A new electrochemical sensor of nitro aromatic compound based on three-dimensional porous Pt–Pd nanoparticles supported by graphene–multiwalled carbon nanotube composite

A highly-sensitive electrochemical sensor based on Ni nanoparticles modified carbon nanotubes/sulfonated reduced graphene oxide for the detection of capsaicinoids in leisure sauced meat products

Unclear labeling of spiciness degrees on leisure sauced meat products is prone to resulting in customer complaints and commercial disputes. The content of capsaicinoids is the basis for evaluating the spiciness of food. In this work, an electrochemical sensor based on nickel nanoparticles modified carbon nanotubes (Ni-CNTs) and sulfonated reduced graphene oxide (S-rGO) was developed for the rapid detection of capsaicinoids content in leisure sauced meat products. The linear ranges of capsaicins are 0.01-100 μmol/L with ultra-low detection limits of 1 nmol/L. The outstanding performances are primarily due to the synergistic effect between Ni-CNTs and S-rGO. This effect not only created a three-dimensional stacked structure that improved the electrochemically active surface area, but also generated an internal electric field that improved the charge transfer rate. This work provides a basis for standardized evaluation of spiciness.

Design of a versatile and selective electrochemical sensor based on dummy molecularly imprinted PEDOT/laser-induced graphene for nitroaromatic explosives detection

Considering the formidable explosive power and human carcinogenicity of nitroaromatic explosives, the implementation of an accurate and sensitive detection technology is imperative for ensuring public safety and monitoring post-blast environmental contamination. In the present work, a versatile and selective electrochemical sensor based on dummy molecularly imprinted poly (3,4-ethylenedioxythiophene)/laser-induced graphene (MIPEDOT/LIG) was successfully developed and the specific detection of multiple nitroaromatic explosives was realized in the single sensor. The accessible and nontoxic trimesic acid (TMA) and superior 3, 4-ethylenedioxythiophene (EDOT) were selected as the dummy-template and the functional monomer, respectively. The interaction between the functional monomer and the template, and the morphology, electrochemical properties and detection performance of the sensor were comprehensively investigated by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry. Benefiting from the alliance of TMA and EDOT, the MIPEDOT/LIG sensor manifested outstanding selectivity and sensitivity for 2,4,6-trinitrotolueen (TNT), 2,4,6-trinitrophenol (TNP), 2,4-dinitrotoluene (DNT), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrophenol (DNP), and 1,3-dinitrobenzene (DNB) (representative nitroaromatic explosives) with limits of determination of 1.95 ppb, 3.06 ppb, 2.49 ppb, 1.67 ppb, 1.94 ppb, and 4.56 ppb, respectively. The sensor also exhibited extraordinary reliability and convenience for environmental sample detection. Therefore, a perfect combination of versatility and selectivity in the MIPEDOT/LIG sensor was achieved. The findings of this work provide a new direction for the development of multi-target electrochemical sensors using a versatile dummy template for explosives detection.

A Multi-Enzyme Cascade Response for the Colorimetric Recognition of Organophosphorus Pesticides Utilizing Core-Shell Pd@Pt Nanoparticles with High Peroxidase-like Activity

In modern agricultural practices, organophosphorus pesticides or insecticides (OPs) are regularly used to restrain pests. Their limits are closely monitored since their residual hinders the capability of acetylcholinesterase (AChE) and brings out a threatening accumulation of the neurotransmitter acetylcholine (ACh), which affects human well-being. Therefore, spotting OPs in food and the environment is compulsory to prevent human health. Several techniques are available to identify OPs but encounter shortcomings like time-consuming, operating costs, and slow results achievement, which calls for further solutions. Herein, we present a rapid colorimetric sensor for quantifying OPs in foods using TMB as a substrate, a multi-enzyme cascade system, and the synergistic property of core-shell Palladinum@Platinum (Pd@Pt) nanoparticles. The multi-enzyme cascade response framework is a straightforward and effective strategy for OPs recognition and can resolve the previously mentioned concerns. Numerous OPs, including Carbofuran, Malathion, Parathion, Phoxim, Rojor, and Phosmet, were successfully quantified at different concentrations. The cascade method established using Pd@Pt had a simple and easy operation, a lower detection limit range of (1-2.5 ng/mL), and a short detection time of about 50 min. With an R2 value of over 0.93, OPs showed a linear range of 10-200 ng/mL, portraying its achievement in quantifying pesticide residue. Lastly, the approach was utilized in food samples and recovered more than 80% of the residual OPs.

