Showing papers in "Nature Nanotechnology in 2009"
TL;DR: The use of colloidal suspensions to produce new materials composed of graphene and chemically modified graphene is reviewed, which is both versatile and scalable, and is adaptable to a wide variety of applications.
Abstract: Interest in graphene centres on its excellent mechanical, electrical, thermal and optical properties, its very high specific surface area, and our ability to influence these properties through chemical functionalization. There are a number of methods for generating graphene and chemically modified graphene from graphite and derivatives of graphite, each with different advantages and disadvantages. Here we review the use of colloidal suspensions to produce new materials composed of graphene and chemically modified graphene. This approach is both versatile and scalable, and is adaptable to a wide variety of applications.
6,178 citations
IBM1
TL;DR: This work demonstrates ultrafast transistor-based photodetectors made from single- and few-layer graphene that do not degrade for optical intensity modulations up to 40 GHz and suggests that the intrinsic bandwidth may exceed 500 GHz.
Abstract: Graphene research so far has focused on electronic rather than photonic applications, in spite of its impressive optical properties. These include its ability to absorb approximately 2% of incident light over a broad wavelength range despite being just one atom thick. Here, we demonstrate ultrafast transistor-based photodetectors made from single- and few-layer graphene. The photoresponse does not degrade for optical intensity modulations up to 40 GHz, and further analysis suggests that the intrinsic bandwidth may exceed 500 GHz. The generation and transport of photocarriers in graphene differ fundamentally from those in photodetectors made from conventional semiconductors as a result of the unique photonic and electronic properties of the graphene. This leads to a remarkably high bandwidth, zero source-drain bias and dark current operation, and good internal quantum efficiency.
2,840 citations
TL;DR: Enhanced fluorescence from carbon nanotubes and advances in near-infrared cameras have opened up a new wavelength window for small animal imaging as discussed by the authors, which has been used for animal detection.
Abstract: Enhanced fluorescence from carbon nanotubes and advances in near-infrared cameras have opened up a new wavelength window for small animal imaging.
2,015 citations
TL;DR: The chemically converted graphene sheets that were produced have the largest area reported to date (up to 20 x 40 microm), making them far easier to process, and field-effect devices have been fabricated by conventional photolithography, displaying currents that are three orders of magnitude higher than previously reported for chemically produced graphene.
Abstract: The electronic properties of graphene, such as high charge carrier concentrations and mobilities, make it a promising candidate for next-generation nanoelectronic devices. In particular, electrons and holes can undergo ballistic transport on the sub-micrometre scale in graphene and do not suffer from the scale limitations of current MOSFET technologies. However, it is still difficult to produce single-layer samples of graphene and bulk processing has not yet been achieved, despite strenuous efforts to develop a scalable production method. Here, we report a versatile solution-based process for the large-scale production of single-layer chemically converted graphene over the entire area of a silicon/SiO(2) wafer. By dispersing graphite oxide paper in pure hydrazine we were able to remove oxygen functionalities and restore the planar geometry of the single sheets. The chemically converted graphene sheets that were produced have the largest area reported to date (up to 20 x 40 microm), making them far easier to process. Field-effect devices have been fabricated by conventional photolithography, displaying currents that are three orders of magnitude higher than previously reported for chemically produced graphene. The size of these sheets enables a wide range of characterization techniques, including optical microscopy, scanning electron microscopy and atomic force microscopy, to be performed on the same specimen.
2,011 citations
TL;DR: It is shown that a protein nanopore with a covalently attached adapter molecule can continuously identify unlabelled nucleoside 5'-monophosphate molecules with accuracies averaging 99.8%.
