Highly specific and sensitive chromo-fluorogenic detection of sarin, tabun, and mustard gas stimulants: a multianalyte recognition approach

Nerve agents are the most notorious substances, which can be fatal to an individual because they block the activity of acetylcholinesterase. Fighting against unpredictable terrorist assaults and wars requires the simple and quick detection of chemical warfare agent vapor. In the present contribution, we have introduced a rhodamine-based chemosensor, BDHA, for the detection of nerve gas-mimicking agents diethylchlorophosphate (DCP) and diethylcyanophosphonate (DCNP) and mustard gas-mimicking agent 2-chloroethyl ethyl sulfide (CEES), both in the liquid and vapor phase. Probe BDHA provides the ability for detection by the naked eye in terms of colorimetric and fluorometric changes. It has been revealed that the interaction between nerve agents mimics and probe BDHA facilitates spirolactam ring opening due to the phosphorylation process. Thus, the highly fluorescent and colored species developed while probe BDHA is colorless and non-fluorescent due to the intramolecular spirolactam ring. Moreover, probe BDHA can effectively recognize DCP, DCNP, and CEES in the µM range despite many toxic analytes and could be identified based on the response times and quantum yield values. Inexpensive, easily carried paper strips-based test kits were developed for the quick, on-location solid and vapor phase detection of these mustard gas imitating agents (CEES) and nerve gas mimicking agents (DCP and DCNP) without needing expensive equipment or skilled personnel. More remarkably, the test strips' color and fluorescence can be rapidly restored, exposing them to triethyl amine (TEA) for cyclic use, suggesting a potential application in the real-time identification of chemical warfare agents. To accomplish the on-location application of BDHA, we have experimented with soil samples to find traces of DCP. Therefore, the chromo-fluorogenic probe BDHA is a promising, instantaneous, and on-the-spot monitoring tool for the selective detection of DCP, DCNP, and CEES in the presence of others.

Killing two birds with one stone: phosphorylation by a tabun mimic and subsequent capture of cyanide using a single fluorescent chemodosimeter

In the presence of the tabun mimic diethylcyanophosphonate (DECP), a fluorescent bifunctional coumarin–enamine chemodosimeter is first phosphorylated and subsequently attacked by the released cyanide ions.

"Turn-on" unsymmetrical azine based fluorophore for the selective detection of diethylchlorophosphate via photoinduced electron transfer to intramolecular charge transfer pathway

The detection of chemical warfare agents (CWAs) in a highly selective, sensitive and speedy manner is essential for public safety in the case of terrorist attacks and achieving this is a challenging task. This study involves in developing a new unsymmetrical azine based fluorophore 4-((E)-(((E)-2-methoxybenzylidene)hydrazono)methyl)benzonitrile[A1] which shows high selectivity and sensitivity to the nerve agent mimic molecule, diethylchlorophosphate (DCP) through fluorescence switch on mechanism. In a fascinating manner, DCP sensing by A1 operates via solvent dependent optical output mechanisms. In the absence of DCP, the fluorescence of A1 was in the off state through photoinduced electron transfer process. In the presence of DCP, a nucleophilic substitution reaction occurs at the imine nitrogen is closer to the anisole moiety that results in the formation of a new intramolecular charge transfer state along with fluorescence enhancement. In acetonitrile, A1 shows 1763-fold fluorescence enhancement in the presence of DCP with a detection limit of 9.86 nM. In Acetonitrile/water (2:8) mixture, protonation at the imine nitrogen leads to 1188-fold fluorescence enhancement. The sensing mechanisms are confirmed by both experimental and time dependent density functional theoretical studies.

Acid is a potential interferent in fluorescent sensing of chemical warfare agent vapors

A common feature of fluorescent sensing materials for detecting chemical warfare agents (CWAs) and simulants is the presence of nitrogen-based groups designed to nucleophilically displace a phosphorus atom substituent, with the reaction causing a measurable fluorescence change. However, such groups are also basic and so sensitive to acid. In this study we show it is critical to disentangle the response of a candidate sensing material to acid and CWA simulant. We report that pyridyl-containing sensing materials designed to react with a CWA gave a strong and rapid increase in fluorescence when exposed to Sarin, which is known to contain hydrofluoric acid. However, when tested against acid-free diethylchlorophosphate and di-iso-propylfluorophosphate, simulants typically used for evaluating novel G-series CWA sensors, there was no change in the fluorescence. In contrast, simulants that had been stored or tested under a standard laboratory conditions all led to strong changes in fluorescence, due to acid impurities. Thus the results provide strong evidence that care needs to be taken when interpreting the results of fluorescence-based solid-state sensing studies of G-series CWAs and their simulants. There are also implications for the application of these pyridyl-based fluorescence and other nucleophilic/basic sensing systems to real-world CWA detection.

