An ESIPT-Based Fluorescence Probe for Colorimetric, Ratiometric, and Selective Detection of Phosgene in Solutions and the Gas Phase

Amine-Imine Tautomeric Excited State Intramolecular Proton Transfer in Metal-Organic Frameworks: Alcohol and Anion Recognition

To study the amine-imine tautomeric alteration through excited state intramolecular proton transfer (ESIPT), three amine-functionalized metal-organic frameworks (MOFs) have been synthesized by using two different metal ions and neutral linkers along with same ESIPT-enable anionic linker through the slow diffusion process. All the MOFs have 2D structure with asymmetric units of {[Mn(2,6-dip)(2-atp)](H2O)(CH3OH)}n (1), {[Mn(3,5-dip)(2-atp)](solvent)x}n (2) and {Zn2(3,5-dip)2(2-atp)(μ2-O2-)](solvent)x}n (3) (where 2,6-dip=2,6-di(1H-imidazol-1-yl)pyridine, 3,5-dip=3,5-di(1H-imidazol-1-yl)pyridine, 2-atp=2-amino terephthalic acid). The 2D networks of desolvated form of compound 1, 2, and 3 show water influencing proton transfer for amine-imine tautomerism in excited state through the ionic interaction with water molecules to the frameworks. However, in case of polar small chain aliphatic alcohols like methanol, ethanol and isopropanol; the compounds do not show any dual emissive ESIPT but exhibit three different intensified single peaks for each of the compounds. This different emission intensity in presence of different alcohols are helpful to detect these alcohols selectively. In addition to that in case of all three compounds, the water assisted-ESIPT is interrupted by some strong oxidizing agents like CrO4 2-, Cr2O7 2- and MnO4 - ions. This phenomenon allows the method of detection for the aforesaid oxidizing ions in water by interruption of the dual emissive fluorescence.

A simple AIE-based indole-benzimidazole probe for the ratiometric fluorescent detection of phosgene in an almost neat aqueous solution

Phosgene is a suffocating toxic gas that seriously threatens human health and public security. With this research, we developed a simple ratiometric fluorescent probe (1) bearing indole and benzimidazole moieties as the sensing sites and employed it for the aggregation-induced emission-based (AIE-based) detection of phosgene. It was the first time that the probe could detect phosgene in an almost pure aqueous solution (fw = 99.5 %). Probe 1 had AIE-activity, and the maximum emission peak was 392 nm with increasing water fraction (0-99.5 %). When reacting with phosgene, the emission peak at 392 nm gradually decreased, while a new peak appeared at 449 nm and continued to increase with increasing water fraction (0-99.5 %). Probe 1 exhibited a rapid response toward aqueous phosgene with high selectivity and sensitivity (limit of detection being 23.8 nM). Additionally, we fabricated 1-loaded test strips for gas phosgene detection, enabling dual-channel detection under 245 nm and 365 nm hand-held UV lamps. Finally, this probe was used to monitor phosgene in bionic samples.

Tailored BODIPY-based fluorogenic probes for phosgene detection: a comparative evaluation of recognition sites

We constructed two novel boron-dipyrromethene (BODIPY)-based fluorescent probes, BOPD and BOBA, each equipped with the phosgene specific recognition units o-phenylenediamine (OPD) and o-aminobenzylamine (OBA) at the 2-position of the BODIPY core. BOPD and BOBA represent rare examples of BODIPY-based probes that operate by modulating an intramolecular charge transfer process (ICT), as validated by computational studies. We systematically compared the analytic performance of those recognition units while focusing on selectivity, fluorescence turn-on ratios and response times. Probe BOBA, equipped with OBA as the recognition unit, demonstrated a remarkably low detection limit (i.e., 1.40 nM) and a rapid response time (<10 s) for triphosgene. By comparison, BOPD, featuring an OPD unit, showed superior selectivity towards triphosgene, with a detection limit of 93 nM and a response time of up to 30 s. A portable sensing platform was developed by loading BOPD onto test strips made of TLC plates, nonwoven materials and small-headed cotton swabs, which were assessed for their effectiveness in detecting phosgene. We additionally performed the first successful application of a fluorescent probe, namely BOPD, for monitoring the accumulation of phosgene in plants.

