Highly selective and sensitive fluorescent paper sensor for nitroaromatic explosive detection

Using eugenol scaffold to explore the explosive sensing properties of Cd(II)-based coordination polymers: experimental studies and real sample analysis

Eugenol, the major constituent of clove oil, has been explored as an essential natural ingredient for ages owing to its versatile pharmacological properties. However, to date, the coordination chemistry of eugenol derivatives has not been much explored. In the present work, an eugenol-based Schiff base ligand (HL) was synthesized and structurally confirmed through ESI-MS, NMR, and FT-IR spectroscopy studies. Consequently, the N,O-donor chelating ligand HL was coordinated with Cd2+, in the presence of bridging pseudohalides (thiocyanate, SCN-, and dicyanamide, N(CN)2-) to synthesize two luminescent coordination polymers (CPs 1 and 2): [Cd2(L)2(X)2]n (where HL = 4-allyl-2-(((2-(benzylamino)ethyl) imino)methyl)-6-methoxyphenol and Xs are bridging pseudohalides, i.e., SCN- and N(CN)2-) on a Cd-eugenol scaffold. The CPs depicted structural diversity, bulk-phase purity, thermal stability, and the presence of interlayer supramolecular C-H⋯π interactions together with C-H⋯S (for CP 1) and C-H⋯N (for CP 2) interactions. The CPs further exemplified themselves as selective and sensitive 'turn-off' probes towards trinitrophenol (TNP) (quenching efficiency: 82.02% and 83.86% for 1 and 2) among a pool of hazardous nitroaromatic compounds (NACs). Accordingly, 1 and 2 exhibited an ultralow limit of detection (LOD) of 0.29 and 0.15 μM, with high quenching constants (KSV) of 5.91 × 104 and 17.60 × 104 M-1, respectively. In addition, TNP sensing events were evidenced to be recyclable and exhibited fast response (∼31 s, 1, and ∼40 s, 2), which increased its real-world viability. Vapor phase TNP sensing was also accomplished upon drop-casted CP films. Experimental investigations and theoretical DFT study confirmed the cooperative occurrence of RET-IFE-PET-collisional quenching and non-covalent π⋯π stacking as key factors involved in the TNP sensing performance. The competency of 1 and 2 in the detection of TNP from several complex environmental matrices (CEMs), viz. matchstick powder, river and sewage water, and soil specimens, was also established with good recovery (∼66-86% and ∼68-93% for 1 and 2, respectively) and high KSV values (3.90-11.39 × 104 and 6.17-18.79 × 104 M-1 for 1 and 2, respectively).

Enhanced Cataluminescence Sensor Based on SiO2/MIL-53(Al) for Detecting Isobutylaldehyde

A simple, rapid, and reliable method for detecting harmful gases is urgently required in environmental security fields. In this study, a highly effective cataluminescence sensor based on SiO2/MIL-53(Al) composites was developed to detect trace isobutylaldehyde. The sensor was designed using isobutylaldehyde to generate an interesting cataluminescence phenomenon in SiO2/MIL-53(Al). Under optimized conditions, a positive linear relationship was observed between the signal intensity of the cataluminescence and isobutylaldehyde concentration. The isobutylaldehyde concentration range of 1.55-310 ppm responded well to the sensing test, with an excellent correlation coefficient of 0.9996. The minimum detectable concentration signal-to-noise ratio (S/N = 3) was found to be 0.49 ppm. In addition, the sensor was effectively utilized for analyzing trace isobutylaldehyde; the analysis resulted in recoveries ranging from 83.4% to 105%, with relative standard deviations (RSDs) of 4.8% to 9.4%. Furthermore, the mechanism of cataluminescence between SiO2/MIL-53(Al) and isobutylaldehyde was explored using GC-MS analysis and density functional theory. We expect that this cataluminescence methodology will provide an approach for the environmental monitoring of isobutylaldehyde.

