Fluorescence "Turn-On" Indicator Displacement Assay-Based Sensing of Nitroexplosive 2,4,6-Trinitrophenol in Aqueous Media via a Polyelectrolyte and Dye Complex

[The study of the features of the determination and nature of the localization of 2-amino-4.6-dinitrophenol in the body of warm-blooded animals in case of lethal poisoning]

The aim of the work is to study the nature of the distribution of 2-A-4.6-DNP in the organisms of warm-blooded animals with intragastric administration of a toxicant. The study was carried out using the methods of TLC, UV-Visible spectroscopy, and GC-MS using derivatives of 2-A-4.6-DNP. Male Wistar rats at the age of 4 months were considered as a model of the body of a warm-blooded animal. An oily suspension of 2-A-4.6-DNF was administered intragastrically in an amount of three times the LD50. Extraction of the target substance from the biomaterial was carried out by double infusion (30 minutes each) with a mixture of acetone-acetonitrile (1:1), the amount of the mixture exceeded the weight of the biomaterial by 2 times. Extractions were purified by TLC method using «Sorbfil» plates and acetone-chloroform (7: 3) mobile phase. Preliminary identification was carried out at the same time using a standard substance. Confirmatory identification was carried out by the absorption of dimethylformamide eluates in «SF-2000», as well as by the retention time and mass spectra of the major compound of the corresponding chromatographic peaks after GC-MS analysis. The quantitative content was determined spectrophotometrically, in DMF, by optical density at the analytical wavelength (490 nm). 2-Amino-4.6-dinitrophenol was found unchanged in the blood and in all the studied hollow and parenchymal organs of poisoned rats. The largest amount of 2-amino-4.6-dinitrophenol (mg/100 g) was found in the stomach walls (199.39±25.43) and stomach contents (143.14±22.63), a significant amount of the substance was found in the heart (33.49±3.66), skeletal muscles (30.70±2.64), as well as in the spleen (24.30±1.96).

A Chromo-fluorogenic Probe for Selective Detection of Picric Acid Alongside Its Recovery by Aliphatic Amines and Construction of Molecular Logic Gates

Nitroaromatic compounds are illicit explosive chemicals. For environmental security and homeland safety, selective and sensitive identification of these secondary-class explosives has been a reason for the exhaustive research arena of chemists for about a decade. We introduced a sensitive optical sensor with desalted neutral red (NR) dye. After ingressing picric acid (PA) in acetonitrile, the probe becomes non-fluorescent, displaying a colorimetric change from yellow to pink. The quenched phenomena and the changed color were re-established with aliphatic amine, trimethylamine (TEA). The reversibility is produced cyclically, both in fluorimetrically and spectrophotometrically. The detection limit for PA with our probe comes out as 0.639 µM; this value is significantly lower than many chemosensors available in the literature. Also, NR-stained filter paper strips-based test kit analysis has been deployed as a displayable photonic device for in-situ detection of PA. Furthermore, the whole system was conceptualized to produce single input, single output, and double input single output logic gates, which can be applied to digital devices. The chronological input manner as NTP (NR- TEA-PA) pushed us to configure a molecular keypad lock system, the basis of digital locking devices. The repeatable & reversible detection system exhibits "Write read- Erase-read Write-read' type memory devices.

A water-soluble conjugated polyelectrolyte for selective and sensitive detection of carcinogenic chromium(VI)

Environmental water pollution caused by hexavalent chromium (Cr(VI)) is a threat to living beings due to its carcinogenic nature. Herein, we report the synthesis of a highly fluorescent water-soluble conjugated polyelectrolyte PPMI and its application as a fluorescence sensor to monitor traces of carcinogenic Cr(VI) ions in water. PPMI was synthesized via the oxidative polymerization method followed by post-polymer functionalization. Fluorescent PPMI exhibited a photoluminescence quantum yield of 23.87 and displayed a rapid, very selective, and sensitive turn-off fluorescence signal in response to Cr(VI), with a significantly high quenching constant of 1.32 × 106 M-1. The mechanism of sensing was found to be static quenching. The limit of detection of this highly accessible analytical method was found to be in nanomolar ranges, i.e. 0.85 nM. Additionally, sensing on solid platforms such as economical paper strips was successfully achieved, which is very challenging and highly recommended for any reliable, portable, and economical analytical method.

