Functionalized CdSe/ZnS QDs for the detection of nitroaromatic or RDX explosives

Colloidal Quantum Dots for Explosive Detection: Trends and Perspectives

Sensitive, accurate, and reliable detection of explosives has become one of the major needs for international security and environmental protection. Colloidal quantum dots, because of their unique chemical, optical, and electrical properties, as well as easy synthesis route and functionalization, have demonstrated high potential to meet the requirements for the development of suitable sensors, boosting the research in the field of explosive detection. Here, we critically review the most relevant research works, highlighting three different mechanisms for explosive detection based on colloidal quantum dots, namely photoluminescence, electrochemical, and chemoresistive sensing. We provide a comprehensive overview and an extensive discussion and comparison in terms of the most relevant sensor parameters. We highlight advantages, limitations, and challenges of quantum dot-based explosive sensors and outline future research directions for the advancement of knowledge in this surging research field.

Simple and Cost-Effective Quantum Dot Chemodosimeter for Visual Detection of Biothiols in Human Blood Serum

An emission "turn-off" chemodosimeter for the naked-eye detection of biothiols using silica-overcoated cadmium selenide quantum dots is developed. Hole scavenging by the thiol group of cysteine, homocysteine, or glutathione on interaction with quantum dots resulted in an instant and permanent emission quenching under physiologically relevant conditions. Also, the emission suppression is so specific that thiols and substituted thiols (methionine and cystine) can easily be distinguished. A pilot experiment for the visual detection of serum thiols in human blood was also conducted. Densitometry analysis proved the potential of this system as a new methodology in clinical chemistry and research laboratories for routine blood and urine analyses using a simple procedure. This method enables one to visually distinguish biothiols and oxidized biothiols, whose ratio plays a crucial role in maintaining "redox thiol status" in the blood.

Fluorescent Carbon Dots Derived From Soy Sauce for Picric Acid Detection and Cell Imaging

Picric acid (PA) is a powerful nitro-aromatic explosive that harms the environment and human health. Developing non-toxic and low-cost sensors for the rapid detection of PA is essential. An environment-friendly fluorescent probe for PA detection is designed based on carbon dots (CDs) directly separated from edible soy sauce by silica gel column chromatography. Neither organic reagents nor heating process was needed to prepare CDs. The obtained CDs exhibit bright blue fluorescence, good water solubility, and photostability. The fluorescent probe for PA was developed according to the CD's fluorescence can be significantly quenched via the inner filter effect between CDs and PA. The linear range was 0.2-24 µM with a limit of detection of 70 nM. This proposed method was successfully employed to detect PA in the real water samples with satisfactory recoveries between 98.0-104.0%. Moreover, the CDs were suitable for fluorescence imaging of HeLa cells owing to their low toxicity and good biocompatibility.

Using a dual-emission Sm(iii)-macrocycle as the perceptive lab-on-a-molecule chemosensor toward selective and discriminative detection of nitroaromatic explosives

A dual-emission Sm(iii)-macrocycle Sm-2l is designed as the perceptive lab-on-a-molecule toward selective and discriminative detection of nitroaromatic explosives by statistical analysis.