Analytical developments in the synergism of copper particles and cysteine: a review

Cysteine, a sulfur-containing amino acid, is a vital candidate for physiology. Coinage metal particles (both clusters and nanoparticles) are highly interesting for their spectacular plasmonic properties. In this case, copper is the most important candidate for its cost-effectiveness and abundance. However, rapid oxidation destroys the stability of copper particles, warranting the necessity of suitable capping agents and experimental conditions. Cysteine can efficiently carry out such a role. On the contrary, cysteine sensing is a vital step for biomedical science. This review article is based on a comparative account of copper particles with cysteine passivation and copper particles for cysteine sensing. For the deep understanding of readers, we discuss nanoparticles and nanoclusters, properties of cysteine, and importance of capping agents, along with various synthetic protocols and applications (sensing and bioimaging) of cysteine-capped copper particles (cysteine-capped copper nanoparticles and cysteine-capped copper nanoclusters). We also include copper nanoparticles and copper nanoclusters for cysteine sensing. As copper is a plasmonic material, fluorometric and colorimetric methods are mostly used for sensing. Real sample analysis for both copper particles with cysteine and copper particles for cysteine sensing are also incorporated in this review to demonstrate their practical applications. Both cysteine-capped copper particles and copper particles for cysteine sensing are the main essence of this review. The aspect of the synergism of copper and cysteine (unlike other amino acids) is quite promising for future researchers.

Aggregation-induced emission enhancement (AIEE) active bispyrene-based fluorescent probe: "turn-off" fluorescence for the detection of nitroaromatics

The detection of nitroaromatic explosives in real samples is essential for environmental monitoring because of their strongly powerful nature and wide applications in industries. Aggregation-induced emission enhancement (AIEE) active fluorescent probe has been widely employed to detect nitroaromatic explosives. Hereby, a simple V-shaped bispyrene-based fluorescent probe (called py-o) with AIEE properties was designed and synthesized, which was fully charactered by 1D NMR, ESI, FTIR, and 2D NOESY spectra. The py-o displayed bright blue-green fluorescence excimer emission at 480 nm in DMF/H2O (v/v 1:1). It is observed that the fluorescence excimer emission of py-o at 480 nm was quenched by PA in solution with a quenching constant of 5.45 × 104 M-1, and the limit of detection was approximately 0.139 μM. The details of the sensing mechanism were explained using 1H NMR titrations, Job's plot and Bensi-Hildebrand methods, which revealed a 1:1 binding ratio via the π-π interactions between PA and py-o. Meanwhile, it exhibited outstanding anti-interference ability in the detection of PA when interfering analytes were added under the same conditions. Furthermore, low-cost thin-layer chromatography (TLC) plates coated with py-o were developed as fluorescent tools for naked-eye detection of PA in the solid state. Therefore, this work provides a new method for constructing an AIEE fluorescent probe for the detection of nitroaromatic explosives to utilize in environmental monitoring.

Label-Free Detection of Unbound Bilirubin and Nitrophenol Explosives in Water by a Mechanosynthesized Dual Functional Zinc Complex: Recognition of Picric Acid in Various Common Organic Media

High levels of unconjugated bilirubin (UB) in serum lead to asymptomatic and neonatal jaundice and brain dysfunctions. Herein, we have reported the detection of UB at as low as 1 μM in an aqueous alkaline medium using a Zn(II) complex. The specificity of the complex has been validated by the HPLC in the concentration window 6-90 μM, which is rare. The sensory response of the probe at physiological pH against nitro explosives developed it as an instant-acting fluorosensor for picric acid (PA) and 2,4-dinitrophenol (2,4-DNP). Spectroscopic titration provided a binding constant of 4×105  M-1 with PA. The naked eye detection was found to be 15 μM. The solid-state photoluminescent nature of the complex enabled it for PA sensing in the solid phase. Interestingly, the probe remained fluorescent in various volatile and non-volatile organic solvents. As a result, it can also detect PA and 2,4-DNP in a wide range of common organic media. NMR studies revealed the coordination of PA, 2,4-DNP, and UB to the Zn(II) center of the probe, which is responsible for the observed quenching of the probe with the analytes.