A highly sensitive and colorimetric fluorescent probe for visualizing hydroxylamine in immune cells

BACKGROUND

Hydroxylamine (HA) is vital industrial raw material and pharmaceutical intermediate. In addition, HA is an important cellular metabolite, which is intermediate in the formation of nitric oxide and nitroxide. However, excessive amounts of HA are toxic to both animals and plants. Conventional methods for the detection of HA are cumbersome and complicated. The detection of HA with fluorescent probes is convenient and sensitive. There are few probes available for the detection of hydroxylamine. Therefore, a fluorescent probe for the sensitive and selective detection of HA was developed in this work.

RESULTS

A coumarin derivative SWJT-22 was synthesized as a colorimetric fluorescent probe to detect hydroxylamine (HA), with high sensitivity and selectivity. The detection limit of the probe to HA was 0.15 μM, which was lower than most probes of HA. Upon the addition of HA to aqueous solution containing SWJT-22, the color of the solution changed from orange to yellow, and the fluorescence color also changed from orange to green. The reaction mechanism of SWJT-22 to HA was confirmed by 1H NMR titrations, mass spectrometry and round bottom flask experiments. Moreover, SWJT-22 had been fabricated into portable test strips for the detection of HA. SWJT-22 had been successfully used in cellular imaging and could detect both endogenous and exogenous HA in HeLa cells and RAW 264.7 cells.

SIGNIFICANCE

Due to the physiological role of hydroxylamine in organisms, it is crucial to detect hydroxylamine selectively and sensitively. This work provided a convenient tool for the detection of hydroxylamine, not only to detect endogenous and exogenous HA in cells, but also made into portable test strips. The HA fluorescent probe SWJT-22 is expected to promote the study of HA in physiological processes.

Coordination Synergistic-Induced J-Aggregation Enhanced Fluorescent Performance of HBT-Excimers and Imaging Applications

Developing a novel strategy to improve the optical performances of fluorescent probes is a vital factor in elevating its practical application; viz., novel biocompatible fluorescent probes with excellent multifunctions exhibited unparalleled advantages in probing functions of intracellular molecules to elucidate intracellular events in living systems. Herein, we have successfully constructed a new strategy that aggregation and coordination synergistically induce (2-hydroxylphenyl-benzothiazole) HBT derivatives to form excimers with large red-shifted fluorescence and application for insight into stress-response zinc fluctuations in living systems. We have synthesized four HBT-based derivatives and deeply investigated the response mechanism by fluorescent spectral studies, demonstrating that probes 3 and 4 showcased large red shifts in emission wavelength due to J-aggregation. More interestingly, the fluorescence of probe 4 was significantly enhanced in the presence of a zinc ion, suggesting that zinc coordination synergistically induced J-aggregation. Probe 4 was successfully applied to image zinc fluctuations in different models of living systems, proving that this probe is a powerful tool to unveil the relationship between invasive stress and diseases by monitoring endogenous zinc fluctuations.

Electron-donating and -withdrawing groups discriminate the fluorometric sensing of phosgene

Phosgene, diphosgene, and chlorine are called choking agents due to their acute toxicity to the respiratory system by directly attacking through inhalation and causing acute hypoxia, asphyxia and death. For these reasons, small-molecule fluorescent probes have been developed for their detection to ensure public safety. In this regard, two thiophene-based chemodosimetric fluorescent probes TCAO ((Z)-3-(4-(dimethylamino)phenyl)thiophene-2-carbaldehyde oxime) and HMBT ((Z)-4-(2-((hydroxyimino)methyl)thiophen-3-yl)benzonitrile) were designed, synthesized and characterized using 1H-NMR, 13C NMR, FT-IR spectroscopy and HRMS methods. Probe TCAO exhibited higher selectivity and sensitivity for detecting phosgene than probe HMBT. The electron-donating group (EDG) and electron-withdrawing group (EWG) play a crucial role in detecting phosgene. TCAO, bearing EDG, exhibited a fluorescence 'turn-on' response by the NGP-assisted conversion of aldoxime to the cyano group in the presence of phosgene; whereas HMBT, bearing EWG, did not show any fluorometric response. Therefore, further studies were conducted on TCAO, and the quantum yield changed from Φ = 0.043 to Φ = 0.155 in the presence of phosgene. The limit of detection for TCAO was estimated to be as low as 51 nm. In addition, onsite monitoring for visual detection was performed using the easy-to-handle paper-strip method.

