Mesoporous Metal Sponges Produced by Explosive Decomposition.

The formation of mesoporous gold sponges by explosive decomposition of 'knallgold' (also known as 'fulminating' gold) is studied. Proof-of-principle experiments are conducted and then the phenomena are further investigated using 'toy physics' molecular dynamics simulations. The simulations invoked various ratios of a volatile Lennard-Jones element G and a noble metal element N. In both experiment and simulation the morphology of the resulting sponge is found to depend on the stoichiometry of the starting material. As the mole fraction of G (χG) is increased from 0.5 to close to 1.0 in the simulations, the morphology of the sponges changes from closed to open, with a corresponding increase in the average mean curvature from 0 to +0.12 inverse Lennard-Jones length (L) units. The average Gaussian curvature of the simulated sponges is always negative, with the minimum value of 0.05 L-2 being found for χG ≈0.65. In broad agreement with experiment, sponge formation in the simulations is bounded by stoichiometry; no sponges form if χG is <0.52, for χG between 0.52 and 0.70 the sponge is characterized by vermicular cavities whereas classic bicontinuous fibrous sponges form for 0.70< χG < 0.85 and, finally, discrete particles result if χG >0.85.

Molecular dynamics simulations reliably identify vibrational modes in far-IR spectra of phospholipids.

The properties of self-assembled phospholipid membranes are of essential importance in biochemistry and physical chemistry, providing a platform for many cellular life functions. Far-infrared (far-IR) vibrational spectroscopy, on the other hand, is a highly information-rich method to characterize intermolecular interactions and collective behaviour of lipids that can help explain, e.g., chain packing, thermodynamic phase behaviour, and sequestration. However, reliable interpretation of the far-IR spectra is still lacking. Here we present a molecular dynamics (MD) based approach to simulate vibrational modes of individual lipids and in an ensemble. The results are a good match to synchrotron far-IR measurements and enable identification of the molecular motions corresponding to each vibrational mode, thus allowing the correct interpretation of membrane spectra with high accuracy and resolving the longstanding ambiguities in the literature in this regard. Our results demonstrate the feasibility of using MD simulations for interpreting far-IR spectra broadly, opening new avenues for practical use of this powerful method.

Super-Resolution Reconstruction for Two- and Three-Dimensional LA-ICP-MS Bioimaging.

The resolution of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) elemental bioimaging is usually constrained by the diameter of the laser spot size and is often not adequate to explore in situ subcellular distributions of elements and proteins in biological tissue sections. Super-resolution reconstruction is a method typically used for many imaging modalities and combines multiple lower resolution images to create a higher resolution image. Here, we present a super-resolution reconstruction method for LA-ICP-MS imaging by ablating consecutive layers of a biological specimen with offset orthogonal scans, resulting in a 10× improvement in resolution for quantitative measurement of dystrophin in murine muscle fibers. Layer-by-layer image reconstruction was also extended to the third dimension without the requirement of image registration across multiple thin section specimens. Quantitative super-resolution reconstruction, combined with Gaussian filtering and application of the Richardson-Lucy total variation algorithm, provided superior image clarity and fidelity in two- and three-dimensions.

Remarkable thermal stability of gold nanoparticles functionalised with ruthenium phthalocyanine complexes.

A gold nanoparticle (AuNP) ruthenium phthalocyanine (RuPc) nanocomposite has been synthesised that exhibits high thermal stability. Electrical resistance measurements revealed that the nanocomposite is stable up to ∼320 °C. Examination of the nanocomposite and the RuPc stabiliser complex using thermogravimetric analysis and differential scanning calorimetry show that the remarkable thermal stability is due to the RuPc molecules, which provide an effective barrier to sintering of the AuNPs.

Structural analysis of bioinspired nano materials with synchrotron far IR spectroscopy.