The Failure of Molecular Imprinting in Conducting Polymers: A Case Study of Imprinting Picric Acid on Polycarbazole

The aims of this study were to investigate the potential of utilising molecularly imprinted polycarbazole layers to detect highly toxic picric acid (PA) and to provide information about their performance. Quantum chemical calculations showed that strong interactions occur between PA and carbazole (bond energy of approximately 31 kJ/mol), consistent with the theoretical requirements for effective molecular imprinting. The performance of the sensors, however, was found to be highly limited, with the observed imprinting factor values for polycarbazole (PCz) layers being 1.77 and 0.95 for layers deposited on Pt and glassy carbon (GC) electrodes, respectively. Moreover, the molecularly imprinted polymer (MIP) layers showed worse performance than unmodified Pt or GC electrodes, for which the lowest limit of detection (LOD) values were determined (LOD values of 0.09 mM and 0.26 mM, respectively, for bare Pt and MIP PCz/Pt, as well as values of 0.11 mM and 0.57 mM for bare GC and MIP PCz/GC). The MIP layers also showed limited selectivity and susceptibility to interfering agents. An initial hypothesis on the reasons for such performance was postulated based on the common properties of conjugated polymers.

Receptor-free phenothiazine derivative as fluorescent probe for picric acid: Investigation of the inner filter effect channel

In this study, a highly fluorescent and receptor-free phenothiazine derivative (PDAB) was developed to detect picric acid. A combination of steady-state and time-resolved fluorescence studies was conducted to examine the excited state behavior of PDAB with picric acid in solution. The PDAB probe displayed a significant degree of selectivity and was highly sensitive to picric acid, with an extremely low detection limit of 9.82 nM. Time-resolved fluorescence quenching studies exhibit direct evidence of an inner filter effect-based sensing mechanism. Using the Parker equation, a thorough analysis was done to correct the inner filter effect on the sensing of picric acid. Overall, these studies provide critical information on the sensing mechanism for picric acid detection.

Mononuclear Zn(II) Complex Based on N2O Ligand Compartment: First Case to Detect Nitro Explosives

This paper scrutinises the development of low-cost hypersensitive fluorescent probes manipulated chemically with Schiff base complexes and their prospective applicability for the detection of nitro explosives in light of the rapidly expanding demand for anti-trafficking measures. In this study, a new Zn(II) metal complex has been synthesized in one pot using the Schiff base ligand L= 2-methoxy-5-methyl-N-(2-pyridin-2-ylmethylene) aniline. The complex was also thoroughly characterised using various spectroscopic tools and subjected to single crystal XRD analysis. In the asymmetric unit, square pyramidal zinc (II) centre exist in the inner N2O compartment of the ligand L. The intermolecular Cg···Cg interactions exist between two different asymmetric residual units lead to supramolecular assembly along b axis. By turning off the fluorescence response, the complex serves as a sensor for the detection of nitro aromatics in CH3CN solution. A significant quenching efficiency has been reported with a quenching constant (KSV) 1.8 × 104 M-1 for 4-nitrobenzoic acid during investigation of sensing phenomenon in solution phase. In addition, determining the binding stoichiometry of the chemosensor with NO2 and the binding constant, the mechanism of fluorescence quenching has also been postulated. The detection limit of NO2 is 7.6×10 -7 M, with the binding constant k = 1.1021× 108 M-1. Additionally, the DFT calculation makes it easier to comprehend the appropriate binding process in light of the findings of experiments. We also designed a paper sensor strip for the visual detection of Nitro Explosive Residues in light of the sensor's potential used in forensic investigations.

A multifunctional cucurbit[6]uril-based supramolecular assembly for fluorescence sensing of TNP and Ba2+ and information encryption

Both nitroaromatic compounds (NACs) and heavy metal ions are accumulative high-risk environmental pollutants, so high-sensitivity detection of these environment pollutants is necessary. In this work, a cucurbit[6]uril (CB[6]) based luminescent supramolecular assembly [Na₂K₂(CB[6])₂(DMF)₂(ANS)(H₂O)₄](1) (CB[6] = cucurbit[6]uril, ANS^2- = 8-Aminonaphthalene-1,3,6-trisulfonic acid ion) has been synthesized under solvothermal conditions, using ANS^2- as a structural inducer. Performance studies have shown that 1 exhibits excellent chemical stability and easy regeneration ability. It can highly selective sensing of 2,4,6-trinitrophenol (TNP) through fluorescence quenching with a strong quenching constant (K_sv = 2.58 × 10⁴ M^-1). Additionally, the fluorescence emission of 1 can be effectively enhanced with Ba²⁺ in aqueous solution (K_sv = 5.57 × 10³ M^-1). More impressively, Ba²⁺@1 was successfully used as anti-counterfeiting fluorescent ink functional material with strong information encryption function. This work illustrates the application prospects of luminescent CB[6]-based supramolecular assembly in environmental pollutants detection and information anti-counterfeiting for the first time, which extends the multifunctional application scope of CB[6]-based supramolecular assembly.

