Real time monitoring of nerve agent mimics: Novel solid state emitter for enhanced precision and reliability

Chemical nerve agents are hazardous compounds that terrorists can exploit to pose a significant threat to public safety and national security. The nucleophilic behaviour of these agents enables their interaction with acetyl cholinesterase in the body, leading to paralysis and potentially fatal consequences. Therefore, developing robust and efficient detection methods for these agents is crucial for preventing their misuse. In this manuscript, (E)-12-(1-hydrazineylideneethyl)benzo[f]pyrido[1,2-a]indole-6,11-dione (HBID) is developed as a novel colorimetric and fluorometric probe for the detection of specific chemical nerve agent simulants in both liquid and vapor phase. HBID reacts rapidly with diethyl chlorophosphate (DCP), a common nerve agent simulant, leading to a significant increase in the fluorescence intensity. Under optimized conditions, HBID exhibits high sensitivity, good recyclability, fast response and low limit of detection (0.092 µM). NMR and mass spectral studies suggest that the reaction involves the nucleophilic addition of HBID to DCP, forming a phosphate ester. Additionally, the developed sensor demonstrates viscosity-sensitive AIE phenomena thus greatly expanding its potential applications in biological systems. This sensitivity enables precise detection and visualization of viscosity changes within cellular environments, making the sensor an invaluable tool for studying complex biological processes. The developed probe also detects pH within biologically relevant range (4-6). In practical applications, the probe-treated strips efficiently detected DCP vapor in real time, showing a noticeable fluorescence response. Further, the probe has a strong potential to detect the presence of DCP in the soil samples.

Water-recyclable and reusable fluorescent sensors for nerve gas mimetic detection

Herein, the serendipitous discovery of two water-recyclable and reusable fluorescent sensors IMPC (cyan-blue-cyan) and IMPC-OH (green-blue-green) is reported for sensing nerve agent simulants diethylcyanophosphonate and diethylchlorophosphate, respectively, with high sensitivity, short response time, and low detection limits. The unique features of these probes are their regeneration with the addition of a green and cheap solvent, namely water in CHCl3, and ease of fabrication into a portable paper-strip system that can also be regenerated. Various spectroscopic studies were employed to understand the mechanism of sensing and regeneration of both probes; the results reveal that water plays a critical role in the hydrolysis of the adduct formed with DCNP and DCP, which enables the retrieval of the probe with its original fluorescence.

Highly sensitive and selective detection of DCP vapors using pyridine-based fluorescent nanofilms

A novel fluorescent nanofilm DBAP-ETTA has been developed for diethyl chlorophosphate (DCP) vapor detection with high sensitivity and selectivity. Its smooth, homogeneous structure and large Stokes shift enable significant fluorescence quenching upon DCP exposure. The protonation-based sensing mechanism makes it ideal for real-time, portable DCP vapor sensing.

A chemodosimetric approach for the visual detection of nerve agent simulant diethyl chlorophosphate (DCP) in liquid and vapour phase

In this work, a novel fluorescent ratiometric switch, 8-((6-(1H-benzo[d]imidazol-2-yl)pyridin-2-yl)methoxy)quinoline (BIPQ), has been introduced for sensing an organophosphorus (OP) chemical vapor threat, diethyl chlorophosphate (DCP), the low-toxic mimic of the real nerve agent sarin (GB). BIPQ is efficient at detecting DCP in both solution and gaseous phase and has potential practical application with high sensitivity and selectivity. The probe shows significant ratiometric emission in the presence of DCP along with a distinct color change from blue to cyan under UV light. The sensing mechanism of the chemodosimeter is based on the generation of a new adduct, BIPQ-DCP, through a nucleophilic substitution reaction with DCP followed by a ring-closure process to form the final product. The detection limit of BIPQ for DCP was determined to be in the order of 10-8 (M) in the liquid state. DFT and TDDFT computational techniques were carried out in order to interpret the electronic properties theoretically.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Recent advances in fluorescent and colorimetric chemosensors for the detection of chemical warfare agents: a legacy of the 21st century

Chemical warfare agents (CWAs) are among the most prominent threats to the human population, our peace, and social stability. Therefore, their detection and quantification are of utmost importance to ensure the security and protection of mankind. In recent years, significant developments have been made in supramolecular chemistry, analytical chemistry, and molecular sensors, which have improved our capability to detect CWAs. Fluorescent and colorimetric chemosensors are attractive tools that allow the selective, sensitive, cheap, portable, and real-time analysis of the potential presence of CWAs, where suitable combinations of selective recognition and transduction can be integrated. In this review, we provide a detailed discussion on recently reported molecular sensors with a specific focus on the sensing of each class of CWAs such as nerve agents, blister agents, blood agents, and other toxicants. We will also discuss the current technology used by military forces, and these discussions will include the type of instrumentation and established protocols. Finally, we will conclude this review with our outlook on the limitations and challenges in the area and summarize the potential of promising avenues for this field.