Abstract: A single-molecule method for sequencing DNA that does not require fluorescent labelling could reduce costs and increase sequencing speeds. An exonuclease enzyme might be used to cleave individual nucleotide molecules from the DNA, and when coupled to an appropriate detection system, these nucleotides could be identified in the correct order. Here, we show that a protein nanopore with a covalently attached adapter molecule can continuously identify unlabelled nucleoside 5'-monophosphate molecules with accuracies averaging 99.8%. Methylated cytosine can also be distinguished from the four standard DNA bases: guanine, adenine, thymine and cytosine. The operating conditions are compatible with the exonuclease, and the kinetic data show that the nucleotides have a high probability of translocation through the nanopore and, therefore, of not being registered twice. This highly accurate tool is suitable for integration into a system for sequencing nucleic acids and for analysing epigenetic modifications. A protein nanopore with a permanent adaptor molecule can continuously identify unlabelled DNA bases with ∼99.8% accuracy. This level of performance could provide the foundation for the development of nanopore-based DNA sequencing technologies that are faster and less expensive than existing approaches.
1,783 citations
TL;DR: It is argued that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons.
Abstract: The regulation of engineered nanoparticles requires a widely agreed definition of such particles. Nanoparticles are routinely defined as particles with sizes between about 1 and 100 nm that show properties that are not found in bulk samples of the same material. Here we argue that evidence for novel size-dependent properties alone, rather than particle size, should be the primary criterion in any definition of nanoparticles when making decisions about their regulation for environmental, health and safety reasons. We review the size-dependent properties of a variety of inorganic nanoparticles and find that particles larger than about 30 nm do not in general show properties that would require regulatory scrutiny beyond that required for their bulk counterparts.
1,656 citations
TL;DR: The results strongly indicate that the long-standing puzzle about the interfacial capacitance in carbon-based electrodes has a quantum origin, and suggest that charged impurities also influences the quantum capacitance.
Abstract: Graphene has received widespread attention due to its unique electronic properties. Much of the research conducted so far has focused on electron mobility, which is determined by scattering from charged impurities and other inhomogeneities. However, another important quantity, the quantum capacitance, has been largely overlooked. Here, we report a direct measurement of the quantum capacitance of graphene as a function of gate potential using a three-electrode electrochemical configuration. The quantum capacitance has a non-zero minimum at the Dirac point and a linear increase on both sides of the minimum with relatively small slopes. Our findings -- which are not predicted by theory for ideal graphene -- suggest that charged impurities also influences the quantum capacitance. We also measured the capacitance in aqueous solutions at different ionic concentrations, and our results strongly indicate that the long-standing puzzle about the interfacial capacitance in carbon-based electrodes has a quantum origin.
1,492 citations
TL;DR: The first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains are reported, elucidate the ripple formation process and can be understood in terms of classical thin-film elasticity theory.
Abstract: Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene
1,281 citations
TL;DR: Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells.
Abstract: A voltage-induced symmetry change in a ferromagnetic material can change its magnetization or magnetic anisotropy, but these effects are too weak to be used in memory devices. Researchers have now shown that a relatively small electric field can cause a large change in the magnetic anisotropy of a few atomic layers of iron. The results could lead to low-power logic devices and non-volatile memory cells.
1,201 citations
TL;DR: It is shown that an array of sensors based on gold nanoparticles can rapidly distinguish the breath of lung cancer patients from the Breath of healthy individuals in an atmosphere of high humidity.
Abstract: Conventional diagnostic methods for lung cancer 1,2 are unsuitable for widespread screening 2,3 because they are expensive and occasionally miss tumours. Gas chromatography/mass spectrometry studies have shown that several volatile organic compounds, which normally appear at levels of 1–20 ppb in healthy human breath, are elevated to levels between 10 and 100 ppb in lung cancer patients 4–6 . Here we show that an array of sensors based on gold nanoparticles can rapidly distinguish the breath of lung cancer patients from the breath of healthy individuals in an atmosphere of high humidity. In combination with solidphase microextraction 7 , gas chromatography/mass spectrometry was used to identify 42 volatile organic compounds that represent lung cancer biomarkers. Four of these were used to train and optimize the sensors, demonstrating good agreement between patient and simulated breath samples. Our results show that sensors based on gold nanoparticles could form the basis of an inexpensive and non-invasive diagnostic tool for lung cancer. Lung cancer accounts for 28% of cancer-related deaths.
1,088 citations
TL;DR: The direct chemical synthesis of carbon nanosheets in gram-scale quantities in a bottom-up approach based on the common laboratory reagents ethanol and sodium is reported, yielding a fused array of graphene sheets that are dispersed by mild sonication.
