Achievement of energy focus for distance-of-flight mass spectrometry with constant momentum acceleration and an ion mirror

Distance-of-flight mass spectrometry (DOF-MS) has not yet been implemented, though it has many potential advantages in a variety of applications. Impeding the implementation of DOF-MS is the development of the required array detectors and working out the equivalents to the focusing methods now used in time-of-flight (TOF) mass analyzers. Ideally, a batch of ions composed of a variety of m/z values, despite initial distributions of space and energy, would be spatially focused at their respective flight distances at the same time. First-order energy focusing, including ion turnaround, is shown to be accomplished by the use of an ion mirror in conjunction with constant momentum acceleration of the initial ion packet. The initial spatial dispersion is maintained throughout the flight path. With zero initial spatial ion spread, energy focusing to achieve resolutions in the tens of thousands is shown to be feasible with ions from the elemental and isotope ratio mass regions through the extremely high m/z range. With moderate spatial spread taken into account, the DOF-MS approach is shown to achieve resolutions competitive with quadrupole and ion trap mass analyzers. Advantages of DOF-MS include all the advantages of TOF-MS plus simpler detector electronics and the improved signal-to-noise ratio and dynamic range afforded by array detection.     

Fluoroalkylated silicon-containing surfaces-estimation of solid-surface energy

The design of robust omniphobic surfaces, which are not wetted by low-surface-tension liquids such as octane (γlv=21.6 mN/m) and methanol (γlv=22.7 mN/m), requires an appropriately chosen surface micro/nanotexture in addition to a low solid-surface energy (γsv). 1H,1H,2H,2H-Heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) offers one of the lowest solid-surface energy values ever reported (γsv≈10 mN/m) and has become the molecule of choice for coating textured surfaces. In this work, we synthesize and evaluate a series of related molecules that either retain the POSS cage and differ in fluoroalkyl chain length or that retain the fluorodecyl chains surrounding a linear or cyclic molecular structure. The solid-surface energy (γsv) of these molecules was estimated using contact angle measurements on flat spin-coated silicon wafer surfaces. Zisman analysis was performed using a homologous series of n-alkanes (15.5≤γlv≤27.5 mN/m), whereas Girifalco-Good analysis was performed using a set of polar and nonpolar liquids with a wider range of liquid surface tension (15.5≤γlv≤72.1 mN/m). The hydrogen-bond-donating, hydrogen-bond-accepting, polar, and nonpolar (dispersion) contributions to the solid-surface energy of each compound were determined by probing the surfaces using a set of three liquid droplets of either acetone, chloroform, and dodecane or diiodomethane, dimethyl sulfoxide, and water.     

A simple route to form magnetic chitosan nanoparticles from coaxial-electrospun composite nanofibers

Composite non-woven mats of poly(vinyl pyrrolidone) (PVP), chitosan, and Fe₃O₄ were successfully fabricated using coaxial-electrospinning technique with PVP/chitosan as the shell and PVP/Fe₃O₄ as the core. Because of the templating and confinement properties of the nanofibers, magnetic chitosan nanoparticles (MCNPs) could be spontaneously formed through molecular self-assembly when the composite fibers were dissolved on treatment with acetum solution. By changing the weight ratio of Fe₃O₄:chitosan, the size of the MCNPs could be varied. The morphology, chemical composition, and magnetic characteristics of composite particles were characterized by means of scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometer. Experimental results indicated that the composite particles were super-paramagnetic with sizes in the range of 15–40 nm. This facile and new synthesis route comprises a convenient strategy to generate composite particles and should be broadly applicable to a wide range of systems, serving as a platform for the facile development of novel composite materials.     

Retrieval of aerosol refractive index from extinction spectra with a damped harmonic-oscillator band model

A new method for the retrieval of the spectral refractive indices of micrometer-sized particles from infrared aerosol extinction spectra has been developed. With this method we use a classical damped harmonic-oscillator model of molecular absorption in conjunction with Mie scattering to model extinction spectra, which we then fit to the measurements using a numerical optimal estimation algorithm. The main advantage of this method over the more traditional Kramers-Kronig approach is that it allows the full complex refractive-index spectra, along with the parameters of the particle size distribution, to be retrieved from a single extinction spectrum. The retrieval scheme has been extensively characterized and has been found to provide refractive indices with a maximum uncertainty of approximately 10% (with a minimum of approximately 0.1%). Comparison of refractive indices calculated from measurements of a ternary solution of HNO3, H2SO4, and H2O with those published in J. Phys. Chem. A 104, 783 (2000) show similar differences as found by other authors.     