Pd-Catalyzed cross-coupling synthesis of 4-aryl-3-formylcoumarins

The threefold cross-coupling of triarylbismuth reagents with 4-chloro-3-formylcoumarins furnished the corresponding 4-aryl-3-formylcoumarins in a chemoselective manner with high yields under Pd-catalyzed conditions. This method was successfully applied to electronically different triarylbismuth reagents and 4-chloro-3-formylcoumarins preserving the 3-formyl group in the coumarin scaffold.

A Double-Site Chemodosimeter for Selective Fluorescence Detection of a Nerve Agent Mimic

A novel two-site chemodosimeter (SWJT-4) based on fluorescein skeleton to detect diethyl chlorophosphate (DCP) was designed and synthesized. It is a turn-on fluorescent probe for DCP with good selectivity and obvious color change in aqueous solution. Interestingly, the two oxime groups of SWJT-4 as dual response sites initiated different reactions with DCP to form a cyano group and an isoxazole ring, respectively. The corresponding mechanism was confirmed by 1H NMR, MS and DFT calculation. Moreover, SWJT-4 could be used as a fluorescent test paper to detect DCP vapor.

Imidazole-Functionalized Y-Shaped Push-Pull Dye for Nerve Agent Sensing as well as a Catalyst for Their Detoxification

A Y-shaped push-pull dye (1) with N,N-dimethylanilino donors and a benzonitrile acceptor connected via an imidazole-based π-conjugated spacer was designed. It showed a dark yellow color in solution due to facile intramolecular charge-transfer interaction, but no fluorescence was detected, presumably due to the photo-induced electron transfer effect of the imidazole moiety. However, addition of nerve agents such as diethyl chlorophosphate (DCP, sarin mimic) and diethyl cyanophosphate (DCNP, Tabun mimic) resulted in a blue-colored fluorescence with fading of the native dark yellow color. Mechanistic studies indicated nucleophilic attack of imidazole at the phosphorus of DCP or DCNP, leading to the formation of a phosphorylated intermediate, which undergoes time-dependent hydrolysis (∼24 h) in aqueous medium. This process recovers the free probe (enzyme-like behavior) and releases a less-toxic organophosphate compound as the byproduct. The phosphorylated derivative of 1, formed during such interaction, shows a different electronic behavior, which reduces the extent of charge-transfer interaction as well as nonradiative decay and supports emissive properties. Considering the high sensitivity of 1 towards DCP and DCNP with LOD 35 and 42 ppb, we prepared easy test strips for on-site vapor-phase detection of nerve agents.

"Covalent-Assembly"-Triggered Striking Far-Red to near-Infrared Emitting Fluorescent Probe for Abrupt Detection of Nerve-Agent Mimic (DCP): Real Time Application in Monitoring the Presence of Trace Amounts in Soil and Live Cells

Detection of chemical warfare agents (CWA) by simple and rapid methods with real-sample applications are quite inevitable in order to ease the threats to living systems caused by uncertain terror attacks and wars. Herein we have developed the first far-red to near infra-red (NIR) probe based on a covalent assembly approach for the detection of trace amounts of nerve agent mimic diethyl chloro phosphate (DCP) in soil and their fluorescent bio imaging in live cells. The probe features abrupt fluorescence turn on sensing of DCP with fluorescence quantum yield Φ = 0.622. It senses DCP selectively over other analytes in excellent sensitivity with a detection limit of 6.9 nM. In real time, the probe treated strips were employed to detect the DCP vapor effectively with eye catching fluorescence response. The presence of trace amounts of these acute warfare agents in the environment were monitored by soil analysis. Further fluorescent bio imaging was carried out to monitor trace level DCP in living cells using the HeLa cell line.

Chromo-fluorogenic sensors for chemical warfare agents in real-time analysis: journey towards accurate detection and differentiation

The existence of chemical weapons (blister and nerve agents) is an unfortunate reality of the modern world. The usage of these chemical agents by rogue states or terrorist groups has showcased their ugly faces in the past and even in recent years. Despite extensive and strenuous efforts by the Organization for the Prohibition of Chemical Weapons (OPCW) to eliminate chemical warfare agents (CWAs) by the prohibition of their production and the destruction of their stockpiles, many countries still possess them in enormous quantities. Given the potential threat from these lethal agents, it is imperative to have a foolproof chemical sensor and detection system, which should consist of readily deployable chemical probes that can operate with high specificity and sensitivity. Over the last decade, our group has been engaged in designing and developing novel field-deployable sensing techniques by exploring approaches based on supramolecular tools, which can result in excellent specificity, sensitivity, high speed, portability and low cost. In this article, I describe our group's journey and success stories in the development of chemical warfare detection protocols, detailing the range of unique chemical probes and methods explored to achieve the specific detection of individual agents under real environmental conditions. It is interesting to note that the combination of three molecular probes (SQ, Fc and LH2) could simply achieve the detection of all CWAs at room temperature in one go without the need for nonportable and expensive instruments. The ease and generality of these techniques/methods suggest great promise for the highly specific chemical sensing of almost the entire class of CWAs. In this paper, a brief introduction is first provided to present the basic chemistry related to CWAs and the importance of supramolecular chemistry in the design of new protocols with new insights. The manipulation of molecular probes is then debated towards the development of a system for the chromo-fluorogenic sensing of CWAs without interference from most relevant analytes. Finally, the outlook of open challenges and the future developments of this rapidly evolving field is discussed.