Abstract: Carbon nanostructures have emerged as likely candidates for a wide range of applications, driving research into novel synthetic techniques to produce nanotubes, graphene and other carbon-based materials. Single sheets of pristine graphene have been isolated from bulk graphite in small amounts by micromechanical cleavage1, and larger amounts of chemically modified graphene sheets have been produced by a number of approaches2,3,4,5,6,7. Both of these techniques make use of highly oriented pyrolitic graphite as a starting material and involve labour-intensive preparations. Here, we report the direct chemical synthesis of carbon nanosheets in gram-scale quantities in a bottom-up approach based on the common laboratory reagents ethanol and sodium, which are reacted to give an intermediate solid that is then pyrolized, yielding a fused array of graphene sheets that are dispersed by mild sonication. The ability to produce bulk graphene samples from non-graphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene. Most techniques for producing graphene use graphite as a starting material and are labour-intensive. The direct chemical synthesis of carbon nanosheets in gram-scale quantities from the common laboratory reagents ethanol and sodium has now been demonstrated. The ability to produce bulk graphene samples from non-graphitic precursors with a scalable, low-cost approach should take us a step closer to real-world applications of graphene.
TL;DR: It is shown that sonicating single-walled carbon nanotubes with sodium cholate, followed by surfactant exchange to form phospholipid-polyethylene glycol coated nanot tubes, produces in vivo imaging agents that are both bright and biocompatible.
Abstract: The near-infrared photoluminescence intrinsic to semiconducting single-walled carbon nanotubes is ideal for biological imaging owing to the low autofluorescence and deep tissue penetration in the near-infrared region beyond 1 µm. However, biocompatible single-walled carbon nanotubes with high quantum yield have been elusive. Here, we show that sonicating single-walled carbon nanotubes with sodium cholate, followed by surfactant exchange to form phospholipid–polyethylene glycol coated nanotubes, produces in vivo imaging agents that are both bright and biocompatible. The exchange procedure is better than directly sonicating the tubes with the phospholipid–polyethylene glycol, because it results in less damage to the nanotubes and improves the quantum yield. We show whole-animal in vivo imaging using an InGaAs camera in the 1–1.7 µm spectral range by detecting the intrinsic near-infrared photoluminescence of the ‘exchange’ single-walled carbon nanotubes at a low dose (17 mg l−1 injected dose). The deep tissue penetration and low autofluorescence background allowed high-resolution intravital microscopy imaging of tumour vessels beneath thick skin. Single-walled carbon nanotubes can be modified into bright and biocompatible agents for high resolution whole-animal imaging at wavelengths in the 1100–1700 nm region.
TL;DR: By establishing many of the basic attributes of monolayer graphene resonators, the groundwork for applications of these devices, including high-sensitivity mass detectors, is put in place.
Abstract: The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical applications. Here, we demonstrate the fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the megahertz range, and the strong dependence of resonant frequency on applied gate voltage can be fitted to a membrane model to yield the mass density and built-in strain of the graphene. Following the removal and addition of mass, changes in both density and strain are observed, indicating that adsorbates impart tension to the graphene. On cooling, the frequency increases, and the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching approximately 1 x 10(4) at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, the groundwork for applications of these devices, including high-sensitivity mass detectors, is put in place.
TL;DR: A flexible power generator that is based on cyclic stretching-releasing of a piezoelectric fine wire that is firmly attached to metal electrodes at both ends, is packaged on a flexible substrate, and does not involve sliding contacts is reported.
Abstract: Converting mechanical energy into electricity could have applications in sensing, medical science, defence technology and personal electronics, and the ability of nanowires to 'scavenge' energy from ambient and environmental sources could prove useful for powering nanodevices. Previously reported nanowire generators were based on vertically aligned piezoelectric nanowires that were attached to a substrate at one end and free to move at the other. However, there were problems with the output stability, mechanical robustness, lifetime and environmental adaptability of such devices. Here we report a flexible power generator that is based on cyclic stretching-releasing of a piezoelectric fine wire that is firmly attached to metal electrodes at both ends, is packaged on a flexible substrate, and does not involve sliding contacts. Repeatedly stretching and releasing a single wire with a strain of 0.05-0.1% creates an oscillating output voltage of up to approximately 50 mV, and the energy conversion efficiency of the wire can be as high as 6.8%.