Selective detection of chemical warfare agents VX and Sarin by the short wavelength inner filter technique (SWIFT)

A novel SWIFT-based strategy for fluorimetric detection of practical amounts (minimal effective dose or lower) of chemical warfare agents is reported. This strategy employs readily available reagents and allows distinguishing between the V and G agents, as well as their discrimination from potential interferents.

D-π-A azine based AIEgen with solvent dependent response towards a nerve agent

We developed a D-π-A based unsymmetrical azine molecule 4-((E)-((E)-(4-(dipropylamino)benzylidene)hydrazono)methyl)benzonitrile [DPBN] and studied its optical and aggregation induced emission properties. The DPBN molecule shows good aggregation induced emission (AIE) behaviour with 1157-fold fluorescence enhancement in the aggregated state. In addition to that, both colorimetric as well as fluorometric sensing studies revealed that DPBN selectively detects diethylchlorophosphate (DCP), a potent nerve agent. Interestingly, DPBN shows solvent dependent optical output in the presence of DCPvia two different mechanisms. In the monomer state, it shows red shifted fluorescence enhancement along with color change from colorless to orange color via the formation of a new intramolecular charge transfer state in pure tetrahydrofuran (THF). In the aggregated state, DPBN shows blue shifted emission with fluorescence enhancement in THF-water mixture by protonation at the amine nitrogen centre. Thus, DPBN can be used as a diagnostic measure to selectively detect nerve agents like DCP. This study also paves the way for further development of molecular probes for nerve agents that would represent immense implications in various fields of chemistry and biology.

Design and synthesis of a novel coumarin-based framework as a potential chemomarker of a neurotoxic insecticide, azamethiphos

A coumarin based receptor has been synthesised and its organic nanoparticles were prepared. Further, these nanoparticles were explored as a chemosensor for copper(ii) ions and azamethiphos.

Organoiridium(III) Complexes as Luminescence Color Switching Probes for Selective Detection of Nerve Agent Simulant in Solution and Vapor Phase

In this work, cationic organoiridium(III) complex based photoluminescent (PL) probes have been developed to selectively detect the chemical warfare nerve agent mimic, diethyl chlorophosphate(DCP) at nanomolar range by distinct bright green to orange-red luminescence color switching (on-off-on) in solution as well as in the vapor phase. Interference of other chemical warfare agents (CWAs) and their mimics was not observed either by PL spectroscopy or with the naked-eye in solution and gas phase. The detection was attained via a simultaneous nucleophilic attack of two -OH groups of the 4,7-dihydroxy-1,10-phenanthroline ligand with DCP by forming bulkier phosphotriester. The detailed reaction mechanism was established through extensive ¹H NMR titration, ³¹P NMR, and ESI-MS analysis. Finally, a test paper strip and solid poly(ethylene oxide) (PEO) film with iridium(III) complex 1[PF₆] were fabricated for the vapor-phase detection of DCP. The solution and vapor-phase detection properties of these luminescent Ir(III) complexes can offer a worthy approach into the design of new metal complex based PL switching probes for chemical warfare agents.

Colorimetric and Fluorescent Detecting Phosgene by a Second-Generation Chemosensor

Because of the current shortage of first-generation phosgene sensors, increased attention has been given to the development of fluorescent and colorimetric based methods for detecting this toxic substance. In an effort focusing on this issue, we designed the new, second-generation phosgene chemosensor 1 and demonstrated that it undergoes a ring-opening reaction with phosgene in association with color and fluorescent changes with a detection limit of 3.2 ppb. Notably, in comparison with the first-generation sensor RB-OPD, 1 not only undergoes a much faster response toward phosgene with an overall response time within 2 min, but it also generates no byproducts during the sensing process. Finally, sensor 1 embedded nanofibers were successfully fabricated and used for accurate and sensitive detection of phosgene.

Recent Advances in the Development of Chromophore-Based Chemosensors for Nerve Agents and Phosgene

The extreme toxicity and ready accessibility of nerve agents and phosgene has caused an increase in the demand to develop effective systems for the detection of these substances. Among the traditional platforms utilized for this purpose, chemosensors including surface acoustic wave (SAW) sensors, enzymes, carbon nanotubes, nanoparticles, and chromophore based sensors have attracted increasing attention. In this review, we describe in a comprehensive manner recent progress that has been made on the development of chromophore-based chemosensors for detecting nerve agents (mimic) and phosgene. This review comprises two sections focusing on studies of the development of chemosensors for nerve agents (mimic) and phosgene. In each of the sections, the discussion follows a format which concentrates on different reaction sites/mechanisms involved in the sensing processes. Finally, chemosensors uncovered in these efforts are compared with those based on other sensing methods and challenges facing the design of more effective chemosensors for the detection of nerve agents (mimic) and phosgene are discussed.

