Smart Sensing of Nerve Agents

The recent international scenario highlights the importance to protect human health and environmental quality from toxic compounds. In this context, organophosphorous (OP) Nerve Agents (NAs) have received particular attention, due to their use in terrorist attacks. Classical instrumental detection techniques are sensitive and selective, but they cannot be used in real field due to the high cost, specialized personnel requested and huge size. For these reasons, the development of practical, easy and fast detection methods (smart methods) is the future of this field. Indeed, starting from initial sensing research, based on optical and/or electrical sensors, today the development and use of smart strategies to detect NAs is the current state of the art. This review summarizes the smart strategies to detect NAs, highlighting some important parameters, such as linearity, limit of detection and selectivity. Furthermore, some critical comments of the future on this field, and in particular, the problems to be solved before a real application of these methods, are provided.

Cortisol sensing by optical sensors

During a stress condition, the human body synthesizes catecholamine neurotransmitters and specific hormones (called "stress hormones"), the most important of which is cortisol. The monitoring of cortisol levels is extremely important for controlling the stress levels. For this reason, it has important medical applications. Common analytical methods (HPLC, GC-MS) cannot be used in real life due to the bulkiness of the instruments and the necessity of specialized operators. Molecular probes solve this problem. This review aims to provide a description of recent developments in this field, focusing on the analytical aspects and the possibility to obtain real practical devices from these molecular probes.

Supramolecular Detection of a Sub-ppm Nerve Agent Simulant by a Smartphone Tool

The widespread use of smartphones and related tools is extending their applications in several fields. Herein, we report a reusable smartphone coupled portable detection system for the sensing of sub-ppm level of a nerve agent mimic (dimethylmethylphosphonate) in the gas phase. The detection system is based on multiple hydrogen-bond interactions of the vapor analyte with an ad-hoc functionalized Bodipy chromophore scaffold. The multitopic approach used for the molecular recognition of DMMP leads to the highest binding constant values, high selectivity, and low limits of detection.

Smartphone-Based Dopamine Detection by Fluorescent Supramolecular Sensor

Supramolecular recognition of dopamine by two quinoxaline cavitands was studied in solution by fluorescence titrations, ESI-MS and ROESY measurements. In addition, the tetraquinoxaline cavitand was dropped onto a siloxane-based polymeric solid support, obtaining a sensor able to detect dopamine in a linear range of concentrations 10 Mm-100 pM, with a detection limit of 1 pM, much lower than the normal concentration values in the common human fluids (plasma, urine and saliva), by using a simple smartphone as detector. This sensor shows also good selectivity for dopamine respect to the other common analytes contained in a saliva sample and can be reused after acid-base cycles, paving the way for the realization of real practical sensor for human dopamine detection.

Photonic Liquid Crystal Polymer Absorbent for Immobilization and Detection of Gaseous Nerve Agent Simulants

Detection and sequestration of chemical warfare agents (CWAs), such as poisonous organophosphates, are highly desirable for both personal security and environmental protection. However, both sensing and absorption in a single device have been rarely reported. In this study, we describe a photonic absorbent based on a cholesteric liquid crystal polymer as a dual sensing and decontamination device for gas-type CWAs. Dimethyl methylphosphonate (DMMP) was used as a simulant compound. A blue reflective photonic polymer was fabricated that was able to detect DMMP vapor through absorption. Hydrogen bond interactions between DMMP and mesogenic carboxylic groups of the polymer allow selectivity and capture. A distinct optical change of the film from blue to bright green indicates the absorption of DMMP vapor molecules and confirms when full absorption of the polymer is achieved. The diffusion of DMMP vapor into the material was observed by the formation of a sharp boundary between swollen and unswollen material, as evidenced by scanning electron microscopy images and the structural color changes. In ambient conditions, DMMP molecules are retained in the photonic absorbent without release to the environment. Heating above approximately 60 °C releases the absorbed DMMP, leading to a reusable optical device. These results confirm the ability of photonic polymers to sense and immobilize dangerous vapor, paving the way for the realization of simple, battery-free optical devices able to simultaneously warn and protect.

Rapid detection of nerve agents in environmental and biological samples using a fluorescent probe

Nerve agents are highly toxic chemical warfare agents that are easy to synthesize and have recently been applied many times in local wars and terrorist attacks. Fluorescent probes have been widely used in life science and medical research due to their features of short reaction time, high sensitivity and good selectivity. Herein, two fluorescent compounds, NMU-1 and NMU-2, were synthesized for the selective detection of nerve agents. NMU-1 exhibited good detection performance for nerve agents. With increasing nerve agent concentration, the fluorescence signal of NMU-1 at 498 nm gradually decreased with an excellent linear relationship. NMU-1 exhibited a low LOD (4.6 μM for DCP and 8.41 μM for soman), a rapid response (less than 3 min) and a large Stokes shift (98 nm) along with obvious color changes. Due to its high sensitivity and good selectivity, NMU-1 was successfully applied to image nerve agents in living PC12 cells. Furthermore, NMU-1 was used as a key element to develop chemical warfare agent test paper, which exhibited significant fluorescent changes under hand-held 365-nm UV light upon contact with nerve agents.