TL;DR: This work focuses on carbon nanotubes that have been studied in preclinical animal models, and draws attention to the promises, facts and challenges of these materials as they transition from research to the clinical phase.
Abstract: The use of carbon nanotubes in medicine is now at the crossroads between a proof-of-principle concept and an established preclinical candidate for a variety of therapeutic and diagnostic applications. Progress towards clinical trials will depend on the outcomes of efficacy and toxicology studies, which will provide the necessary risk-to-benefit assessments for carbon-nanotube-based materials. Here we focus on carbon nanotubes that have been studied in preclinical animal models, and draw attention to the promises, facts and challenges of these materials as they transition from research to the clinical phase. We address common questions regarding the use of carbon nanotubes in disease imaging and therapy, and highlight the opportunities and challenges ahead.
TL;DR: This review provides an introduction to the theory of nanofluidic transport, focusing on the various forces that influence the movement of both solvents and solutes through nanochannels, and reviews the applications of nan offluidic devices in separation science and energy conversion.
Abstract: The evolution from microfluidic to nanofluidic systems has been accompanied by the emergence of new fluid phenomena and the potential for new nanofluidic devices. This review provides an introduction to the theory of nanofluidic transport, focusing on the various forces that influence the movement of both solvents and solutes through nanochannels, and reviews the applications of nanofluidic devices in separation science and energy conversion.
TL;DR: The fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 microm using a novel electrochemistry approach is reported.
Abstract: Dye-sensitized solar cells consist of a random network of titania nanoparticles that serve both as a high-surface-area support for dye molecules and as an electron-transporting medium. Despite achieving high power conversion efficiencies, their performance is limited by electron trapping in the nanoparticle film. Electron diffusion lengths can be increased by transporting charge through highly ordered nanostructures such as titania nanotube arrays. Although titania nanotube array films have been shown to enhance the efficiencies of both charge collection and light harvesting, it has not been possible to grow them on transparent conducting oxide glass with the lengths needed for high-efficiency device applications (tens of micrometres). Here, we report the fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 µm using a novel electrochemistry approach. Dye-sensitized solar cells containing these arrays yielded a power conversion efficiency of 6.9%. The incident photon-to-current conversion efficiency ranged from 70 to 80% for wavelengths between 450 and 650 nm. Transparent films of titania nanotubes up to 30-μm long are fabricated on transparent conducting oxide glass, and used to make dye-sensitized solar cells.
TL;DR: The epitaxial deposition of a compressive shell onto a soft nanocrystalline core to form a lattice-mismatched quantum dot can dramatically change the conduction and valence band energies of both the core and the shell.
Abstract: Lattice strain is a structural parameter that has been exploited in microelectronic devices with great success, but its role in colloidal nanocrystals is still poorly understood. Here we have developed strain-tunable colloidal nanocrystals by using lattice-mismatched heterostructures that are grown by epitaxial deposition of a compressive shell (e.g., ZnSe or CdS) onto a soft and small nanocrystalline core (e.g., CdTe). This combination of a “squeezed” core and a “stretched” shell causes dramatic changes in both the conduction and valence band energies. As a result, we show that core-shell QDs with standard type-I behavior are converted into type-II nanostructures, leading to spatial separation of electrons and holes, extended excited state lifetimes, and giant spectral shifting. This new class of strain-tunable QDs exhibits narrow light emission with high quantum yield across a broad range of visible and near-infrared wavelengths (500 nm to 1050 nm).
TL;DR: In this article, the authors quantitatively analyzed the adsorption of human serum albumin onto small polymer-coated FePt and CdSe/ZnS nanoparticles by using fluorescence correlation spectroscopy.
