Detection Of Chemical Threats Research Articles

Differentiating Between V- and G-Series Nerve Agent and Simulant Vapours Using Fluorescent Film Responses.

In-field rapid and reliable identification of nerve agents is critical for the protection of Defence and National Security personnel as well as communities. Fluorescence-based detectors can be portable and provide rapid detection of chemical threats. However, most current approaches cannot differentiate between dilute vapors of nerve agent classes and are susceptible to false positives due to the presence of common acids. Here a fluorescence-based method is shown for rapid differentiation between the V-series and phosphonofluoridate G-series nerve agents and avoids false positives due to common acids. Differentiation is achieved through harnessing two different mechanisms. Detection of the V-series is achieved using photoinduced hole transfer whereby the fluorescence of the sensing material is quenched in the presence of the V-series agent. The G-series is detected using a turn-on mechanism in which a silylated excited state intramolecular proton transfer sensing molecule is selectively deprotected by hydrogen fluoride, which is typically found as a contaminant and/or breakdown product in G-series agents such as sarin. The strategy provided discrimination between classes, as the sensor for the G-series agent class is insensitive to the V-series agent, and vice versa, and neither responded to common acids.

Improved detection of chemical threats by sensor data fusion

1. Jensen, F.V. and Nielsen, T.D. (2007) Bayesian networks and decision graphs. New York, NY: Springer. CrossRef Google Scholar

Architecture for microcomb-based GHz-mid-infrared dual-comb spectroscopy

Dual-comb spectroscopy (DCS) offers high sensitivity and wide spectral coverage without the need for bulky spectrometers or mechanical moving parts. And DCS in the mid-infrared (mid-IR) is of keen interest because of inherently strong molecular spectroscopic signatures in these bands. We report GHz-resolution mid-IR DCS of methane and ethane that is derived from counter-propagating (CP) soliton microcombs in combination with interleaved difference frequency generation. Because all four combs required to generate the two mid-IR combs rely upon stability derived from a single high-Q microcavity, the system architecture is both simplified and does not require external frequency locking. Methane and ethane spectra are measured over intervals as short as 0.5 ms, a time scale that can be further reduced using a different CP soliton arrangement. Also, tuning of spectral resolution on demand is demonstrated. Although at an early phase of development, the results are a step towards mid-IR gas sensors with chip-based architectures for chemical threat detection, breath analysis, combustion studies, and outdoor observation of trace gases.

Tri-molybdenum phosphide (Mo3P) and multi-walled carbon nanotube junctions for volatile organic compounds (VOCs) detection

Detection and analysis of volatile organic compounds' (VOCs) biomarkers lead to improvement in healthcare diagnosis and other applications such as chemical threat detection and food quality control. Here, we report on tri-molybdenum phosphide (Mo3P) and multiwalled carbon nanotube (MWCNT) junction-based vapor quantum resistive sensors (vQRSs), which exhibit more than one order of magnitude higher sensitivity and superior selectivity for biomarkers in comparison to pristine MWCNT junctions based vQRSs. Transmission electron microscope/scanning tunneling electron microscope with energy dispersive x-ray spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy studies reveal the crystallinity and the presence of Mo and P elements in the network. The presence of Mo3P clearly enhanced the performance of vQRS as evidenced in sensitivity and selectivity studies. The vQRSs are stable over extended periods of time and are reproducible, making them a potential candidate for sensing related applications.

Enhanced detection of volatile organic compounds (VOCs) by caffeine modified carbon nanotube junctions

Detection of vapor phase analytes and gas molecules is primarily essential for numerous applications including medical diagnostic, environmental monitoring, chemical threat detection, food quality control, and chemical warfare agents. Here, we developed Caffeine functionalized carbon nanotubes (CNTs) random network based vapor quantum resistive sensors (vQRSs) for volatile organic compounds (VOCs) detection. The localized transmission electron microscopy (TEM) image and energy dispersive X-ray spectroscopy (EDS) confirm migration of caffeine to CNT–CNT junction (CNTj). We have recorded more than one order of magnitude higher sensitivity and unique selectivity towards​ selective VOCs (e.g., acetone, toluene, ethanol, methanol, etc.) with short response time (few seconds) for caffeine modified CNT junction (Caf-CNTj) vQRSs. Molecular dynamics (MD) calculations suggest that the sensitivity of the sensor is diffusion limited, with an advective contribution for ethanol. The designed Caf-CNTj sensors can potentially be important candidate to be a part of electronic nose used for various application such as breath analysis and food quality monitoring.

