Detection of nitrobenzene compounds in surface water by ion mobility spectrometry coupled with molecularly imprinted polymers

Selective identification of p-nitroaniline by bromine-mediated polarization of carbon dots

A fluorometric method based on boron, bromide-codoped carbon dots (BBCNs) was developed for the first time for the highly selective detection of p-nitroaniline (PNA) in wastewater samples. It should be noted that the introduction of bromine greatly increases the molecular polarizability of the probe, which can regulate the energy level matching between the probe and PNA, resulting in the interaction between BBCNs and PNA. In the presence of PNA, the fluorescence of BBCNs is obviously quenched and accompanied by a red shift of the fluorescence band, which might be attributed to the formation of aggregates caused by the polar adsorption of BBCNs and PNA. It is beneficial for constructing a highly selective sensing platform for PNA determination compared to its isomers (o-nitroaniline and m-nitroaniline) through atomic bromine-mediated polarization of the BBCNs. With the help of this mechanism, an excellent linear range of 0.5-300 μM with a low detection limit of 0.24 μM toward PNA was obtained. This work further confirms that there is a significant relationship between the nature of doping elements and the optical and physicochemical properties of fluorescent materials.

An extensive experimental and DFT studies on highly selective detection of nitrobenzene through deferasirox based new fluorescent sensor

A deferasirox based substituted triazole amine sensor TAD has been synthesized for the highly selective detection of nitrobenzene in real samples. Sensor TAD exhibited selective quenching response against nitrobenzene among the other nitroaromatic compounds (NACs). Photoinduced electron transfer (PET) process was devised as plausible sensing mechanisms which was supported via UV-visible and fluorescence spectroscopy, 1H NMR titration experiment, density functional theory (DFT) analysis and Job's plot. Non-covalent interaction (NCI) analysis and Bader's quantum theory of atoms in molecules (QTAIM) analysis were performed to investigate the presence of non-covalent interactions and symmetry perturbation theory (SAPT0) was performed for energy decomposition and quantitative analysis of interaction energies between sensor TAD and NB. Furthermore, sensor TAD was practically applied for the identification of NB in real samples.

A facile strategy of using MoS2 quantum dots for fluorescence-based targeted detection of nitrobenzene

We present a simple approach for producing photoluminescent MoS₂ quantum dots (QDs) using commercial MoS₂ powder as a precursor along with NaOH and isopropanol. The synthesis method is particularly easy and environmentally friendly. The successful intercalation of Na⁺ ions into MoS₂ layers and subsequent oxidative cutting reaction leads to the formation of luminescent MoS₂ QDs. The present work, for the first time, shows the formation of MoS₂ QDs without any additional energy source. The as-synthesized MoS₂ QDs were characterized using microscopy and spectroscopy. The QDs have a few layer thicknesses and a narrow size distribution with an average diameter of ∼3.8 nm. Nitrobenzene (NB), an industrial chemical, is both toxic to human health and dangerously explosive. The present MoS₂ QDs can be used as an effective photoluminescent probe, and a new turn-off sensor for NB detection. The selective quenching was operated via multiple mechanisms; electron transfer between the nitro group and MoS₂ QDs through dynamic quenching and the primary inner filter effect (IFE). The quenching has a linear relationship with NB concentrations from 0.5 μM to 11 μM, with a calculated detection limit of 50 nM.

Relative capability demonstration of luminescent Al-MOFs for ideal detection of nitroaromatic explosives

Here, we have synthesised three luminescent Al MOFs i.e., Al-NTP, Al-FDA, and Al-TDA, using common metal ions (AlCl₃·6H₂O) with different carboxylic acid organic linkers (5-nitroisophthalic acid, 2,5-furan dicarboxylic acid, and 2,5-thiophenedicarboxylic acid) in a semi-aqueous medium. The structural analysis of Al-MOFs has been confirmed through powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy and absorption spectroscopy. Afterward, the optical properties of all three Al-MOFs were confirmed using photoluminescence spectroscopy and demonstrated for the detection of nitroaromatic explosives. We have observed host-guest interaction through a quenching mechanism. Among the three synthesised Al-MOFs, Al-NTP MOF exhibit 0.014 ppm lowest limit of detection in chloroform at room temperature. Our comparative study results reveal that the selection of the organic linker and solvent plays a critical role in MOF based sensing applications.