Paper-Based Probes with Visual Response to Vapors from Nitroaromatic Explosives: Polyfluorenes and Tertiary Amines

Although it is well-known that nitroaromatic compounds quench the fluorescence of different conjugated polymers and form colored Meisenheimer complexes with proper nucleophiles, the potential of paper as a substrate for those macromolecules can be further developed. This work undertakes this task, impregnating paper strips with a fluorene-phenylene copolymer with quaternary ammonium groups, a bisfluorene-based cationic polyelectrolyte, and poly(2-(dimethylamino)ethyl methacrylate) (polyDMAEMA). Cationic groups make the aforementioned polyfluorenes attachable to paper, whose surface possesses a slightly negative charge and avoid interference from cationic quenchers. While conjugated polymers had their fluorescence quenched with nitroaromatic vapors in a non-selective way, polyDMAEMA-coated papers had a visual response that was selective to 2,4,6-trinitrotoluene (TNT), and that could be easily identified, and even quantified, under natural light. Far from implying that polyfluorenes should be ruled out, it must be taken into account that TNT-filled mines emit vapors from 2,4-dinitrotoluene (DNT) and dinitrobenzene isomers, which are more volatile than TNT itself. Atmospheres with only 790 ppbv TNT or 277 ppbv DNT were enough to trigger a distinguishable response, although the requirement for certain exposure times is an important limitation.

Amplifying inorganic chirality using liquid crystals

Chiral inorganic nanostructures have drawn extensive attention thanks to their unique physical properties as well as multidisciplinary applications. Amplifying inorganic chirality using liquid crystals (LCs) is an efficient way to enhance the parented inorganic asymmetry owing to chirality transfer. Herein, the universal synthetic methods and structural characterizations of chiral inorganic-doped LC hybrids are introduced. Additionally, the current progress and status of recent experiment and theory research about chiral interactions between inorganic nanomaterials (e.g. metal, semiconductor, perovskite, and magnetic oxide) and LCs are summarized in this review. We further present representative applications of these new hybrids in the area of encryption, sensing, optics, etc. Finally, we provide perspectives on this field in terms of material variety, new synthesis, and future practice. It is envisaged that LCs will act as a pivotal part in the amplification of inorganic chirality with versatile applications.

In Silico Studies and Design of Scrupulous Novel Sensor for Nitro Aromatics Compounds and Metal Ions Detection

A Novel calix[4]pyrrole system bearing carboxylic acid functionality [ABuCP] has been synthesized and its interaction towards various nitroaromatics compounds [NACs] were investigated. ABuCP showed significant color change with 1,3-dinitro benzene (1,3-DNB) in comparison to the solution of other nitroaromatic compounds such as 2,3-dinitro toluene (2,3-DNT), 2,4-dinitro toluene (2,4-DNT), 2,6-dinitro toluene (2,6-DNT), 4-NBB (4-nitrobenzyl bromide) and 4-nitro toluene (4-NT). The ABuCP-1,3-DNB complex produces a red shift in absorption spectra based on charge transfer mediated recognition. Additionally, the density functional theory calculation confirmed the possible mechanism for the binding of 1,3-DNB as a guest is well supported by the calculation of other parameters such as hardness, stabilization energy, softness, electrophilicity index and chemical potential. The TDDFT calculation facilitates the understanding of the proper binding mechanism in reference to experimental results. Additionally we have also developed its derivative which acts as a new fluorescent sensor which can selectively recognize Sr(II) ions. In this view its aminoanthraquinone derivative of calix[4]pyrrole i.e. ABuCPTAA is synthesized which also results in generation of high fluorescence capability sensor.

