Time filter

Source Type

Aberdeen Proving Ground, MD, United States

A panel of 15 biological toxins ranging between ∼60-28,000 g/mol was used to evaluate the feasibility of screening aqueous samples for toxin analytes based on their translational diffusion coefficients, D t. Toxin D t values were measured by pulsed-field gradient 1H NMR spectroscopy using a bipolar pulse pair, longitudinal eddy current delay pulse sequence incorporating water suppression to achieve the maximum dynamic range for toxin signals. To collect data for an effective screening protocol, reference D t values were determined from five independent measurements at both 25 and 37 °C for all toxins in the panel. In the protocol, D t values are measured at both temperatures for a suspected toxin target in a sample, and for assignment as a potential toxin analyte, the measurements are required to fall within ±0.25×10 -6∈cm2/s of both reference D t values for at least one toxin in the panel. Only solution viscosity was found to influence sample D t measurements appreciably; however, the measurements are easily corrected for viscosity effects by calculating the D t value of the suspected toxin at infinite dilution. In conclusion, the protocol provides a rapid and effective means for screening aqueous samples for all toxins in the panel, narrowing toxin identification to ≤2 possibilities in virtually all cases. © 2009 Springer-Verlag. Source

Decoste J.B.,SAIC | Peterson G.W.,Edgewood Chemical Biological Center | Jasuja H.,Georgia Institute of Technology | Glover T.G.,SAIC | And 2 more authors.
Journal of Materials Chemistry A | Year: 2013

Metal-organic frameworks (MOFs) with the Zr6O 4(OH)4 secondary building unit (SBU) have been of particular interest for potential commercial and industrial uses because they can be easily tailored and are reported to be chemically and thermally stable. However, we show that there are significant changes in chemical and thermal stability of Zr6O4(OH)4 MOFs with the incorporation of different organic linkers. As the number of aromatic rings is increased from one to two in 1,4-benzene dicarboxylate (UiO-66, ZrMOF-BDC) and 4,4′-biphenyl dicarboxylate (UiO-67, ZrMOF-BPDC), the Zr6O 4(OH)4 SBU becomes more susceptible to chemical degradation by water and hydrochloric acid. Furthermore, as the linker is replaced with 2,2′-bipyridine-5,5′-dicarboxylate (ZrMOF-BIPY) the chemical stability decreases further as the MOF is susceptible to chemical breakdown by protic chemicals such as methanol and isopropanol. The results reported here bring into question the superior structural stability of the UiO-67 analogs as reported by others. Furthermore, the degradation mechanisms proposed here may be applied to other classes of MOFs containing aromatic dicarboxylate organic linkers, in order to predict their structural stability upon exposure to solvents. This journal is © 2013 The Royal Society of Chemistry. Source

Ben-David A.,Edgewood Chemical Biological Center | Davidson C.E.,Science and Technology Inc.
Journal of Microbiological Methods | Year: 2014

Titration of microorganisms in infectious or environmental samples is a corner stone of quantitative microbiology. A simple method is presented to estimate the microbial counts obtained with the serial dilution technique for microorganisms that can grow on bacteriological media and develop into a colony. The number (concentration) of viable microbial organisms is estimated from a single dilution plate (assay) without a need for replicate plates. Our method selects the best agar plate with which to estimate the microbial counts, and takes into account the colony size and plate area that both contribute to the likelihood of miscounting the number of colonies on a plate. The estimate of the optimal count given by our method can be used to narrow the search for the best (optimal) dilution plate and saves time. The required inputs are the plate size, the microbial colony size, and the serial dilution factors. The proposed approach shows relative accuracy well within ±0.1log10 from data produced by computer simulations. The method maintains this accuracy even in the presence of dilution errors of up to 10% (for both the aliquot and diluent volumes), microbial counts between 104 and 1012 colony-forming units, dilution ratios from 2 to 100, and plate size to colony size ratios between 6.25 to 200. © 2014 Published by Elsevier B.V. Source

Tran H.,Columbia University | Killops K.L.,Edgewood Chemical Biological Center | Campos L.M.,Columbia University
Soft Matter | Year: 2013

In recent years, the patterning of biomolecules with sub-50 nanometer resolution has enabled fundamental studies on cellular interactions with their environment and the development of densely packed biosensors. To further these efforts, the ability to precisely position multicomponent, single biomolecules and small clusters in various shapes and patterns has emerged as a major challenge. We highlight recent strategies to immobilize biomolecules with sub-50 nanometer resolution, emphasizing the advancements and challenges associated with each approach. © 2013 The Royal Society of Chemistry. Source

Ben-David A.,Edgewood Chemical Biological Center | Davidson C.E.,Science and Technology Inc.
Optics Express | Year: 2013

We extend the probability model for 3-layer radiative transfer [Opt. Express 20, 10004 (2012)] to ideal gas conditions where a correlation exists between transmission and temperature of each of the 3 layers. The effect on the probability density function for the at-sensor radiances is surprisingly small, and thus the added complexity of addressing the correlation can be avoided. The small overall effect is due to (a) small perturbations by the correlation on variance population parameters and (b) cancelation of perturbation terms that appear with opposite signs in the model moment expressions. © 2013 Optical Society of America. Source

Discover hidden collaborations