Porous {P6Mo18O73}-type Poly(oxometalate) Metal-Organic Frameworks for Improved Pseudocapacitance and Electrochemical Sensing Performance

{P₆Mo₁₈} poly(oxometalate) (POM) clusters have huge steric hindrance and limited active oxygen atoms, which make them difficult to combine with metal-organic units to form three-dimensional (3D) porous structures. Therefore, functionalization of such POMs has always been a bottleneck that is difficult to break through. In this study, {P₆Mo₁₈} POM was successfully grafted on a lock-like metal-organic chain to generate a multiporous coordination polymer, [{Na(H₂O)(H₂btb)}{Cu₄^I(H₂O)(pz)₅Cl}{H₂Sr⊂P₆Mo₂^VMo₁₆^VIO₇₃}]·3H₂O (1) (pz = pyrazine; btb = 1,4-bis(1,2,4-triazole) butane). Meanwhile, a zero-dimensional (0-D) control compound with only btb ligands as counterions, (H₄btb)[H₄Sr⊂P₆Mo₂^VMo₁₆^VIO₇₃]·3H₂O (2), was also obtained via a hydrothermal reaction. Compound 1 represents the first basket-type 3D poly(oxometalate) metal-organic framework (POMOF) assembly, which possesses interpenetrating pores and complex topology. 1-GO-CPE displays improved supercapacitor (SC) performance (the specific capacitance of 929.4 F g^-1 at a current density of 3 A g^-1 with 94.1% of cycle efficiency after 5000 cycles) compared with 2-GO-CPE and most reported POMOF electrode materials, which may be due to the outstanding redox capability of basket-POM, introduction of metal-organic chains, intersecting pores, and excellent conductivity of graphene. An asymmetric SC device with 1-GO-CPE as the negative electrode exhibits an energy density of 29.7 Wh kg^-1 with a power density of 3148.2 W kg^-1 and long-lasting cycling life. In addition, 1-GO-GCE as an electrochemical sensor responds to dopamine (DA) at a voltage of 0.40 V and shows lower detection limits (0.19 μM (signal-to-noise ratio (SNR) = 3)), higher selectivity, and good reproducibility in the linear range of 0.56 μM to 0.24 mM. The ability to accurately detect the content of DA in biological samples further proves the feasibility of the sensor in practical applications.

Polyoxometalate-based materials in extraction, and electrochemical and optical detection methods: A review

Polyoxometalates (POMs) as metal-oxide anions have exceptional properties like high negative charges, remarkable redox abilities, unique ligand properties and availability of organic grafting. Moreover, the amenability of POMs to modification with different materials makes them suitable as precursors to further obtain new composites. Due to their unique attributes, POMs and their composites have been utilized as adsorbents, electrodes and catalysts in extraction, and electrochemical and optical detection methods, respectively. A survey of the recent progress and developments of POM-based materials in these methods is therefore desirable, and should be of great interest. In this review article, POM-based materials, their properties as well as their identification methods, and analytical applications as adsorbents, electrodes and catalysts, and corresponding mechanisms of action, where relevant, are reviewed. Some current issues of the utilization of these materials and their future prospects in analytical chemistry are discussed.

Nanomaterial-enhanced 3D-printed sensor platform for simultaneous detection of atrazine and acetochlor

The widespread use of herbicides in agriculture and gardening causes environmental and safety issues such as water pollution. Thus, efficient and convenient analysis of the levels of herbicide residues is of significant importance. Here, we employed 3D-printing to design a multiplex immunosensor for simultaneous detection of two widely used herbicides, atrazine and acetochlor. Multiplexing was achieved through customization of a lateral flow immunoassay, and then integrated with an electrochemical analyzer for ultrasensitive detection. Quantification of herbicide residues was realized through the detection of a novel nanomaterial label, the mesoporous core-shell palladium@platium nanoparticle (Pd@Pt NP), for its outstanding peroxidase-like property. During the electrochemical analysis, the catalytic activity of Pd@Pt NPs on the redox reaction between thionin acetate and hydrogen peroxide provided an electrochemically driven signal that accurately indicated the level of herbicide residues. Using this Nanomaterial-enhanced multiplex electrochemical immunosensing (NEMEIS) system, simultaneous detection of atrazine and acetochlor was realized with a limit of detection of 0.24 ppb and 3.2 ppb, respectively. To further evaluate the feasibility, the optimized NEMEIS was employed for detection in atrazine and acetochlor residue-containing spiked samples, and an overall recovery with 90.8% - 117% range was obtained. The NEMEIS constructed with the aid of 3D-printing provides a rapid, precise, economical, and portable detection device for herbicides, and its success suggests potential broad applications in chemical analysis, biosensors and point-of-care monitoring.

A flower-like ZnO–Ag2O nanocomposite for label and mediator free direct sensing of dinitrotoluene

2,4-Dinitrotoluene (2,4-DNT) is a nitro aromatic compound used as a raw material for trinitrotoluene (TNT) explosive synthesis along with several other industrial applications. Easy, rapid, cost-effective, and selective detection of 2,4-DNT is becoming essential due to its hepato carcinogenic nature and presence in surface as well as ground water as a contaminant. Keeping this in view, this research, for the first-time, reports the synthesis of novel ZnO–Ag₂O composite nanoflowers on a gold (Au) substrate, to fabricate an electrochemical sensor for label-free, direct sensing of 2,4-DNT selectively. The proposed ZnO–Ag₂O/Au sensor exhibits a sensitivity of 5 μA μM⁻¹ cm⁻² with a low limit of detection (LOD) of 13 nM, in a linear dynamic range (LDR) of 0.4 μM to 40 μM. The sensor showed reasonably high re-usability and reproducibility, with reliable results for laboratory and real-world samples.

