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.

A chemodosimetric chemosensor for the ratiometric detection of nerve agent-mimic DCP in solution and vapor phases

Nerve agents are among the most deadly and lethal chemical warfare agents (CWAs). Rapid identification is crucial for specialized individuals to take action against dangerous drugs. This paper describes the synthesis and characterisation of a probe (MNFZ) based on the methoxy naphthalene-furoic hydrazide group. The probe rapidly (100 s) detects and quantifies the nerve-agent simulant diethyl chlorophosphate (DCP) in both solution and vapor phases. This sensor uses a new recognition center, furoic hydrazide, where the nitrogen atom of the imine group (CN) attacks the electrophilic core phosphorus atom of DCP, followed by the hydrolysis of the imine group in the acetonitrile (ACN) solution to produce the corresponding aldehyde MNPA. The development of ICT character resulted in a distinct red-shifted ratiometric fluorescence response to DCP, with a very low limit of detection (12.2 nM). The probe is an efficient chemosensor due to its high selectivity over other organophosphorus compounds as well as its chemical stability across a wide pH range. DFT calculations, 1H NMR and HRMS were performed to finalize the sensing mechanism. Lastly, the as-designed sensor was successfully used to build a highly sensitive portable kit in test strips and a cotton biopolymer for simple and safe real-time monitoring of DCP.

Zirconium-based metal-organic framework loaded agarose hydrogels for fluorescence turn-on detection of nerve agent simulant vapor

Developing reliable sensors that accurately detect deadly chemical gases is critical to global security. Nerve agents are one of the most dangerous chemicals in the world and are often found in gaseous forms in the environment, which remain a challenge to detect because of their low levels. In this paper, a fluorescent probe based on a Zr-based metal-organic framework UiO-66-NH2 was proposed. The specific binding between the Zr-O site of UiO-66-NH2 and diethyl chlorophosphate (DCP) blocked the ligand-to-metal charge transfer (LMCT) process in UiO-66-NH2, thereby enabling the fluorescence turn-on detection of DCP. More importantly, a simple and portable hydrogel soft-solid platform (UiO-66-NH2@Aga) was constructed by incorporating UiO-66-NH2 into the formation process of agarose (Aga) hydrogel for fast and sensitive detection of gaseous DCP. When the hydrogel was exposed to a low concentration of DCP vapor, its fluorescence changed from colorless to bright blue, allowing visualization of the DCP gas for analysis. The UiO-66-NH2@Aga integrated solid-state platform showed an excellent response to DCP vapor in the detection range of 1.98 to 9.90 ppm and with a detection limit of 1.16 ppm. This work opened up a unique way to design a convenient, low cost and practical gas physical examination platform.

Visual and Rapid Detection of Nerve Agent Mimics in Gas and Solution Phase by a Simple Fluorescent Probe

Chemical nerve agents are highly toxic organophosphorus compounds that are easy to obtain and can be utilized by terrorists to threaten homeland security and human safety. Those organophosphorus nerve agents contain nucleophilic ability that can react with acetylcholinesterase leading to muscular paralysis and human death. Therefore, there is great importance to explore a reliable and simple method to detect chemical nerve agents. Herein, the o-phenylenediamine-linked dansyl chloride as a colorimetric and fluorescent probe has been prepared to detect specific chemical nerve agent stimulants in the solution and vapor phase. The o-phenylenediamine unit serves as a detection site that can react with diethyl chlorophosphate (DCP) in a rapid response within 2 min. A satisfied relationship line was obtained between fluorescent intensity and the concentration of DCP in the range of 0-90 μM. In the optimized conditions, we conducted the fluorescent titration to measure the limits of detection (0.082 μM) with the fluorescent enhancement up to 18-fold. Fluorescence titration and NMR studies were also conducted to explore the detection mechanism, indicating that the formation of phosphate ester causes the intensity of fluorescent change during the PET process. Finally, probe 1 coated with the paper test is utilized to detect DCP vapor and solution by the naked eye. We expect that this probe may give some admiration to design the small molecule organic probe and applied in the selectivity detection of chemical nerve agents.

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.

