The paper deals with the study of the stability of solutions of 5-(2-aminoethyl)dithio-2-nitrobenzoate (ADNB), a chromogenic reagent for thiol detection, in a mixture with butyrylthiocholine iodide, a synthetic analog of the neurotransmitter acetylcholine. The aim of the study was to assess the suitability of these solutions for an enzymatic (cholinesterase-based) method for detecting cholinesterase inhibitors. The core of the study involved evaluating the thermal stability of the solutions at 60 °C over a period of 150 days. The results show that aqueous solutions of the ADNB-substrate mixture retained their original analytical properties after 30 days of thermal stress, with some functionality still observed even after 90 days. Similar results were obtained when 10

This paper presents the results of experiments aiming for the detection and differentiation of selected nerve agents of the Novichok and V-group using simple strip detectors containing colourimetric indicator, specifically chemosensor Nile Blue A, immobilized in cellulose matrix. In all experimental modifications, the contact of the active zone of the strip detector and respective nerve agent excited an immediate development of significant colouration visible to the naked eye. Alkaline solutions containing various hydroxides, carbonates and bicarbonates, and/or chloramine B were used to demonstrate the relevant reaction. The proposed strip detectors indicate a promising approach towards the development of low-cost, easily portable, and usable means of detection of the respective nerve agents.

The significant physiological effect of capsaicinoids on the human body is utilized in the fields of food industry, medicine, and internal state security (riot control agents, RCAs). Detection and determination of capsaicinoids in solutions and extracts are fairly well developed, but only marginal attention is given to their detection in the form of aerosols and vapors, which are the primary form of their use as RCAs. In the article, three variants of a simple tube detector for direct detection of capsaicinoids in air (using pelargonic acid vanillylamide - PAVA, as the standard) are presented, utilizing classical color reactions with Turnbull's blue, Gibbs reagent, and Marquis reagent. The use of these reactions for these purposes is innovative. Each reaction has been optimized and the proposed detectors have been compared, emphasizing their sensitivity, selectivity, and stability. PAVA in the air at a concentration of 0.1 mg/m3 can be detected with the naked eye. The stability of the proposed detectors allows for their commercial use.

The extreme toxicity of nerve agents and the broad spectrum of their physical and chemical properties, enabling the use of these agents in a variety of tactical situations, is a continuing challenge in maintaining the knowledge and capability to detect them, as well as in finding new effective methods. Despite significant advances in the instrumentation of the analysis of nerve agents, relatively simple methods based on the evaluation of colour signals (absorption and fluorescence), in particular those using the cholinesterase reaction, continue to be of importance. This review provides a brief presentation of the current status of these simple methods, with an emphasis on military applications, and illustrates the high interest of the professional community in their further development. At the same time, it also contains some peculiarities (high reliability and durability, resistance to extreme climatic conditions, work in deployed means of protection, low purchase prices, economic availability especially in a state of war, etc.) that the authors believe research and development of simple methods and means for the detection of nerve agents should respect.

The emergence of modern chemical weapons and chemical warfare is traditionally associated with World War I, but the use of poisons in the military has its roots deep in the past. The sources of these poisons have always been natural agents that also served as medicines. This relationship between poison and medicine, and nowadays between chemical warfare and medicine, or between ‘military chemistry’ and pharmacy, appears to be very important for understanding not only the history but also the possible future of both phenomena. This article looks at some historical examples of the use of drugs as chemical weapons and, conversely, the use of chemical weapons as medicines. It seeks to find answers to some questions that are particularly relevant to the implementation of the Chemical Weapons Convention, which aims to achieve a world without chemical warfare.

Here is described a new approach for the simple and rapid detection of 2-chlorobenzylidene malonitrile (CS riot control agent) based on the reaction with isatin (1H-indole-2,3-dione) and, alternatively, with ninhydrin (2,2-dihydroxy-1H-indene-1,3(2H)-dione), both in an environment of ammonium acetate, dimethyl sulfoxide, and dimethylformamide. The method was designed for the preparation of detection tubes for air analysis, test strips for the analysis of liquid samples, and for spectrophotometric determination. The use of ninhydrin appears to be more sensitive, but isatin provides higher stability and practical applicability.