Abstract: It is now known that nanoparticles, when exposed to biological fluid, become coated with proteins and other biomolecules to form a 'protein corona'. Recent systematic studies have identified various proteins that can make up this corona, but these nanoparticle-protein interactions are still poorly understood, and quantitative studies to characterize them are few in number. Here, we have quantitatively analysed the adsorption of human serum albumin onto small (10-20 nm in diameter) polymer-coated FePt and CdSe/ZnS nanoparticles by using fluorescence correlation spectroscopy. The protein corona forms a monolayer with a thickness of 3.3 nm. Proteins bind to the negatively charged nanoparticles with micromolar affinity, and time-resolved fluorescence quenching experiments show that they reside on the particle for approximately 100 s. These new findings deepen our quantitative understanding of the protein corona, which is of utmost importance in the safe application of nanoscale objects in living organisms.
TL;DR: This is the first demonstration of viable chip-scale refrigeration technology and has the potential to enable a wide range of currently thermally limited applications.
Abstract: There is a significant need for site-specific and on-demand cooling in electronic, optoelectronic and bioanalytical devices, where cooling is currently achieved by the use of bulky and/or over-designed system-level solutions. Thermoelectric devices can address these limitations while also enabling energy-efficient solutions, and significant progress has been made in the development of nanostructured thermoelectric materials with enhanced figures-of-merit. However, fully functional practical thermoelectric coolers have not been made from these nanomaterials due to the enormous difficulties in integrating nanoscale materials into microscale devices and packaged macroscale systems. Here, we show the integration of thermoelectric coolers fabricated from nanostructured Bi2Te3-based thin-film superlattices into state-of-the-art electronic packages. We report cooling of as much as 15 degrees C at the targeted region on a silicon chip with a high ( approximately 1,300 W cm-2) heat flux. This is the first demonstration of viable chip-scale refrigeration technology and has the potential to enable a wide range of currently thermally limited applications.
TL;DR: By selectively tuning the crystal structure, this work fabricates highly reproducible polytypic and twin-plane superlattices within single nanowires, which could lead to bandgap engineering and novel electronic behaviour.
Abstract: Semiconductor nanowires show promise for use in nanoelectronics, fundamental electron transport studies, quantum optics and biological sensing. Such applications require a high degree of nanowire growth control, right down to the atomic level. However, many binary semiconductor nanowires exhibit a high density of randomly distributed twin defects and stacking faults, which results in an uncontrolled, or polytypic, crystal structure. Here, we demonstrate full control of the crystal structure of InAs nanowires by varying nanowire diameter and growth temperature. By selectively tuning the crystal structure, we fabricate highly reproducible polytypic and twin-plane superlattices within single nanowires. In addition to reducing defect densities, this level of control could lead to bandgap engineering and novel electronic behaviour.
TL;DR: In this article, a nanoelectromechanical-based mass spectrometer was used for the detection of individual molecular species in real-time with a few to single molecules.
Abstract: Mass spectrometry provides rapid and quantitative identification of protein species with relatively low sample consumption. The trend towards biological analysis at increasingly smaller scales, ultimately down to the volume of an individual cell, continues, and mass spectrometry with a sensitivity of a few to single molecules will be necessary. Nanoelectromechanical systems provide unparalleled mass sensitivity, which is now sufficient for the detection of individual molecular species in real time. Here, we report the first demonstration of mass spectrometry based on single biological molecule detection with a nanoelectromechanical system. In our nanoelectromechanical–mass spectrometry system, nanoparticles and protein species are introduced by electrospray injection from the fluid phase in ambient conditions into vacuum, and are subsequently delivered to the nanoelectromechanical system detector by hexapole ion optics. Precipitous frequency shifts, proportional to the mass, are recorded in real time as analytes adsorb, one by one, onto a phase-locked, ultrahigh-frequency nanoelectromechanical resonator. These first nanoelectromechanical system–mass spectrometry spectra, obtained with modest mass sensitivity from only several hundred mass adsorption events, presage the future capabilities of this approach. We also outline the substantial improvements that are feasible in the near term, some of which are unique to nanoelectromechanical system based-mass spectrometry.
TL;DR: It is shown that gold-plated carbon nanotubes-termed golden carbon nanOTubes-can be used as photoacoustic and photothermal contrast agents with enhanced near-infrared contrast agents for targeting lymphatic vessels in mice using extremely low laser fluence levels of a few mJ cm(-2).