Curcumin Is an Iconic Ligand for Detecting Environmental Pollutants

The rapid increase in industrial revolution and the consequent environmental contamination demands continuous monitoring and sensitive detection of the pollutants. Nanomaterial-based sensing system has proved to be proficient in sensing environmental pollutants. The development of novel ligands for enhancing the sensing efficiency of nanomaterials has always been a challenge. However, the amendment of nanostructure with molecular ligand increases the sensitivity, selectivity, and analytical performance of the resulting novel sensing platform. Organic ligands are capable of increasing the adsorption efficacy, optical properties, and electrochemical properties of nanomaterials by reducing or splitting of band gap. Curcumin (diferuloylmethane) is a natural organic ligand that exhibits inherent fluorescence and electrocatalytic property. Due to keto-enol tautomerism, it is capable of giving sensitive signals such as fluorescence, luminescence, ultraviolet absorption shifts, and electrochemical data. Curcumin probes were also reported to give enhanced meterological performances, such as low detection limit, repeatability, reproducibility, high selectivity, and high storage stability when used with nanosystem. Therefore, research on curcumin-modified nanomaterials in the detection of environmental pollution needs a special focus for prototype and product development to enable practical use. Hence, this article reviews the role of curcumin as a natural fluorophore in optical and electrochemical sensing of environmentally significant pollutants. This review clearly shows that curcumin is an ideal candidate for developing and validating nanomaterials-based sensors for the detection of environmental pollutants such as arsenic, lead, mercury, boron, cyanide, fluoride, nitrophenol, trinitrotoluene, and picric acid and toxic gases such as ammonia and hydrogen chloride. This review will afford references for future studies and enable researchers to translate the lab concepts into industrial products.

Optimization and Characterization of Electrodeposited Cadmium Selenide on Monocrystalline Silicon

In this work, the optimal conditions for the electrodeposition of a CdSe film on n-Si were demonstrated. The structural and optical properties of the bare films and after annealing were studied. In particular, the crystallinity and photoluminescence of the samples were evaluated, and after annealing at 400 °C under a nitrogen atmosphere, a PL increase by almost an order of magnitude was observed. This paper opens the route towards the use of electrochemical deposition as a cost-effective and easy fabrication approach that can be used to integrate other interesting materials in the silicon-manufacturing processes for the realization of optoelectronic devices.

Theoretical Perspective on the Sensing Mechanism of a Novel Fluorescent Probe for Nitramine Explosives: The Role of Radical Reactions

Rapid detection of hidden nitramine explosives in public areas is a pressing concern for public safety. Deep insight into the sensing mechanism is significant and inspiring to the design of new high-efficiency nitramine probes. This study has theoretically investigated the recognition and fluorescence mechanism of a newly reported high-efficiency nitramine probe, proposing a new reaction pattern and sensing product for the probe with the photodegraded radical nitro dioxide (NO₂) of nitramines. The rationality of the new detection product is confirmed by the fluorescence properties, IR analysis, and energy profiles. The recognition mechanism is found to be an H-abstraction reaction via NO₂ and the turn-off fluorescence mechanism is suggested as a photoinduced electron transfer (PET) process based on the results of the frontier molecular orbital (FMO) analysis. The high selectivity of the probe toward NO₂ is illustrated based on the energy analysis of the sensing products.

An Eu3+-functionalized metal–organic framework (Eu@Zn-MOF) for the highly sensitive detection of rotenone in serum

An Eu3+-functionalized hybrid material (Eu@Zn-MOF) is successfully prepared by the postmodification of Eu3+ ions on its free sulfonic groups. Eu@Zn-MOF can serve as a visual probe to specifically recognize and detect rotenone on the basis of fluorescence quenching effect.

Synthetic Approaches, Modification Strategies and the Application of Quantum Dots in the Sensing of Priority Pollutants

Polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) are two classifications of environmental pollutants that have become a source of health concerns. As a result, there have been several efforts towards the development of analytical methods that are efficient and affordable that can sense these pollutants. In recent decades, a wide range of techniques has been developed for the detection of pollutants present in the environment. Among these different techniques, the use of semiconductor nanomaterials, also known as quantum dots, has continued to gain more attention in sensing because of the optical properties that make them useful in the identification and differentiation of pollutants in water bodies. Reported studies have shown great improvement in the sensing of these pollutants. This review article starts with an introduction on two types of organic pollutants, namely polycyclic aromatic hydrocarbons and nitro-aromatic explosives. This is then followed by different quantum dots used in sensing applications. Then, a detailed discussion on different groups of quantum dots, such as carbon-based quantum dots, binary and ternary quantum dots and quantum dot composites, and their application in the sensing of organic pollutants is presented. Different studies on the comparison of water-soluble quantum dots and organic-soluble quantum dots of a fluorescence sensing mechanism are reviewed. Then, different approaches on the improvement of their sensitivity and selectivity in addition to challenges associated with some of these approaches are also discussed. The review is concluded by looking at different mechanisms in the sensing of polycyclic aromatic hydrocarbons and nitro-aromatic compounds.

