A brief overview is provided of recent developments in the use of block copolymer self-assembly to create morphologies that may be used to template the fabrication of nanostructures in other materials. The patterning of semiconductor surfaces using block copolymer film masks and the production of high-density arrays of magnetic domains are discussed. The use of block copolymer micelles as 'nanoreactors' to prepare metal and semiconductor nantoparticles is considered, and methods to pattern nanoparticles are highlighted. A number of approaches to design nanocapsules are summarized. Finally, applications of bulk nanostructures to make mesoporous materials with controlled pore structures and sizes, or to create photonic crystals, are discussed.
Due to their interesting properties, research on colloidal nanocrystals has moved in the last few years from fundamental research to first applications in materials science and life sciences. In this review some recent biological applications of colloidal nanocrystals are discussed, without going into biological or chemical details. First, the properties of colloidal nanocrystals and how they can be synthesized are described. Second, the conjugation of nanocrystals with biological molecules is discussed. And third, three different biological applications are introduced: (i) the arrangement of nanocrystal-oligonucleotide conjugates using molecular scaffolds such as single-stranded DNA, (ii) the use of nanocrystal-protein conjugates as fluorescent probes for cellular imaging, and (iii) a motility assay based on the uptake of nanocrystals by living cells.
Molecular electronics offer an alternative pathway to construct nanoscale circuits in which the critical dimension is naturally associated with molecular sizes. We describe the fabrication and testing of nanoscale molecular-electronic circuits that comprise a molecular monolayer of rotaxanes sandwiched between metal nanowires to form an 8 x 8 crossbar within a 1 mum(2) area. The resistance at each cross point of the crossbar can be switched reversibly. By using each cross point as an active memory cell, crossbar circuits were operated as rewritable, nonvolatile memory with a density of 6.4 Gbits cm(-2). By setting the resistances at specific cross points, two 4 x 4 subarrays of the crossbar were configured to be a nanoscale demultiplexer and multiplexer that were used to read memory bits in a third subarray.
Au-nanoclusters between 2 and 8 nm in diameter were deposited onto solid substrates in different pattern geometries. The basis of this approach is the self-assembly of polystyrene-b-poly[2-vinylpyridine (HAuCl4)] diblock copolymer micelles into uniform monomicellar films on solid supports such as Si-wafers or glass cover slips. HAuCl4 as metallic precursor or a single solid Au-nanoparticle caused by reduction of the precursor are embedded in the centre of diblock copolymer micelles. Subsequent hydrogen, oxygen or argon gas plasma treatment of the dry film causes deposition of Au-nanoparticles onto the substrate by entire removal of the polymer. The Au-dot patterns resemble the micellar patterns before the plasma treatment. Separation distances between the dots is controlled by the molecular weight of the diblock copolymers. The limitation of the separation distance between individual dots or the pattern geometry is overcome by combining self-assembly of diblock copolymer micelles with pre-structures formed by photo or e-beam lithography. Capillary forces of a retracting liquid film due to solvent evaporation on the pre-structured substrate push micelles in the corners of these defined topographies. A more direct process is demonstrated by applying monomicellar films as negative e-beam resist. Micelles that are irradiated by electrons are chemically modified and can hardly be dissolved from the substrate while non-exposed micelles can be lifted-off by suitable solvents. This process is also feasible on electrical isolating substrates such as glass cover slips if the monomicellar film is coated in addition with a 5 nm thick conductive layer of carbon before e-beam treatment. The application of cylindrical block copolymer micelles also allows for the formation of 4 nm wide lines which can be 1-50 mum long and also be organized in defined aperiodic structures.
Silver nanoparticles in the size range of 2-5 nm were synthesized extracellularly by a silver-tolerant yeast strain MKY3, when challenged with 1 mM soluble silver in the log phase of growth. The nanoparticles were separated from dilute suspension by devising a new method based on differential thawing of the sample. Optical absorption, transmission electron microscopy, x-ray diffraction and x-ray photoelectron spectroscopy investigations confirmed that metallic (elemental) silver nanoparticles were formed. Extracellular synthesis of nanoparticles could be highly advantageous from the point of view of synthesis in large quantities and easy downstream processing.