Two-dimensional MS/MS scans on a linear ion trap mass analyzer: Identification of V-series chemical warfare agents

Chemical warfare agents (CWAs) are devastating weapons of terror due to their highly lethal and dispersive nature. Powerful analytical tools are required to help create a knowledge base that will contribute to preventing attacks using these agents. Highly sensitive measurements must be made quickly with high selectivity for a wide range of potential molecular targets. Portable mass spectrometers have emerged as a robust platform for in-situ detection of chemical threats. However, due to size, weight, and power constraints, they are typically limited to a single mass analyzer with limited MS/MS capabilities, most notably the provision of full scan and product ion MS/MS spectra.Here we demonstrate the application of a new, highly efficient scanning methodology that uses a single linear quadrupole ion trap to acquire two-dimensional mass spectrometry data (2D MS/MS). With only a single scan, we show that it is possible to acquire mass-to-charge information on V-series chemical warfare agents– namely,: (1) Ethyl ({2-[bis(propan-2-yl)amino]ethyl}sulfanyl)(methyl)phosphinate (V1), (2) N,N-diethyl-2-(methyl-(2-methylpropoxy)phosphoryl)sulfanylethanamine (VR), (3) O-Butyl S-[2-(diethylamino)ethyl] methylphosphonothioate (VX) and (4) S-[2-(Diethylamino)ethyl] O-ethyl methylphosphonothioate (VM) - as precursors while simultaneously (in the same scan) acquiring product ion spectra for each CWA via mass spectral microfeatures. For mixtures of V-series agents, 2D MS/MS is a time- and sample-efficient method for obtaining MS/MS data. Discussed here are advantages and limitations of 2D MS/MS compared to conventional data-dependent product ion MS/MS scans.

Nanotechnology Based Cell-All Phone-Sensors for Extended Network Chemical Sensing

Today’s chemical sensing networks work effectively to cover limited and specific physical area and environments with significant cost and overhead. In order to greatly expand coverage and realize greater WMD protection for the nation, a revolutionary breakthrough that provides for a much larger and lower cost sensing distributed network is required. In order to practice this idea, US department of homeland security, HSARPA program made a call for Cell-All Ubiquitous Biological and Chemical Sensing.NASA Ames Research Center responded to the call and won the proposal award. The work presented here is a first ever complete intelligent network chemical sensing system with 1) a compact, low-cost, low-power, high-speed nanosensor array-based detector integrated with 2) a smartphone for detection of chemical threats and transmit the sensor data via cellphone communication system to 3) a network cloud for centralizing the chemical sensing information from multiple phone-sensors from various locations.At NASAARC, we have developed miniaturized sensing modules that can connect with an iPhone for chemical detection using carbon nanotubes (CNT) based nanostructure materials. Our devices possess high sensitivity (ppmv - ppbv), fast response (in sec), high selectivity, low power (5mW without sampling fan and 27mW with sampling fan), and very small size like a postage stamp, and they have been demonstrated for integration with an iPhone for chemical sensing of ppm concentration level of carbon monoxide, and ammonia in Windex and chlorine gas in Bleach.The prototype-sensing module can be easily connected with an iPhone. Software has been developed to control the sensor chip for chemical detection; to collect and process sensor data, to display the chemical identification and associated concentration, and the sensor response in real time on the iPhone screen, and to transmit sensor data via 3G and/or Wi-Fi to a central location – an Internet server, to build a wider range of sensing network.An effective cell phone-based chemical detection network will take advantage of both the standalone computing capability of modern cellular phones and the ability to aggregate sensor data over the cellular network for distributed processing or to a centralized processing location. This chemical detection network expands the coverage and realizes greater protection for the nation from hazardous chemical attack.Note: This work is funded by DHS HSARPA Cell_All Program.

Preparation of TNT, RDX and Ammonium Nitrate Standards on Gold-on-Silicon Surfaces by Thermal Inkjet Technology

This research examines the surface contamination properties, trace sample preparation methodologies, detection systems response and generation of explosive contamination standards for trace detection systems. Homogeneous and reproducible sample preparation is relevant for trace detection of chemical threats, such as warfare agents, highly energetic materials (HEM) and toxic industrial chemicals. The objective of this research was to develop a technology capable of producing samples and standards of HEM with controlled size and distribution on a substrate to generate specimens that would reproduce real contamination conditions. The research activities included (1) a study of the properties of particles generated by two deposition techniques: sample smearing deposition and inkjet deposition, on gold-coated silicon, glass and stainless steel substrates; (2) characterization of composition, distribution and adhesion characteristics of deposits; (3) evaluation of accuracy and reproducibility for depositing neat highly energetic materials such as TNT, RDX and ammonium nitrate; (4) a study of HEM-surface interactions using FTIR-RAIRS; and (5) establishment of protocols for validation of surface concentration using destructive methods such as HPLC.