The use of a cellulose detection film as a carrier for a colorimetric sensor to detect phosgene and allied compounds to be evaluated primarily visually is studied. For the case study, a benzimidazole-rhodamine dye and an acetyl cellulose film were selected. The detection complex was modified using cyclic ether 18-crown-6 to achieve more desirable analytic properties. The chromatic properties of detection film was verified using reflectance colorimetry in the visible light spectrum. The employed detection agent demonstrated high sensibility to phosgene vapours, but acid gases, acyl chlorides, base organic solvents, and in higher concentrations, even some organophosphorus substances interfered. The detection film application was adjusted to the in-situ preparation of simple detection devices (a spray or a marker) as well as to manufacture detection strips with beforehand excluded polymer film.

Pharmaceutical technology offers various dosage forms that can be applied interdisciplinary. One of them are spherical pellets which could be utilized as a carrier in emerging second-generation detection tubes. This detection system requires carriers with high specific surface area (SSA), which should allow better adsorption of toxic substances and detection reagents. In this study, a magnesium aluminometasilicate with high SSA was utilized along with various concentrations of volatile substances (menthol, camphor and ammonium bicarbonate) to increase further the carrier SSA after their sublimation. The samples were evaluated in terms of physicochemical parameters, their morphology was assessed by scanning electron microscopy, and the Brunauer–Emmett–Teller (BET) method was utilized to measure SSA. The samples were then impregnated with a detection reagent o-phenylenediamine-pyronine and tested with diphosgene. Only samples prepared using menthol or camphor were found to show red fluorescence under the UV light in addition to the eye-visible red-violet color. This allowed the detection of diphosgene/phosgene at a concentration of only 0.1 mg/m3 in the air for samples M20.0 and C20.0 with their SSA higher than 115 m2/g, thus exceeding the sensitivity of the first-generation DT-12 detection tube.

BACKGROUND Maintaining the stability of an immobilized enzyme during storage is generally very problematic. However, various substances have been reported to have a positive effect on enzyme stability. These include reducing disaccharide lactose, which is used in carriers in the form of pellets with immobilized cholinesterase. These carriers serve as a filling for detection tubes (biosensor), which are used for detecting nerve agents, wherein the detection itself is based on a colorimetric Ellman's reaction. To date, however, no study has been performed on the effect of different types of lactose monohydrate on the properties of such carriers. RESULTS The effect of five different types of lactose monohydrate on carrier properties and enzyme stability was examined. The lactose powders used differed in the particle size distribution, shape, compactability and flowability. The carriers were prepared in triplicate and subjected to a 24-month stability test under three storage conditions, with the results being statistically analyzed by analysis of variance, principal component analysis and t-test. Samples containing lactose with spherical particles were more resistant to degradation by heat and moisture than samples containing crystalline particles; in addition they had higher hardness and better sensitivity. All samples were also tested with soman after 24 months of storage and were found to retain very good sensitivity. CONCLUSION Samples containing spherical types of lactose proved to be more stable in some critical parameters compared to the samples with lactose in the form of single crystals, which are currently used in commercially available detection tubes. (c) 2021 Society of Chemical Industry (SCI).

Pellets with an immobilized enzyme (acetyl- or butyrylcholinesterase) are the up-to-date type of carriers used for the detection of nerve agents (soman, sarin, tabun, VX, Novichok) and other cholinesterase inhibitors such as organophosphate and carbamate insecticides (parathion, malathion). They are used in the glass detection tubes as a layer containing the enzyme together with the second layer, which contains a colorimetric reagent and substrate. The detection method is based on the visually or spectrophotometrically observable Ellman's reaction, which develops a yellow color in the absence of the cholinesterase inhibitor; otherwise, the detector preserves its original color (preferably white). This reaction occurs very fast and has a high sensitivity to nerve agents but it suffers from an indistinctive color transition from white to yellow. In the presented study, a new approach with the use of the synergic effect of magnesium aluminometasilicate with a high surface area marketed as Neusilin®US2 and a protective semipermeable Eudragit® RL layer was utilized. The prepared pellets have been evaluated for their properties such as the activity of the enzyme, intensity of the developed yellow color, sensitivity to cholinesterase inhibitor physostigmine, which acts as a nerve agent simulant, and physical parameters such as hardness, pycnometric density and sphericity. After the initial evaluation, all samples underwent a stability test under three different storage conditions for 24 months during which they were evaluated at given time points (0, 3, 6, 12 and 24 months). It was found that the prepared samples achieved a much higher intensity of developed yellow color than in the published studies while maintaining similar or better sensitivity, speed of detection and suitable physico-chemical properties.