A Ratiometric Benzimidazole-Based Fluorescent Probe for The Recognition of Phosgene in Solution and Gaseous Phases

Considering the high toxicity and widespread application of phosgene, there is an urgent need to develop a simple and sensitive method for detecting phosgene. In this work, we designed and synthesized a novel ratiometric fluorescent probe 1 containing fluorophores of benzimidazole and benzothiazole. Probe 1 showed excellent sensitivity (< 30 s) and selectivity (LOD = 3.82 nM) for phosgene and significant ratiometric fluorescence changes. In addition, 1-loaded polystyrene membrane test strips were used to conveniently and efficiently detect phosgene gas (0.5 ppm) via the naked eye and the RGB APP of the smartphone, indicating that this probe has great potential for phosgene detection in the gaseous phase.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

Ratiometric Fluorescent Probe for the Detection of Nanomolar Phosgene in Solution and Gaseous Phase: Advancing Crime Detection Applications

Phosgene, an exceptionally hazardous gas, poses a grave concern for the health and safety of the general public. The present study describes a fluorescent ratiometric probe for phosgene employing 2-(naphthalen-2-yl) benzo[d]oxazol-5-amine (NOA) with an amino group as the recognition site. NOA detects phosgene through the intramolecular charge transfer mechanism. The electron-rich amine group of NOA attacks the electrophilic carbonyl group of phosgene, resulting in a quick response within 20 s. NOA demonstrates a low detection limit of 60 nM while maintaining high selectivity and sensitivity toward phosgene. The final product was isolated and verified by nuclear magnetic resonance spectroscopy. The probe can detect phosgene not just quickly in a solution environment but also in its solid state. The probe's applications in fingerprint imaging and bioimaging are also demonstrated.

Pattern Recognition and Visual Detection of Aldehydes Using a Single ESIPT Dye

The accurate discrimination and quantification of aldehydes is a worthy objective made challenging by their similar chemical reactivities. Considering the nucleophilic reaction mechanism between an aldehyde and a primary amine, it is reasonable to vary the reaction pH to manipulate the reactivity of aldehydes and the stability of the resulting Schiff base for analytical purposes. We have designed and synthesized three benzothiazole-based fluorescent molecules (BS1-BS3) containing an amino group substituted at the ortho-, meta-, and para-positions for aldehyde sensing. It was determined that only BS1 having an amino group at the ortho-position exhibits a significant fluorescence response in the presence of formaldehyde at a particular pH, whereas BS2 and BS3 gave negligible responses, indicating that the ESIPT process in BS1 should be responsible for the changes in its fluorescence. Accordingly, a pH-mediated sensor array BS1SA was constructed by dissolving BS1 in aqueous solvents with different pH values. BS1SA was found to be reliable for the discrimination of seven different aldehydes and identification of unknown aldehyde samples. Moreover, BS1 was successfully applied to prepare a fluorescent test paper for the visual detection of formaldehyde vapor.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

A novel benzo hemicyanine-based fluorescent probe for susceptible visualizing detection of phosgene

Leakage and misuse of phosgene, a common and highly hazardous industrial chemical, have always constituted a safety risk. Therefore, it is crucial to develop sensitive detection methods for gaseous phosgene. This work describes the design and development of a new fluorescent dye based on benzohemicyanine, as well as the synthesis of fluorescent probes for the sensitive detection of gaseous phosgene. Due to the excellent intramolecular charge transfer (ICT) effect from the strong electron-donating impact of the o-aminophenol group on benzo hemicyanine, the probe does not emit fluorescence. When the probe reacts with phosgene, the ICT effect is inhibited, and the result exhibits observable green fluorescence, thereby visualizing the response to phosgene. The probe offers exceptional sensitivity, a rapid response, and a low phosgene detection limit. In addition, we developed probe-loaded, portable test strips for the quick and sensitive detection of phosgene in the gas phase. Finally, the constructed probe-loaded test strips were utilized effectively to monitor the simulated phosgene leakage.

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.

Rapid and ratiometric fluorescent detection of phosgene by a red-emissive ESIPT-based-benzoquinolone probe

Phosgene is a highly toxic gas that poses a serious threat to human health and public safety. Therefore, it is of great importance to develop an available detection method enabling on-the-spot measurement of phosgene. In this paper, we report a novel ESIPT fluorescent probe for phosgene detection based on quinolone fluorophore. This probe exhibits rapid response (in 10 s), stable signal output (last for 10 min), high sensitivity (LOD ∼ 6.7 nM), and distinct emission color change (red to green) towards phosgene. The sensing mechanism was investigated by using ¹H NMR, HRMS and fluorescence lifetime techniques, confirming that the amidation reaction between phosgene and quinolone effectively suppressed the ESIPT process of probe. Eventually, this probe was fabricated into polymer nanofibers by electrospinning and successfully employed to monitor gaseous phosgene with high specificity. This work provided a promising analytical tool for rapid and ratiometric detection of phosgene both in solution and in the gas phase.

