4-(Hexafluoro-2-hydroxy isopropyl)aniline functionalized highly sensitive flexible SWCNT sensor for detection of nerve agent simulant dimethyl methylphosphonate

Hydrogen-Bond Acidic Materials in Acoustic Wave Sensors for Nerve Chemical Warfare Agents' Detection

The latest trends in the field of the on-site detection of chemical warfare agents (CWAs) involve increasing the availability of point detectors to enhance the operational awareness of commanders and soldiers. Among the intensively developed concepts aimed at meeting these requirements, wearable detectors, gas analyzers as equipment for micro- and mini-class unmanned aerial vehicles (UAVs), and distributed sensor networks can be mentioned. One of the analytical techniques well suited for use in this field is surface acoustic wave sensors, which can be utilized to construct lightweight, inexpensive, and undemanding gas analyzers for detecting CWAs. This review focuses on the intensively researched and developed variant of this technique, utilizing absorptive sensor layers dedicated for nerve CWAs' detection. The paper describes the mechanism of the specific interaction occurring between the target analyte and the sensing layer, which serves as the foundation for their selective detection. The main section of this paper includes a chronological review of individual achievements in the field, largely based on the peer-reviewed scientific literature dating back to the mid-1980s to the present day. The final section presents conclusions regarding the prospects for the development of this analytical technique in the targeted application.

Synergy of Two Intermolecular Hydrogen Bonds Promotes Highly Sensitive and Selective Room-Temperature Dimethyl Methylphosphonate Sensing: A Case of rGO-Based Gas Sensors

The development of room-temperature chemiresistive gas sensors with low limit of detection, high sensitivity, and selectivity for dimethyl methylphosphonate (DMMP) detection remains a challenge. Herein, a synergy of the two intermolecular hydrogen bond-promoted approach was proposed to fabricate a room-temperature DMMP sensor with enhanced performances. As a proof of concept, ternary p-hexafluoroisopropanol phenyl (HFIP) functionalized polypyrrole-reduced graphene oxide hybrids (HFIP-PPy-rGO) were rationally designed. During the sensing process, rGO serves as a conductive carrier, ensuring that the sensors operate at room temperature, and both HFIP and PPy act as adsorption sites for DMMP through hydrogen bonding interactions. As expected, the HFIP-PPy-rGO sensor exhibits high selectivity and sensitivity to DMMP. Besides, the HFIP-PPy-rGO sensor also possesses excellent linear response to DMMP and long-term stability. Experimental results and quartz crystal microbalance measurements prove that the specific recognition of DMMP is realized by forming two intermolecular hydrogen bonds between HFIP and DMMP, as well as PPy and DMMP. Additionally, the introduction of HFIP groups also contributes to adjusting device conductivity, enhancing signal conversion function. To put the DMMP sensor into potential practical application, the obvious sensing response to different DMMP concentrations in soil was confirmed, and a wireless detection system was built to realize real-time monitoring of DMMP concentrations in the surroundings. Overall, this study provides a facile and practical solution for improving the sensing performance of room-temperature sensors based on the hydrogen bond theory.

Semiconductor Gas Sensors for Detecting Chemical Warfare Agents and Their Simulants

On-site detection of chemical warfare agents (CWAs) can be performed by various analytical techniques. Devices using well-established techniques such as ion mobility spectrometry, flame photometry, infrared and Raman spectroscopy or mass spectrometry (usually combined with gas chromatography) are quite complex and expensive to purchase and operate. For this reason, other solutions based on analytical techniques well suited to portable devices are still being sought. Analyzers based on simple semiconductor sensors may be a potential alternative to the currently used CWA field detectors. In sensors of this type, the conductivity of the semiconductor layer changes upon interaction with the analyte. Metal oxides (both in the form of polycrystalline powders and various nanostructures), organic semiconductors, carbon nanostructures, silicon and various composites that are a combination of these materials are used as a semiconductor material. The selectivity of a single oxide sensor can be adjusted to specific analytes within certain limits by using the appropriate semiconductor material and sensitizers. This review presents the current state of knowledge and achievements in the field of semiconductor sensors for CWA detection. The article describes the principles of operation of semiconductor sensors, discusses individual solutions used for CWA detection present in the scientific literature and makes a critical comparison of them. The prospects for the development and practical application of this analytical technique in CWA field analysis are also discussed.