The development of reliable, eco-friendly processes for the synthesis of nanoscale materials is an important aspect of nanotechnology. In this paper, we report on the use of an alkalotolerant actinomycete (Rhodococcus sp.) in the intracellular synthesis of gold nanoparticles of the dimension 5-15 nm. Electron microscopy analysis of thin sections of the gold actinomycete cells indicated that gold particles with good monodispersity were formed on the cell wall as well as on the cytospasmic membrane. The particles are more concentrated on the cytoplasmic membrane than on the cell wall, possibly due to reduction of the metal ions by enzymes present in the cell wall and on the cytoplasmic membrane. The metal ions were not toxic to the cells and the cells continued to multiply after biosynthesis of the gold nanoparticles.
We demonstrate continuous label-free detection of two cardiac biomarker proteins (creatin kinase and myoglobin) using an array of microfabricated cantilevers functionalized with covalently anchored anti-creatin kinase and anti-myoglobin antibodies. This method allows biomarker proteins to be detected via measurement of surface stress generated by antigen-antibody molecular recognition. Reference cantilevers are used to eliminate thermal drifts, undesired chemical reactions and turbulences from injections of liquids by calculating differential deflection signals with respect to sensor cantilevers. The sensitivity achieved for myoglobin detection is below 20 mug ml(-1). Both myoglobin and creatin kinase could be detected independently using cantilevers functionalized with the corresponding antibodies, in unspecitic protein background. This approach permits the use of up to seven different antigen-antibody reactions simultaneously, including an additional thermomechanical and chemical in situ reference. Applications lie in the field of early and rapid diagnosis of acute myocardial infarction.
The scientific community needs a rapid and reliable way of accurately determining the stiffness of atomic-force microscopy cantilevers. We have compared the experimentally determined values of stiffness for ten cantilever probes using four different methods. For rectangular silicon cantilever beams of well defined geometry, the approaches all yield values within 17% of the manufacturer's nominal stiffness. One of the methods is new, based on the acquisition and analysis of thermal distribution functions of the oscillator's amplitude fluctuations. We evaluate this method in comparison to the three others and recommend it for its ease of use and broad applicability.
The aim of this paper is to describe the possibility of achieving super-hydrophobic materials by tailoring their surface topography. Water droplets easily slip or roll down on such surfaces. However, it is found that microtextures on a solid can generate sticky surfaces as well, and the conditions for avoiding such an effect are discussed.
The last decade has witnessed the development of a variety of metal nanoparticle-based techniques for DNA detection. High sensitivity and specificity, miniaturization, and cost-efficient detection are problems addressed by the use of nanoparticle labels in heterogeneous DNA detection schemes. The small label size, established bioconjugation chemistry, and the unusual optical and electrical properties of metal nanoparticles make them unique tools for DNA detection. This paper reviews the different physical characteristics of metal nanoparticles and their implementation in assays. It covers various optical as well as gravimetric, electrochemical and electrical methods for analysing nanoparticle-labelled analytes, and particularly DNA, at sensing surfaces.
Integrated optical sensors have become important in recent years since they are the only technology which allows the direct detection of biomolecular interactions. Moreover, silicon microelectronics technology allows mass production as well as the fabrication of nano-/macrosystems on the same platform by hybrid integration of sources, sensors, photodetectors and complementary metal-oxide semiconductor electronics. For the fabrication of an optical sensor nanodevice with an integrated Mach-Zehnder interferometric (MZI) configuration, the optical waveguides must have two main features: monomode behaviour and a high surface sensitivity. In this paper we present the development of a MZI sensor based on total internal reflection waveguides with nanometre dimensions. The aim is to use these sensors in environmental control to detect water pollutants by immunoassay techniques.
We report on a method of synthesizing arrays of individually seeded nanowires. An electron beam lithography and metal lift-off method was used to pattern InP(111)B substrates with catalysing gold particles. Vertical InP(111)B nanowire arrays were then grown from the gold particles, using metal-organic vapour phase epitaxy. The lithographic nature of the method allows individual control over each nanowire. Possible applications for such deterministic and uniform arrays include producing arrays of nanowire devices, two-dimensional photonic band gap structures and field emission displays, amongst others.
The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.