Synthesis of p-Azaquinodimethane-based Quinoidal Fluorophores

Quinoidal π-conjugated systems are sought-after materials for semiconducting applications because of their rich optical and electronic characteristics. However, the analogous fluorescent compounds are extremely rare, with just two reports in the literature. Here, we present the design and development of a third series of quinoidal fluorophores [(2,5-diarylidene)-3,6-bis(hexyloxy)-2,5-dihydropyrazine (Q1-Q5)] that incorporates p-azaquinodimethane. The fluorophores are synthesized in a two-step synthetic approach employing Knoevenagel condensation of N,N-diacetyl-piperazine-2,5-dione with different aromatic aldehydes followed by O-alkylation in high yields. Q1-Q5 are strongly emissive, and by altering the aryl-substituents, the emission colors can be modulated from blue to orange. The compounds possess emission maxima (λem) at 475-555 nm in the solution state and 510-610 nm in the solid state, with fluorescence quantum yields of up to 60%. To the best of our knowledge, the reported systems are the first quinoidal dual-state emissive (solution- and solid-state) compounds. In trifluoroacetic acid, Q5 exhibits halochromic behavior, with a dramatic color change from yellow to blue. Furthermore, the preliminary fluorescent sensing studies demonstrated that Q5 could act as a selective turn-off fluorescence probe for electron-deficient picric acid (PA), with an emission quenching of >90% in the solution state. The thin-layer chromatography (TLC) strip sensor of Q5 was also designed to detect PA in water.

Molecular Dynamics Simulations of Rhodamine B Zwitterion Diffusion in Polyelectrolyte Solutions

Polyelectrolytes continue to find wide interest and application in science and engineering, including areas such as water purification, drug delivery, and multilayer thin films. We have been interested in the dynamics of small molecules in a variety of polyelectrolyte (PE) environments; in this paper, we report simulations and analysis of the small dye molecule rhodamine B (RB) in several very simple polyelectrolyte solutions. Translational diffusion of the RB zwitterion has been measured in fully atomistic, 2 μs long molecular dynamics simulations in four different polyelectrolyte solutions. Two solutions contain the common polyanion sodium poly(styrene sulfonate) (PSS), one with a 30-mer chain and the other with 10 trimers. The other two solutions contain the common polycation poly(allyldimethylammonium) chloride (PDDA), one with two 15-mers and the other with 10 trimers. RB diffusion was also simulated in several polymer-free solutions to verify its known experimental value for the translational diffusion coefficient, D_RB, of 4.7 × 10^-6 cm²/s at 300 K. RB diffusion was slowed in all four simulated PE solutions, but to varying degrees. D_RB values of 3.07 × 10^-6 and 3.22 × 10^-6 cm²/s were found in PSS 30-mer and PSS trimer solutions, respectively, whereas PDDA 15-mer and trimer solutions yielded values of 2.19 × 10^-6 and 3.34 × 10^-6 cm²/s. Significant associations between RB and the PEs were analyzed and interpreted via a two-state diffusion model (bound and free diffusion) that describes the data well. Crowder size effects and anomalous diffusion were also analyzed. Finally, RB translation along the polyelectrolytes during association was characterized.

Efficient Detection of 2,6-Dinitrophenol with Silver Nanoparticle-Decorated Chitosan/SrSnO3 Nanocomposites by Differential Pulse Voltammetry

Herein, an ultra-sonication technique followed by a photoreduction technique was implemented to prepare silver nanoparticle-decorated Chitosan/SrSnO₃ nanocomposites (Ag-decorated Chitosan/SrSnO₃ NCs), and they were successively used as electron-sensing substrates coated on a glassy carbon electrode (GCE) for the development of a 2,6-dinitrophenol (2,6-DNP) efficient electrochemical sensor. The synthesized NCs were characterized in terms of morphology, surface composition, and optical properties using FESEM, TEM, HRTEM, BET, XRD, XPS, FTIR, and UV-vis analysis. Ag-decorated Chitosan/SrSnO₃ NC/GCE fabricated with the conducting binder (PEDOT:PSS) was found to analyze 2,6-DNP in a wide detection range (LDR) of 1.5~13.5 µM by applying the differential pulse voltammetry (DPV) approach. The 2,6-DNP sensor parameters, such as sensitivity (54.032 µA µM^-1 cm^-2), limit of detection (LOD; 0.18 ± 0.01 µM), limit of quantification (LOQ; 0.545 µM) reproducibility, and response time, were found excellent and good results. Additionally, various environmental samples were analyzed and obtained reliable analytical results. Thus, it is the simplest way to develop a sensor probe with newly developed nanocomposite materials for analyzing the carcinogenic contaminants from the environmental effluents by electrochemical approach for the safety of environmental and healthcare fields in a broad scale.

