polymer nanoparticles composed of styrene and 4-vinylbenzaldehyde monomers. The polymer nanoparticles had mean diameters in the range 90-150 nm depending on the reaction conditions, however all samples showed narrow particle size distributions, as determined by dynamic light scattering and atomic force microscopy. The Si-QDs were found to have a small, but beneficial effect on the polymerization process by reducing the polydispersity of the final polymer particles, which we attribute to co-surfactant action of the undecene used to form the alkyl capping layer on the Si-QDs. Confocal microspectroscopy was used to confirm that the luminescent alkylated Si-QDs were encapsulated within the polymer nanoparticles and also provided luminescence and Raman spectra which show peaks corresponding to both alkylated Si-QDs and the polymer nanoparticles. Treatment of the polymer nanoparticles with dilute aqueous sodium hydroxide solution, which is known to corrode Si and extinguish the luminescence of alkylated Si-QDs, results in only a partial reduction in luminescence suggesting that the majority of the alkylated Si-QDs are encapsulated sufficiently deep within the polymer matrix to protect them from alkaline attack. Miniemulsion polymerization of the monomers styrene and 4-vinylbenzaldehyde affords polymer nanoparticles displaying reactive aldehyde groups upon their surfaces, which could then be decorated with a selection of molecules through imine, oxime or hydrazone condensation reactions. We speculate that polymer-SiQD composite nanoparticles whose surfaces can be further decorated will increase the utility of luminescent Si-QDs in applications such as anti-counterfeiting and as probes of biological processes.
Nanoscale 11/2011; 3(11):4733-41. · 5.91 Impact Factor
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ABSTRACT: Self-complementary oligonucleotides were synthesized at atomically-flat Si(111) surfaces and their hybridization reaction was studied using atomic force microscopy. Annealing these surfaces in aqueous media, in the absence of any other reagents or DNA, resulted in a self-organization process in which hybridization produced well-defined features in the AFM images. By varying the surface coverage of DNA we provide evidence that the features observed are due to inter-strand rather than intra-strand hybridization reactions.
Science of Advanced Materials 05/2011; 3(3):483-489. · 3.31 Impact Factor
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ABSTRACT: A series of modified nucleosides based on thymidine have been prepared by Pd-catalysed cross-coupling between N-alkyl-alkynyl functionalised pyrrolyl- (py), 2-(2-thienyl)pyrrolyl- (tp) or 2,5-bis(2-thienyl)pyrrolyl (tpt) groups with 5-iodo-2'-deoxyuridine. The length of the alkyl chain linking the nucleoside and pyrrolyl-containing unit, N(CH(2))(n)C[triple bond, length as m-dash]C-nucleoside (where n = 1-3) was also varied. The compounds have been characterised by (1)H NMR, ES-MS, UV-vis, cyclic voltammetry (CV) and, in some cases, single-crystal X-ray diffraction. Cyclic voltammetry studies demonstrated that all the py-, tp- and tpt-alkynyl derivatives 1-7 can be electrochemically polymerised to form conductive materials. It was found that increasing the N-alkyl chain length in these cases resulted in only minor changes in the oxidation potential. The same behaviour was observed for the tp- and tpt-modified nucleosides 9-12; however, the py-derivative, 8, produced a poorly conducting material. DFT calculations on the one-electron oxidised cation of the modified nucleosides bearing tp or tpt showed that spin density is located on the pyrrolyl and thienyl units in all cases and that the coplanarity of adjacent rings increases upon oxidation. In contrast, in the corresponding pyrrolyl cases the spin density is distributed over the whole molecule, suggesting that polymerisation does not occur solely at the pyrrolyl-Cα position and the conjugation is interrupted.
Organic & Biomolecular Chemistry 03/2011; 9(5):1555-64. · 3.70 Impact Factor
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ABSTRACT: The functionalization of silicon as elemental crystalline wafer, nanoporous layers, or nanocrystalline particles with DNA oligonucleotides using automated solid phase synthesis is described. The procedures provide semiconductor surfaces covalently modified with oligomers suitable for capturing complementary oligonucleotide strands.
Methods in molecular biology (Clifton, N.J.) 01/2011; 749:199-207.
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ABSTRACT: DNA templated nanowires of a pentynyl-modified poly2-(2-thienyl)-pyrrole undergo functionalisation via"click chemistry" and retain their 1D-nanostructure and conductive properties.
Chemical Communications 08/2010; 46(32):5870-2. · 6.17 Impact Factor
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ABSTRACT: Polyindole (PIn) nanowires were formed on a λ-DNA template by chemical oxidation of indole using aqueous FeCl3. The resulting nanowires are smooth, regular, conductive and had diameters in the range of 5−30 nm. These features allow them to be aligned by molecular combing and studied by scanned conductance microscopy, conductive AFM, and two-terminal I−V measurements. Using this combination of measurements, we find that the conductivity of PIn/DNA nanowires is between 2.5 and 40 S cm−1 at room temperature, which is substantially greater than that in previous reports on the bulk polyindole conductivity (typically 10−2−10−1 S cm−1). The conductance at zero bias shows an Arrhenius-type of dependence on temperature over the range of 233 to 373 K, and the values observed upon heating and cooling are repeatable within 5%; this behavior is consistent with a hopping mechanism of conductivity.Keywords: conducting polymer; DNA; nanowires; polyindole; template synthesis; temperature dependence
03/2010;
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ABSTRACT: Polyindole (PIn) nanowires were formed on a lambda-DNA template by chemical oxidation of indole using aqueous FeCl3. The resulting nanowires are smooth, regular, conductive and had diameters in the range of 5-30 nm. These features allow them to be aligned by molecular combing and studied by scanned conductance microscopy, conductive AFM, and two-terminal I-V measurements. Using this combination of measurements, we find that the conductivity of PIn/DNA nanowires is between 2.5 and 40 S cm(-1) at room temperature, which is substantially greater than that in previous reports on the bulk polyindole conductivity (typically 10(-2)-10(-1) S cm(-1)). The conductance at zero bias shows an Arrhenius-type of dependence on temperature over the range of 233 to 373 K, and the values observed upon heating and cooling are repeatable within 5%; this behavior is consistent with a hopping mechanism of conductivity.
