A Pyrene Derived CO2-Responsive Polymeric Probe for the Turn-On Fluorescent Detection of Nerve Agent Mimics with Tunable Sensitivity

Diaminonaphthalene functionalized LUS-1 as a fluorescence probe for simultaneous detection of Hg2+ and Fe3+ in Vetiver grass and Spinach

One of the important problems in the environment is heavy metal pollution, and fluorescence is one of the best methods for their detection due to its sensitivity, selectivity, and relatively rapid and easy operation. In this study, 1,8-diaminonaphthalene functionalized super-stable mesoporous silica (DAN-LUS-1) was synthesized and used as a fluorescence probe to identify Hg2+ and Fe3+ in food samples. The TGA and FT-IR spectra illustrated that 1,8-diaminonaphthalene was grafted into LUS-1. XRD patterns verified that the LUS-1 and functionalized mesoporous silica have a hexagonal symmetrical array of nano-channels. SEM images showed that the rod-like morphology of LUS-1 was preserved in DAN-LUS-1. Also, surface area and pore diameter decreased from 824 m2 g⁻1 and 3.61 nm for the pure LUS-1 to 748 m2 g⁻1 and 3.43 nm for the DAN-LUS-1, as determined by N₂ adsorption-desorption isotherms. This reduction demonstrated that 1,8-diaminonaphthalene immobilized into the pore of LUS-1. The DAN-LUS-1 fluorescence properties as a chemical sensor were studied with a 340/407 nm excitation/emission wavelength that was quenched by Hg2+ and Fe3+ ions. Hg2+ and Fe3+ were quantified using the fluorescence response in the working range 8.25-13.79 × 10-6 and 3.84-10.71 × 10-6 mol/L, with detection limits of 8.5 × 10-8 M and 1.3 × 10-7 M, respectively. Hg2+ and Fe3+ were measured in vetiver grass and spinach. Since the Fe3+ quenching can move in the opposite direction with sodium hexametaphosphate (SHMP) as a hiding compound for Fe3+, consequently, the circuit logic system was established with Fe3+, Hg2+, and SHMP as inputs and the fluorescent quench as the output.

Pyrene-Based "Turn-On" Fluorescent Polymeric Probe with Thioacetal Units in the Main Chain for Mercury(II) Detection in Aqueous Solutions and Living Cells

A water-soluble polymeric pyrene-based polythioacetal (PTA-Py) with thioacetal units in the main chain is simply synthesized by direct polycondensation of 3, 6-dioxa-1, 8-octanedithiol, 1-pyrene formaldehyde, and mPEG2k-SH. The probe PTA-Py shows a good fluorescence response to Hg2+ ions due to the Hg2+-promoted deprotection reaction of thioacetal groups to regenerate the original 1-pyrene formaldehyde compound. After adding Hg2+ to the PTA-Py solution, the fluorescence intensity (FI) gradually increases with increasing concentrations of Hg2+. Compared with other metal ions, the probe exhibits high sensitivity, good selectivity, and rapid response to Hg2+. The low detection limits are 12.3 nm in ethanol-PBS buffer and 13.3 nm in water, respectively. The results imply that the simply synthesized water-soluble polymeric probe had potential applications in the rapid detection of Hg2+ ions in aqueous solutions. Moreover, the polymeric PTA-Py shows high sensitivity for CH3Hg+ with detection limits of 26.5 nm in ethanol/PBS buffer. In addition, PTA-Py can efficiently detect Hg2+ ions in HeLa cells. The results demonstrate that a valuable method is developed for biocompatible polymeric sensors for Hg2+ ions in biological and environmental samples.

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.

Dual Gas-responsive Fluorescent Diblock Copolymer Synthesized via RAFT Polymerization

Stimulus-responsive polymers with luminescence properties have a wide range of applications in the fields of controlled drug release, fluorescent probes, and biological stents. In this paper, carbon dioxide (CO₂)/oxygen (O₂) dual-responsive fluorescent diblock copolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization method with two fluorescent monomers synthesized as its luminescence source, DEAEMA (CO₂ responsive monomer) and tFMA (O₂ responsive monomer). An experimental study demonstrated that the synthesized stimulus-responsive fluorescent polymer had a high sensitivity to CO₂; the double-responsive fluorescent diblock copolymer could form and achieve the reversal of polymer micelles in the aqueous solution when it was sequentially subjected to the introduction of CO₂ and O₂.

