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This paper describes the development, design and characterization of a resistive pulse sensing (RPS) system for the analysis of size distributions of extracellular vesicles (EVs). The system is based on microfluidic chips fabricated using soft-lithography and operated in pressure-driven mode. This fabrication approach provided reproducible pore dimensions and the best performing chip design enabled, without calibration, sizing of both 252 nm and 460 nm test particles within 8% of theoretically calculated values, based on the size specifications provided by suppliers. The number concentration measurement had higher variations and without calibration provided estimates within an order of magnitude, for sample concentrations across 4 orders of magnitude. The RPS chips could also measure successfully EVs and other biological nanoparticles in purified samples from cell culture media and human serum. A compact, fast and inexpensive RPS system based on this design could be an attractive alternative to current gold-standard techniques for routine characterization of EV samples. [ABSTRACT FROM AUTHOR]

To investigate magnetostructural relationships in colloidal magnetite (Fe3O4) nanoparticles (NPs) at high temperature (300-900 K), we measured the temperature dependence of magnetization (M) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of M for these NPs, with dip and loop features observed during heating-cooling cycles. Detailed characterizations of as-synthesized and annealed Fe3O4 NPs as well as reference ligand-free Fe3O4 NPs indicate that both types of features in M(T) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe3+ to Fe2+ and the associated dip in M, leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent M curves featuring loops. The increase in M with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe3+/Fe2+ ratio with heat treatment. The interpretation of irreversible features in M(T) indicates that reversible M(T) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature M(T) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials.

To investigate magnetostructural relationships in colloidal magnetite (Fe3O4) nanoparticles (NPs) at high temperature (300-900 K), we measured the temperature dependence of magnetization (M) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of M for these NPs, with dip and loop features observed during heating-cooling cycles. Detailed characterizations of as-synthesized and annealed Fe3O4 NPs as well as reference ligand-free Fe3O4 NPs indicate that both types of features in M(T) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe3+ to Fe2+ and the associated dip in M, leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent M curves featuring loops. The increase in M with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe3+/Fe2+ ratio with heat treatment. The interpretation of irreversible features in M(T) indicates that reversible M(T) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature M(T) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials.

Quantitative and reproducible data can be obtained from surface-based DNA sensors if variations in the conformation and surface density of immobilized single-stranded DNA capture probes are minimized. Both the conformation and surface density can be independently and deterministically controlled by taking advantage of the preferential adsorption of adenine nucleotides (dA) on gold, as previously demonstrated using a model system in Opdahl, A.; Petrovykh, D. Y.; Kimura-Suda, H.; Tarlov, M. J.; Whitman, L. J. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 9-14. Here, we describe the immobilization and subsequent hybridization properties of a 15-nucleotide DNA probe sequence that has additional m adenine nucleotides, [(dA).sub.m], at the 5' end. Quantitative analysis of immobilization and hybridization for these probes indicates that the [(dA).sub.m] block preferentially adsorbs on gold, forcing the probe portion of the strand to adopt an upright conformation suited for efficient hybridization. In addition, a wide range of probe-to-probe lateral spacing can be achieved by coimmobilizing the probe DNA with a lateral spacer, a strand of k adenine nucleotides, [(dA).sub.k]. Altering either the length or relative concentration of the [(dA).sub.k] spacers added during probe immobilization controls the average surface density of probes; the density of probes, in turn, systematically modulates their hybridization with solution targets. 10.1021/ac902765g

The use of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTR) spectroscopy to quantitatively characterize the immobilization of thilated (dT)(sub 25) single-stranded DNA (ssDNA) on gold is presented. At higher immobilization densities, the (dT)(sub 25) film consists of randomly coiled SSDNA molecules.

The cost‐effectiveness and excellent performance of conductive‐carbon‐supported Ni‐based electrocatalysts make them attractive materials for hydrogen oxidation and evolution reactions. However, they were previously unused in gas‐phase hydrogenation reactions. In this work, we have expanded the applicability of commercially available advanced Ni/C, NiMo/C and NiRe/C materials from electrocatalysis to heterogeneous catalysis of CO2 methanation. Our catalytic testing efforts indicate that the monometallic Ni/C material demonstrates the best CO2 methanation properties, achieving an excellent CO2 conversion of 83 % at 400 °C with nearly complete selectivity to CH4 of 99.7 %, plus exhibiting intact performance during 90 h of time‐on‐stream testing. Such catalytic properties are among the highest reported to date among carbon‐supported Ni‐based methanation catalysts. Excellent performance of Ni/C stems from the good dispersion of the Ni nanoparticles over N‐containing carbon support material. [ABSTRACT FROM AUTHOR]

The structure of single-stranded DNA (ssDNA) is characterized by using complementary spectroscopies that probe electronic and vibrational states of nucleobases. The results show that ex situ characterization can be used to study the structure of biosurfaces and it also establishes a foundation for in situ analysis, as both fluorescence yield near-edge X-ray absorption fine structure (NEXAFS) and Fourier transform infrared (FITR) can be adapted to aqueous environment.

A study is conducted to examine room-temperature adsorption of homo-oloiginucleotides onto polycrystalline Au films, including competitive adsorption between all possible pairs of such unmodified oligomers. Results suggest that the unlabeled (dA)(Sub 20), single stranded DNA, preferentially adsorbed undetected onto the electrode.