An aggregation-induced emission-active bis-heteroleptic ruthenium(ii) complex of thiophenyl substituted phenanthroline for the selective “turn-off” detection of picric acid

A bis-heteroleptic Ru(ii) polypyridine complex-based AIEgen has been developed for the selective detection of nitroaromatic explosive picric acid in aqueous media.

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.

Recent advances of environmental pollutants detection via paper-based sensing strategy

Paper has become one of the most promising substrates for building low-cost and powerful sensing platforms due to its self-pumping ability and compatibility with multiple patterning methods. Paper-based sensors have been greatly developed in the field of environmental monitoring. In this review, we introduced the research and application of paper-based sensors in environmental monitoring, focusing on the deposition and patterning methods of building paper-based sensors, and summarized the applications of detecting environmental pollutants, including metal ions, anions, explosives, neurotoxins, volatile organic compounds, and small molecules. In addition, the development prospects and challenges of promoting paper-based sensors are also discussed. The current review will provide references for the construction of portable paper-based sensors, and has implications for the field of on-site real-time detection of the environment.

Fluorescent nucleotide-lanthanide nanoparticles for highly selective determination of picric acid

A new method based on coordination polymer nanoparticles (CPNs) derived from nucleotides and Tb³⁺ ions (GMP/Tb) for the selective and sensitive determination of aqueous 2,4,6-trinitrophenol (TNP) (picric acid) is established. The fluorescence of GMP/Tb nanoparticles is effectively quenched by TNP via photo-induced charge transfer (PCT), thus achieving its selectivity toward TNP over other nitroaromatic explosives. The decreased fluorescence of GMP/Tb shows a good linear relationship to the concentrations of TNP ranging from 5.0 to 40.0 μM, and the limit of detection is 26.0 nM (5.96 ppb). The proposed GMP/Tb probe also achieves satisfactory results in real samples. The obtained recoveries of this method in river water samples are in the range 93.15-106.10%. The relative standard deviation (RSD) are 0.57 to 1.01% based on three repeated determinations. This fabricated detector provides a feasible path for determination of ppb-level TNP in natural water samples, which can help humans to avoid TNP-contaminated drinking water. Graphical abstract.

Facile Microwave-Assisted Synthesis of Functionalized Carbon Nitride Quantum Dots as Fluorescence Probe for Fast and Highly Selective Detection of 2,4,6-Trinitrophenol

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5 nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104 M-1. This sensing system exhibits a fast response time within 1 min and a wide linear response range from 0.1 to 15 μM. The limit of detection is as low as 87 nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. Graphical Abstract An optical sensor based on functionalized carbon nitride quantum dots (CNQDs) were fabricated from L-tartaric acid and urea by a facile one-pot microwave-assisted solvothermal method, and were effectively utilized to the detection of 2,4,6-trinitrophenol (TNP) based on fluorescence (FL) quenching.

PEI-capped KMgF3:Eu2+ nanoparticles for fluorescence detection of nitroaromatics in municipal wastewater

The probing and quantitative detection of nitroaromatics is key for public safety and the monitoring of wastewater. Currently, most techniques used for the detection of nitroaromatics require ideal conditions rather than real conditions, making practical applications challenging. As nitroaromatics have strong absorption in the range of 350-370 nm, we can design a kind of KMgF₃:Eu²⁺ nanophosphor with a strong f-f transition emission located at 362 nm, and an energy resonance transfer system based on the overlap of the emission peak of nanophosphors and the absorption peak of nitroaromatics can be constructed to realize the quantitative detection of nitroaromatics in municipal wastewater. Based on this, in this paper, a fluorescence resonance energy transfer (FRET) sensor is designed by choosing polyethylenimine (PEI)-capped KMgF₃:Eu²⁺ nanoparticles as an energy donor for the ultrasensitive detection of nitroaromatics, which can also work as an energy acceptor. The KMgF₃:Eu²⁺ nanoparticle sensor shows great sensitivity and selectivity and good linear characteristics in both DI water and wastewater. The detection limits in municipal wastewater were 0.456, 0.598, 0.667, 0557 and 0.678 ng/mL for TNT, TNP, p-nitrotoluene, dinitrobenzene (DNB), and nitrobenzene (NB), respectively. The detection accuracy was identified by high-performance liquid chromatography (HPLC). The results showed that the sensor had superior sensitivity and great accuracy and could be used in practical applications.

