Mechanical and optical properties of ultralarge flakes of a metal-organic framework with molecular thickness

The isolation of 2D-materials is already a success for graphene, graphene oxide, boron nitride and a few clays or metal chalcogenides, however despite the fact that some of them show very interesting physical properties, they lack useful functionalities. Metal-Organic Frameworks (MOFs) are multifunctional materials showing a wide range of physical and chemical properties that can be structurally designed by suitable selection of their building-blocks. This strategy may allow the production of layers with a variety of useful electronic and molecular recognition functionalities. Herein we isolate 2D-MOF flakes with areas of hundreds of square microns and an excellent control of the molecular thickness (from single up to ca. 50 layers). The samples exhibit such good photoluminescence and mechanical properties as to allow free-standing characterization of few layers' flakesThe authors acknowledge financial support from MICINN (MAT2013-46753-C2-1-P and MAT2013-46753-C2-2-P and Consolider CSD2010-00024

Solution-based DNA-templating of sub-10 nm conductive copper nanowires

Templating the electroless reduction of metal ions on DNA is now an established route to the preparation of nanowires and can be particularly useful for the formation of nanowires in the desirable <10 nm size range. However, different preparation conditions produce nanowires of widely different morphologies and conductivities. We describe a method for the synthesis of Cu nanowires in which electroless metal deposition is carried out on DNA 'template' molecules in bulk solution. Though analogous to previous surface-based routes, importantly this now produces conductive material. AFM was used to evaluate the size and morphology of the resulting nanowires; a mean nanowire diameter of 7.1 nm (standard deviation = 4.7 nm) was determined from a statistical analysis of 100 nanowires and the Cu coatings were continuous and smooth. These findings represent a notable improvement in nanowire morphology in comparison to the previous surface-based routes. UV-vis spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were used to confirm formation of Cu(0) metal takes place during nanowire synthesis, and additional scanning probe microscopy techniques were employed to probe the electrical properties of the nanowires. The nanowires are less conductive [resistivity ∼ 2 Ω cm] than bulk Cu, but much more conductive than nanowires prepared by the analogous method on surface-bound DNA. Using an extension of our thermodynamic model for DNA-templating, we show that the templating process in bulk solution favours the formation of continuous nanowires compared to templating on surface-bound DNAX-ray photoelectron spectra were obtained at the National EPSRC XPS User's Service (NEXUS) at Newcastle University, an EPSRC mid-range facility. This work was financially supported by Newcastle University, EU ITN NANOEMBRACE (Contract No. 316751) and Intel Ireland Ltd (with special thanks to Bernie D. Capraro, Research Programme Manager

Detecting RNA base methylations in single cells by in situ hybridization.

Methylated bases in tRNA, rRNA and mRNA control a variety of cellular processes, including protein synthesis, antimicrobial resistance and gene expression. Currently, bulk methods that report the average methylation state of ~104-107 cells are used to detect these modifications, obscuring potentially important biological information. Here, we use in situ hybridization of Molecular Beacons for single-cell detection of three methylations (m62A, m1G and m3U) that destabilize Watson-Crick base pairs. Our method-methylation-sensitive RNA fluorescence in situ hybridization-detects single methylations of rRNA, quantifies antibiotic-resistant bacteria in mixtures of cells and simultaneously detects multiple methylations using multicolor fluorescence imaging

Gas Sensing Using One-Dimensional (1D) DNA Templated Cadmium Sulphide Nanowire

One-dimensional (1D) nanostructured inorganic materials have generated increasing interest in recent years due to their use as transducers in gas sensors because of their large surface to volume ratio and extraordinary opto-electronic properties. [...

Publication V Electrochemical detection of lateral charge transport in metal complex-DNA monolayers synthesized on Si(1 1 1) electrodes

Abstract The lateral charge transport in films comprising metal complexes bound to DNA monolayers on Si electrodes was measured by scanning electrochemical microscopy (SECM) in the steady-state feedback mode. Single-stranded (ss) DNA monolayers covalently bonded to the Si surface were prepared by automated solid-phase synthesis on hydroxyl-terminated n-alkyl monolayers at atomically flat Si(1 1 1)-H surfaces. Duplex (ds) DNA films were produced by hybridisation to the ssDNA monolayers. Our previous STM imaging investigations showed these dsDNA films exhibit considerable alignment, but the ssDNA films were observed by AFM to be rather disordered. Using solutions of FeðCNÞ as redox mediators, we compared the rate of charge transport in dsDNA films to that in ssDNA films. Lateral charge transport on the substrate -the source of the SECM feedback -depends on the selfexchange rate between the surface and solution as well as the rate of diffusion of charged, surface-bound species. Several mechanisms of lateral charge transfer (physical surface diffusion, electron hopping between DNA-bound redox species, charge injection into Si and DNA-mediated long-range electron transfer) were explored as possible explanations for the positive feedback observed in RuðbipyÞ 2þ 3 and RuðNH 3 Þ 3þ 6 solutions. While RuðbipyÞ 3þ 3 was found to inject holes into the silicon valence band across the organic monolayer, the fast charge transport in RuðNH 3 Þ 3þ 6 /dsDNA films (effective diffusion coefficient, (2.2 ± 0.3) · 10 À5 cm 2 s À1 ) was attributed to a combination of physical diffusion of the ruthenium centres on the surface and charge injection into the Si electrode. For analysis of the SECM feedback experiments with lateral charge transport coupled to electron transfer to dissolved mediators, an analytical approximation was developed and validated by comparison with the results of finite difference simulations. This model successfully accounts for the variation in the SECM feedback with the concentration of the mediator in the solution

Electron energy loss spectroscopy on alkylated silicon nanocrystals

Alkyl-passivated silicon nanoparticles have been studied via aberration-corrected scanning transmission electron microscopy (STEM) in conjunction with electron energy loss spectroscopy in order to characterize both their chemical composition and structural make-up. Energy loss spectra indicate a predominantly silicon core structure with some oxide species and Si–C surface bonds. Shifts in the Si?L-edge onset to higher energies are attributed to quantum confinement effects in the material although the magnitudes are greater than theoretical values expected for silicon nanocrystals bound by alkyl chains. Nanocrystal STEM samples formed by direct evaporation and deposition of intact nanocrystals show evidence of crystalline planes and structural rearrangements, which can be observed under extended irradiation by the electron probe beam

Mechanical and optical properties of ultralarge flakes of a metal-organic framework with molecular thickness

The isolation of 2D-materials is already a success for graphene, graphene oxide, boron nitride and a few clays or metal chalcogenides, however despite the fact that some of them show very interesting physical properties, they lack useful functionalities. Metal-Organic Frameworks (MOFs) are multifunctional materials showing a wide range of physical and chemical properties that can be structurally designed by suitable selection of their building-blocks. This strategy may allow the production of layers with a variety of useful electronic and molecular recognition functionalities. Herein we isolate 2D-MOF flakes with areas of hundreds of square microns and an excellent control of the molecular thickness (from single up to ca. 50 layers). The samples exhibit such good photoluminescence and mechanical properties as to allow free-standing characterization of few layers' flakes.The authors acknowledge financial support from MICINN (MAT2013-46753-C2-1-P and MAT2013-46753-C2-2-P and Consolider CSD2010-00024)