Dimethyl Methylphosphonate Detection Research Articles

A new strategy for low temperature gas sensing by nano-sized metal oxides: Development a new nerve agent simulant sensor

The need to apply high operation temperature when working with metal oxide gas sensors is a well-known drawback of these kinds of gas sensors in spite of their wide applications even commercially. In this approach, a new strategy was introduced for gas sensing with metal oxides in ambient temperature. The principal is based on the addition of a desiccant material in the metal oxide based nanocomposite. For this aim, nano-sized α-Fe2O3, graphite and calcium sulfate was combined and the nanocomposite obtained was used as an efficient gas sensor. Calcium sulfate was used either as desiccant or binder to tighten together the nonocomposite components. Sensing nanocomposite was tested for sensing of dimethyl methylphosphonate (DMMP) vapor, as a nerve agent stimulant. The results obtained showed excellent sensitivity and selectivity for DMMP. It was demonstrated that the presence of CaSO4 in the nanocomposite is crucially important for observing the sensing characteristic of nano-sized α-Fe2O3 in room temperature. It was also shown that the modification of iron oxide with sulfate functionalities improved the DMMP detection capability of the related nanocomposite. Based on the observed result a mechanism was proposed for sensing performance of the sensor. The developed sensor showed very low detection limit of 1 ppb for DMM.

Detection of dimethyl methylphosphonate by thin water film confined surface-enhanced Raman scattering method

It is important and necessary to effectively detect the chemical warfare agents, such as highly toxic never agent sarin. However, based on the surface-enhanced Raman scattering (SERS) effect, detection of nerve agent simulant dimethyl methylphosphonate (DMMP) which is weakly interacted with SERS-active substrate has been the most challenge for the routine SERS detection method. To overcome this challenge, we put forward a thin water film confined SERS strategy. Under the space-confinement of water film, Raman measurements are carried out in the water evaporation process. The subsequent water evaporation induces concentrating of the DMMP molecules, which are thus successfully restricted within the strong electromagnetic field enhanced area above the SERS substrates, leading to the enhancement of their Raman signals. This study provides a new way to achieve the efficient SERS-based detection of the target molecules weakly interacted with the metal substrates.

Highly sensitive gas sensor based on Al-doped ZnO nanoparticles for detection of dimethyl methylphosphonate as a chemical warfare agent simulant

In this paper, we report a dimethyl methylphosphonate (DMMP) gas sensor using synthesized Al-doped ZnO nanoparticles (NPs) via a hydrothermal method. The average particle size of the Al-doped ZnO NPs is ∼25nm. The single crystalline phase was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The variation in the response of the Al-doped ZnO NP sensors within operating temperatures showed the highest response and recovery at 2 and 96s, respectively, at 10ppm in DMMP at 350°C compared with undoped ZnO NP sensors. Our results showed remarkable sensitivity and selectivity of the Al-doped ZnO NPs sensor toward DMMP. Such increased O2 vacancies and surface reactions with small nanocrystals in the Al-doped ZnO NP sensors offer outstanding sensing performance for DMMP detection.

Origin and role of elasticity in the enhanced DMMP detection by ZnO/SAW sensor

ZnO/Quartz based surface acoustic wave (SAW) sensors have been fabricated for the detection of DMMP (di-methyl methyl phosphonate) at room temperature. The as-deposited ZnO thin films are c-axis oriented. The sensitivity of the sensor toward DMMP vapors increases with increase in the thickness of ZnO thin films. A change in elasticity of ZnO films with exposure to DMMP vapors is the dominant sensing mechanism. Various properties of ZnO thin films (roughness, porosity, crystallite size, bond strength etc.) responsible for elastic changes are analyzed by depositing the films under different processing conditions. The ZnO/SAW sensor is also highly selective toward DMMP vapors as compared to other interferants. The results throw light into the elasticity mechanism for SAW sensing along with the possibility of utilizing ZnO/SAW sensor for DMMP detection.