Europium (III) complex-based fluorescent probe for instantaneous, selective, and sensitive detection of phosgene

Phosgene (carbonyl chloride, COCl₂) is a widely used colorless gas in organic synthesis. However, its high toxicity sets a severe potential damage of public safety. As the fluorescence method has the advantages of simple operation and real-time detection of phosgene, it is extremely important to develop a fluorescent phosgene probe for public health and safety. This study aimed to present a simple Eu³⁺ complex (1) with 2-hydroxyl-1H-benzimidazole moiety as a novel phosgene probe. Probe 1 exhibited characteristic emission of Eu³⁺ in CH₃CN solution, which was specifically quenched after encountering phosgene. The change in the solution color from light red to dark could be easily distinguished with the naked eye under a 365 nm ultraviolet lamp. Finally, the test paper with probe 1 was fabricated for effortless, selective, and visual detection of phosgene gas.

A dual-channel chemodosimetric sensor for discrimination between hypochlorite and nerve-agent mimic DCP: application on human breast cancer cells

A styryl bridge containing a triphenylamine-thioimidazole hydrazine-based dual-analyte-responsive fluorescent sensor was designed and synthesized for the detection of the nerve gas simulant diethyl chlorophosphate (DCP) and hypochlorite (OCl^-) for the first time. Hypochlorite induces oxidative intramolecular cyclization to give a triazole structure, which exhibited blue fluorescence with excellent selectivity and a low detection limit (8.05 × 10^-7 M) in solution. Conversely, the probe forms a phosphorylated intermediate with diethyl chlorophosphate, which undergoes further hydrolyzation and presents green fluorescence in a ratiometric mode with a low detection limit (3.56 × 10^-8 M). Additionally, the as-designed sensor was utilized to construct a portable kit for real-time monitoring of DCP in a discriminatory, simple and safe manner. Lastly, the probe was also productively employed for in situ imaging of OCl^- and DCP in the living cell.

A naphthimide-based ratiometric fluorescent probe for selective and visual detection of phosgene in solution and the gas phase

As a colorless, highly toxic and widely used chemical reagent, phosgene poses a potentially serious threat to public health and environmental safety. Therefore, there is an urgent need to develop a simple and sensitive method for detecting phosgene. In this work, a ratiometric fluorescent probe (NED) for phosgene was developed by utilizing 4-substituted 1,8-naphthimide unit as the fluorophore and ethylenediamine as the recognition moiety. The probe NED undergoes intramolecular cyclization reaction with phosgene, resulting in a remarkable ratiometric fluorescence response. The probe NED displays high sensitivity (LOD = 4.9 nM), excellent ratiometric fluorescence signal, and high selectivity toward phosgene over other relevant analytes. In addition, paper test strip capable of visually detecting gaseous phosgene has also been fabricated.

A specific esterase and pH logically regulate ESIPT: different kinds of granulocyte sorting

Simultaneously detecting naphthol AS-D chloroacetate esterase (NAS-DCE) and pH is an effective way to separate different granulocytes, which is of great significance for the analysis of blood. A series of fluorescent small molecules (HBT-ASDs) were designed, whose ESIPT process could be logically regulated by NAS-DCE and pH. One typical molecule, HBT-ASD-2, emits three kinds of fluorescence output signal at 438 nm and 545 nm for NAS-DCE under different pH values (5.0, 7.4 and 10, respectively). According to such differential signals, the acid, neutrophil and alkaline granulocytes can be sorted, and the activity of NAS-DCE can also be simultaneously monitored in real-time. Thus, a simple analytical tool for clinical blood monitoring and analysis is provided.