Abstract: Carbon nanotubes have shown promise as contrast agents for photoacoustic and photothermal imaging of tumours and infections because they offer high resolution and allow deep tissue imaging. However, in vivo applications have been limited by the relatively low absorption displayed by nanotubes at near-infrared wavelengths and concerns over toxicity. Here, we show that gold-plated carbon nanotubes-termed golden carbon nanotubes-can be used as photoacoustic and photothermal contrast agents with enhanced near-infrared contrast ( approximately 10(2)-fold) for targeting lymphatic vessels in mice using extremely low laser fluence levels of a few mJ cm(-2). Antibody-conjugated golden carbon nanotubes were used to map the lymphatic endothelial receptor, and preliminary in vitro viability tests show golden carbon nanotubes have minimal toxicity. This new nanomaterial could be an effective alternative to existing nanoparticles and fluorescent labels for non-invasive targeted imaging of molecular structures in vivo.
TL;DR: The construction of a DNA nanomachine called the I-switch, which is triggered by protons and functions as a pH sensor based on fluorescence resonance energy transfer (FRET) inside living cells and is an efficient reporter of pH from pH 5.5 to 6.8.
Abstract: DNA nanomachines are synthetic assemblies that switch between defined molecular conformations upon stimulation by external triggers. Previously, the performance of DNA devices has been limited to in vitro applications. Here we report the construction of a DNA nanomachine called the I-switch, which is triggered by protons and functions as a pH sensor based on fluorescence resonance energy transfer (FRET) inside living cells. It is an efficient reporter of pH from pH 5.5 to 6.8, with a high dynamic range between pH 5.8 and 7. To demonstrate its ability to function inside living cells we use the I-switch to map spatial and temporal pH changes associated with endosome maturation. The performance of our DNA nanodevices inside living systems illustrates the potential of DNA scaffolds responsive to more complex triggers in sensing, diagnostics and targeted therapies in living systems.
TL;DR: The self-assembly of a DNA scaffold made of DNA strips that include 'hinges' to which biomolecules can be tethered is reported, and it is shown that enzyme cascades or cofactor-mediated biocatalysis can proceed effectively; similar processes are not observed in diffusion-controlled homogeneous mixtures of the same components.
Abstract: The ability of DNA to self-assemble into one-, two- and three-dimensional nanostructures, combined with the precision that is now possible when positioning nanoparticles or proteins on DNA scaffolds, provide a promising approach for the self-organization of composite nanostructures. Predicting and controlling the functions that emerge in self-organized biomolecular nanostructures is a major challenge in systems biology, and although a number of innovative examples have been reported, the emergent properties of systems in which enzymes are coupled together have not been fully explored. Here, we report the self-assembly of a DNA scaffold made of DNA strips that include 'hinges' to which biomolecules can be tethered. We attach either two enzymes or a cofactor-enzyme pair to the scaffold, and show that enzyme cascades or cofactor-mediated biocatalysis can proceed effectively; similar processes are not observed in diffusion-controlled homogeneous mixtures of the same components. Furthermore, because the relative position of the two enzymes or the cofactor-enzyme pair is determined by the topology of the DNA scaffold, it is possible to control the reactivity of the system through the design of the individual DNA strips. This method could lead to the self-organization of complex multi-enzyme cascades.
TL;DR: It is shown that 4,4'-bipyridine-gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression, and could form the basis of a new class of mechanically activated single- molecule switches.
Abstract: Molecular-scale components are expected to be central to the realization of nanoscale electronic devices1,2,3. Although molecular-scale switching has been reported in atomic quantum point contacts4,5,6, single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. To date, switching in single-molecule junctions has been attributed to changes in the conformation or charge state of the molecule7,8,9,10,11,12. Here, we demonstrate reversible binary switching in a single-molecule junction by mechanical control of the metal–molecule contact geometry. We show that 4,4'-bipyridine–gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression. Using first-principles calculations, we attribute the different measured conductance states to distinct contact geometries at the flexible but stable nitrogen–gold bond: conductance is low when the N–Au bond is perpendicular to the conducting π-system, and high otherwise. This switching mechanism, inherent to the pyridine–gold link, could form the basis of a new class of mechanically activated single-molecule switches. Molecular-scale switches will be central components in nanoscale electronic devices. Switching in single-molecule junctions has so far been achieved through changes in the conformation or charge state of the molecule. Now, reversible binary switching has been demonstrated by mechanical control of the metal–molecule contact geometry—a mechanism which could form the basis for a new class of mechanically activated single-molecule switches.