Novel metal enhanced dual-mode fluorometric and SERS aptasensor incorporating a heterostructure nanoassembly for ultrasensitive T-2 toxin detection

Fluorescent gold (Au) nanostructures have emerged as burgeoning materials to fabricate nanomaterial assemblies which play a vital role in improving the detection sensitivity and specificity for various biomolecules. In this work, a fluorescence labelled (Rhodamine-B-Isothiocyanate) silica shell with Au metal core (AuNPs@PVP@RITC@SiO₂) and a graphene-Au nanostar nanocomposite (rGO-AuNS) are presented as a metal enhanced fluorescence (MEF) material and Raman signal enhancer, respectively. Their composite (AuNPs@PVP@RITC@SiO₂NPs/rGO-AuNS) was employed as a dual-mode fluorescence (FL) and surface-enhanced Raman scattering (SERS) nanoprobe for selective and sensitive detection of T-2 toxin. To comprehend the dual-modality, a core-shell nanostructure, AuNPs@PVP@RITC@SiO₂, was functionalized with an aptamer (donor) and adsorbed on the surface of rGO-AuNS through electrostatic forces and π-π stacking which act as a FL quencher and SERS signal enhancer. When exposed to T-2 toxin, the apt-AuNPs@PVP@RITC@SiO₂NPs move away from the surface of rGO-AuNS, resulting in the restoration of FL and reduction of the SERS signal. There was distinct linearity between the T-2 toxin concentration and the dual FL and SERS signals with lower limits of detection (LOD) of 85 pM and 12 pM, as compared to the previous methods, respectively. The developed FL and SERS aptasensor presented excellent recovery ratio and RSD in wheat and maize, respectively, as compared with the standard ELISA method. The complementary performances of the developed stratagem revealed a high correlation between the FL and SERS sensing modes with exquisite detection properties.

Array-based chemical warfare agent discrimination via organophosphorus-H2O2 reaction-regulated chemiluminescence

It has been a challenge to achieve rapid, simple, and effective discrimination of organophosphorus nerve agents (typical chemical warfare agents) due to the similar chemical properties of the targets such as sarin, soman, cyclosarin and VX. In this study, we propose a chemiluminescence sensor array that can effectively discriminate organophosphorus nerve agents by organophosphorus-H₂O₂ reaction, which produces peroxyphosphonate intermediate and regulates the chemiluminescence intensity. A simple chemiluminescence sensor array based on different chemiluminescence characteristics of the four organophosphorus nerve agents in the luminol–H₂O₂ system and layered double hydroxide–luminol–H₂O₂ system has been constructed. Four agents can be well distinguished at a concentration of 1.0 mg L⁻¹ when linear discriminant analyses and hierarchical cluster analyses are smartly combined. The high accuracy (100%) evaluation of 20 blind samples demonstrates the practicability of this proposed chemiluminescence sensor array.

A chemical warfare agent sensor array based on organophosphorus-H₂O₂ reaction-regulated chemiluminescence is proposed.

Chain length effect of spiro-ring N-alkylation on photophysical signalling parameters in Fe(III) selective rhodamine probes

Manifestation of photophysical signalling parameters in rhodamine derivatives exhibiting complexation induced spiro-ring opening is crucial for the realization of selective metal ion detection at trace levels. Substitution of various functional groups, such as alkylation to the core architecture, modulates the physico-chemical properties of such molecular probes. Despite a few studies, relationships between the extent of photophysical signal modulations and the chain lengths of n-alkyl substituents are still elusive. In this investigation, a few molecular probes based on the rhodamine B (1-5) and rhodamine 6G (6-10) platform were synthesized by their derivatization with n-alkyl substituents of varying chain lengths at the amino-donor of their spiro-ring end, which exhibited Fe(III)-selective absorption and fluorescence 'off-on' signal transduction along with colorization of solution. The Fe(III)-selectivity in these probes remained the same despite their structural distinctions through varied n-alkyl chain lengths of the substituents; however, the quantifiable signalling parameters such as spectroscopic enhancement factors, sensitivity, the kinetics of spiro-ring opening and effectiveness of probe-Fe(III) interactions were analyzed. These parameters were also correlated in terms of the influence of different chain lengths of n-alkyl substituents that efficiently contributed to their inter-componential interactive stereo-electronic environment.

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.