NIR-Responsive Lysosomotropic Phototrigger: An "AIE + ESIPT" Active Naphthalene-Based Single-Component Photoresponsive Nanocarrier with Two-Photon Uncaging and Real-Time Monitoring Ability

In recent times, organelle-targeted drug delivery systems have gained tremendous attention due to the site-specific delivery of active drug molecules, resulting in enhanced bioefficacy. In this context, a phototriggered drug delivery system (DDS) for releasing an active molecule is superior, as it provides spatial and temporal control over the release. So far, a near-infrared (NIR) light-responsive organelle-targeted DDS has not yet been developed. Hence, we introduced a two-photon NIR light-responsive lysosome-targeted "AIE + ESIPT" active single-component DDS based on the naphthalene chromophore. The two-photon absorption cross section of our DDS is 142 GM at 850 nm. The DDS was converted into pure organic nanoparticles for biological applications. Our nano-DDS is capable of selective targeting, AIE luminogenic imaging, and drug release within the lysosome. In vitro studies using cancerous cell lines showed that our single-component photoresponsive nanocarrier exhibited enhanced cytotoxicity and real-time monitoring ability of drug release.

A rhodamine–TPE scaffold-based fluorescent probe for visualizing phosgene with a portable smartphone via test TLC strips

A rhodamine–TPE scaffold-based ratiometric signal readout probe was developed for sensitive, rapid, and in situ phosgene determination.

Ruthenium(II) Polypyridine Complex-Based Aggregation-Induced Emission Luminogen for Rapid and Selective Detection of Phosgene in Solution and in the Gas Phase

A bis-heteroleptic ruthenium(II) complex, Ru-1, of 4,7-bis(2-aminoethylamino)-1,10-phenanthroline for selective "turn-on" detection of highly toxic chemical warfare agent phosgene is presented. Probe Ru-1 exhibits aggregation-induced emission (AIE), and the restricted intramolecular motion is responsible for the AIE activity. In a CHCl₃/CH₃CN [95:5 (v/v)] solvent mixture, a unique self-assembled vesicular structure was formed after aggregation, which was supported by transmission electron microscopy, field emission scanning electron microscopy, and atmoic force microscopy studies. Probe Ru-1 showed a rapid and highly selective luminescence turn-on response for phosgene over other competitive chemical warfare agents with a low detection limit (13.9 nM) in CH₃CN. The 2-aminoethylamino groups in Ru-1 act as a reacting site for nucleophilic addition to the carbonyl center of phosgene and undergo intramolecular cyclization. The final product of the phosgene-mediated reaction, Ru-1-Phos, contains 2-imidazolidinone groups, which has been confirmed by electrospray ionization mass spectometry and ¹H nuclear magnetic resonance (NMR) spectroscopy. ¹H NMR titration of Ru-1 with phosgene supported the reaction mechanism and also pointed to the simultaneous reaction of phosgene at two 2-aminoethylamino sites. For the first time, the crystal structure of the phosgene reaction product, Ru-1-Phos, containing the cyclized 2-imidazolidinone group was confirmed by single-crystal X-ray diffraction, which indubitably validates the reaction mechanism. Triplet state time-dependent density functional theory calculations showed that the weak luminescence of Ru-1 was mostly due to the population of the non-emissive ³MC state. The cyclization reaction with phosgene and the corresponding 2-imidazolidinone product formation populated the emissive ³MLCT state in Ru-1-Phos and is the key reason for the enhanced luminescence. Furthermore, a low-cost portable test paper strip has been fabricated with Ru-1 for the real-time selective monitoring of phosgene gas at the nanomolar level.

Film Nanoarchitectonics of Pillar[5]arene for High-Performance Fluorescent Sensing: a Proof-of-Concept Study

Substrates play crucial roles for the sensing performances of fluorescent films owing to their effect on the formation of a fluorescent adlayer. However, no such film has been developed through synthesizing a substrate with a defined structure. We herein report a kind of self-standing, uniform, and thickness tunable pillar[5]arene-based nanofilms to serve as substrates for fabricating fluorescent sensing films. In comparison with a glass plate, the pillar[5]arene-based nanofilms can ensure spatial and electronic isolation of immobilized fluorophores and circumvent aggregation-caused quenching in a film state. For conceptual proof, a formic acid fluorescent sensing film was developed through simple loading of a fluorophore, a 4-azetidine-1,8-naphthalimide derivative of cholesterol (NA-Ch), onto the prepared nanofilm. Sensing performance studies demonstrated that the fluorescent film showed a sensitive, fast, and highly selective response to formic acid in air with a detection limit of lower than 2.8 mg m^-3 and a response time of less than 3 s. Moreover, the sensing is fully reversible and highly repeatable. Further studies showed that the film sensor can be used for fast determination of methanol acidity via vapor sampling. Clearly, innovation of substrates with defined structures can be taken as an effective and efficient way to develop new sensing films via combination with known fluorophores.