Highly selective and sensitive fluorescent zeolitic imidazole frameworks sensor for nitroaromatic explosive detection

Nitroaromatic explosives, such as 2-4-6 trinitrotoluene (TNT) are dangerous materials that pose safety and environmental risks. Even though many sensors have been reported for the detection of nitroaromatic explosives, a facile, rapid, cost-effective sensor is still sought-after in the field. Here we demonstrate a facile and rapid method to synthesize a fluorescent metal-organic framework for the highly selective and sensitive detection of nitroaromatic explosives. Zeolitic imidazole framework-8 (ZIF-8) is synthesized and enhanced with fluorescent 8-hydroxyquinoline zinc (ZnQ). The synthesized material shows visible colour changes upon exposure to TNT from ivory to light red. In addition, fluorescence quenching is noted under UV illumination when the ZnQ@ZIF-8 is exposed to TNT. The ZnQ@ZIF-8-coated paper sensors show the highest fluorescence quenching at an emission wavelength of 455 nm with TNT concentration as low as 1 ppm. Therefore, the proposed strategy not only offers a fast and convenient protocol for selective detection of TNT but also offers great potential in practical applications, especially for airport/railway security inspection and prevention of terrorist attacks.

Highly sensitive and ultrafast film sensor based on polyethyleneimine-capped quantum dots for trinitrophenol visual detection

Real-time detection of nitroaromatic explosives is a pressing problem for public security and environmental monitoring. Although many efforts have been devoted, sensing of explosives still suffers limitations of complicated and time-consuming sensing procedure. In this work, we develop a fluorescent film for rapid and visual detection of 2,4,6-trinitrophenol (TNP) by using polyethyleneimine-capped quantum dots (QDs-PEI) as fluorescent sensing probe and electrospun membrane as matrix. Fluorescent sensing is mainly based on effective reaction between amino groups of PEI and nitro groups, phenol hydroxyl groups of TNP. It also benefits from the rapid absorption of TNP in aqueous solution by PA6 nanofiber membranes with high hydrophilicity and porosity. As a result, visual sensing could be realized when TNP is >100 ng·mL^-1 by obvious fluorescent change with a thirty-second response time. We believe this fluorescent membrane sensor holds a promising prospect for real time and visual detection of TNP in environmental science and analytical fields.

A reliable and facile fluorescent sensor from carbon dots for sensing 2,4,6-trinitrophenol based on inner filter effect

2,4,6-Trinitrophenol (TNP) has absorbed much concerns because of its toxic effect and threat on the environment, which results from the fact that it is an important and universal reagent widely utilized for manufacturing many products. It is of great necessity to explore facile and efficient methods for monitoring TNP. In present study, carbon dots (CDs), a new carbonaceous nanomaterial with strong fluorescence, was applied to build a novel sensor for highly sensitive and selective detection of TNP. In the sensing procedure, the fluorescence intensity of as-prepared CDs was diminished with the presence of TNP due to inner filter effect (IFE) quenching mechanism. The sensitivity of the fluorescent sensor was very high with limit of detection down to 5.37 ng mL^-1. This fluorescent sensor was evaluated and excellent spiked recoveries were gained, which demonstrated that the developed sensor would be a robust tool for environmental applications.

A simple and ubiquitous device for picric acid detection in latent fingerprints using carbon dots

This work addresses the synthetic optimization of carbon dots (CDs) and their application in sensing picric acid from latent fingerprints by exploiting a smartphone-based RGB tool. The optimization of the synthesis of CDs is investigated towards achieving shorter reaction time, better product yield and fluorescence quantum efficiency. Precursors such as citric acid and thiourea were chosen for the synthesis of CDs. Among the various synthetic methodologies, it is found that the pyrolysis method offers ∼50% product yield within 15 min. The morphology and optical properties of the prepared CDs are characterized using the typical microscopic and spectroscopic techniques, respectively. The synthesized CDs exhibit quasi-spherical shape with an average particle size of 1.7 nm. The excitation dependent emissive properties of CDs are investigated by time resolved fluorescence spectroscopy. Furthermore, the excellent fluorescence properties (φ = 11%) of CDs are explored as a fluorescent fingerprint powder for the identification of latent fingerprints on various substrates. In addition, the presence of picric acid in latent fingerprints was detected. Furthermore, this study is extended to perform real time detection of fingerprints and harmful contaminants in fingerprints by utilizing a smartphone-based RGB color analysis tool. Based on these investigations, the prepared CDs could be a prospective fluorescent material in the field of forensics.

