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Ben-David A.,Edgewood Chemical Biological Center | Davidson C.E.,Science and Technology Corporation
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.

Ben-David A.,Edgewood Chemical Biological Center | Davidson C.E.,Science and Technology Corporation
Optics Express | Year: 2012

A probability model for a 3-layer radiative transfer model (foreground layer, cloud layer, background layer, and an external source at the end of line of sight) has been developed. The 3-layer model is fundamentally important as the primary physical model in passive infrared remote sensing. The probability model is described by the Johnson family of distributions that are used as a fit for theoretically computed moments of the radiative transfer model. From the Johnson family we use the SU distribution that can address a wide range of skewness and kurtosis values (in addition to addressing the first two moments, mean and variance). In the limit, SU can also describe lognormal and normal distributions. With the probability model one can evaluate the potential for detecting a target (vapor cloud layer), the probability of observing thermal contrast, and evaluate performance (receiver operating characteristics curves) in clutternoise limited scenarios. This is (to our knowledge) the first probability model for the 3-layer remote sensing geometry that treats all parameters as random variables and includes higher-order statistics. © 2012 Optical Society of America.

Ben-David A.,Edgewood Chemical Biological Center | Davidson C.E.,Science and Technology Corporation
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.

News Article | November 13, 2015
Site: phys.org

Anthrax spores as photographed under an electron microscope. Credit: Courtesy of Centers for Disease Control and Prevention These days, mail addressed to selected government offices gets irradiated, in order to kill any biological agents, notably anthrax spores. The downside of this is that viable spores have been needed to identify the anthrax strain, which can be critical to treating those infected. But now Henry S. Gibbons, PhD, has shown that full sequences can quickly be determined from irradiated spores. The research is published November 13 in Applied and Environmental Microbiology, a journal of the American Society for Microbiology. In the study, the investigators irradiated spores of Bacillus atrophaeus, a non-pathogenic strain that, like anthrax, makes spores. The strain the authors used has a number of genetic mutations, as compared to the reference strain, which they hoped they would detect. They also used a vaccine strain of Yersinia pestis, the bacterium that causes plague, but which does not form spores. Irradiation breaks DNA sequences into fragments. The investigators sequenced the fragments, and then documented the sequences. They entered the fragment sequences into a computer, which they programmed to determine the full sequences of the strains. "The full sequences were almost indistinguishable from control materials," said Gibbons. "All known mutations were found in the irradiated materials." The research was motivated by the need for quick recovery of microbial signatures following deliberate releases such as the 2001 anthrax attacks, said Gibbons, who is a research microbiologist at the US Army Edgewood Chemical Biological Center, Aberdeen Proving Ground, Maryland. These attacks, which began a week after 9-11, and were aimed partly at Congressional offices, killed a photo editor, two postal workers, and two others, the first anthrax deaths in the US in 25 years. "Rapid sequencing of irradiated materials from a biocrime would allow quick characterization of the material," said Gibbons. That could answer important questions. For example, the genome might contain a drug resistance cassette, important information for knowing how to treat any infections. More generally, rapid sequencing could also reveal whether a strain had been genetically engineered, said Gibbons. "This was one of the first questions asked during the anthrax investigation. It was motivated by the fact that the Soviet program had developed some engineered pathogens." It would also help determine the sophistication of the perpetrators, which would be important in tracking them down, he said.

News Article | October 4, 2016
Site: www.cemag.us

Researchers have created a fabric material containing nanoscale fibers that are capable of degrading chemical warfare agents (CWAs). Uniform coatings of metal-organic frameworks (MOFs) were synthesized on top of the nanofibers, forming unique kebab-like structures. These MOFs are what break down the CWAs, rendering them harmless. “Current technologies for addressing CWAs rely on carbon-based materials — but these carbon materials can only adsorb hazardous compounds, they can’t degrade them,” says Junjie Zhao, a former Ph.D. student at North Carolina State University and lead author of a paper on the work. “Our goal was to develop new materials that can detoxify these CWA compounds, and we’ve been successful.” The CWA degradation research was conducted by researchers in Gregory Parsons’ group at NC State, and co-workers at RTI International and the Edgewood Chemical Biological Center. “Previous research had found that MOFs can be effective at degrading CWAs,” Zhao says. “However, MOFs normally come in the form of a powder. We wanted to see if we could grow MOFs as functional coatings onto fibers, so that they could be used in masks, filters and protective garments.” “We think that this demonstration of well-controlled MOF thin films that retain their chemical functionality is an important step for personal security and has implications for many other civilian and commercial uses,” adds Parsons, who is Alcoa Professor of Chemical and Biomolecular Engineering at NC State.