Dual-factor Synergistically Activated ESIPT-based Probe: Differential Fluorescence Signals to Simultaneously Detect α-Naphthyl Acetate and Acid α-Naphthyl Acetate Esterase

α-Naphthyl acetate esterase (α-NAE) and acid α-naphthyl acetate esterase (ANAE), a class of special esterases, are important for lymphocyte typing and immunocompetence-monitoring. As such, the simultaneous detection of α-NAE and ANAE has become a target to effectively improve the accuracy in lymphocyte typing. Therefore, we developed a dual-factor synergistically activated ESIPT-based probe (HBT-NA) to detect α-NAE and ANAE sensitively, rapidly, and simultaneously in a differential manner. HBT-NA exhibits differential fluorescence signal outputs toward small changes of α-NAE and ANAE activities. HBT-NA displays a weak fluorescence signal at 392 nm over a pH range from 6.0 to 7.4. However, when it interacts with α-NAE (0-25 U) at pH = 7.4, the fluorescence intensity at 392 nm enhanced linearly within 60 s (F_392 nm/F0_392 nm = 0.042 C_α-NAE + 1.1, R² = 0.99). Furthermore, HBT-NA emits ratiometric fluorescence signals (F_505 nm/F_392 nm) for ANAE (0-25 U) at pH = 6.0 within 2.0 min, exhibiting a good linear relationship (F_505 nm/F_392 nm = 0.83C_ANAE - 1.75, R² = 0.99). The differential fluorescence signals can be used to simultaneously detect the activities of α-NAE and ANAE in solutions and complex living organisms. More importantly, based on the differential fluorescence signals toward α-NAE and ANAE, T lymphocytes and B lymphocytes could be successfully typed and differentiated among nontyped lymphocytes, facilitating the real-time evaluation of their immune functions using flow cytometry. Hence, HBT-NA could be used for the ultrasensitive detection of the enzyme activities of α-NAE and ANAE, the real-time precise typing of lymphocytes, and the monitoring of immunocompetence.

Smartphone as a simple device for visual and on-site detection of fluoride in groundwater

Developing a portable device for visual and on-site detection of fluoride in groundwater is highly anticipated. In this paper, 2-(tert-butyl-diphenylsilanyloxy)-5-nitro-1H-benzoimidazole (1) has been rationally designed via a silanization reaction for self-calibration detection of fluoride, and the detection limit was calculated as 0.11 μM. The contact of 1 with fluoride would induce the cleavage of Si-O bond and trigger the emergence of excited state intramolecular proton transfer (ESIPT) process, and then the enol-like emission at 437 nm decreased accompanying with the increase of keto-like tautomerism emission at 550 nm. More importantly, considering the demand of field detection for fluoride in groundwater and combining the function of smartphone to obtain the chroma of photos. The chroma value of the fluorescence color changes from blue to yellow could be conveniently determined through a color recognizer application installed in smartphone. The device can accurately reflect the concentration of fluoride by analyzing the chroma value. The test in actual water samples confirmed that the simple device based on smartphone could be used efficiently for visual, on-site and accurate detection of fluoride in groundwater.

Rapid and Effective Reaction of 2-Methylpyridin-N-oxides with Triphosgene via a [3,3]-Sigmatropic Rearrangement: Mechanism and Applications

A facile and effective synthesis of 2-chloromethylpyridines was developed by a one-pot reaction of 2-alkylpyridin-N-oxides and triphosgene at room temperature. As starting materials, N-oxides of 2-alkylpyridine derivatives, including 2-alkylpyridines, 2-methyl quinolines, and phenanthroline, can react rapidly with triphosgene in the presence of triethylamine, affording 2-chloromethylpyridines in good to excellent yields (52-95%). Using the 2-methylquinoline substrate for the mechanistic study, it has been well demonstrated that the chlorination reaction undergoes a [3,3]-sigmatropic rearrangement, which can be observed as a reversible process by monitoring the intermediates. Moreover, the chlorination reaction can be used to construct a rapid and sensitive fluorescent probe for the detection of phosgene.