On the response of ballistic soap to one-dimensional shock loading

The effects of projectile penetration into soft tissue are often studied using the tissue simulant ballistic soap. Consequently, a full understanding of the high strain-rate response of ballistic soap is desirable. Using the plate-impact technique, key shock parameters have been measured for impacts in the range 81–968 m/s, allowing derivation of the Hugoniot equation-of-state for soap in the U_S–u_P and σ_X–u_P planes. A polynomial Hugoniot relationship was found in the U_S–u_P plane, with the general form U_S = 1.96 + 2.41u_P − 0.72u_P² (ρ₀ = 1.107 g/cc). Further, embedded lateral manganin stress gauges were employed to interrogate the evolution of lateral stress within the soap. A gradient in lateral stress, whose magnitude increased incrementally with impact stress, was apparent behind the shock for σ_X >1 GPa. It is proposed that at higher values of σ_X, increased compression of hydrocarbon chains acts to increase the materials resistance to shear, a phenomenon consistent with steric hindrance.     

Fast and Highly Sensitive Ionic‐Polymer‐Gated WS2–Graphene Photodetectors

The combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer‐scale electronic devices. Presently, long‐lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gate‐voltage pulses, have been employed to achieve bandwidths suitable for applications such as video‐frame‐rate imaging. Here, atomically thin graphene–WS₂ heterostructure photodetectors encapsulated in an ionic polymer are reported, which are uniquely able to operate at bandwidths up to 1.5 kHz whilst maintaining internal gain as large as 10⁶. Highly mobile ions and the nanometer‐scale Debye length of the ionic polymer are used to screen charge traps and tune the Fermi level of the graphene over an unprecedented range at the interface with WS₂. Responsivity R = 10⁶ A W^?1 and detectivity D* = 3.8 × 10¹¹ Jones are observed, approaching that of single‐photon counters. The combination of both high responsivity and fast response times makes these photodetectors suitable for video‐frame‐rate imaging applications.     

The yeast nascent polypeptide-associated complex initiates protein targeting to mitochondria in vivo

The yeast nascent polypeptide-associated complex (NAC) is encoded by two genes, EGD1 and EGD2, and is associated with cytoplasmic ribosomes. Yeast mutants lacking NAC (Deltaegd2) are viable but suffer slight defects in the targeting of nascent polypeptides to several locations including the endoplasmic reticulum and mitochondria. If both NAC and Mft52p are missing from yeast cells, inefficient targeting of mitochondrial precursor proteins leads to defects in both mitochondrial function and morphology. We suggest that NAC provides a ribosomal environment for nascent mitochondrial targeting sequences to achieve secondary structure, thereby enhancing the efficiency of protein targeting.     

Dextran coated ultrafine superparamagnetic iron oxide nanoparticles: compatibility with common fluorometric and colorimetric dyes

Due to the unique physicochemical properties of nanomaterials (NM) and their unknown reactivity, the possibility of NM altering the optical properties of fluorometric/colorimetric probes that are used to measure their cyto- and genotoxicity may lead to inaccurate readings. This could have potential implications given that NM, such as ultrafine superparamagnetic iron oxide nanoparticles (USPION), are increasingly finding their use in nanomedicine and the absorbance/fluorescence based assays are used to assess their toxicity. This study looks at the potential of dextran-coated USPION (dUSPION) (maghemite and magnetite) to alter the background signal of common probes used for evaluating cytotoxicity (MTS, CyQUANT, Calcein, and EthD-1) and oxidative stress (DCFH-DA and APF). In the present study, both forms of dUSPION caused an increase in MTS signal but a decrease in background signal from calcein and 3'-(p-aminophenyl) fluorescein (APF) and no effect on CyQUANT and EthD-1 fluorescence responses. Magnetite caused a decrease in fluorescence signal of DCFH, but it did not decrease fluorescence signal in the presence of the reactive oxygen species-inducer tert-butyl hydroperoxide (TBHP). In contrast, maghemite caused an increase in fluorescence, which was substantially reduced in the presence of the antioxidant N-acetyl cysteine. This study emphasizes the importance of considering and controlling for possible interactions between NM and fluorometric/colorimetric dyes and, most importantly, the oxidation state of dUSPION that may confound their sensitivity and specificity.     

Improving pulse sequences for 3D diffusion-ordered NMR spectroscopy: 2DJ-IDOSY

An improved pulse sequence for the 3D DOSY experiment 2DJ-DOSY, using diffusion encoding internal to the parent 2DJ spectroscopy sequence (2DJ-IDOSY), is presented. The diffusion-encoding pulses are used to enforce the desired coherence transfer pathway, reducing the minimum experimental time by at least a factor of 4, as compared to existing techniques, and approximately doubling the signal-to-noise ratio for small molecules. The new sequence is demonstrated on a simple mixture and on a complex sample with a high dynamic range (port wine). The principle of internal diffusion encoding can be applied with profit to a range of other 3D DOSY experiments.