Enhanced dimethyl methylphosphonate (DMMP) detection sensitivity by lead magnesium niobate-lead titanate/copper piezoelectric microcantilever sensors via Young's modulus change

We have examined the detection of dimethyl methylphosphonate (DMMP) using lead magnesium niobate-lead titanate (PMN-PT) piezoelectric microcantilever sensor (PEMS) coated with various planar and particulate receptor coatings. We showed that a two-order-of-magnitude enhancement in the flexural-mode resonance frequency shift, Δf, in DMMP detection that was not accountable for by mass loading alone could be achieved by using a planar Cu2+ adsorbed 11-Mercaptoundecanoic Acid (MUA/Cu2+) or planar 3-mercaptopropyltrimethoxysilane (MPS) coated PEMS. We also showed that the enhancement of Δf of PEMS was a result of the Young's modulus change in the PMN-PT layer induced by the surface stress generated by the binding of DMMP on a continuous receptor coating. Furthermore, the Young's modulus-change enhanced Δf in PEMS with a planar receptor coating was shown to be inversely proportional to the product of the average Young's modulus and thickness of the PEMS and independent of the PEMS lateral dimension. We also showed that with an array of three PEMS, one uncoated, one coated with planar MUA/Cu2+ and the other with planar MPS, the detection Δf pattern for DMMP was distinctively different from those of acetone and ammonia.

Corona Discharge Ionization Source for a Planar High-Field Asymmetric Waveform Ion Mobility Spectrometer

A corona discharge (CD) ionization source was prepared for a planar high-field asymmetric waveform ion mobility spectrometer (FAIMS). The effects of discharge current and discharge distance on ionization efficiency were investigated; and the electric field dependence of the ion injection in the reaction region was studied. The results showed that the discharge current of CD source had good linearity with the intensity of reactant ion peak (RIP), and the RIP intensity increased to a stable level at the discharge distance of >5 mm. An injection electrode was introduced to improve the ionization efficiency. A square-wave voltage applied to the electrode was found to provide optimal performance of ion injection and utilization. The operating parameters of the CD-FAIMS were optimized to achieve trace level detection of dimethyl methylphosphonate (DMMP) sample. The detection limit for DMMP was 0.5 µg/m3.

The Effect of Density and Surface Area on Carbon Nanotube Capacitive Sensors for Dimethyl Methylphosphonate Detection

Capacitive sensors for dimethyl methylphosphonate (DMMP) detection were prepared on interdigitated electrodes by airbrush process. Multi-walled carbon nanotubes (MWNTs) and single-walled carbon nanotubes (SWNTs) were used as the chemically sensitive materials, respectively. Different airbrush carbon nanotube thin films were observed and compared by field-emission scanning electron microscope. It indicated that the capacitance of airbrush MWNT sensor decreased immediately when exposed to DMMP and recovered rapidly when removed DMMP in the range of 12-60 mg/m3(2.4-12 ppm). The sensitivity of airbrush MWNT sensor was about -1.39% at the concentration of 12 mg/m3(2.4 ppm). It was obvious that the capacitance sensitivity was higher when the MWNTs were more and the film was denser by airbrush. It was also found that the capacitance sensitivity of airbrush SWNT sensor was higher than the corresponding airbrush MWNT sensor.

Dimethyl methylphosphonate detection with a single-walled carbon nanotube capacitive sensor fabricated by airbrush technique

Single-walled carbon nanotube (SWNT) films were prepared on interdigitated electrodes by airbrush technique, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT films were characterized by field-emission scanning electron microscope. The response to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the capacitance of airbrush SWNT sensor decreased rapidly in varying concentrations ranging from 12 to 60 mg/m3 (2.4–12 ppm). The capacitance sensitivity was about 12.5 % when exposed to 12 mg/m3 DMMP vapor. The capacitance sensitivity was higher when the initial capacitance and loss tangent were higher and the SWNT film was denser. It was found that the capacitance sensitivity was nearly 10 times to the resistance sensitivity. The airbrush SWNT sensor exhibited highly and fast capacitance response, good repeatability and selectivity for DMMP vapor.