ACS Nano 03/2010; 4(4):2149-59. · 10.77 Impact Factor
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ABSTRACT: The synthesis of one-dimensional metal nanostructures can be achieved through the use of DNA molecules as templates to control and direct metal deposition. Copper nanostructures have been fabricated using this strategy, through association of Cu(2+) ions to DNA templates and reduced with ascorbic acid. Due to the possibility that the reduction of the Cu(2+) can result in the preferential formation of Cu(2)O over metallic Cu(0), X-ray photoelectron spectroscopy and X-ray diffraction have been carried out to establish the chemical identity of the nanostructures. Conclusive evidence is found that reduction of the Cu(2+) ions does result in the formation of the desired metallic Cu(0) structures. The morphology of the nanostructured Cu(0) material has also been observed by atomic force microscopy, showing the structures to have a "beads-on-a-string" appearance and being 3.0-5.5 nm in height. The electrical properties of the structures have been investigated by scanned conductance microscopy, showing the Cu(0) structures exhibit much larger electrical resistance than expected for a metallic nanowire. This is thought to be a consequence of their "beads-on-a-string" morphology and small lateral dimensions (sub-10 nm); both these factors would be expected to increase the electron scattering rate, and, further, there are likely to be significant tunneling barriers at the Cu(0) particle-particle junctions.
Langmuir 09/2009; 26(3):2068-75. · 4.19 Impact Factor
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ABSTRACT: The controlled preparation and assembly of opto-electronic nanoscale materials is being tackled by top-down and bottom-up approaches. The latter draws inspiration from biology, where complex hierarchical systems are assembled from simpler building blocks. One of these, DNA, is proving especially useful: its size, stability, topology; the assorted chemical functional groups; plus its capacity for self-assembly provide a powerful nanoscale toolbox for materials preparation. Here we review recent research that shows the roles DNA can play in the preparation and organisation of semiconductor nanomaterials. Studies show that both hard inorganic and soft polymer materials can be directed to grow at nanoscale lengths using DNA and its constituents. In some cases the resulting materials have been used as components in simple electrical devices and the methodology has been extended to analytical tools. Intriguingly, these DNA-semiconductor hybrid materials have been found to self-assemble themselves, forming highly regular rope-like assemblies and conducting network structures.
Chemical Communications 05/2009; · 6.17 Impact Factor
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ABSTRACT: We describe a simple method for the covalent immobilisation of proteins to hydrogen-terminated silicon surfaces and demonstrate various protein detection strategies. Using hydrosilation chemistry, 1-undecenylaldehyde is attached to the surface through stable Si-C bonds; the reaction occurs primarily via the vinyl group and mainly aldehyde groups are presented at the top surface of the monolayer. Proteins are then captured by reaction with their surface lysines. The proteins are bound via a Schiff base, whose formation is reversible, but can be fixed by reduction with cyanoborohydride in a one-pot reaction. Using standard methods of patterning, we were able to specifically localise proteins (urease, amyloid beta (Abeta1-42), GFP and TolAIII-GFP) with little non-specific adsorption at non-reactive sites. We characterised the immobilised proteins by X-ray photoemission spectroscopy, atomic force microscopy and FTIR, and showed that they retain their functionality using potentiometry, fluorescence and coupled antibody systems with chromogenic substrates. We also exploited the conductivity of the silicon substrate to demonstrate electrochemical detection of surface-bound proteins. These protocols will aid the development of protein biochips based on silicon, which gives rise to the possibility of detecting protein-protein and protein-small molecule interactions electronically. Such chips would be expected to be of utility for comparative proteomics and in molecular medicine, drug discovery and diagnostics.
The Analyst 04/2009; 134(3):593-601. · 4.23 Impact Factor
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ABSTRACT: Nanocrystals of various inorganic materials are being considered for application in the life sciences as fluorescent labels and for such therapeutic applications as drug delivery or targeted cell destruction. The potential applications of the nanoparticles are critically compromised due to the well-documented toxicity and lack of understanding about the mechanisms involved in the intracellular internalization. Here intracellular internalization and toxicity of alkyl-capped silicon nanocrystals in human neoplastic and normal primary cells is reported. The capped nanocrystals lack cytotoxicity, and there is a marked difference in the rate and extent of intracellular accumulation of the nanoparticles between human cancerous and non-cancerous primary cells, the rate and extent being higher in the malignant cells compared to normal human primary cells. The exposure of the cells to the alkyl-capped nanocrystals demonstrates no evidence of in vitro cytotoxicity when assessed by cell morphology, apoptosis, and cell viability assays. The internalization of the nanocrystals by Hela and SW1353 cells is almost completely blocked by the pinocytosis inhibitors filipin, cytochalasin B, and actinomycin D. The internalization process is not associated with any surface change in the nanoparticles, as their luminescence spectrum is unaltered upon transport into the cytosol. The observed dramatic difference in the rate and extent of internalization of the nanocrystals between malignant and non-malignant cells therefore offers potential application in the management of human neoplastic conditions.
Small 01/2009; 5(2):221-8. · 8.35 Impact Factor