Tb-doped BSA-gold nanoclusters as a bimodal probe for the selective detection of TNT

Trinitrotoluene (TNT) is a widely used explosive belonging to the family of nitroaromatic compounds, and its misuse poses a significant threat to society. Herein, we propose a Tb-BSA-AuNC fluorescent and colorimetric sensing probe for the selective onsite detection of TNT in the aqueous phase. Tb-doped BSA-protected gold nanoclusters (Tb-BSA-AuNCs) were synthesized by a microwave-assisted method, and TNT detection was carried out utilizing the chemistry of Meisenheimer complex formation. Tb doping of gold nanoclusters was demonstrated to facilitate better electron shuttling effects and thereby improve the efficiency of complex formation between the TNT and gold nanoclusters. A paper strip assay was also developed for TNT detection with the designed probe. Limits of detection and quantification of 0.2136 mM and 0.7120 mM, respectively, were achieved. Graphical abstract.

A Highly Sensitive and Selective Isobutyraldehyde Sensor Based on Nanosized Sm2O3 Particles

A highly sensitive and selective sensor for isobutyraldehyde (IBD) is demonstrated based on intensive cataluminescence (CTL) emission from the surface of nanosized Sm₂O₃ particles. The characteristics and optimum conditions for the CTL sensor, including the working temperature, wavelength, and flow rate, were investigated in detail. Under the optimized experimental conditions, the CTL intensity varied linearly with the concentration of IBD, in the two-order-of-magnitude range of 0.015-3.9 μg/mL, with a correlation coefficient (r) of 0.99991 and a limit of detection (LOD), at a signal-to-noise ratio (S/N = 3) of 4.6 ng/mL. The sensor was quite specific: butyraldehyde, methanol, ethanol, acetone, formaldehyde, acetaldehyde, benzene, ethylbenzene, and cumene could not produce significant CTL intensities; specifically, butyraldehyde, ethanol, acetone, and acetaldehyde produced low CTL intensities, with values that were 3.8%, 2.8%, 0.60%, and 0.57% that of IBD. As a test of sensor stability, we found that the relative standard deviation (RSD) of 30 measurements of the CTL at an IBD concentration of 1.6 μg/mL within a period of 72 h was 2.2%, indicating good stability and long service life of the sensor. The sensor was tested against spiked samples containing IBD, and recoveries between 89.7% and 97.4% were obtained with an RSD of 6.1%-8.6%. The performance of the sensor indicated its utility for practical sample analysis.

Selective determination of 2,4,6-trinitrophenol by using a novel carbon nanoparticles as a fluorescent probe in real sample

2,4,6-Trinitrophenol (TNP) is widely used in our daily life; however, excessive use of TNP can lead to a large number of diseases. Therefore, it is necessary to find an effective method to detect TNP. Herein, the rapid fluorescence quenching by TNP was developed for the fluorometric determination of TNP in aqueous medium based on the internal filter effect. Nitrogen-sulfur-codoped carbon nanoparticles (N,S-CNPs), synthesized by a one-pot solvothermal method with the precursors of L-cysteine and citric acid, were applied for the determination of TNP as a fluorescent probe. The excitation peak center of N,S-CNPs and the emission peak center are 340 nm and 423 nm, respectively. The probe can be used in a variety of conditions to detect TNP due to its relatively stable properties. Meanwhile, it has a fast response time (< 1 min), wide linear response range (0.1-40 μM), and low detection limit (43.0 nM). This probe still has excellent selectivity and high sensitivity. The method was also used to detect standard water samples with a satisfactory recovery rate, and it will be used in the application of pollutants and clinical diseases. Graphical abstract.