A "turn-off" fluorescent sensor based on electrospun polycaprolactone nanofibers and fluorene(bisthiophene) derivative for nitroaromatic explosive detection

The preparation of fluorene(bisthiophene)-based fluorescent nanofibers for nitroaromatic explosive detection provides a convenient rapid and low-cost strategy aiming at forensic applications. Polycaprolactone (PCL) and fluorene(bisthiophene) derivative (FBT) nanofibers were obtained by electrospinning technique as a free-standing mat and characterized by SEM, FTIR, thermal analysis and fluorescence spectroscopy. The PCL/FBT nanofibers presented high sensitivity towards 2,4,6-trinitrotoluene (TNT) and picric acid (PA), with fluorescence quenching (turn-off mechanism), and selectivity to another kind of explosives. The free-standing mats were used as a cloth strip that was swiped on surfaces contaminated with TNT traces allowing its visual detection under UV light source. These findings are particularly important for the development of a facile and promising strategy to assembly portable optical devices for nitroaromatic explosive detection.

A critical review on genotoxicity potential of low dimensional nanomaterials

Low dimensional nanomaterials (LDNMs) have earned attention among researchers as they exhibit a larger surface area to volume and quantum confinement effect compared to high dimensional nanomaterials. LDNMs, including 0-D and 1-D, possess several beneficial biomedical properties such as bioimaging, sensor, cosmetic, drug delivery, and cancer tumors ablation. However, they threaten human beings with the adverse effects of cytotoxicity, carcinogenicity, and genotoxicity when exposed for a prolonged time in industry or laboratory. Among different toxicities, genotoxicity must be taken into consideration with utmost importance as they inherit DNA related disorders causing congenital disabilities and malignancy to human beings. Many researchers have performed NMs' genotoxicity using various cell lines and animal models and reported the effect on various physicochemical and biological factors. In the present work, we have compiled a comparative study on the genotoxicity of the same or different kinds of NMs. Notwithstanding, we have included the classification of genotoxicity, mechanism, assessment, and affecting factors. Further, we have highlighted the importance of studying the genotoxicity of LDNMs and signified the perceptions, future challenges, and possible directives in the field.

Novel and Reliable Chemosensor Based on C. dots from Sunflower seeds for the Distinct Detection of Picric Acid and Bilirubin

Based on the green chemistry approach, highly fluorescent and novel carbon dots (C. dots) were synthesized from naturally available and cost effective sunflower seeds. The obtained C. dots showed a fluorescence quantum yield (Q.Y) of 9.5% with high water dispersibility and photostability. The obtained C. dots were employed for the detection of picric acid (PA) and bilirubin. A good linear relationship in the range of 20-60 nM was obtained for PA with a limit of detection (LOD) as low as 3.86 nM. C. dots were successfully incorporated in the agarose matrix which enabled them to be employed as a solid platform for the in situ detection of PA. The fluorescence of C. dots was selectively quenched by bilirubin compared to other biomolecules with a LOD of 2.03 μM. Use of C. dots as potential candidate for bilirubin detection was verified by real sample analysis. Further, the separation of C. dots was performed using column chromatography and the optical properties of the two different fractions obtained were studied. The blue fraction of C. dots was found to exhibit a higher fluorescence Q.Y and excitation independent emission, with an improved detection of PA and bilirubin.