Template Free Synthesis of Hollow Ball-Like Nano-Fe2O3 and Its Application to the Detection of Dimethyl Methylphosphonate at Room Temperature

This paper is focused on the template-free synthesis of nanosized ferric oxide (nano-Fe2O3) and its application in quartz crystal microbalance (QCM) resonators to detect dimethyl methylphosphonate (DMMP), a simulant of Sarin. The X-ray diffraction (XRD) patterns confirm that the synthesized samples are made of Fe2O3 and the scanning electron microscopy (SEM) pictures show that the samples have ball-like shapes. The DMMP sensors with a sensing film of hollow ball-like and solid ball-like Fe2O3 are fabricated and their sensing characteristics are compared. The sensitivity of the hollow ball-like Fe2O3 sensor is more than 500% higher than the one of the solid ball-like Fe2O3 sensor. The hollow ball-like nano-Fe2O3 can be synthesized by a novel low temperature hydrothermal method. The sensors with the hollow ball-like Fe2O3 film perform well in a range of 1 to 6 ppm, with a sensitivity of 29 Hz/ppm at room temperature, while the appropriate recoverability and selectivity are maintained. In addition, the performance of different thicknesses of the sensing film of the hollow ball-like nano-Fe2O3 is investigated and the optimized relative film thickness of the hollow ball-like nano-Fe2O3 is found to be 20 μg/mm2.

Screen-printed single-walled carbon nanotube networks and their use for dimethyl methylphosphonate detection

Single-walled carbon nanotube (SWNT) films were prepared on silicon/silica substrates by screen-printed technique at a wafer scale, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT networks were characterized by field-emission scanning electron microscope. The resistance responses to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the resistance changes of the screen-printed SWNT films increased rapidly in varying concentrations ranging from 20 to 200 ppm. The sensor exhibited high resistance responses, good reproducibility and excellent long-term stability for DMMP vapor detection. The screen-printed SWNT networks would be potentially extended to large-scale, low cost and simple manufacturing sensor applications.

ZnO Surface Acoustic Wave Sensor for the Enhanced Detection of DMMP

This article reports the development of ZnO coated one port Surface Acoustic Wave (SAW) resonators for the detection of DMMP (dimethyl methyl phosphonate), a simulant of chemical warfare agent Sarin at room temperature. For enhanced sensitivity high frequency SAW devices (433Mhz) were used. Frequency shift with DMMP exposure was found to increase with increase in thickness of ZnO film from 20 to 80 nm with maximum shift of 52 kHz. The cross sensitivity of the sensor with commonly available volatile organic compounds (VOCs), gases and water vapors has been performed and was found that the sensitivity towards other interferants is very less as compared to that of DMMP vapors. The sensing mechanism has been explained in detail. It has been shown that there was no significant change in the resistance of the film with exposure to DMMP vapors and hence the contribution of the acoustoelectric interaction is negligible. Further mass loading was not dominant. The negative differential frequency shifts proved that change in elasticity of the film with exposure to DMMP vapors is the dominant sensing mechanism.

Gas sensor based on p-phenylenediamine reduced graphene oxide

We present a useful gas sensor based on chemically reduced graphene oxide (CRG) by drop drying method to create conductive networks between interdigitated electrode arrays. CRG, which is formed from the reduction of graphene oxide by p-phenylenediamine (PPD), can be used as an excellent sensing material. Its efficient dispersion in organic solvents (i.e., ethanol) benefits the formation of conductive circuits between electrode arrays through drop drying method. Preliminary results, which have been presented on the detection of dimethyl methylphosphonate (DMMP) using this simple and scalable fabrication method for practical devices, suggest that PPD reduced CRG exhibits much better (5.7 times with the concentration of DMMP at 30ppm) response to DMMP than that of CRG reduced from hydrazine. Furthermore, this novel gas sensor based on CRG reduced from PPD shows excellent responsive repeatability to DMMP. Overall, the efficient dispersibility of CRG reduced from PPD in organic solvents facilitates the device fabrication through drop drying method, the resultant CRG-based sensing devices, with miniature, low cost, portable characteristics, as well as outstanding sensing performances, can ensure its potential application in gas sensing fields.

Detection of chemical warfare agents based on quantum cascade laser cavity ring-down spectroscopy

Chemical warfare agents (CWAs) are recognized as serious threats of terrorist acts against the civilian population. Minimizing the impact of these threats requires early detection of the presence of CWAs. Cavity ring-down spectroscopy (CRDS) is an exquisitely sensitive technique for the detection of trace gaseous species. In this letter, the CRDS technique is employed using a pulsed quantum cascade laser for the detection of dimethyl methylphosphonate (DMMP). A limit of DMMP detection of approximately 77 ppb is achieved. The best achievable sensitivity that corresponds to noise-equivalent absorption is approximately 2 x 10(-7) cm(-1).