TL;DR: This approach allows circulating tumour cells to be concentrated from a large volume of blood in the vessels of tumour-bearing mice, and this could have potential for the early diagnosis of cancer and the prevention of metastasis in humans.
Abstract: The spread of cancer cells between organs, a process known as metastasis, is the cause of most cancer deaths. Detecting circulating tumour cells -- a common marker for the development of metastasis -- is difficult because ex vivo methods are not sensitive enough owing to limited blood sample volume and in vivo diagnosis is time-consuming as large volumes of blood must be analysed. Here, we show a way to magnetically capture circulating tumour cells in the bloodstream of mice followed by rapid photoacoustic detection. Magnetic nanoparticles, which were functionalized to target a receptor commonly found in breast cancer cells, bound and captured circulating tumour cells under a magnet. To improve detection sensitivity and specificity, gold-plated carbon nanotubes conjugated with folic acid were used as a second contrast agent for photoacoustic imaging. By integrating in vivo multiplex targeting, magnetic enrichment, signal amplification and multicolour recognition, our approach allows circulating tumour cells to be concentrated from a large volume of blood in the vessels of tumour-bearing mice, and this could have potential for the early diagnosis of cancer and the prevention of metastasis in humans.
TL;DR: It is shown that a novel class of core-shell nanoparticles formed by self-assembly of an amphiphilic peptide have strong antimicrobial properties against a range of bacteria, yeasts and fungi and can cross the blood-brain barrier and suppress bacterial growth in infected brains.
Abstract: Antimicrobial cationic peptides are of interest because they can combat multi-drug-resistant microbes. Most peptides form alpha-helices or beta-sheet-like structures that can insert into and subsequently disintegrate negatively charged bacterial cell surfaces. Here, we show that a novel class of core-shell nanoparticles formed by self-assembly of an amphiphilic peptide have strong antimicrobial properties against a range of bacteria, yeasts and fungi. The nanoparticles show a high therapeutic index against Staphylococcus aureus infection in mice and are more potent than their unassembled peptide counterparts. Using Staphylococcus aureus-infected meningitis rabbits, we show that the nanoparticles can cross the blood-brain barrier and suppress bacterial growth in infected brains. Taken together, these nanoparticles are promising antimicrobial agents that can be used to treat brain infections and other infectious diseases.
TL;DR: In this article, the Mott transition between a low-temperature insulating phase and a high temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature.
Abstract: Correlated electron materials can undergo a variety of phase transitions, including superconductivity, the metal-insulator transition and colossal magnetoresistance. Moreover, multiple physical phases or domains with dimensions of nanometres to micrometres can coexist in these materials at temperatures where a pure phase is expected. Making use of the properties of correlated electron materials in device applications will require the ability to control domain structures and phase transitions in these materials. Lattice strain has been shown to cause the coexistence of metallic and insulating phases in the Mott insulator VO(2). Here, we show that we can nucleate and manipulate ordered arrays of metallic and insulating domains along single-crystal beams of VO(2) by continuously tuning the strain over a wide range of values. The Mott transition between a low-temperature insulating phase and a high-temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature. In addition to device applications, the ability to control the phase structure of VO(2) with strain could lead to a deeper understanding of the correlated electron materials in general.
TL;DR: Fluorescence correlation spectroscopy has been used as a quantitative method to understand the binding and exchange behavior of proteins on the surfaces of nanoparticles as discussed by the authors, and it has been shown that it can be used to detect the presence of proteins in nanoparticles.
Abstract: Fluorescence correlation spectroscopy is used as a quantitative method to understand the binding and exchange behaviour of proteins on the surfaces of nanoparticles.