Biosensing platforms based on silicon nanostructures: A critical review

Biosensors are revolutionizing the health-care systems worldwide, permitting to survey several diseases, even at their early stage, by using different biomolecules such as proteins, DNA, and other biomarkers. However, these sensing approaches are still scarcely diffused outside the specialized medical and research facilities. Silicon is the undiscussed leader of the whole microelectronics industry, and novel sensors based on this material may completely change the health-care scenario. In this review, we will show how novel sensing platforms based on Si nanostructures may have a disruptive impact on applications with a real commercial transfer. A critical study for the main Si-based biosensors is herein presented with a comparison of their advantages and drawbacks. The most appealing sensing devices are discussed, starting from electronic transducers, with Si nanowires field-effect transistor (FET) and porous Si, to their optical alternatives, such as effective optical thickness porous silicon, photonic crystals, luminescent Si quantum dots, and finally luminescent Si NWs. All these sensors are investigated in terms of working principle, sensitivity, and selectivity with a specific focus on the possibility of their industrial transfer, and which ones may be preferred for a medical device.

Charge carrier pairing can impart efficient reduction efficiency to core/shell quantum dots: applications for chemical sensing

Semiconductor quantum dots (QDs) are bright fluorophores that have significant utility for imaging and sensing applications. Core QDs are often employed in chemosensing via redox processes that modulates their fluorescence in the presence of an analyte. However, such particles lack robust surface passivation and generally contain a sizable portion of nonfluorescent QDs, which is detrimental to the detection limit. We investigated an approach to "turn on" non-fluorescent core QDs by lightly overcoating them with a thin shell of a higher bandgap semiconductor. The shell augments the population of sensing chromophores and increases the emission lifetime; however, it simultaneously mollifies redox processes that are responsible for analyte sensitivity to begin with. This balancing act was successfully applied to enhance the sensitivity of CdZnS/ZnS QDs towards 2,4,6-trinitrotoluene (TNT). Unexpectedly, it was found that CdZnS/ZnS QDs with very thick shells retained substantial sensitivity to TNT. This observation may be due to close coupling of the reduced substrate with the QD hole that is enabled by the near-degeneracy of holes in the core CdZnS and ZnS shell. The ability of core/shell QDs to retain substantial reducing power may have implications for other applications that can benefit from the enhanced stability of robust core/shell nanomaterials.

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.

Ultrasensitive detection of Cr(VI) (Cr2O72-/CrO42-) ions in water environment with a fluorescent sensor based on metal-organic frameworks combined with sulfur quantum dots

Accurate, simple and quick detection methods for Cr(VI) detection are urgently needed for water quality monitoring. Herein, a novel and facile method of detecting Cr(VI) (Cr₂O₇^2-/CrO₄^2-) ions is developed via the fluorescent detection technology based on metal-organic frameworks (MOFs) doped with sulfur quantum dots (SQDs) (SQDs@UiO-66-NH₂). The blue-light-emitting SQDs@UiO-66-NH₂ composites exhibit excellent fluorescent properties in water environment with high quantum yield (68%) and ideal fluorescent stability, thus demonstrating excellent potential for serving as a chemical sensor. After characterizing the performance and stability of SQDs@UiO-66-NH₂, qualitative and quantitative detection of Cr₂O₇^2- and CrO₄^2- ions was successfully conducted. The fluorescence of SQDs@UiO-66-NH₂ composites in aqueous solution was quenched effectively with more than 90% quenching efficiency by Cr(VI) via the inner filter effect. The detection system provides considerable advantages such as rapid response (10 s), high sensitivity with a low detection limit of 0.16 μM in a broad linear range of 0-200 μM (R² = 0.99) for Cr₂O₇^2- and 0.17 μM for CrO₄^2- in a broad linear range of 0-220 μM (R² = 0.99), high selectivity and reproducibility for at least five cycles with simple washing with alcohol. In practical applications, the sensor showed rapid response, high sensitivity and excellent recoveries (96.7%-105.4%) for detecting Cr₂O₇^2- in real water samples. Furthermore, a SQDs@UiO-66-NH₂-based fluorescent test paper was successfully developed, providing a simple, reliable and portable method for Cr(VI) (Cr₂O₇^2-/CrO₄^2-) detection in water environment.