A highly sensitive and selective detection of picric acid using fluorescent sulfur-doped graphene quantum dots

The development of an analytical probe to monitor highly mutagenic picric acid (PA) carries enormous significance for the environment and for health. A novel, simple and rapid fluorescence analytical assay using sulfur-doped graphene quantum dots (SGQDs) was designed for the highly sensitive and selective detection of PA. SGQDs were synthesized via simple pyrolysis of 3-mercaptopropionic acid and citric acid and characterized using advanced analytical techniques. Fluorescence intensity (FI) of SGQDs was markedly quenched by addition of PA, attributed to the inner filter effect and dominating static quenching mechanism between the two, in addition to a significant colour change. The calibration curve of the proposed assay exhibited a favourable linearity between quenched FI and PA concentration over the 0.1-100 μΜ range with a lowest detection limit of 0.093 μΜ and a correlation coefficient of 0.9967. The analytical assay was investigated for detection of trace amounts of PA in pond and rain water samples and showed great potential for practical applications with both acceptable recovery (98.0-100.8%) and relative standard deviation (1.24-4.67%). Analytical performance of the assay in terms of its detection limit, linearity range, and recovery exhibited reasonable superiority over previously reported methods, thereby holding enormous promise as a simple, sensitive, and selective method for detection of PA.

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.

Copper-based ionic liquid-catalyzed click polymerization of diazides and diynes toward functional polytriazoles for sensing applications

An efficient copper-based ionic liquid-catalyzed azide–alkyne click polymerization was developed, and functional polytriazoles were produced which could be used as sensors.

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.

Hydrothermal synthesis of WS2 quantum dots and their application as a fluorescence sensor for the selective detection of 2,4,6-trinitrophenol

Selective and sensitive detection of 2,4,6-trinitrophenol (TNP), a member of the nitroaromatic explosives family, was demonstrated using luminescent WS₂ quantum dots.

Synthesis of Nano-Praseodymium Oxide for Cataluminescence Sensing of Acetophenone in Exhaled Breath

In this work, we successfully developed a novel and sensitive gas sensor for the determination of trace acetophenone based on its cataluminescence (CTL) emission on the surface of nano-praseodymium oxide (nano-Pr₆O₁₁). The effects of working conditions such as temperature, flow rate, and detecting wavelength on the CTL sensing were investigated in detail. Under the optimized conditions, the sensor exhibited linear response to the acetophenone in the range of 15-280 mg/m³ (2.8-52 ppm), with a correlation coefficient (R²) of 0.9968 and a limit of detection (S/N = 3) of 4 mg/m³ (0.7 ppm). The selectivity of the sensor was also investigated, no or weak response to other compounds, such as alcohols (methanol, ethanol, n-propanol, iso-propanol, n-butanol), aldehyde (formaldehyde and acetaldehyde), benzenes (toluene, o-xylene, m-xylene, p-xylene), n-pentane, ethyl acetate, ammonia, carbon monoxide, carbon dioxide. Finally, the present sensor was applied to the determination of acetophenone in human exhaled breath samples. The results showed that the sensor has promising application in clinical breath analysis.

A Highly Efficient and Durable Fluorescent Paper Produced from Bacterial Cellulose/Eu Complex and Cellulosic Fibers

The general method of producing fluorescent paper by coating fluorescent substances onto paper base faces the problems of low efficiency and poor durability. Bacterial cellulose (BC) with its nanoporous structure can be used to stabilize fluorescent particles. In this study, we used a novel method to produce fluorescent paper by first making Eu/BC complex and then processing the complex and cellulosic fibers into composite paper sheets. For this composting method, BC can form very stable BC/Eu complex due to its nanoporous structure, while the plant-based cellulosic fibers reduce the cost and provide stiffness to the materials. The fluorescent paper demonstrated a great fluorescent property and efficiency. The ultraviolet absorbance or the fluorescent intensity of the Eu-BC fluorescent paper increased with the increase of Eu-BC content but remained little changed after Eu-BC content was higher than 5%. After folding 200 times, the fluorescence intensity of fluorescent paper decreased by only 0.7%, which suggested that the Eu-BC fluorescent paper has great stability and durability.