Fabrication and application of 2,4,6-trinitrophenol sensors based on fluorescent functional materials

2,4,6-Trinitrophenol (TNP) has been widely used for a long time. The adverse effects of TNP on ecological environment and human health have promoted researchers to develop various methods for detecting TNP. Among multifarious technologies utilized for the TNP detection, fluorescence strategy based on different functional materials has become an effective and efficient method attributed to its merits such as preferable sensitivity and selectivity, rapid response speed, simple operation, and lower cost, which is also the focus of review. This review summarizes the development status of fluorescence sensors for TNP in a detailed and systematic way, especially focusing on the research progress since 2015. The sensing properties of fluorescent materials for TNP are the core of this review, including nanomaterials, organic small molecules, emerging supramolecular systems, aggregation induced emission materials and others. Moreover, the development direction and prospect of fluorescence sensing method in the field of TNP detection are introduced and discussed at the end of review.

Water-soluble ionic liquid as a fluorescent probe towards distinct binding and detection of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol in aqueous medium

Owing to the escalating threat of criminal activities and pollution aroused by 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP), development of a proficient sensor for the detection of these explosives is highly demanded. Herein, a water-soluble ionic liquid-tagged fluorescent probe, 1-ethyl-3-(3-formyl-4-hydroxybenzyl)-1H-benzimidazol-3-ium chloride (EB-IL) has been designed and synthesized for the detection of TNT and TNP in 100% aqueous medium. The EB-IL fluorescent probe displayed strong cyan-blue fluorescence at 500 nm which gets quenched upon the addition of TNT/TNP over other concomitant nitro-compounds. The distinct binding response of EB-IL towards TNT could be due to the formation of hydrogen bonding between the acidic proton of benzimidazolium (C2-H) and nitro group of TNT. Meanwhile, the selective binding of TNP with EB-IL could be due to the exchange of counter Cl^- anion of EB-IL with picrate anion. The fluorescence quenching of EB-IL by TNT could be attributed to the resonance energy transfer (RET) and that of TNP is ascribed to the anion-exchange process. The developed sensor is extremely selective and sensitive towards TNT and TNP with high quenching constants of 1.94 × 10⁵ M^-1 and 2.32 × 10⁶ M^-1 and shows a lower detection limit of 159 nM and 282 nM, respectively.

A pyrazinium-based fluorescent chemosensor for the selective detection of 2,4,6-trinitrophenol in an aqueous medium

A fluorescent pyrazinium-based chemosensor has been synthesized, characterized, and employed for the selective detection of 2,4,6-trinitrophenol in an aqueous medium.

Mechanism of a Disassembly-Driven Sensing System Studied by Stopped-Flow Kinetics

We carried out steady-state and stopped-flow photophysical measurements to determine the kinetics of a discrete disassembly driven turn-on fluorescent system. On and off rates for both DimerDye1 assembly and nicotine binding were determined. Relative rates for these competing processes provide insight on how this system can be optimized for sensing applications. Kinetics studies in artificial saliva showed that moving to more complex media has minimal effects on the sensing ability of the system.

Indicator displacement assays: from concept to recent developments

Overcoming the synthetic burden related to covalently connected receptors with appropriate indicators for sensing various analytes via an indicator spacer receptor (ISR) approach, the indicator displacement assay (IDA) seems to be a very sophisticated and versatile supramolecular sensing paradigm, and it has taken the phenomenon of molecular recognition to the next level in the realm of host-guest chemistry. Due to the unavailability of a comprehensive report on what has been done in the last decade in relation to IDAs, we decided to set down this account illustrating diverse indicator displacement assays (IDAs) in detail from the concept stage to recent developments relating to the detection of cationic, anionic, and neutral analytes. The authors conclude this account with future perspectives and highlight the limitations and challenges relating to IDAs which need to be overcome in order to realize the full potential of this popular sensing phenomenon. While we were finalizing our account for publication, a tutorial review by the research groups of Anslyn, Sessler, and Sun was published, which focuses mainly on diverse aspects of the chemistry related to IDAs. As can be seen, our review, besides discussing various basic IDA concepts, has a vast collection of information published in the past decade and hence, hopefully, will be very informative for the supramolecular community. We believe that this work will offer new insights for the construction of novel sensors operating through the IDA approach.