From children's toy to versatile sensor: One-step doping of Play-Doh with primary amino group for explosive detection both on surfaces and in solution

2,4,6-trinitrotoluene (TNT) sensing on surfaces and in solution is an important issue in sensor fabrication for homeland security and environmental protection. Herein, Play-Doh, a modeling material popular for kids, was proposed as a versatile sensor for on-site fluorescent (FL), visual FL (VFL), and colorimetric detection of TNT both on surfaces and in solution after being doped with -NH₂ through a one-step approach. Play-Doh exhibits FL emission due to the main ingredient of flour. After -NH₂ doping, amino-Play-Doh (APD) was utilized to construct a FL sensor based on FL resonance energy transfer and inner filter effect for TNT detection. The advantage of APD was that no additional fluorophore was needed compared with the traditional sensors for FL and VFL analysis. The orange complex visible to the naked eye was also recorded for smartphone-based colorimetric detection of TNT. In both cases, the APD demonstrated good analytical performance for TNT. Finally, APD was successfully utilized for TNT sensing on fingerprints, luggage, and in environmental water samples, respectively. Play-Doh might be a potential sensor for future on-site detection of TNT owing to the merits of being cost-effective and versatile.

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.

Fabrication of amine functionalized CdSe@SiO2 nanoparticles as fluorescence nanosensor for highly selective and sensitive detection of picric acid

In this work, amino functionalized CdSe-silica core-shell nanoparticles (NH₂-CdSe@SiO₂ NPs) were constructed as probe to detect picric acid (PA). The CdSe QDs were embedded in SiO₂ nanoparticles and modified with amino groups on the surface. The nitro explosives are electron deficient in nature, which will have stronger affinity for amines and resulted in fluorescence quenching of quantum dots. It was proved that this strategy is selective, easy and sensitive enough for sensing PA with a detection limit of 0.5 × 10^-7 M.

Application of Zero-Dimensional Nanomaterials in Biosensing

Zero-dimensional (0D) nanomaterials, including graphene quantum dots (GQDs), carbon quantum dots (CQDs), fullerenes, inorganic quantum dots (QDs), magnetic nanoparticles (MNPs), noble metal nanoparticles, upconversion nanoparticles (UCNPs) and polymer dots (Pdots), have attracted extensive research interest in the field of biosensing in recent years. Benefiting from the ultra-small size, quantum confinement effect, excellent physical and chemical properties and good biocompatibility, 0D nanomaterials have shown great potential in ion detection, biomolecular recognition, disease diagnosis and pathogen detection. Here we first introduce the structures and properties of different 0D nanomaterials. On this basis, recent progress and application examples of 0D nanomaterials in the field of biosensing are discussed. In the last part, we summarize the research status of 0D nanomaterials in the field of biosensing and anticipate the development prospects and future challenges in this field.

A novel sustainable metal organic framework as the ultimate aqueous phase sensor for natural hazards: detection of nitrobenzene and F− at the ppb level and rapid and selective adsorption of methylene blue

A novel metal organic framework (MOF) exhibits good aqueous phase sensing properties towards nitrobenzene and fluoride anions and selective adsorption/separation ability for methylene blue.

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.

Assembly of four new cobalt coordination polymers modulated by N-coligands: sensitive and selective sensing of nitroaromatics, Fe3+and Cr2O72−in water

Four new Co-CPs (1to4) have been obtained with the modulation of N-coligands.2and3can serve as multi-responsive sensors for rapid and sensitive detection of nitroaromatics, Fe³⁺and Cr₂O₇²⁻in water.