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.

The application of amide units in the construction of neutral functional dyes for mitochondrial staining

To develop a new class of neutral fluorescent dyes with mitochondrial staining capacity, a series of functional dyes were obtained from Nile red (2a–e) and coumarin (3a–e) with different amide compounds via Suzuki coupling reactions.

Bis-heteroleptic Ru(ii) polypyridine complex-based luminescent probes for nerve agent simulant and organophosphate pesticide

Two bis-heteroleptic Ru(ii) complexes of a 4,7-dihydroxy-1,10-phenanthroline ligand were synthesized for the detection of the nerve agent gas mimic, DCP, and the organophosphate pesticide, dichlorvos, through the “off–on” luminescence response.

Luminescent Europium(III) "Turn-On" Sensor for G-Series Chemical Warfare Simulants: A Mechanistic Investigation

A thermodynamically stable terpyridine-dicarboxylate based emissive Eu(III) probe, [Eu(OH-TPDC)] (1), was designed as a time-resolved "turn-on" luminescent probe for the selective sensing of diethyl chlorophosphate (DCP), a G-series nerve agent simulant through modulation of sensitization of ⁵D₀ → ⁷F_J transitions from Eu(III) via quenching of nonradiative vibrational energy transfer.

A naphthalimide-based fluorescent probe for the highly sensitive and selective detection of nerve agent mimic DCP in solution and vapor phase

The fluorescent probe for DCP displays excellent selectivity and sensitivity with a low detection limit of 5.5 nM in DMF.

A Selective Fluorescence Turn-On Probe for the Detection of DCNP (Nerve Agent Tabun Simulant)

Diethylcyanophosphonate (DCNP) is a simulant of Tabun (GA) which is an extremely toxic chemical substance and is used as a chemical warfare (CW) nerve agent. Due to its toxic properties, monitoring methods have been constantly come under the spotlight. What we are proposing within this report is a next-generation fluorescent probe, DMHN1, which allows DCNP to become fully traceable in a sensitive, selective, and responsive manner. This is the first fluorescent turn-on probe within the dipolar naphthalene platform induced by ESIPT (excited state intramolecular proton transfer) suppression that allows us to sense DCNP without any disturbance by other similar G-series chemical weapons. The successful demonstrations of practical applications, such as in vitro analysis, soil analysis, and the development of an on-site real-time prototype sensing kit, encourage further applications in a variety of fields.

A selective diaminomaleonitrile-based dual channel emissive probe for Al3+ and its application in living cell imaging

A selective diaminomaleonitrile-based fluorescent probe for Al³⁺(L) has been synthesized and characterized. The sensing behavior of L towards different metal ions was investigated by fluorescent spectra and competition experiment. The results showed that L exhibited a dual channel emission (λ_em 522 & 558 nm) with yellow fluorescence in the presence of Al³⁺ over other metal ions in EtOH solution. The probe L was bound to Al³⁺ in a 1:2 stoichiometric manner as supported by Job's plot analysis. The binding constant was 9.55 × 10⁸ M^-2 with the detection limit of 10.3 nM. The turn-on response was attributed to the inhibition of PET and CN isomerization after binding with Al³⁺ while the dual emissions were due to ESIPT and ICT processes. In addition, the application of L for imaging Al³⁺ in living Hela cells was achieved.

Facile detection of organophosphorus nerve agent mimic (DCP) through a new quinoline-based ratiometric switch

Here a new quinoline-based (BIMQ) probe was developed which displayed ratiometric detection of organophosphorus chemical vapor threat, DCP.

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.

Triphenylamine–benzimidazole based switch offers reliable detection of organophosphorus nerve agent (DCP) both in solution and gaseous state

Triphenylamine-conjugated imidazole dye acts as a potential sensor for the liquid and vapour phase detection of nerve agent simulantDCP.

A chromogenic and ratiometric fluorogenic probe for rapid detection of a nerve agent simulant DCP based on a hybrid hydroxynaphthalene–hemicyanine dye

A new cyanine dye (CYD) has been synthesized for DCP sensing.

Discrimination of tabun mimic diethyl cyanophosphonate from sarin mimic diethyl chlorophosphate via Zn(ii)-triggered photoinduced electron transfer-decoupled excited state intramolecular proton transfer processes

PET-coupled ESIPT platform and its Zn²⁺ complex are used for the discrimination of the nerve agent mimics DCNP and DCP.