High-performance p-hexafluoroisopropanol phenyl functionalized multi-walled carbon nanotube film on surface acoustic wave device for organophosphorus vapor detection

A delay line-type surface acoustic wave (SAW) gas sensor based on p-hexafluoroisopropanol phenyl (HFIPPH) functionalized multi-walled carbon nanotube (MWCNT) film is developed to detect organophosphorus dimethyl methylphosphonate (DMMP) vapor (a simulant of chemical nerve agent sarin). Inspired by the transfer process of Cu-based graphene, a uniform and size-controllable HFIPPH-MWCNT film is successfully prepared on the SAW device via a wet-etching transfer method. For the first time, we use the method of measuring the change of the sensor's insertion loss to achieve the detection of ultra-low concentration DMMP vapor. The designed sensor exhibits a fast response/recovery time about 3 s/50 s, and a low detection limit of 0.1 ppm. Additionally, the stability and selectivity of the sensor and the influence of humidity on its response are evaluated through experiments. The acoustoelectric effect is proved to be the sensing mechanism of the sensor insertion loss response.

A dimethyl methylphonate sensor based on HFIPPH modified SWCNTs

In order to meet the requirements of ultra-fast real-time monitoring of sarin simulator with high sensitivity and selectivity, it is of great significance to develop high performance dimethyl methylphonate (DMMP) sensor. Herein, we proposed a DMMP sensor based on p-hexafluoroisopropanol phenyl (HFIPPH) modified self-assembled single-walled carbon nanotubes (SWCNTs) with field effect transistor (FET) structure. The self-assembly method provides a 4 nanometres thick and micron sized SWCNT channel, with high selectivity to DMMP. The proposed SWCNTs-HFIPPH based sensor exhibits remarkably higher response to DMMP than bare SWCNT based gas sensor within only few seconds. The gas sensing response of SWCNTs-HFIPPH based sensor for 1 ppm DMMP is 18.2%, and the response time is about 10 s. What's more, the gas sensor we proposed here shows excellent selectivity and reproducibility, and the limitation of detection is as low as ppb level. The proposed method lays the foundation for miniaturization and integration of DMMP sensors, expecting to develop detection system for practical sarin sensing application.

Supramolecular Sensing of Chemical Warfare Agents

Chemical warfare agents are a class of organic molecules used as chemical weapons due to their high toxicity and lethal effects. For this reason, the fast detection of these compounds in the environment is crucial. Traditional detection methods are based on instrumental techniques, such as mass spectrometry or HPLC, however the use of molecular sensors able to change a detectable property (e. g., luminescence, color, electrical resistance) can be cheaper and faster. Today, molecular sensing of chemical warfare agents is mainly based on the "covalent approach", in which the sensor reacts with the analyte, or on the "supramolecular approach", which involves the formation of non-covalent interactions between the sensor and the analyte. This Review is focused on the recent developments of supramolecular sensors of organophosphorus chemical warfare agents (from 2013). In particular, supramolecular sensors are classified by function of the sensing mechanism: i) Lewis Acids, ii) hydrogen bonds, iii) macrocyclic hosts, iv) multi-topic sensors, v) nanosensors. It is shown how the supramolecular non-covalent approach leads to a reversible sensing and higher selectivity towards the selected analyte respect to other interfering molecules.

Room temperature DMMP gas sensing based on cobalt phthalocyanine derivative/graphene quantum dot hybrid materials

In this study, two kinds of cobalt phthalocyanine (CoPc) derivatives containing hexafluoroisopropanol (HFIP) and hexafluorbisphenol A (6FBPA) substituents have been obtained. Graphene quantum dots (GQDs) were anchored to CoPc derivatives by π-π bonding, forming hybrid materials. They were employed to detect dimethyl methylphosphonate (DMMP) gas, an ideal simulant gas for sarin nerve gas, and achieved good gas response performance at room temperature. There are strong hydrogen bonds between the two functional group molecules (HFIP and 6FBPA) and the DMMP molecule, leading to their excellent response performance to DMMP molecules. GQDs can effectively increase the electrical conductivity of hybrid materials by π-π bonding with CoPc derivatives. Therefore, the response speed of the hybrid materials to DMMP gas has been significantly improved, and the minimum detection limit is 500 ppb, while maintaining excellent repeatability, stability and selectivity. Laser-assisted irradiation was used to solve the problem of the slow recovery of CoPc derivatives. This result demonstrates that these CoPc derivative/GQD hybrid materials are expected to be the raw materials of the sarin gas sensor.