Exploration of fluorescent organotin compounds of α-amino acid Schiff bases for the detection of organophosphorous chemical warfare agents: quantification of diethylchlorophosphate

Fluorescent Schiff base organotin probes for the detection of chemical warfare agents.

Real time detection of the nerve agent simulant diethylchlorophosphate by nonfluorophoric small molecules generating a cyclization-induced fluorogenic response

Herein, we report the detection of DCP by nonfluorophoric small molecules.

Highly selective and sensitive chromogenic detection of nerve agents (sarin, tabun and VX): a multianalyte detection approach

A novel strategy using ferrocenyl dye (1) was developed for highly selective chromogenic detection of all nerve agents.

Carboxylic Acid-Functionalized Conducting-Polymer Nanotubes as Highly Sensitive Nerve-Agent Chemiresistors

Organophosphates are powerful inhibitors of acetylcholinesterase, which is critical to nerve function. Despite continuous research for detecting the highly toxic organophosphates, a new and improved methodology is still needed. Herein we demonstrate simple-to-fabricate chemiresistive gas sensors using conducting-polymer polypyrrole (PPy) nanotube transducers, which are chemically specific and capable of recognizing sub-ppb concentrations (ca. 0.5 ppb) of dimethyl methylphosphonate (DMMP), a simulant of nerve agent sarin. Interestingly, the introduction of carboxylic groups on the surface of PPy nanotube transistors resulted in enhanced sensitivity to DMMP via intermolecular hydrogen bonding. Furthermore, it was found that the sensitivity of the nanotube transducer depended on the degree of the carboxylic group introduced. Finally, a sensor array composed of 5 different transducers including the carboxylated nanotubes exhibited excellent selectivity to DMMP in 16 vapor species.

Effective Strategy for Colorimetric and Fluorescence Sensing of Phosgene Based on Small Organic Dyes and Nanofiber Platforms

Three o-phenylendiamine (OPD) derivatives, containing 4-chloro-7-nitrobenzo[c][1,2,5]oxadiazole (NBD-OPD), rhodamine (RB-OPD), and 1,8-naphthalimide (NAP-OPD) moieties, were prepared and tested as phosgene chemosensors. Unlike previously described methods to sense this toxic agent, which rely on chemical processes that transform alcohols and amines to respective phosphate esters and phosphoramides, the new sensors operate through a benzimidazolone-forming reaction between their OPD groups and phosgene. These processes promote either naked eye visible color changes and/or fluorescence intensity enhancements in conjunction with detection limits that range from 0.7 to 2.8 ppb. NBD-OPD and RB-OPD-embedded polymer fibers, prepared using the electrospinning technique, display distinct color and fluorescence changes upon exposure to phosgene even in the solid state.

A Fluorescent Sensor for Dual-Channel Discrimination between Phosgene and a Nerve-Gas Mimic

The ability to analyze highly toxic chemical warfare agents (CWAs) and related chemicals in a rapid and precise manner is essential in order to alleviate serious threats to humankind and public security caused by unexpected terrorist attacks and industrial accidents. In this investigation, we designed a o-phenylenediamine-pyronin linked dye that is capable of both fluorogenic and colorimetric discrimination between phosgene and the prototypical nerve-agent mimic, diethyl chlorophosphate (DCP) in the solution or gas phase. Moreover, this dye has been used to construct a portable kit that can be employed for real-time monitoring of DCP and phosgene in the field, both in a discriminatory manner, and in a simple and safe way.

Chromogenic and fluorogenic multianalyte detection with a tuned receptor: refining selectivity for toxic anions and nerve agents

In the present study, a chemical probe was finely tuned for the highly selective and sensitive chromogenic and fluorogenic detection of toxic anions and a nerve agent.

A cyclization-induced emission enhancement (CIEE)-based ratiometric fluorogenic and chromogenic probe for the facile detection of a nerve agent simulant DCP

The first ratiometric fluorescent probe for the detection of a nerve agent simulant was developed based on tandem phosphorylation and intramolecular cyclization.

Chromogenic and fluorogenic detection and discrimination of nerve agents Tabun and Vx

Chromogenic and fluorogenic detection and discrimination of nerve agents Tabun and Vx are presented.

Assorted morphosynthesis: access to multi-faceted nano-architectures from a super-responsive dual π-functional amphiphilic construct

An electronically segmented amphiphile was created by conjugating two π-functional units (HQ/NDI) for the first time.