Trace detection and discrimination of explosives using electrochemical potentiometric gas sensors.

In this article, selective and sensitive detection of trace amounts of pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) is demonstrated. The screening system is based on a sampling/concentrator front end and electrochemical potentiometric gas sensors as the detector. Preferential hydrocarbon and nitrogen oxide(s) mixed potential sensors based on lanthanum strontium chromite and Pt electrodes with yttria stabilized zirconia (YSZ) solid electrolyte were used to capture the signature of the explosives. Quantitative measurements based on hydrocarbon and nitrogen oxide sensor responses indicated that the detector sensitivity scaled proportionally with the mass of the explosives (1-3 µg). Moreover, the results showed that PETN, TNT, and RDX samples could be discriminated from each other by calculating the ratio of nitrogen oxides to hydrocarbon integrated area under the peak. Further, the use of front-end technology to collect and concentrate the high explosive (HE) vapors make intrinsically low vapor pressure of the HE less of an obstacle for detection while ensuring higher sensitivity levels. In addition, the ability to use multiple sensors each tuned to basic chemical structures (e.g., nitro, amino, peroxide, and hydrocarbon groups) in HE materials will permit the construction of low-cost detector systems for screening a wide spectrum of explosives with lower false positives than present-day technologies.

Dielectric properties of novel polyurethane/silica nanowire composites.

An aliphatic isocyanate, polyether, polyol thermoplastic polyurethane, Tecoflex SG-85A, was solution processed with the varying amounts of silica nanowire. The dielectric permittivity (epsilon') and loss factor (epsilon") were measured via Dielectric Analysis (DEA) in the frequency range 1 Hz to 100 kHz and between the temperature -150 to 150 degrees C. The electric modulus formalism was used to reveal alpha, beta and conductivity relaxations. The activation energies for the relaxations are presented. Nanocomposites were also characterized by differential scanning calorimetry (DSC) to determine glass transition temperatures. The onset of decomposition temperature was measured by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) provided images of the polymer-nanocomposites.

Ionic liquid-mediated sol-gel coatings for capillary microextraction.

Ionic liquid (IL)-mediated sol-gel hybrid organic-inorganic materials present enormous potential for effective use in analytical microextraction. This opportunity, however, has not yet been explored. One obstacle to materializing this prospect arises from high viscosity of ILs significantly slowing down sol-gel reactions. In this work, we developed a method that overcomes this hurdle and provides IL-mediated advanced sol-gel materials for capillary microextraction (CME). We examined two different ILs: (a) a phosphonium-based IL, trihexyltetradecylphosphonium tetrafluoroborate, and (b) a pyridinium-based ionic liquid, N-butyl-4-methylpyridinium tetrafluoroborate. These ILs were evaluated in conjunction with two types of hydroxy-terminated polymers: (a) two Si-OH terminated polymers (PDMS and BMPO), and (b) two C-OH terminated polymers (PEG and polyTHF) that differ in their sol-gel reactivity. Scanning electron microscopy results demonstrate that ILs can serve as porogenic agents in sol-gel reactions. The IL-mediated sol-gel coatings prepared with silanol-terminated polymers provided up to 28 times higher extractions in off-line CME-GC compared to analogous sol-gel coatings prepared without any IL in the sol solution. Contrary to this, the IL-mediated sol-gel coatings prepared with C-OH terminated polymers provided lower extraction efficiencies compared to their IL-free counterparts. These observations were explained by (a) lower sol-gel reactivity of C-OH groups in PEG and polyTHF compared to Si-OH groups in PDMS and in hydrolyzed alkoxysilane precursors and (b) extremely high viscosity of ionic liquids. This study shows that IL-generated porous morphology alone is not enough to provide effective extraction media: careful choice of the organic polymer and the precursor with close sol-gel reactivity must be made to ensure effective chemical bonding of the organic polymer to the created sol-gel material to be able to provide the desired sorbent characteristics. Additionally, IL-mediated sol-gel PDMS coatings provided run-to-run RSD values of 4.2-5.0% and detection limits ranging from 3.2 ng/L to 17.4 ng/L. PDMS sol-gels prepared without ILs provided RSD values of 2.8-14.1%, and detection limits ranging from 4.9 ng/L to 487.0 ng/L.

Selective growth of silica nanowires using an Au catalyst for optical recognition of interleukin-10.

The vapor-liquid-solid (VLS) growth procedure has been extended for the selective growth of silica nanowires on SiO(2) layer by using Au as a catalyst. The nanowires were grown in an open tube furnace at 1100 °C for 60 min using Ar as a carrier gas. The average diameter of these bottom-up nucleated wires was found to be 200 nm. Transmission electron microscopy analysis indicates the amorphous nature of these nanoscale wires and suggests an Si-silica heterostructure. The localized silica nanowires have been used as an immunoassay template in the detection of interleukin-10 which is a lung cancer biomarker. Such a nanostructured platform offered a tenfold enhancement in the optical response, aiding the recognition of IL-10 in comparison to a bare silica substrate. The role of nanowires in the immunoassay was verified through the quenching behavior in the photoluminescence (PL) spectra. Two orders of reduction in PL intensity have been observed after completion of the immunoassay with significant quenching after executing every step of the protocol. The potential of this site-specific growth of silica nanowires on SiO(2) as a multi-modal biosensing platform has been discussed.