High-Performance Quantum Dots with Synergistic Doping and Oxide Shell Protection Synthesized by Cation Exchange Conversion of Ternary-Composition Nanoparticles

The insertion of cation impurities into quantum dots (QDs) as a dopant has been proved to be an efficient way to tailor their optical, electronic, and magnetic properties; however, the low quantum yield (QY) and poor photostability strongly limit their further applications. We report a strategy to coat a thin oxide shell around the heterovalent doped QDs to enhance their QYs and photostabilities simultaneously. In the case of Ag⁺-doped CdS QDs, the controlled cation exchange reaction between Cd²⁺ and ternary Ag₃SbS₃ nanoparticles not only realizes the Ag⁺ doping in CdS QDs but also generates a thin Sb₂O₃ shell around the surface of the QDs. Enabled by such, as-prepared CdS:Ag@Sb₂O₃ QDs exhibited enhanced photostability and high QY of 66.5%. We envision that the findings presented here will inspire more novel protocols for advancing the practical applications of doped QDs.

Facet-Dependent Interfacial Charge Transfer in TiO2/Nitrogen-Doped Graphene Quantum Dots Heterojunctions for Visible-Light Driven Photocatalysis

Interfacial charge transfer is crucial in the efficient conversion of solar energy into fuels and electricity. In this paper, heterojunction composites were fabricated, comprised of anatase TiO2 with different percentages of exposed {101} and {001} facets and nitrogen-doped quantum dots (NGQDs) to enhance the transfer efficiency of photo-excited charge carriers. The photocatalytic performances of all samples were evaluated for RhB degradation under visible light irradiation, and the hybrid containing TiO2 with 56% {001} facets demonstrated the best photocatalytic activity. The excellent photoactivity of TiO2/NGQDs was owed to the synergistic effects of the following factors: (i) The unique chemical features of NGQDs endowed NGQDs with high electronic conductivities and provided its direct contact with the TiO2 surface via forming Ti–O–C chemical bonds. (ii) The co-exposed {101} and {001} facets were beneficial for the separation and transfer of charge carriers in anatase TiO2. (iii) The donor-acceptor interaction between NGQDs and electron-rich {101} facets of TiO2 could remarkably enhance the photocurrent, thus hindering the charge carriers recombination rate. Extensive characterization of their physiochemical properties further showed the synergistic effect of facet-manipulated electron-hole separation in TiO2 and donor-acceptor interaction in graphene quantum dots (GQDs)/TiO2 on photocatalytic activity.

Luminescent Lanthanide-Based Probes for the Detection of Nitroaromatic Compounds in Water

A new mixed pyridyl-carboxylate ligand with two picolinate chromophores and a flexible linear spacer, potassium 2,2'-(butane-1,4-diylbis((pyridin-2-ylmethyl)azanediyl))diacetate (K₂bpbd), which is obtained in high yield and spectroscopically characterized, has been utilized to make new lanthanide complexes, namely, [Ln(bpbd) (H₂O)₂(NO₃)]·xH₂O, where Ln = Tb (1) and x = 6, Ln = Sm (2) and x = 7, and Ln = Dy (3) and x = 7. These complexes have been extensively characterized by various spectroscopic techniques (UV-vis and Fourier transform infrared spectroscopy), elemental analyses, thermogravimetric analysis, field emission scanning electron microscopy, and powder X-ray diffraction. These show very intense characteristic luminescence features that confirm the antenna effect of the ligand on the metal center. These complexes have been utilized for the detection of various nitroaromatic compounds. Among these three complexes, 1 is found to be the best for the selective sensing of 2,4,6-trinitrophenol in water with a detection limit of (0.35 ± 0.05) ppm. Its Stern-Volmer constant, K _SV [(5.48 ± 0.1) × 10⁴ M^-1], is one of the highest among similar sensors reported so far.