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.

Dummy Molecularly Imprinted Polymers Using DNP as a Template Molecule for Explosive Sensing and Nitroaromatic Compound Discrimination

This work reports a rapid, simple and low-cost voltammetric sensor based on a dummy molecularly imprinted polymer (MIP) that uses 2,4-dinitrophenol (DNP) as a template for the quantification of 2,4,6-trinitrotoluene (TNT) and DNP, and the identification of related substances. Once the polymer was synthesised by thermal precipitation polymerisation, it was integrated onto a graphite epoxy composite (GEC) electrode via sol–gel immobilisation. Scanning electron microscopy (SEM) was performed in order to characterise the polymer and the sensor surface. Responses towards DNP and TNT were evaluated, displaying a linear response range of 1.5 to 8.0 µmol L−1 for DNP and 1.3 to 6.5 µmol L−1 for TNT; the estimated limits of detection were 0.59 µmol L−1 and 0.29 µmol L−1, for DNP and TNT, respectively. Chemometric tools, in particular principal component analysis (PCA), demonstrated the possibilities of the MIP-modified electrodes in nitroaromatic and potential interfering species discrimination with multiple potential applications in the environmental field.

Lanthanide-Titanium Oxo Clusters as the Luminescence Sensor for Nitrobenzene Detection

A luminescent lanthanide-titanium oxo cluster of Eu₂Ti₄(μ₂-O)₂(μ₃-O)₄(phen)₂(tbza)₁₀·4CH₃CN (1, Eu₂Ti₄-phen-tbza, phen = 1,10-phenanthroline, Htbza = 4-tert-butylbenzoic acid) was prepared through the reaction of phen, Htbza, Eu(Ac)₃·xH₂O, and Ti(OⁱPr)₄ in acetonitrile. Its overall absolute quantum yield is 65.4% in solid state and 30.2% in CH₂Cl₂, and the detection limit of 1 for the nitrobenzene (NB) is 10.5 ppb. When the concentration of NB is 40 ppm, the luminescence quenching of 1 can be observed with the naked eye. Time-resolved excited-state decay measurements indicate that the static quenching process is dominated across the NB concentration of 0-9 ppm. The distinguishable shifts in ¹H NMR spectra of NB together with 1 confirm the presence of π···π stacking interactions between the organic ligands in 1 and the NB, which plays a key contribution for the quenching of luminescence.

Template-directed synthesis of Sm2Ti2O7 nanoparticles: a FRET-based fluorescent chemosensor for the fast and selective determination of picric acid

Fluorescence “turn off” detection of picric acid using a Sm₂Ti₂O₇ nanoprobe.

Evaluation of the solid state form of tadalafil in sub-micron thin films using nanomechanical infrared spectroscopy

Assessing physical stability of drugs is important both in the development as well as in the production phase in the pharmaceutical industry. We used nanomechanical infrared (NAM-IR) spectroscopy based on photothermal response of a nanomechanical resonator, to investigate the solid state forms of tadalafil (TAD), under various storage conditions in sub-micron thin films. The amorphous TAD was stable, when kept at normal storage conditions of 24 °C, 45% relative humidity (RH) and shielded from light, however, it crystallized after four days when it was at stress storage conditions (40 °C, 70% RH, and direct sunlight). Additionally, we found that the signals recorded with NAM-IR were comparable with the attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and that NAM-IR proved to be a suitable and time efficient method when evaluating TAD in sub 500 nm layers.