Bioinspired fibres and hierarchical nano-materials are based on the self-assembly of organic building blocks such as polypeptides. Confirming the core structure of such materials is often challenging as they lack the long-range order required by crystallographic methods. Far-IR spectroscopy characterizes the vibrational modes of large molecular units. These vibrational modes are very sensitive to angle strain and second order interactions such as hydrogen bonding. As such, far-IR spectra hold information about the secondary structure and interactions of large biomolecules. Here we analyze the far-IR vibrational spectra of fibrous nano-materials based on three isomeric unnatural tripeptides, Ac-ß(3)Leu-ß(3)Ile-ß(3)Ala, Ac-ß(3)Ile-ß(3)Ala-ß(3)Leu, and Ac-ß(3)Ala-ß(3)Leu-ß(3)Ile. These peptides have well described self-assembly characteristics, forming one-dimensional nanorods that impose tight conformational constraints on the constituent molecules. The synchrotron far-IR spectroscopic results were interpreted by using density functional theory (DFT) modelling based vibrational analysis. The sensitivity of the spectra to peptide conformation was assessed by comparing the experimental spectra with DFT predictions. In high dielectric implicit solvent, intramolecular hydrogen-bonding is inhibited and thus the energy minimized peptide structure remains close to the 14-helix folding characteristic of substituted ß(3)-peptides, giving good agreement between the experimental and predicted vibration spectra. In contrast, energy minimization in vacuum alters the peptide conformation leading to intramolecular hydrogen bonds, and hence the predicted vibration spectra do not agree with the experimental data. Therefore, our results demonstrate the ability of far-IR spectroscopy to identify correct structural predictions and thus open the way for using far-IR spectroscopy for the characterization and structural analysis of bioinspired nano-materials and potentially their interactions with surfaces, ionic environments and other biomolecules. Far-IR structural analysis is particularly powerful in case of one- and two-dimensional materials such as fibres, hydrogels and thin layers where standard crystallographic analysis is not available.

Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications.

Zinc hydroxyacetate and its transformation to nanocrystalline zinc oxide.

The synthesis of nanocrystalline ZnO by thermal decomposition of zinc hydroxyacetate, Zn(5)(OH)(8)(CH(3)CO(2))(2)·nH(2)O, was investigated. The decomposition process was examined using X-ray diffraction, thermogravimetric analysis, mass spectrometry, electron microscopy, Brunauer-Emmett-Teller surface area analysis, and solid-state NMR spectroscopy. Intermediate Zn(5)(OH)(8)(CH(3)CO(2))(2)·nH(2)O phases form at temperatures up to 110 °C from the starting compound Zn(5)(OH)(8)(CH(3)CO(2))(2)·2H(2)O by partial dehydration. At ∼110 °C, 4 equiv of ZnO and 1 equiv of Zn(CH(3)CO(2))(2) are formed. Further heating causes Zn(CH(3)CO(2))(2) to decompose to acetone, acetic acid, acetic anhydride, and ZnO. Notably, a portion of Zn(CH(3)CO(2))(2) sublimes during the process. Overall, the product of the calcination is equiaxed ZnO nanocrystals of 20-100 nm diameter.

The preparation of a plasmonically resonant VO2 thermochromic pigment.

Vanadium dioxide (VO(2)) undergoes a reversible metal-insulator transition, normally at approximately 68 degrees C. While the properties of continuous semi-transparent coatings of VO(2) are well known, there is far less information available concerning the potential use of discrete VO(2) nanoparticles as a thermochromic pigment in opaque coatings. Individual VO(2) nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO(2) nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO(2) powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.

Optical readout of the intracellular environment using nanoparticle transducers.

There is rapid growth in the use of multi-functional nanoparticles as transducers to probe the intracellular environment. New designs of nanoparticles can provide quantitative information at sub-cellular resolution on parameters such as pH, temperature and concentration of nicotinamide adenine dinucleotide (NADH) or selected metal ions. This new work builds on the existing practice of using nanoparticles and fluorescent dyes to provide enhanced microscopic images of cells, but goes beyond it by adding new functionalities and analytical capabilities. In this review, we discuss the recent literature on the development of such nanoparticles for simultaneous biosensing and imaging. We explore and examine the different measurements that will be possible, and analyze the likely accuracy and resolution that could be achieved.

Effect of precursor stoichiometry on the morphology of nanoporous platinum sponges.

Nanoscale sponges formed by de-alloying suitable metallic alloys have a wide variety of potential applications due to their enhanced catalytic, optical, and electrochemical properties. In general, these materials have a bi-continuous, vermicular morphology of pores and ligaments with a fibrous appearance; however, other morphologies are sometimes reported. Here, we investigate how stoichiometry and process parameters control the characteristics of sponges formed from thin film precursors of AlxPt. Materials deposited at elevated temperatures and with mole fraction of Al between 0.65 and 0.90 produce the classic isotropic fibrous sponges with a morphology that varies systematically with precursor stoichiometry; however, de-alloying of material deposited at room temperature produced unusual isotropic foamy sponges. The evidence suggests that formation of a conventional fibrous sponge requires an equilibrated precursor whereas foamy morphologies will result if the precursor is metastable. Modeling was used to investigate the range of possible morphologies. As stoichiometry changed in the model system, the average mean and Gaussian curvature of the sponges systematically changed, too. The evolution of these shapes passed through certain special morphologies; for example, modelled structures with 0.80 Al had a zero average Gaussian curvature and might represent a structural optimum for some applications. These observations provide a means to control sponge morphology at the nanoscale.