Fluorescence Sensing Approach for High Specific Detection of 2,4,6-Trinitrophenol Using Bright Cyan Blue Color-Emittive Poly(vinylpyrrolidone)-Supported Copper Nanoclusters as a Fluorophore

In this paper, we illustrate an efficient, convenient, and simplistic fluorescence technique for the specific identification for nitro explosive 2,4,6-trinitrophenol (TNP) in 100% water medium by bright cyan blue color-emitting poly(vinylpyrrolidone)-supported copper nanoclusters (PVP-CuNCs) as a fluorescence probe. PVP-CuNCs exhibited linear fluorescence quenching response toward the increasing concentration of TNP analyte. Surprisingly, TNP only reduces the emission signal of PVP-CuNCs, whereas various nitro explosives cause very slight reducing emission intensity, validating the good specificity of the PVP-CuNC probe toward TNP. The highest Stern-Volmer quenching constant (K _sv) value of 1.03 × 10⁷ dm³ mol^-1 and the extremely lowest limit of detection of 81.44 × 10^-12 mol dm^-3 were achieved solely for TNP in 100% water medium which is astonishing and exclusive for this nanoprobe. The sensing pathway for the high sensitivity of PVP-CuNCs assay to quantify the TNP is expected to combine with the inner filter effect process and static quenching. The static quenching mechanism between TNP and PVP-CuNCs is further verified by fluorescence decay measurements. Furthermore, the developed fluorescence sensing platform is applied for the quantification of a trace amount of TNP in real samples named dam water, sea water, and match stick.

Nanostructured Graphene Oxide Dots: Synthesis, Characterization, Photoinduced Electron Transfer Studies, and Detection of Explosives/Biomolecules

Herein, we report the preparation of graphene oxide dots (GO dots) by fine-tuning the carbonization degree of citric acid. The structure of GO dots was characterized by absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, as well as high-resolution scanning electron microscopy and transmission electron microscopy analyses. The typical particle size of the GO dots was 42 nm. The fluorescent characteristics of the GO dots were analyzed by fluorescence spectroscopy. Once excited at 360 nm, the GO dots were fluorescent in the range of 450-550 nm, which was dependent on the excitation wavelength. Further, GO dots were effectively utilized for multifarious applications such as photoinduced electron transfer and detection of explosives and biomolecules. The emission property of GO dots was competently quenched by viologens, picric acid (PA), and bilirubin (BR). The mechanism of quenching by viologens and explosives/biomolecules was found to be due to photoinduced electron transfer and the internal filter effect, respectively. Intriguingly, the detection minimum of PA is in the nanomolar level. Toward commercialization, the economic test strips have also been introduced for the identification of PA. Furthermore, the GO dots have been applied as an efficient luminescent bioprobe for a selective and perceptive finding of BR.

Photostable and Low-Toxic Yellow-Green Carbon Dots for Highly Selective Detection of Explosive 2,4,6-Trinitrophenol Based on the Dual Electron Transfer Mechanism

Advances in the development of fluorescent carbon dots (CDs) for detecting nitro-explosives have attracted great interest. However, developing long-wavelength luminescence CDs for highly selective determination of 2,4,6-trinitrophenol (TNP) and getting insight into the detection mechanism remain further to be investigated. Here, excitation-independent yellow-green emission CDs with good photostability and low biotoxicity were introduced for detecting TNP selectively. Then, two types of electron transfer (ET) processes including hydrogen-bond interaction-assisted ET and proton transfer-assisted ET are suggested to be responsible for their photophysical behavior. Finally, the visual detection of TNP has been successfully developed by a CD-based indicator paper. The facile, highly sensitive, and selective detection for TNP in both of a solution and a solid phase makes CDs potentially useful in environmental sensor applications.

Engineering design toward exploring the functional group substitution in 1D channels of Zn–organic frameworks upon nitro explosives and antibiotics detection

Three MOFs (1, 2, 3) with distinct functional groups were prepared. 2 exhibited moderate sensitivity for the detection of specific explosives/antibiotics at the same concentration, which was lower and higher than that of 3 and 1, respectively.