We have developed a second-generation detection tube for colorimetric and fluorescence detection of phosgene and diphosgene in air. The tube is packed with pellets made of a mixture of microcrystalline cellulose and magnesium aluminum metasilicate treated with a suitable monoterpene (camphor, menthol) to increase porosity and specific surface area. We impregnated the pellets with a specific o-phenylenediamine-pyronin (PY-OPD) based reagent. The detector with this novel indication charge enables phosgene or diphosgene to be selectively and sensitively detected at concentrations lower than as would those posing acute health risk. Owing to the analytical colorimetric and, at the same time, fluorescence signal, the detector is very robust while featuring good sensitivity and variability. The colorimetric limits of detection were 0.3 mg/m(3) (tristimulus colorimeter), resp. 5 mg/m(3) (with the naked eye), fluorescence detection limits of 0.3 mg/m(3) (with the naked eye), all at an air sample volume of 1 dm(3). The response was practically immediate, acid vapors and gases, or diethyl chlorophosphate as a simulant of nerve warfare chemical agents, were disruptive.

Currently, nerve agents are often used in terrorist attacks or assassinations. In such cases, it is necessary to detect them quickly, accurately and easily right in the field. Detection tubes, which are small devices containing pellets with immobilized cholinesterase and detection reagents, meet these conditions. Their detection mechanism is based on a highly sensitive enzymatic Ellman reaction, when in the absence of cholinesterase inhibitors the pellets develop a visible yellow color, whereas in their presence the carriers retain the original color. The rate of reaction, its sensitivity and the distinct color transition are the key points of the research. In this experiment, double-coated pellets were prepared. The first coating contained the butyrylcholinesterase immobilized in hypromellose, while the second coating consisted of ethylcellulose and triethyl citrate. Based on the properties of such carriers, samples containing lactose dispersed in the ethylcellulose coating were also prepared, which was expected to have an effect on increasing the permeability of the coating and hence the detection rate and color intensity. In addition to selected physicochemical properties, carriers were evaluated for enzyme activity, sensitivity and color transition intensity. Samples showing the best properties were subjected to a 24-months stability test at three different temperatures and humidity.

Detection tubes are small devices for the colorimetric enzymatic detection of cholinesterase inhibitors such as sarin, soman, VX nerve agents and substances denoted as Novichok. These detectors contain carriers in the form of pellets with immobilized cholinesterase, substrate and detection reagent. Their advantages are portability, sensitivity and simplicity, enabling fast detection of such compounds from air and water in case of a terrorist attack or war. In general, maintaining the stability of an enzyme for a longer time is very problematic; therefore, its further enhancement is required for safety and financial reasons. In this study, the stability of our patented carriers in the form of pellets with immobilized butyrylcholinesterase containing an increasing amount of the unique sorbent Neusilin® US2 was evaluated. The samples containing Neusilin maintained the stability of the immobilized enzyme for a longer time even at higher temperature and humidity than the currently commercially used carrier without Neusilin, allowing improved detection of nerve agents.

The paper presents the results of the study of the possibilities of using color metal complexes to detect the presence of chemical warfare agents (CWA) in liquid or aerosol form. Aluminon/Fe3+ and Eriochrome Cyanine R/Cu2+ coordination complexes and their ability to detect CWA in liquid phase are discussed. Detection systems have been demonstrated on instances of simple detection papers exposed to drops of real CWAs. Detection papers showed a positive response to G-series nerve agents and vesicant lewisite. Other liquid CWA do not interfere and the systems are also resistant to common organic solvents and a wide range of industrial chemicals.

This work provides a summary of our results in the area of the experimental development of detection paper for the detection of liquid phase chemical warfare agents (drops, aerosol), the presence of which is demonstrated by the development of characteristic coloring visible to the naked eye. The basis of the detection paper is a cellulose carrier saturated with the dithienobenzotropone monomer (RM1a)–chromogenic chemosensor sensitive to nerve agents of the G type, blister agent lewisite, or choking agent diphosgene. We achieve a higher coloring brilliance and the limit certain interferences by using this chemosensor in the mix of the o-phenylendiamine-pyronine (PY-OPD). We prove that the addition of the Bromocresol Green pH indicator even enables detection of nerve agents of the V type, or, nitrogen mustards, while keeping a high stability of the detection paper and its functions for other chemical warfare agents. We resolve the resistance against the undesirable influence of water by providing a hydrophobic treatment of the carrier surface.