Molecularly Imprinted Polymer Materials as Selective Recognition Sorbents for Explosives: A Review

Explosives are of significant interest to homeland security departments and forensic investigations. Fast, sensitive and selective detection of these chemicals is of great concern for security purposes as well as for triage and decontamination in contaminated areas. To this end, selective sorbents with fast binding kinetics and high binding capacity, either in combination with a sensor transducer or a sampling/sample-preparation method, are required. Molecularly imprinted polymers (MIPs) show promise as cost-effective and rugged artificial selective sorbents, which have a wide variety of applications. This manuscript reviews the innovative strategies developed in 57 manuscripts (published from 2006 to 2019) to use MIP materials for explosives. To the best of our knowledge, there are currently no commercially available MIP-modified sensors or sample preparation methods for explosives in the market. We believe that this review provides information to give insight into the future prospects and potential commercialization of such materials. We warn the readers of the hazards of working with explosives.

Cavitand-Decorated Silicon Columnar Nanostructures for the Surface Recognition of Volatile Nitroaromatic Compounds

Nanocolumnar Si substrates (porous silicon (PSi)) have been functionalized with a quinoxaline-bridged (EtQxBox) cavitand in which the quinoxaline moieties are bonded to each other through four ethylendioxy bridges at the upper rim of the cavity. The receptor, which is known to selectively complex aromatic volatile organic compounds (VOCs) even in the presence of aliphatic compounds, has been covalently anchored to PSi. The larger surface area of PSi, compared to that of flat substrates, allowed one to study the recognition process of the surface-grafted receptors through different techniques: Fourier-transform infrared spectroscopy, thermal desorption, and X-ray photoelectron spectroscopy. The experiments proved that surface-grafted cavitands retain the recognition capability toward aromatic VOCs. In addition, the affinities of EtQxBox for various aromatic compounds (i.e., benzene, toluene, nitrobenzene, and p-nitrotoluene) have been studied combining density functional theory computations and thermal desorption experiments. Computational data based on the crystal structures of the complexes indicate that this cavitand possesses a higher affinity toward aromatic nitro-compounds compared to benzene and toluene, making this receptor of particular interest for the detection of explosive taggants. The results of computational studies have been validated also for the surface-grafted receptor through competitive recognition experiments. These experiments showed that EtQxBox-functionalized PSi can recognize nitrobenzene in the presence of a significant excess of aromatic vapors such as benzene (1:300) or toluene (1:100).

Trace analysis by ion mobility spectrometry: From conventional to smart sample preconcentration methods. A review

Ion mobility spectrometry (IMS) is a rapid and high sensitive technique widely used in security and forensic areas. However, a lack of selectivity is usually observed in the analysis of complex samples due to the scarce resolution of the technique. The literature concerning the use of conventional and novel smart materials in the pretreatment and preconcentration of samples previous to IMS determinations has been critically reviewed. The most relevant strategies to enhance selectivity and sensitivity of IMS determinations have been widely discussed, based in the use of smart materials, as immunosorbents, aptamers, molecularly imprinted polymers (MIPs), ionic liquids (ILs) and nanomaterial. The observed trend is focused on the development of IMS analytical methods in combination of selective sample treatments in order to achieve quick, reliable, sensitive, and selective methods for the analysis of complex samples such as biological fluids, food, or environmental samples.

Molecular Imprinting Applications in Forensic Science

Producing molecular imprinting-based materials has received increasing attention due to recognition selectivity, stability, cast effectiveness, and ease of production in various forms for a wide range of applications. The molecular imprinting technique has a variety of applications in the areas of the food industry, environmental monitoring, and medicine for diverse purposes like sample pretreatment, sensing, and separation/purification. A versatile usage, stability and recognition capabilities also make them perfect candidates for use in forensic sciences. Forensic science is a demanding area and there is a growing interest in molecularly imprinted polymers (MIPs) in this field. In this review, recent molecular imprinting applications in the related areas of forensic sciences are discussed while considering the literature of last two decades. Not only direct forensic applications but also studies of possible forensic value were taken into account like illicit drugs, banned sport drugs, effective toxins and chemical warfare agents in a review of over 100 articles. The literature was classified according to targets, material shapes, production strategies, detection method, and instrumentation. We aimed to summarize the current applications of MIPs in forensic science and put forth a projection of their potential uses as promising alternatives for benchmark competitors.

