Low-cost reduced graphene oxide-based conductometric nitrogen dioxide-sensitive sensor on paper

The fabrication concept for a low-cost sensor device using reduced graphene oxide (rGO) as the sensing material on a porous paper substrate is presented. The sensors were characterized using conductivity and capacitance measurements, atomic force microscopy and X-ray photoelectron spectroscopy. The effects of different reducing agents, graphene oxide (GO) flake size and film thickness were studied. The sensor was sensitive to NO₂, and devices based on a thin (10-nm) hydrazine-reduced GO layer had the best sensitivity, reaching a 70 % reduction in resistance after 10 min of exposure to 10 ppm NO₂. The sensitivity was high enough for the detection of sub-parts per million levels of NO₂. Desorption of gas molecules, i.e. the recovery of the sensor, could be accelerated by UV irradiation. The structure and preparation of the sensor are simple and up-scalable, allowing their fabrication in bulk quantities, and the fabrication concept can be applied to other materials, too.

Nanoscale reversed-phase liquid chromatography–mass spectrometry of permethylated N-glycans

Reversed-phase liquid chromatography on the nanoscale coupled to electrospray tandem mass spectrometry was used to analyse a mixture of four commercial glycan standards, and the method was further adapted to N-glycans enzymatically released from alpha-1-acid glycoprotein and immunoglobulin gamma. Glycans were permethylated to enable their separation by reversed-phase chromatography and to facilitate interpretation of fragmentation data. Prior to derivatization of glycans by permethylation, they were reduced to cancel anomerism because, although feasible, it was not desired to separate α- and β-anomers. The effect of supplementing chromatographic solvent with sodium hydroxide to guide adduct formation was investigated. Raising the temperature in which the separation was performed improved chromatographic resolution and affected retention times as expected. It was shown by using the tetrasaccharides sialyl Lewis X and sialyl Lewis A that reversed-phase chromatography could achieve the separation of methylated isobaric glycan analytes. Isobaric glycans were detected among the N-glycans of immunoglobulin gamma and further analysed by tandem mass spectrometry.     

Competitive immunoassay by hot electron-induced electrochemiluminescence detection and using a semiautomatic electrochemiluminometer

A homogeneous immunoassay of T4 was developed using a semiautomatic electrochemiluminometer modified from a commercially available fluorometer. In addition, from the same analyte panel an immunometric immunoassay of TSH at similar disposable oxide-covered aluminum rake electrodes was studied using this instrument both on homogeneous and heterogeneous basis. Detection was based on hot electron-induced cathodic electrochemiluminescence utilizing a commercially available Tb(III) chelate label. The assays were reasonably sensitive and comparison was made with other older methods. Thus, it is possible to develop both non-competitive and competitive immunoassays based on detection of hot electron-induced ECL of the labels.     

Laterally-corrugated ridge-waveguide distributed feedback lasers at 980 nm

The paper presents a simulation-based analysis of laterally-corrugated ridge-waveguide distributed feedback semiconductor lasers emitting at 980 nm. The simulations were performed using software developed in-house and the PICS3D software package from Crosslight Software Inc. The effects of the corrugation geometry, phase-shift section, and mirror reflectivities on single longitudinal mode operation are discussed. The lasers, designed along the guidelines derived from the simulation results, were fabricated by using molecular beam epitaxy for wafer growth and low-cost nano-imprint lithography. They exhibited stable single-mode operation with up to 50 dB side-mode suppression ratio.     

Core level studies of calcite and dolomite

Conventional X‐ray photoelectron spectroscopy (XPS) and synchrotron‐based X‐ray photoelectron spectroscopy (HRXPS) have been used to study Iceland spar calcite (CaCO₃) and dolomite (CaMg(CO₃)₂). The obtained full widths at half maximum (FWHMs) are mostly narrower than in the previous results, which together with the symmetry of the fitted peaks indicate effective neutralisation of surface charging. Some previously unidentified features observed in the Ca 2p, C 1s and O 1s spectra of calcite have been suggested to be bulk plasmons. Also, surface core level shifts in Ca 2p (in calcite) and Mg 2p (in dolomite) spectra have been obtained and found to be consistent between XPS and HRXPS measurements. A peak attributed to carbide (CaC₂) has been suggested to indicate beam‐assisted interaction with hydrocarbons found on the surface. Copyright © 2014 John Wiley & Sons, Ltd.     

Time resolved exciton migration in mixed naphthalene crystals: triplet and singlet critical concentrations

The contrasting temporal characteristics of the triple and singlet transport (below 4 K) correlate with dynamic and quasistatic percolation, respectively. They do not support an Anderson—Mott transition (AMT) for the triplet nor an AMT followed by a kinetic threshold for the singlet critical concentration. The triplet decay-time displays the critical exponent γ.     

Adjustable wettability of paperboard by liquid flame spray nanoparticle deposition

Liquid flame spray process (LFS) was used for depositing TiO_x and SiO_x nanoparticles on paperboard to control wetting properties of the surface. By the LFS process it is possible to create either superhydrophobic or superhydrophilic surfaces. Changes in the wettability are related to structural properties of the surface, which were characterized using scanning electron microscope (SEM) and atomic force microscope (AFM). The surface properties can be ascribed as a correlation between wetting properties of the paperboard and the surface texture created by nanoparticles. Surfaces can be produced inline in a one step roll-to-roll process without need for additional modifications. Furthermore, functional surfaces with adjustable hydrophilicity or hydrophobicity can be fabricated simply by choosing appropriate liquid precursors.     

Surface-enhanced Raman scattering active substrates by liquid flame spray deposited and inkjet printed silver nanoparticles

Surface-enhanced Raman scattering (SERS) active substrates were made via liquid flame spray deposition and inkjet printing of silver nanoparticles. Both processes are suitable for cost-effective fabrication of large-area SERS substrates. Crystal violet (CV) solutions were used as target molecules and in both samples the detection limit was approximately 10 nM. In addition, sintering temperature of the inkjet printed silver nanoparticles was found to have a large effect on the SERS activity with the higher curing temperature of 200 °C resulting in contamination layer on silver and cancelation of the SERS signal. This layer was characterized using an X-ray photoelectron spectroscopy (XPS).