Two-phase activated colorimetric and ratiometric fluorescent sensor for visual detection of phosgene via AIE coupled TICT processes

In this paper, we specifically designed and synthesized an excellent colorimetric and ratiometric fluorescent sensor DPA-CI for rapid and convenient detection of the highly toxic phosgene. DPA-CI was developed by incorporated a diphenylamine (DPA) and a 2-imine-3-benzo[d]imidazole as the enhanced push-pull electronic structure into the coumarin fluorophore matrix. The sensor DPA-CI towards phosgene sensing exhibited both visible colorimetric and ratiometric fluorescent color change in solution and in gaseous conditions with TICT and AIE mechanism respectively, which can be easily distinguished by using the naked eye. Also, the sensor DPA-CI showed splendid sensing performance such as excellent selectivity, rapid response (less than 8 s in THF and 2 min in gaseous condition), and fair sensitivity (limit of detection less than 0.11 ppm in gaseous condition and 0.27 μM in solution). The design strategy based on enhanced push-pull electronic structure with AIE and TICT properties will be helpful to construct a solid optical sensor with excellent potential application prospects for portable and visual sensing of gaseous phosgene through distinct color and ratiometric fluorescence change by the naked eyes.

Sensitive and Visual Detection of Phosgene by a TICT-Based BODIPY Dye with 8-(o-Hydroxy)aniline as the Active Site

Phosgene and its substitutes (diphosgene and triphosgene) are widely utilized as chemical industrial materials and chemical warfare agents and pose a threat to public health and environmental safety due to their extreme toxicity. Research efforts have been directed to develop selective and sensitive detection methods for phosgene and its substitutes. In this paper, we have prepared two BODIPY-based fluorescent probes, o-Pah and o-Pha, which are two isomers with different active sites, ortho-aminohydroxy (3',4' or 4',3') phenyls at meso position of BODIPY, and compared their sensing performance toward triphosgene. The probe with o-(4'-amino-3'-hydroxyl), o-Pha, exhibits better sensing performance over the o-(3'-amino-4'-hydroxyl), o-Pah, for instance, a lower limit of detection (LOD) (0.34 nm vs. 1.2 nm), and more rapid response (10 s vs. 200 s). Furthermore, based on the above comparative studies, a red-fluorescence probe o-Phae has been constructed through extending 3,5-conjugation of o-Pha. The probe o-Phae displays rapid response (60 s), high sensitivity to triphosgene (LOD=0.88 nm), and high selectivity for triphosgene over relevant analytes including nitric oxide. Finally, a facile test strip for phosgene was fabricated by immobilizing o-Phae in a polyethylene oxide membrane for sensitive (<2 ppm) and selective detection of phosgene in the gas phase.

A facile dual-function fluorescent probe for detection of phosgene and nitrite and its applications in portable chemosensor analysis and food analysis

Due to the potential threats of phosgene and nitrite to public health and safety, in this work, we first proposed the application of a facile dual-function fluorescent probe 2-(1H-Benzimidazol-2-yl)Aniline (BMA) for the detection of phosgene and nitrite in different solvent environments. BMA had fast response (1 min), high selectivity and sensitivity (the limit of detection was 1.27 nM) to phosgene in CH₃CN solution (containing 10% DMSO), which manifested as a ratiometric fluorescent mode from 416 nm to 480 nm. The response of BMA to nitrite in HCl solution (pH = 1, containing 10% CH₃CN) was also highly selective and sensitive (the limit of detection was 60.63 nM), which shown as a turn-off fluorescent mode at 485 nm. In addition, two portable chemosensors (BMA-loaded TLC plates and test strips) had also been successfully manufactured for the detection of phosgene in the gas phase and nitrite in solution, which displayed good responses. Most importantly, BMA had also been successfully used for detection of nitrite in food samples, and a good recovery (88.5%-107.2%) was obtained by adding standard sodium nitrite.

A new fluorescent probe for ultrasensitive detection of phosgene in solution and the gas phase

A new fluorescent probe has been developed for sensitive and selective detection of phosgene in solution and vapor.

An amino-substituted 2-(2′-hydroxyphenyl)benzimidazole for the fluorescent detection of phosgene based on an ESIPT mechanism

In this work, an ESIPT-based fluorescence probe, 5′-amino-2-(2′-hydroxyphenyl)benzimidazole (P1), was synthesized and explored for the ratiometric detection of phosgene. Compared to 2-(2′-hydroxyphenyl)benzimidazole (HBI), P1 exhibits high sensitivity (LoD = 5.3 nM) and selectivity toward phosgene with the introduction of the amine group. Furthermore, simple P1 loaded test papers are manufactured and display selective fluorescent detection of phosgene in the gas phase.