Ratiometric Turn-On Fluorophore Displacement Ensembles for Nitroaromatic Explosives Detection

There is a recognized need in the area of explosives detection for fluorescence-based sensing systems that are capable of not only producing a turn-on response but also generating a distinctive spectral signature for a given analyte. Here, we report several supramolecular ensembles displaying efficient fluorophore displacement that give rise to an increase in fluorescence intensity upon exposure to various nitroaromatic compounds. The synthetic supramolecular constructs in question consist of a tetrathiafulvalene (TTF)-based pyrrolic macrocycle, benzo-TTF-calix[4]pyrrole (Bz-TTF-C4P), and fluorescent dyes, monomeric or dimeric naphthalenediimide (NDI) and perylenediimide (PDI) derivatives, as well as chloride or hexafluorophosphate (PF₆^-) salts of rhodamine 6G (Rh-6G). In chloroform solution, these assemblies exist in the form of discrete supramolecular complexes or oligomeric aggregates depending on the specific dye combinations in question. Each ensemble was tested as a potential explosive-responsive fluorescence indicator displacement assay (FIDA) by challenging it with a series of di- and trinitroaromatic compounds and examining the change in fluorescence spectral characteristics. Upon addition of nitroaromatic compounds (NACs), either a "turn-on" or a "turn-off" fluorescent response was observed depending on the nature of the constituent fluorophore and, where applicable, the counteranion. The FIDAs based on the PDI derivatives were found to display not only a ratiometric fluorescence enhancement but also analyte-dependent spectral changes when treated with NACs. The NAC-induced fluorescence spectral response of each ensemble was rationalized on the basis of various solution-phase spectroscopic studies, as well as single-crystal X-ray diffraction analyses.

A composite nanosensing array with two response channels for trinitrobenzoic acid optical test

In this paper, the authors reported a composite platform for the optical sensing of 2,4,6-trinitrobenzoic acid (TBA). This composite sensing platform consisted of luminescent rare earth MOF and a rhodamine-derived sensing probe. Its composite structure was confirmed by means of XRD, IR, TGA and photophysical measurement. It was found that there were two emission components in this sensing platform, which were rhodamine emission component and Eu(III) emission component, respectively. The rhodamine emission was enhanced with increasing TBA concentration, while the Eu(III) emission component was quenched by increasing TBA concentration, showing self-calibrated sensing signals for ratiometric fluorescent sensing. In addition, rhodamine absorption in visible region was increased with increasing TBA concentration, showing colorimetric sensing. The above mentioned two sensing channels both showed high selectivity and linear response towards TBA with LOD of 2.4 μM. By comparing emission lifetime under various TBA concentrations, the sensing mechanism was convinced as the combination of rhodamine emission turn on effect initiated by TBA -released protons and Eu(III) emission turn off effect caused by an ET (energy transfer) procedure from EuBTC to TBA. This sensing platform showed naked eye sensing and two sensing channels with linear response and high selectivity.

A recyclable fluorescent probe for picric acid detection in water samples based on inner filter effect

1-Aminopyrene@ZIF-8 composite was synthesized as the fluorescent probe for picric acid (PA) based on inner filter effect. The probe displayed selective response toward PA within 10s, and a linear range was obtained from 1 to 150μM with detection limit of 0.3μM, which is much lower than the permissible level of PA in drinking water reservoir (0.5mgL^-1/2.2μM) set by China's State Environmental Protection Administration (GB3838-2002). Most importantly, the probe possessed excellent recyclability and could be recycled for at least six times. It was further applied to the detection of PA in water samples, and satisfactory recoveries were obtained in the range of 96.0-104.0%.

Azine based AIEgens with multi-stimuli response towards picric acid

Selective detection of picric acid using AIEgens via fluorescence enhancement and quenching in the monomer and aggregated from respectively.

Stepwise elucidation of fluorescence based sensing mechanisms considering picric acid as a model analyte

The precise study of fluorescence-based sensing mechanisms and a step-by-step design experiment for the elucidation of the mechanism of sensing for newly designed sensing systems can be ascertained using the presented tutorial review.

An Unprecedented Blueshifted Naphthalimide AIEEgen for Ultrasensitive Detection of 4-Nitroaniline in Water via "Receptor-Free" IFE Mechanism

The development of a new naphthalene appended naphthalimide derivative (NMI) with aggregation-induced enhanced emission (AIEE) property for the sensitive detection of 4-nitroaniline (4-NA) in aqueous media is presented here. The newly designed naphthalimide AIEEgen has an exceptional blue-shifted condensed state emission that is devoid of any receptor site, accomplished ultrasensitive detection of 4-NA, which is one of the broad-spectrum pesticides that belong to the class III toxic chemical, at parts per billion level (LOD/36 ppb, K_sv =4.1×10⁴  m^-1 ) in water with excellent selectivity even in the presence of potentially competing aliphatic and aromatic amines. The reported probe is the first of its kind, demonstrating major advantages of receptor-free inner filter effect (IFE) mechanism for the sensitive detection of 4-NA using an AIEEgenic probe. Excellent sensitivity for 4-NA is also achieved on paper-based test-strip for low-cost on-site detection.