Evaluation of Cu-ZSM-5 zeolites as QCM sensor coatings for DMMP detection

Nanosized Cu-ZSM-5 zeolites are used as novel and selectively sensitive materials for the detection of the nerve agent stimulant gas dimethyl methylphosphonate (DMMP). ZSM-5 and Cu-ZSM-5 zeolites, containing different amounts of copper cations, are synthesized and self-assembled on the surface of sensitive quartz crystal microbalance (QCM) films. The results demonstrate that Cu-ZSM-5 zeolite shows good selectivity and high sensitivity to DMMP vapor. Cu-ZSM-5 zeolite shows sensitivity of up to 8.8Hz/ppm with a detection limit of 0.1ppm, thus proving that these materials are preferable for DMMP detection. Five Cu-ZSM-5 zeolite samples containing different copper ion contents are synthesized and tested to explore the influence of copper ions on the detection of DMMP. The results indicate that sensitivity increases in proportion to the copper content before saturation. A novel desorption method for strong polar molecule DMMP using high frequency alternative electric fields is proposed. Compared with the thermal desorption method, desorption time decreases from 30min to 25s. Good repeatability is obtained under these conditions as well.

Chemical Vapor Detection Using a Capacitive Micromachined Ultrasonic Transducer

Distributed sensing of gas-phase chemicals using highly sensitive and inexpensive sensors is of great interest for many defense and consumer applications. In this paper we present ppb-level detection of dimethyl methylphosphonate (DMMP), a common simulant for sarin gas, with a ppt-level resolution using an improved capacitive micromachined ultrasonic transducer (CMUT) as a resonant chemical sensor. The improved CMUT operates at a higher resonant frequency of 47.7 MHz and offers an improved mass sensitivity of 48.8 zg/Hz/μm(2) by a factor of 2.7 compared to the previous CMUT sensors developed. A low-noise oscillator using the CMUT resonant sensor as the frequency-selective device was developed for real-time sensing, which exhibits an Allan deviation of 1.65 Hz (3σ) in the presence of a gas flow; this translates into a mass resolution of 80.5 zg/μm(2). The CMUT resonant sensor is functionalized with a 50-nm thick DKAP polymer developed at Sandia National Laboratory for dimethyl methylphosphonate (DMMP) detection. To demonstrate ppb-level detection of the improved chemical sensor system, the sensor performance was tested at a certified lab (MIT Lincoln Laboratory), which is equipped with an experimental chemical setup that reliably and accurately delivers a wide range of low concentrations down to 10 ppb. We report a high volume sensitivity of 34.5 ± 0.79 pptv/Hz to DMMP and a good selectivity of the polymer to DMMP with respect to dodecane and 1-octanol.

Detection of dimethyl methyl phosphonate – a simulant of sarin: The highly toxic chemical warfare – using platinum activated nanocrystalline ZnO thick films

Nanocrystalline ZnO powder was prepared using ultrasonic atomization technique. Thick films of this powder were prepared using simple screen printing technique. Pt-modified-ZnO (platinum activated) films were obtained by dipping pure ZnO films into an aqueous solution of chloroplatnic acid for different intervals of time, followed by firing at 500 °C for 30 min. The sensing performance of the unmodified (pure) and Pt-modified ZnO (Pt–ZnO) films was tested on exposure of CWAs (chemical warfare agents) simulants, such as, dimethyl methyl phosphonate (DMMP), 2-chloroethyl ethyl sulfide (CEES) and 2-chloroethyl phenyl sulfide (CEPS). Both pure ZnO and Pt–ZnO films showed higher response to DMMP than their responses to CEES and CEPS. The simulant response, selectivity, response time and recovery time of the sensors were measured and presented. The role played by surface platinum species in the better simulant sensing performance is discussed.