This paper deals with the innovation of the Czech colorimetric biosensor Detehit designed for the simple, fast, and sensitive detection of nerve agents. The innovation is based on the use of an indicator consisting of a mixture of two triphenylmethane dyes, Guinea green B and a basic fuchsin, on a glass nanofiber filter paper carrier. The advantage of this solution is the blue-red color transition, which is much more visible than the white-yellow transition of other Detehit biosensors. The newly designed biosensor allows the users to visually detect (with the naked eye) the presence of the most significant paralytic substances (sarin, soman, cyclosarin, tabun, VX) in water at concentrations of at least 0.001 μg/mL. This biosensor design also enables one to detect these substances in air or on contaminated surfaces.

We propose a new method of spectrophotometric determination of o -chlorobenzylidene malononitrile (CS riot control agent) in solid samples of various origins and compositions (soil, brickwork, silica gel, glass wool). The method is based on colouring reaction of malononitrile with Ellman’s reagent in the presence of ammonium acetate as a catalyst. The reaction proceeds in a non-aqueous medium. The analysis takes place in an aprotic solvent N,N -dimethylformamide, which is also an extraction reagent. A detection limit is 0.18 μg mL-1, calibration curve is linear in the range of 0.34 – 10.20 μg mL-1. The method is suitable for an analysis in laboratory as well as in field conditions.

Cholinesterase inhibitors are widely used as pesticides in agriculture, but also form a group of organophosphates known as nerve chemical warfare agents. This calls for close attention regarding their detection, including the use of various biosensors. One such biosensor made in the Czech Republic is the Detehit, which is based on a cholinesterase reaction that is assessed using a colour indicator-the Ellman's reagent-which is anchored on cellulose filter paper together with the substrate. With the use of this biosensor, detection is simple, quick, and sensitive. However, its disadvantage is that a less pronounced yellow discoloration occurs, especially under difficult light conditions. As a possible solution, a new indicator/substrate carrier has been designed. It is made of glass nanofibres, so the physical characteristics of the carrier positively influence reaction conditions, and as a result improve the colour response of the biosensor. The authors present and discuss some of the results of the study of this carrier under various experimental conditions. These findings have been used for the development of a modified Detehit biosensor.

The enzyme immobilization is a very important process providing an attachment of the enzyme to a certain type of the carrier. This allows to maintain the enzyme activity during the storage and it also simplifies the detection procedure. When designing a new detector based on the enzymatic reaction, the proper immobilization method must be chosen depending on the advantages and disadvantages of the available methods of immobilization. Examples of immobilization method for colorimetric detection include, e.g., adsorption to the insoluble carrier, covalent bonding, attachment to ion exchangers, incorporation into gels and foams, immobilization in the form of crosslinked aggregates or nanostructures or with the utilization of antibodies.

The main objective of the presented research was to prepare an innovative carrier as a filler for detection tubes in the form of double-coated pellets with a very significant color transition during the detection of cholinesterase inhibitors such as nerve agents, organophosphorus or carbamate insecticides in liquids that is observable visually and also spectrophotometrically at 412 nm. The pellet cores were prepared by the extrusion/spheronization method. Consecutively, two different coats were applied on the pellet cores in the coating device using the Wurster column method. To increase the color change intensity, the second semipermeable coat based on Eudragit (R) RL was applied on top of the first coat, which was formed by butyrylcholinesterase immobilized in hydroxypropyl methylcellulose. Prepared samples differing in thickness of the second coat were evaluated for their quality parameters, enzymatic activity and inhibition. The detection mechanism was based on the standard Ellman's colorimetric reaction. It was observed that the semipermeable coat prevented leaching of the enzyme into the solution and led to an increased intensity of color transition from white - yellow to white - deep yellow/orange, thus enabling a more accurate visual detection. This system allows easy, rapid and safe identification of cholinesterase inhibitors in liquids, especially chemical warfare agents. (C) 2018 Elsevier B.V. All rights reserved.