ZnO, MgO, and GeO2 nanowires were successfully synthesized by simply heating the desired metal powder to a temperature above its melting point in a flow of mixed gases (20% O-2, 80% Ar, with the total flow rate of 120 seem). Transmission electron microscopy observations show that as-synthesized products are exclusively nanowires, structurally uniform and single crystalline. The same technique was used to fabricate arrays of ZnO nanowires on silicon substrates, which would be of particular interest for direct integration in the current silicon-technology-based optoelectronic devices. Based on our experimental results, a metal self-catalytic growth mechanism was proposed and described conceptually. Because of the absence of impurities such as transition metal or noble metal throughout the whole growth process, the intrinsic properties of the resulting metal oxide nanowires could be expressed and utilized. And with in-depth understanding of the growth mechanism, our method could be efficient and controllable in extension to many other low-melting-point metals, such as Al, In, and Sn, for the synthesis of corresponding metal oxide nanostructures.
We present a method for controlled deposition of oriented polymeric nanofibres. The method uses a microfabricated scanned tip as an electrospinning source. The tip is dipped in a polymer solution to gather a droplet as a source material. A voltage applied to the tip causes the formation of a Taylor cone, and at sufficiently high voltages, a polymer jet is extracted from the droplet. By moving the source relative to a surface, acting as a counter-electrode, oriented nanofibres can be deposited and integrated with microfabricated surface structures. For example, we deposited fibres of polyethylene oxide with diameters ranging from 100 to 1800 nm, with the diameter primarily depending on the concentration of the polymeric solution. In addition to the uniform fibre deposition, the scanning tip electrospinning source can produce self-assembled composite fibres of micro- and nanoparticles aligned in a polymeric fibre. We also deposited oriented conductive polymeric fibres of polyaniline and investigated the conductivity of these fibres as components for polymeric nanoelectronics.
Colloidal Ti has been synthesized following a method described in the literature. Extended x-ray absorption fine structure measurements indicate the presence of small colloidal entities, consisting of only a few core Ti atoms which are coordinated by O atoms from tetrahydrofuran (THF). The results can be explained by the proposed structure of Ti-13.6THF, in which the Ti cluster has the shape of a distorted icosahedron. The Ti colloid was used to prepare a functional nanocomposite by ball-milling the clusters with NaAlH4. The nanocomposite showed superior hydrogen exchange kinetics when compared to the state of the art in the literature.
In this study, different weight fractions of multiwalled carbon nanotubes were dispersed in epoxy to produce toughened adhesives. The reinforced adhesives were used to bond the graphite fibre/epoxy composite adherends. Single lap joint samples were prepared and the average shear strengths were experimentally measured. Significant enhancement of the bonding performance was observed as the weight fraction of carbon nanotubes was increased.
Nanotechnology (NT) is a rapidly progressing field. Advances will have a tremendous impact on fields such as materials, electronics, and medicine. A thorough review of the current literature, governmental funding, and policy documents was undertaken. Despite the potential impact of NT, and the abundance of funds, our research revealed that there is a paucity of serious, published research into the ethical, legal, and social implications of NT. As the science leaps ahead, the ethics lags behind. There is danger of derailing NT if the study of ethical, legal, and social implications does not catch up with the speed of scientific development.
The use of recent advances in resonance Raman spectroscopy studies on isolated carbon nanotubes and the scientific knowledge achieved so far from these studies is discussed in the context of advancing carbon nanotube-based technology. Changes in the Raman spectra can be used to probe and monitor structural modifications of the nanotube sidewalls that come from the introduction of defects and the attachment of different chemical species. The former effect can be probed through the analysis of the disorder-induced Raman modes and the latter through the upshifts/downshifts observed in the various Raman modes due to charge transfer effects.
A new method for the growth of high-quality ZnO nanoparticles is presented here; it is a novel, low-cost, and easy operation. This approach, using solid-state heat decomposition at low temperature, allows one to produce ZnO nanoparticles with relatively high dispersivity. The optical properties of the ZnO nanoparticles have been investigated. It is demonstrated that ZnO nanoparticles show strong ultraviolet emission, while the low-energy visible emission is nearly fully quenched at room temperature. This is a result of the high quality of the ZnO. X-ray diffraction patterns reveal that the ZnO nanoparticles have polycrystalline hexagonal wurtzite structure. The Raman spectrum shows a typical resonant multi-phonon form for the ZnO nanoparticles. Similar synthesis routes for other metal oxide nanoparticles may be possible.