Supramolecular Sensing of 2,4,6-Trinitrophenol by a Tetrapyrenyl Conjugate of Calix[4]arene: Applicability in Solution, in Solid State, and on the Strips of Cellulose and Silica Gel and the Image Processing by a Cellular Phone

A calix[4]arene conjugate possessing a tetrapyrenyl moiety at its upper rim (R) is designed as a receptor for sensing trinitrophenol (TNP). To understand the role of the calix[4]arene platform and that of pyrenyl moieties in R, two other control molecules were synthesized. These are as follows: the one possessing a tetraphenyl moiety in place of tetrapyrenyl (R 1 ) and the other one is a p-pyrenyl-hydroxy benzene (R 2 ) that is devoid of the calix[4]arene platform. The R shows high sensitivity toward TNP in tetrahydrofuran (THF) over eleven other nitroaromatic compounds (NACs) studied by exhibiting large fluorescence enhancement and hence is selective to TNP over the other NACs studied. However, the control molecules R 1 and R 2 showed only marginal fluorescence enhancement, supporting the need of a calixarene platform and the presence of a tetrapyrenyl moiety in the receptor system for the selective sensing of TNP. Further, R 1 and R 2 are not suitable for sensing, since these exhibit similar fluorescence response over several NACs studied. The binding of TNP by R has been addressed by fluorescence titration and isothermal titration calorimetry. The nature of the complexation of TNP by R has been revealed by the computational calculations, wherein the data showed the entrapment of TNP by two adjacent pyrene moieties via π-π stacking interactions. Such host-guest complexation is expected to restrict the mobility of the pyrene moieties present in R. The reduction of the flexibility of the pyrenyl moieties of R upon TNP binding is evidenced by the 1H NMR spectral study, wherein this acts as an additional evidence for the complexation. In the present study, the sensing of TNP by R has been shown in THF solution, on the surface of silica gel and the cellulose paper to result in lowest detection limits (LODs) of 1.5, 3.5, and 6.5 μM, respectively. Even the solid mixture of R and TNP showed LOD of 2.1 μmol. Since R is expected to show supramolecular aggregation that is dependent on the guest species, the corresponding details were probed by microscopy techniques, using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy methods, and significant changes in the aggregation of R upon interaction with TNP were found. Such aggregation is responsible for the observed fluorescence enhancement. Thus, the tetrapyrenyl calix[4]arene conjugate (R) acts as a sensitive and robust platform for selective detection of TNP from a mixture of nitroaromatic compounds (NACs) wherein the fluorescence intensities can be imaged and managed by a cellular phone.

“Receptor free” inner filter effect based universal sensors for nitroexplosive picric acid using two polyfluorene derivatives in the solution and solid states

“Receptor free” and “interaction free” detection of nitroexplosive PA at remarkably low limit of detection (LOD) values of 110 nM and 219 nM using two new fluorescent polymers via the inner filter effect mechanism.

Inner Filter Effect and Resonance Energy Transfer Based Attogram Level Detection of Nitroexplosive Picric Acid Using Dual Emitting Cationic Conjugated Polyfluorene

A novel conjugated cationic polyfluorene (polyelectrolyte) derivative, PFBT, was developed by means of simple and cost-effective oxidative coupling polymerization method. PFBT displayed dual state emission in dimethyl sulfoxide (DMSO) as well as in water, a characteristic phenomenon of polyfluorene homopolymers, and tested for nitroexplosive analytes detection to observe a remarkable fluorescence quenching response for picric acid (PA) in the both solvents. The polymer PFBT demonstrated substantial selectivity and ultrasensitivity toward nitroexplosive PA in both the solvents (DMSO and H₂O) with exceptional quenching constant values of 2.69 × 10⁴ and 2.18 × 10⁵ M^-1 and a ultralow limit of detection of 92.7 nM (21.23 ppb) and 0.19 nM (43.53 ppt) in respective solvents. Furthermore, economical portable test strip devices were prepared for easy and fast on-site PA sensing, which can detect up to 0.22 ag level of PA. PA sensing in vapor phase was also established, that could detect up to 42.6 ppb level of PA vapors. Interestingly, the mechanism of sensing in DMSO solvent was attributed to substantial inner filter effect and photoinduced electron transfer, while in H₂O the sensing occurs via possible resonance energy transfer and photoinduced electron transfer, which is exceptional and not reported earlier for a single probe.