Tailoring the structure of metal oxide nanostructures towards enhanced sensing properties for environmental applications

The present article reviews recent works in our laboratory about the sensing properties to toxic gases using nanostructured WO3, TiO2, FTiO2, and CuO functionalized quartz crystal microbalance (QCM) sensors. WO3 and TiO2 functionalized QCM sensors have much shorter response time than those functionalized by conventional hydrogen-bond acidic branched copolymers for detection of dimethyl methylphosphonate (DMMP). FTiO2 functionalized QCM sensors can improve the gas sensing characteristics by shortening the response time but at the price of partial irreversibility. The sensing mechanism was examined by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Varied CuO nanostructures were synthesized by simple modulation of reaction conditions. All the as-prepared CuO was applied on QCM resonators and explored for HCN sensing. Surprisingly, responses of all the sensors to HCN were found to be in an opposite direction as compared with other common volatile substances, offering excellent selectivity for HCN detection. The sensitivity was very high, and the response and recovery were very fast. Comparison of the specific surface areas of CuO nanostructures showed that CuO of higher surface area is more sensitive than that of lower surface area, indicating that the specific surface area of these CuO nanostructures plays an important role in the sensitivity of related sensors. Based on experimental results, a sensing mechanism was proposed in which a surface redox reaction occurs between CuO and Cu2O on the CuO nanostructures reversibly upon contact with HCN and air, respectively. The CuO functionalized QCM sensors are considered to be a promising candidate for trace HCN gas detection in practical applications.

Effects of Additives on the DMMP Sensing Behavior of SnO2Nanoparticles Synthesized by Hydrothermal Method

<TEX>$SnO_2$</TEX> nanoparticles were synthesized by a hydrothermal method and gas sensors were fabricated using nanoparticles to detect dimethyl methylphosphonate(DMMP) gas. The prepared <TEX>$SnO_2$</TEX> nanoparticles exhibited a high response(72 at <TEX>$500^{\circ}C$</TEX>) to 5 ppm DMMP gas compared to commercial <TEX>$SnO_2$</TEX> nanopowders, but their recovery was relatively poor. Various metals(Ni, Sb, Nb) were added to the <TEX>$SnO_2$</TEX> nanoparticles to improve their recovery properties. The focus of this study was to investigate the effects of metal oxide additives on DMMP sensing behavior in <TEX>$SnO_2$</TEX> nanoparticles.

Capacitive micromachined ultrasonic transducer (CMUT) as a chemical sensor for DMMP detection

We present a chemical sensor based on a capacitive micromachined ultrasonic transducer (CMUT) configured as a resonant mass sensor with a chemically selective polymer coating. The sensing unit of the CMUT consists of 100s to 1000s of resonators connected in parallel and acts as a single resonator. The high resonant frequency (18.2 MHz) and the small mass (296 pg) enable the CMUT to have a good mass sensitivity of 130 zg/Hz/μm 2. We functionalized the CMUT with polyisobutylene (PIB) as the sorbent film, which targets dimethyl methylphosphonate (DMMP), a simulant for nerve agent, sarin. An oscillator circuit was populated to trace the resonant frequency of the CMUT with a fast response time and low noise. We characterized the noise performance of the sensor system and identified the optimal gate time of the read-out frequency counter. Based on the noise measurement, the calculated limit of detection (LOD) of mass loading is 0.192 ag/μm 2 (3- σ confidence level). Chemical experiments were performed on the CMUT sensor with several analytes including DMMP, water, and ethanol. The limit of detection of the CMUT chemical sensor to DMMP vapor was measured as 56 ppb (3- σ confidence level).

Quantitative detection of a simulant of organophosphonate chemical warfare agents using liquid crystals

The performance characteristics of liquid crystal (LC)-based sensors for detection of dimethylmethylphosphonate (DMMP), a representative organophosphonate compound and simulant of chemical warfare agent sarin, are presented. The equilibration coordination interaction among the aluminum ions on a surface, the cyano group in LCs, and the phosphoryl group in DMMP have been exploited to achieve sensitive, fast, and reversible sensor responses. Measurement of the response time of the sensor allows quantitative detection of an unknown concentration of DMMP with high accuracy. The strong coordination interaction between the cyano group present in the LC and the aluminum ions supporting the film of LC provides immunity to exposure to a number of potentially interfering compounds including high humidity. Exposure studies under varied temperature and humid conditions show a minimal effect on the sensor performance. Although the sensors stored at room temperature exhibited slightly diminished sensitivity, the sensors stored at 4 °C remained functionally stable for at least six months. These results combined with the ease of fabrication using the established processes, low cost associated with off-the-shelf components, and small foot print suggest that these LC-based sensors can form the basis of a new class of low cost, light weight, robust sensors for a number of detection applications.