Synthesis of Photo, Oxidative, and Reductive Triple-Stimuli-Responsive Block Copolymer Micelles as Nanocarriers for Controlled Release

With the rapid development of nanotechnology, stimuli-responsive nanomaterials have provided an alternative for designing controllable drug delivery systems due to their spatiotemporally controllable properties. The environment of the human body is complex and cancer cells proliferate rapidly; the traditional nanocarriers could not release the loaded drugs sufficiently, and the release level of the drug is not sufficient for the requirement of treatment. Herein, a photoresponsive, glutathione, and reactive oxygen species block copolymer mPEG_2k-ONB-SS-PO-mPEG_2k is prepared by Cu(I)-catalyzed azide-alkyne cycloaddition click polymerization. The ο-nitrobenzyl groups, peroxalate ester bonds, disulfide bonds, and triazole units are regularly and repeatedly arranged in hydrophobic blocks. The photo, oxidative, and reductive responsive characteristics of the copolymers in different conditions were investigated by ultraviolet and visible spectrophotometry, dynamic light scattering, and transmission electron microscopy. Nile Red is encapsulated into the core of micelles as a model drug and exhibits the drug release behaviors in various environments. This research provides a way to design potential drug carriers and a promising platform for efficient intracellular drug delivery in cancer therapy.

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.

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.

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 flavonoid-based fluorescent test strip for sensitive and selective detection of a gaseous nerve agent simulant

Developing fluorescent sensors with ability of monitoring gaseous nerve agents in a sensitive and selective manner is of great importance due to the extreme toxicity and volatility of organophosphorus nerve agents. Herein we reported a novel oxime-modified flavonoid sensor and carefully investigated its sensing behavior towards nerve agent simulants, diethylchlorophosphate (DCP). In the presence of DCP, a remarkable fluorescence enhancement accompanied with emission color change could be observed by naked eyes in solution. The response time was less than 90 s and LOD value was calculated as 0.78 μmol/L in solution. The sensing mechanism could be ascribed to the specific reaction between halophosphate and hydroxyl group of oxime. Furthermore, sensor strips have been successfully constructed by using PEG as matrix with a simple preparation process, and also achieved the sensitive and selective detection of DCP vapor. These results in this study may provide important references for further design of dye-based sensor strips for detection of nerve agents both in solution and gas phase.

Ultrasensitive Detection of Sulfur Mustard via Differential Noncovalent Interactions

In this work, we fabricate two types of hierarchical microspheres, i.e., one coassembled from two fluorene-based oligomers (1 and 2) and one self-assembled from a fluorene-based oligomer (1), for ultrasensitive and selective detection of trace sulfur mustard (SM) vapor. On the basis of distinct fluorescence responses of 1-2 coassembled and individual 1 hierarchical microspheres that originate from differential noncovalent interactions between analytes and these sensors, SM vapor can be ultrasensitively detected (30 ppb) and easily discriminated from various sulfides and other potential interferents. Our work that utilizes differential noncovalent interactions to give sensitive and selective fluorescence response patterns represents a new detection approach for SM and other hazardous chemicals.

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.

Recyclable Polymeric Thin Films for the Selective Detection and Separation of Picric Acid

Thin-film probes have been developed for the reversible detection and separation of picric acid (PA) with extreme sensitivity in aqueous media. The free radical copolymerization of dimethylacrylamide (DMA), benzophenone acrylamide (BPAM), and glycidyl methacrylate (GMA) with a feed ratio of 95:1:4 yielded [p(DMA- co-BPAM- co-GMA)] (P1). P1 was transformed to the final polymeric probe, P2, by a subsequent ring-opening reaction between N-(pyren-1-yl-methyl)propan-1-amine (Py-PA) with the epoxide unit of P1. P2 exhibited rapid and selective sensing properties toward PA in aqueous media via turn-off fluorescence emission. The detection sensitivity was tuned precisely by varying the pH of the solution. After the immobilization of P2 on a quartz slide by spin-coating, followed by exposure to UV light, the resulting film exhibited an attogram-level detection limit toward PA. The photoinduced electron transfer together with an energy-transfer process between PA and the pyrene units of P2 were maximized by the strong π-π stacking of pyrene units of P2, which, in turn, induced rapid exciton energy diffusion. Furthermore, the separation of PA from the mixture of the various nitroaromatic compounds by the P2 film was achieved. Whereas the detection process of PA was reversible and repeatable over multiple cycles, the P2 film could be recycled.

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.

BODIPY-derived multi-channel polymeric chemosensor with pH-tunable sensitivity: selective colorimetric and fluorimetric detection of Hg2+ and HSO4− in aqueous media

A water-soluble BODIPY-containing polymeric chemosensor was synthesized for the selective colorimetric and turn-on fluorimetric detection of Hg²⁺ and HSO₄⁻ ions, respectively, in 100% aqueous media at physiological pH.

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.