Enhanced dimethyl methylphosphonate detection based on two-dimensional WSe2 nanosheets at room temperature

Chemical warfare agents, particularly nerve agents such as sarin, are exceptionally harmful and incredibly perilous to people. Thus, the sensitive detection of these gases is indispensable for reducing the risk of chemical weapons. Herein, we fabricated a room-temperature chemiresistive gas sensor based on two-dimensional few-layer tungsten diselenide (WSe2) nanosheets, which were prepared through a facile liquid-phase exfoliation method. The WSe2-based sensor has demonstrated sensitive and selective detection of dimethyl methylphosphonate (DMMP), which is a well-known simulant of the nerve agent sarin. The sensor based on WSe2 nanosheets revealed a high response reaching 8.91% to 10 ppm DMMP with a fast response time of 100 s. Furthermore, the sensor displayed reliable stability, excellent selectivity, and a low theoretical limit of detection of about 122 ppb. The enhanced sensing performance of WSe2 nanosheets can be ascribed to the increase of the specific surface area, which provides more active adsorption sites for DMMP molecules, thereby facilitating the charge transfer process between DMMP molecules and WSe2 nanosheets. Overall, our results indicate that two-dimensional transition metal dichalcogenide materials have the potential for the design and fabrication of high-performance nerve agent sensing devices.

Study of Light-Activated Regioregular Poly(3-Hexyltiophene) Photoconductive Polymer Sensing Properties in Nerve Agent Simulant (DMMP) Detection†

In the present work, we report the use of regioregular poly(3-hexyltiophene) polymer (RR-P3HT) as a potential light-activated material for sensing the chemical nerve agent simulant dimethyl methylphosphonate (DMMP). The electrical response of thick films of RR-P3HT, deposited by spray-coating method onto a porous laminate substrate at room temperature, to DMMP vapours was investigated. The studied material was activated by light-emitting diodes that emitted light of different wavelengths. The sensing properties of RR-P3HT are considerably enhanced upon exposure to blue and yellow light. However, excitation by the low wavelength light (blue) caused degeneration of the material, resulting in lowered stability. In the case of the yellow light, degeneration was much slower and the limit of detection was 0.4 ppm. The studied material exhibited high selectivity, as it did not respond to 6 ppm of acetone and methanol vapours.

Carbon Nanotube Chemical Sensors

Carbon nanotubes (CNTs) promise to advance a number of real-world technologies. Of these applications, they are particularly attractive for uses in chemical sensors for environmental and health monitoring. However, chemical sensors based on CNTs are often lacking in selectivity, and the elucidation of their sensing mechanisms remains challenging. This review is a comprehensive description of the parameters that give rise to the sensing capabilities of CNT-based sensors and the application of CNT-based devices in chemical sensing. This review begins with the discussion of the sensing mechanisms in CNT-based devices, the chemical methods of CNT functionalization, architectures of sensors, performance parameters, and theoretical models used to describe CNT sensors. It then discusses the expansive applications of CNT-based sensors to multiple areas including environmental monitoring, food and agriculture applications, biological sensors, and national security. The discussion of each analyte focuses on the strategies used to impart selectivity and the molecular interactions between the selector and the analyte. Finally, the review concludes with a brief outlook over future developments in the field of chemical sensors and their prospects for commercialization.

Temperature dependent time resolved mid-IR photoacoustic spectroscopy of a nerve gas simulant DMMP

The paper reports the temperature dependent pulsed photoacoustic spectroscopy of Dimethyl methylphosphonate (DMMP) a nerve gas simulant between 50 and 180 °C temperature range. The time domain PA spectra are recorded using two mid-IR wavelengths i.e. 3374 nm, 3495 nm of pulse duration 1.5 ns at 1 kHz repetition rate obtained from optical parametric oscillator. Two anti-symmetric stretching vibrational modes of (CH₃P) and (CH₃O) groups of DMMP molecules have very strong vibrational peaks at 2861.2 cm^-1 (3495 nm) and 2963.8 cm^-1 (3374 nm), respectively. In addition, we have also recorded the PA spectra of acetone at the vibrational frequency 3115.2 cm^-1 (3210 nm), which is the strong vibrational mode of CH band. The comparison of two PA spectra of DMMP and acetone recorded using similar PA cavity help us to understand the effect of other functional groups with respect to different excitation wavelengths. The presence of additional acoustic modes in the PA spectra of DMMP (3374 nm) above the boiling point confirms the slow process of thermal decomposition. Finally, the low level detection limit of DMMP in air is of the of the order of 0.91 ppbV.