An easily prepared phosgene probe, 5′-amino-2-(2′-hydroxyphenyl)benzimidazole (P1), is designed and studied. Based on ESIPT mechanism, P1 exhibits ratiometric, sensitive and selective detection of phosgene both in solution and gas phase.

Second-Generation Phosgene and Diphosgene Detection Tube

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/m3 (tristimulus colorimeter), resp. 5 mg/m3 (with the naked eye), fluorescence detection limits of 0.3 mg/m3 (with the naked eye), all at an air sample volume of 1 dm3. The response was practically immediate, acid vapors and gases, or diethyl chlorophosphate as a simulant of nerve warfare chemical agents, were disruptive.

Sensitive and selective detection of phosgene with a bis-(1H-benzimidazol-2-yl)-based turn-on fluorescent probe in the solution and gas phase

As one of the chemical weapons in World War I, phosgene (COCl2) is an extremely toxic gas. Due to wide applications in industrial production, phosgene can easily leak inadvertently and poses a serious threat to the environment and human health and safety. In this study, we report for the first time a new fluorescent probe (bis-(1H-benzimidazol-2-yl)-methanone) for the rapid detection of phosgene. The probe is based on the easily prepared bis-(1H-benzimidazol-2-yl), which can quickly combine with phosgene to obtain a six-membered cyclic carbamylation product showing fluorescence turn-on. The combination of phosgene caused the maximum absorption of the probe shifting from 361 nm to 373 nm, which showed a color change from colorless to yellow under visible light. Meanwhile, a strong fluorescence emission peak appeared at 428 nm, which showed change from no fluorescence to blue-violet fluorescence under a UV lamp (365 nm). The response of the probe towards phosgene is fast (within 30 s), highly selective and sensitive (the detection limit in solution being 3.3 nM). Furthermore, the portable test strips manufactured using the probe can conveniently perform visual and fluorescence detection of phosgene in the gas phase.

Derivatization and rapid GC-MS screening of chlorides relevant to the Chemical Weapons Convention in organic liquid samples

A simple derivatization technique was developed for the analysis of seven Schedule 3 chemicals and one Schedule 2 chemical listed in the Chemical Weapons Convention (CWC). Phosgene, phosphorus oxychloride, phosphorus trichloride, phosphorus pentachloride, thionyl chloride, sulfur monochloride and sulfur dichloride (Schedule 3) as well as arsenic trichloride (Schedule 2) were derivatized using 1-propanol in 40% pyridine solution for analysis with gas chromatography-mass spectrometry (GC-MS). Derivatization temperature and concentration of the derivatization solution were optimized for maximum derivatization recovery. The stabilities of the target analytes and their derivatives in different solvents were studied. The derivatization yield showed a linear response within the analyte concentration range of 0.1-2 mM (10-200 μg ml-1) with correlation coefficients >0.99 (r2), except for AsCl3 which did not show a linear response after derivatization. Good reproducibility with relative standard deviations (RSDs) from 3 to 13% was achieved. The derivatization recovery was 66% for phosgene and 67-80% for the P-containing chemicals phosphorus oxychloride, phosphorus trichloride and phosphorus pentachloride. Recommendations to use the method for screening the presence of these chemicals in organic liquid samples are given. The method is used when CWC-related samples are screened at VERIFIN.

Selectively Light-up Detection of Phosgene with an Aggregation-Induced Emission-Based Fluorescent Sensor

Phosgene, a widely used but highly toxic substance, may pose a serious risk to public safety and health because of the potential abuse and possible accidental leakage. Consequently, it is of great significance to develop a rapid, reliable, and sensitive detection method for this noxious agent. In this work, an aggregation-induced emission-based sensor, 3,6-bis(1,2,2-triphenylvinyl)benzene-1,2-diamine (DATPE), has been rationally designed for detecting phosgene by conjugation of o-phenylenediamine (OPD) core as the reactive recognition moiety decorated with two peripheral triphenylethylene (TPE) units. A light-up fluorescence response is achieved by the fast cyclization reaction of OPD part and phosgene along with the formation of 2-imidazolidinone ring, thus inhibiting the intramolecular charge transfer quenching process in the sensor. Moreover, an easy-to-use test paper with DATPE is fabricated for onsite visual detection of phosgene in the gas phase even at a concentration of as low as 0.1 ppm.