Colorimetric sensor arrays based on pattern recognition for the detection of nitroaromatic molecules

This research demonstrated that, in a colorimetric sensor array, 2,4,6-trinitrotoluene (TNT), 2,6-dinitrotoluene (2,6-DNT), 2,4-dinitrotoluene (2,4-DNT) and 4-nitrotoluene (4-MNT) were identifiable through a unique pattern in a qualitative and semi-quantitative manner. The adsorption capacity of the molecularly imprinted colloidal particles (MICs) for their corresponding templates was 0.27mmol TNT/g, 0.22mmol 2,6-DNT/g, 0.31mmol 2,4-DNT/g and 0.16mmol 4-MNT/g, respectively. Every optical sensor utilized in the arrays contained three-dimensional molecularly imprinted photonic crystal (MIPC) sensor with different imprinted templates. The intelligent materials can display different colors from green to red to 20mM corresponding nitroaromatics with varying diffraction red shifts of 84nm (TNT), 46nm (2,6-DNT), 54nm (2,4-DNT) and 35nm (4-MNT), respectively. With the assistance of principal component analysis (PCA) and rational design, the sensor array can illustrate the influence of the nitryl quantity and generate a separate response region of nitroaromatics for pattern recognition with 95.25% of variance explained in the measurements by the first three principal components (PCs). The statistical analysis endowed the cross-reactive array with better classification and identification ability and this novel detection platform provided a wider applied range among other harmful chemicals in a simple sensor array with customized functionality.

Visual detection of 2,4,6-trinitrotolune by molecularly imprinted colloidal array photonic crystal

We developed a photonic crystal (PhC) sensor for the quantification of 2,4,6-trinitrotoluene (TNT) in solution. Monodisperse (210nm in diameter) molecularly imprinted colloidal particles (MICs) for TNT were prepared by the emulsion polymerization of methyl methacrylate and acrylamide in the presence of TNT as a template. The MICs were then self-assembled into close-packed opal PhC films. The adsorption capacity of the MICs for TNT was 64mg TNT/g. The diffraction from the PhC depended on the TNT concentration in a methanol/water (3/2, v/v) potassium dihydrogen phosphate buffer solution (pH=7.0, 30mM). The limit of detection (LOD) of the sensor was 1.03μg. The color of the molecularly imprinted colloidal array (MICA) changed from green to red with an 84nm diffraction red shift when the TNT concentration increased to 20mM. The sensor response time was 3min. The PhC sensor was selective for TNT compared to similar compounds such as 2,4,6-trinitrophenol, 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2-nitromesitylene, 4-nitrotoluene, 2-nitrotoluene, 1,3-dinitrobenzene, methylbenzene, 4-nitrophenol, 2-nitroaniline, 3-aminophenol and 3-nitroaniline. The sensor showed high stability with little response change after three years storage. This sensor technology might be useful for the visual determination of TNT.

A non-enzymatic urine glucose sensor with 2-D photonic crystal hydrogel

A novel polymerized crystalline colloidal array (PCCA) sensing material for the detection of urine glucose was developed by embedding a two-dimensional (2-D) polystyrene crystalline colloidal array (CCA) in 3-acrylamidophenylboronic acid (3-APBA)-functionalized hydrogel. After adjusting the cross-linker concentration, this material showed significant sensitivity for glucose under lab conditions, the particle spacing of the PCCA changed from 917 to 824 nm (93 nm) within 3 min as the glucose concentration increased from 0 to 10 mM, and the structural color of the PCCA changed from red through orange, to green, and finally, to cyan. In further experiments, this material was used to semi-quantitatively detect glucose in 20 human urine (HU) samples. Compared with the traditional dry-chemistry method, which was applied widely in clinical diagnosis, the PCCA method was more accurate and cost-effective. Moreover, this method can efficiently avoid the errors induced by most of the urine-interfering elements like vitamin C and ketone body. With a homemade portable optical detector, this low-cost intelligent sensing material can provide a more convenient and efficient strategy for the urine glucose detection in clinical diagnosis and point-of-care monitoring.