KUALA LUMPUR (Reuters) - VX nerve agent, a chemical the United Nations classifies as a weapon of mass destruction, was used to kill the estranged half-brother of North Korean leader Kim Jong Un in a bizarre murder in Malaysia last week, police said on Friday. Kim Jong Nam was killed on Feb. 13, shortly after being assaulted at the airport in the Malaysian capital, Kuala Lumpur, by two women who wiped the chemical on his face as he prepared to board a flight to the Chinese territory of Macau. South Korean and U.S. officials have said they believe North Korean agents assassinated Kim Jong Nam. He had been living with his family in Macau under Beijing's protection and had spoken out against the North Korean regime. Malaysian police were investigating whether the VX - which is believed to be the most toxic known nerve agent and is banned globally except for research - was brought into the country or made there. "If the amount of the chemical brought in was small, it would be difficult for us to detect," police chief Khalid Abu Bakar told reporters. The two women suspects - one Vietnamese and the other Indonesian - are in police detention along with a North Korean man. Seven other North Koreans are wanted in connection with the case, including a diplomat at the embassy in Kuala Lumpur. Malaysia has repeatedly urged the victim's family to come forward to help with the inquiry, while North Korea has demanded the body be handed over to its embassy directly, sparking tension between the two usually friendly countries. Malaysia's chemical weapons analysis unit found traces of VX, or S-2 Diisopropylaminoethyl methylphosphonothioate, on swabs taken from the eye and face of the victim, according to police. "Other exhibits are under analysis," Khalid said in a statement, citing a preliminary report. Police have said the two women were paid to carry out the assault and had been told to wash their hands before fleeing from the airport. They had rehearsed the attack in shopping malls before carrying it out on Kim. One of the women had suffered from the effects of the chemical and had been vomiting, Khalid said. Airport camera footage released on Monday by Japanese broadcaster Fuji TV shows the moment they assaulted Kim Jong Nam. In later clips he is seen asking airport officials for medical help, and rubbing his eyes and stumbling as he entered an airport clinic. Authorities said he complained of dizziness and died on the way to hospital. Authorities raided an apartment in an upscale Kuala Lumpur suburb on Wednesday in connection with the killing, but no chemicals were found, said an official with direct knowledge of the matter. VX is tasteless and odorless, and is outlawed under the Chemical Weapons Convention, except for "research, medical or pharmaceutical purposes". It can be manufactured as a liquid, cream or aerosol. Experts say it has no commercial uses. "This is not something you make in a kitchen lab. This is something that is made in a very sophisticated chemicals weapons lab," said Bruce Bennet, a senior defense researcher at the California-based RAND Corporation. North Korea is believed to have the world's third-largest stockpile of chemical weapons, according to the Nuclear Threat Initiative project, which analyses weapons of mass destruction. South Korean analysts have identified sarin and VX as the focus of the North Korean chemical weapons program. VX in liquid form can be absorbed into the body through skin or eye contact and does not evaporate easily. After giddiness and nausea, exposure to VX quickly progresses to convulsions and respiratory failure before death, according to the U.S. Centers for Disease Control and Prevention (CDC). It can be fatal after 15 minutes, according to the U.S. Army's Edgewood Chemical Biological Center. Police chief Khalid said authorities intended to sweep Kuala Lumpur airport, and other locations the suspects had visited, for "radioactive" material. VX is not known to contain radioactive elements and Reuters calls to police for clarification went unanswered. Malaysian authorities on Thursday requested Interpol to put an alert out to apprehend four North Korean suspects who are believed to have fled from Malaysia on the day of the attack.

Decoste J.B.,Edgewood Chemical Biological Center | Peterson G.W.,Edgewood Chemical Biological Center | Smith M.W.,UK Defence Science and Technology Laboratory | Stone C.A.,UK Defence Science and Technology Laboratory | Willis C.R.,UK Defence Science and Technology Laboratory
Journal of the American Chemical Society | Year: 2012

Metal organic frameworks (MOFs) are a leading class of porous materials for a wide variety of applications, but many of them have been shown to be unstable toward water. Cu-BTC (1,3,5 benzenetricarboxylic acid, BTC) was treated with a plasma-enhanced chemical vapor deposition (PECVD) of perfluorohexane creating a hydrophobic form of Cu-BTC. It was found that the treated Cu-BTC could withstand high humidity and even submersion in water much better than unperturbed Cu-BTC. Through Monte Carlo simulations it was found that perfluorohexane sites itself in such a way within Cu-BTC as to prevent the formation of water clusters, hence preventing the decomposition of Cu-BTC by water. This PECVD of perfluorohexane could be exploited to widen the scope of practical applications of Cu-BTC and other MOFs. © 2012 American Chemical Society.

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.

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.

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.

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