Agile Detection of Chemical Warfare Agents by Machine Vision: a Supramolecular Approach

The supramolecular detection by image analysis of a simulant chemical warfare agent on a solid device containing a selective molecular sensor based on a BODIPY scaffold is reported. The recognition properties were investigated in solution, demonstrating high affinity (log K 6.60) and sensitivity (LOD 10 ppt). A test strip also confirmed the sensing properties in gas phase. Image analysis of the solid device allows quantitative information about the simulant to be obtained, recovering the sensor almost 5 times and thus confirming the goal of the supramolecular approach.

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.

A [15]paracyclophenone and its fluorenone-containing derivatives: syntheses and binding to nerve agent mimics via aryl-CH hydrogen bonding interactions

A [1₅]paracyclophenone and its fluorenone-containing derivatives were synthesized. The novel macrocyclic host I binds nerve agent mimics through the ‘non-traditional’ aryl-CH hydrogen bonding interactions.

Light-up photoluminescence sensing of a nerve agent simulant by a bis-porphyrin–salen–UO2 complex

A luminescent bis-porphyrin–salen–UO₂ complex, showing a significant fluorescence light-up response upon reacting with DMMP (a simulant of nerve agents), is reported. The fluorescence change of this complex by excitation at 365 nm can be clearly observed with the naked eye, and this complex was successfully employed to construct a test paper to detect nerve agents.

The exposure of a nerve agent simulant to a fluorogenic sensor results in a significant increase in fluorescence response, allowing the construction of a paper test for the naked-eye detection of DMMP.

Supramolecular Sensing of a Chemical Warfare Agents Simulant by Functionalized Carbon Nanoparticles

Real-time sensing of chemical warfare agents by optical sensors is today a crucial target to prevent terroristic attacks by chemical weapons. Here the synthesis, characterization and detection properties of a new sensor, based on covalently functionalized carbon nanoparticles, are reported. This nanosensor exploits noncovalent interactions, in particular hydrogen bonds, to detect DMMP, a simulant of nerve agents. The nanostructure of the sensor combined with the supramolecular sensing approach leads to high binding constant affinity, high selectivity and the possibility to reuse the sensor.

Catalytic Degradation of Nerve Agents

Nerve agents (NAs) are a group of highly toxic organophosphorus compounds developed before World War II. They are related to organophosphorus pesticides, although they have much higher human acute toxicity than commonly used pesticides. After the detection of the presence of NAs, the critical step is the fast decontamination of the environment in order to avoid the lethal effect of these organophosphorus compounds on exposed humans. This review collects the catalytic degradation reactions of NAs, in particular focusing our attention on chemical hydrolysis. These reactions are catalyzed by different catalyst categories (metal-based, polymeric, heterogeneous, enzymatic and MOFs), all of them described in this review.

Challenges in Fluorescence Detection of Chemical Warfare Agent Vapors Using Solid-State Films

Organophosphorus (OP)-based nerve agents are extremely toxic and potent acetylcholinesterase inhibitors and recent attacks involving nerve agents highlight the need for fast detection and intervention. Fluorescence-based detection, where the sensing material undergoes a chemical reaction with the agent causing a measurable change in the luminescence, is one method for sensing and identifying nerve agents. Most studies use the simulants diethylchlorophosphate and di-iso-propylfluorophosphate to evaluate the performance of sensors due to their reduced toxicity relative to OP nerve agents. While detection of nerve agent simulants in solution is relatively widely reported, there are fewer reports on vapor detection using solid-state sensors. Herein, progress in organic semiconductor sensing materials developed for solid-state detection of OP-based nerve agent vapors is reviewed. The effect of acid impurities arising from the hydrolysis of simulants and nerve agents on the efficacy and selectivity of the reported sensing materials is also discussed. Indeed, in some cases it is unclear whether it is the simulant that is detected or the acid hydrolysis products. Finally, it is highlighted that while analyte diffusion into the sensing film is critical in the design of fast, responsive sensing systems, it is an area that is currently not well studied.

Supramolecular recognition of phosphocholine by an enzyme-like cavitand receptor

The first example of supramolecular recognition of phosphocholine by a cavitand receptor has been reported here. The chemical structure of the receptor has been optimized by DFT calculations. The recognition mechanism is based on a "multi-topic approach", which leads to highly efficient (K value up to 10⁷ M^-1), selective and sensitive (ppb level) sensing of phosphocholine. The recognition mechanism proposed here is similar to those exploited by Nature, and paves the way for the realization of new sensors with important applications in medicine and security fields.

Supramolecular Detection of a Nerve Agent Simulant by Fluorescent Zn-Salen Oligomer Receptors

We report on new Zn-Salen oligomer receptors able to recognize a nerve agent simulant, namely dimethyl methylphosphonate (DMMP), by a supramolecular approach. In particular, three Zn-Salen oligomers (Zn-Oligo-A, -B, and -C), differing by the length distribution, were obtained and characterized by NMR, Gel Permeation Chromatography (GPC), UV-Vis, and fluorescence spectroscopy. Furthermore, we investigated their recognition properties towards DMMP by using fluorescence measurements. We found that the recognition ability depends on the length of the oligomeric chain, and the Zn-Oligo-C shows a binding constant value higher than those already reported in literature for the DMMP detection.