Multichannel Discriminative Detection of Explosive Vapors with an Array of Nanofibrous Membranes Loaded with Quantum Dots

The multichannel fluorescent sensor array based on nanofibrous membranes loaded with ZnS quantum dots (QDs) was created and demonstrated for the discriminative detection of explosives. The synergistic effect of the high surface-to-volume ratio of QDs, the good permeability of nanofibrous membranes and the differential response introduced by surface ligands was played by constructing the sensing array using nanofibrous membranes loaded with ZnS QDs featuring several surface ligands. Interestingly, although the fluorescence quenching of the nanofibrous membranes is not linearly related to the exposure time, the fingerprint of each explosive at different times is very similar in shape, and the fingerprints of the three explosives show different shapes. Three saturated vapors of nitroaromatic explosives could be reliably detected and discriminated by the array at room temperature. This work is the first step toward devising a monitoring system for explosives in the field of public security and defense. It could, for example, be coupled with the technology of image recognition and large data analysis for a rapid diagnostic test of explosives. This work further highlights the power of differential, multichannel arrays for the rapid and discriminative detection of a wide range of chemicals.

Explosives in the Cage: Metal-Organic Frameworks for High-Energy Materials Sensing and Desensitization

An overview of the current status of coordination polymers and metal-organic frameworks (MOFs) pertaining to the field of energetic materials is provided. The explosive applications of MOFs are discussed from two aspects: one for detection of explosives, and the other for explosive desensitization. By virtue of their adjustable pore/cage sizes, high surface area, tunable functional sites, and rich host-guest chemistry, MOFs have emerged as promising candidates for both explosive sensing and desensitization. The challenges and perspectives in these two areas are thoroughly discussed, and the processing methods for practical applications are also discussed briefly.

Base-driven sunlight oxidation of silver nanoprisms for label-free visual colorimetric detection of hexahydro-1,3,5-trinitro-1,3,5-triazine explosive

Here we report a label-free method for visual colorimetric detection of hexahydro-1,3,5-trinitro-1,3,5-triazine (HTT) explosive based on base-driven sunlight oxidation of silver nanoprisms (AgNPRs). Under natural sunlight illumination, the surface plasmon of AgNPRs is excited, which populates O₂ antibonding orbitals to generate negative-ion state (O₂^-). The resultant O₂^- with a strong oxidation activity can etch AgNPRs to smaller nanodisks with the aid of NaOH aqueous solution, leading to a blue shift of the absorption peak and color change from blue to pink. However, when HTT is introduced, the resultant O₂^- will be consumed by the nitrite and formaldehyde that are produced from the alkaline hydrolysis of HTT. Under this condition, the etching of AgNPRs does not occur, and the detection solution remains blue. This assay can sensitively detect as low as 1nM HTT, a level which is three orders of magnitude lower than that of gold nanoparticle-based colorimetric assays (2.6μM), and shows linearity in the range of 0.003-3.3μM. The lowest detectable concentration with the naked eye is 0.1μM. Additionally, the present assay exhibits good selectivity, and can be applied in the detection of HTT in natural water and soil samples with recoveries ranging from 90% to 100%.

A single molecular fluorescent probe for selective and sensitive detection of nitroaromatic explosives: A new strategy for the mask-free discrimination of TNT and TNP within same sample

A simple naphthalene based fluorescent probe was first time reported as dual sensing of 2,4,6-trinitrotolune (TNT) and 2,4,6-trinitrophenol (TNP) by distinguishable changes in both solution color change and fluorescence within same sample without any mask agent. Upon addition of TNT and TNP, the strong emission quenching at 412nm and a new emission band at 530nm was observed, respectively. In addition, the sensing mechanism was evaluated by DFT calculations by Gaussian 09 software.

Advances in single quantum dot-based nanosensors

We review the advances in single quantum dot-based nanosensors and their biomedical applications. We highlight their challenges and future direction.

Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives

The detection of nitro explosives by transition metal complexes/metallosupramolecules with their designs and sensing mechanisms are comprehensively reviewed.

A nonconjugated macromolecular luminogen for speedy, selective and sensitive detection of picric acid in water

A conventional fluorophore-free water-soluble copolymer based on poly(styrene-alt-maleimide) has been found to be selective and sensitive detection of picric acid in a 100% aqueous environment with prompt response.