2,4-Dinitrotoluene (2,4-DNT) is a nitro aromatic compound used as a raw material for trinitrotoluene (TNT) explosive synthesis along with several other industrial applications.

Binder-Free Modification of a Glassy Carbon Electrode by Using Porous Carbon for Voltammetric Determination of Nitro Isomers

In this study, Liquidambar formosana tree leaves have been used as a renewable biomass precursor for preparing porous carbons (PCs). The PCs were produced by pyrolysis of natural waste of leaves after 10% KOH activation under a nitrogen atmosphere and characterized by a variety of state-of-the-art techniques. The PCs possess a large surface area, micro-/mesoporosity, and functional groups on its surface. A glassy carbon electrode modified with high PCs was explored as an efficient binder-free electrocatalyst material for the voltammetric determination of nitro isomers such as 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA). Under optimal experimental conditions, the electrochemical detection of 3-NA and 4-NA was found to have a wide linear range of 0.2-115.6 and 0.5-120 μM and a low detection limit of 0.0551 and 0.0326 μM, respectively, with appreciable selectivity. This route not only enhanced the benefit from biomass wastes but also reduced the cost of producing electrode materials for electrochemical sensors. Additionally, the sensor was successfully applied in the determination of nitro isomers even in the presence of other common electroactive interference and real samples analysis (beverage and pineapple jam solutions). Therefore, the proposed method is simple, rapid, stable, sensitive, specific, reproducible, and cost-effective and can be applicable for real sample detection.

Three-dimensional Pd/Pt bimetallic nanodendrites on a highly porous copper foam fiber for headspace solid-phase microextraction of BTEX prior to their quantification by GC-FID

The preparation of bimetallic Pd/Pt nanofoam for use in fiber based solid-phase microextraction (SPME) is described. First, a highly porous copper foam was prepared on the surface of an unbreakable copper wire by an electrochemical method. Then, the substrate was covered with metallic Pd and Pt using galvanic replacement of the Cu nanofoam substrate by applying a mixture of Pd(II) and Pt(IV) ions. The procedure provided an efficient route to modify Pd/Pt nanofoams with large specific surface and low loading with expensive noble metals. The fiber was applied to headspace SPME of benzene, toluene, ethylbenzene and xylene (BTEX) (as the model compounds) in various spiked water and wastewater samples. It was followed by gas chromatography-flame ionization detection (GC-FID). A Plackett-Burman design was performed for screening the experimental factors prior to Box-Behnken design. Compared with the commercial PDMS SPME fiber (100 μm), it had higher extraction efficiency for BTEX. Under the optimum conditions, the method has low limits of detection (0.16-0.35 μg L^-1), a wide linear range (1-200 μg L^-1), relative standard deviations between 5.8 and 10.5%, and good recoveries (>85% from spiked samples). Graphical abstract Schematic presentation of a three-dimensional Pd/Pt bimetallic nanodendrites supported on a highly porous copper foam fiber for use in headspace solid phase microextraction of BTEX. They were then quantified by gas chromatography-flame ionization detector.

Nanozyme-Mediated Dual Immunoassay Integrated with Smartphone for Use in Simultaneous Detection of Pathogens

Nanozymes are an excellent class of optical reporters for the development of sensitive biosensors for widespread applications. In this study, mesoporous core-shell palladium@platinum (Pd@Pt) nanoparticles were synthesized and then applied as signal amplifier in a dual lateral flow immunoassay (LFIA) and integrated with a smartphone-based device for use in simultaneous detection of Salmonella Enteritidis and Escherichia coli O157:H7. After optimization, the limit of detections were calculated to be ∼20 cfu/mL for S. Enteritidis and ∼34 cfu/mL for E. coli O157:H7, respectively. The greatly improved sensitivity was contributed by the peroxidase-like catalytic activity of the Pd@Pt nanoparticles for signal enhancement and the parallel design of dual detection for eliminating the cross-interference. The estimated recoveries of the dual LFIA range from 91.44 to 117.00%, which indicated that the developed method is capable of detecting live bacteria in food samples. This approach provides an attractive platform for S. Enteritidis and E. coli O157:H7 detection using a smartphone-based device as the sole piece of equipment, indicating great promise for foodborne pathogen analysis or in-field food safety tracking.

Highly sensitive shape dependent electro-catalysis of TNT molecules using Pd and Pd–Pt alloy based nanostructures

This study demonstrates the fabrication of a highly sensitive electrochemical sensor designed for the quantification of 2,4,6-trinitrotoluene (TNT).

Graphene Nanoribbon-Supported PtPd Concave Nanocubes for Electrochemical Detection of TNT with High Sensitivity and Selectivity

In this work, PtPd concave nanocubes anchored on graphene nanoribbons (PtPd-rGONRs) were successfully fabricated through a hydrothermal process. The structural characterizations confirmed that PtPd concave cubes with an average size of around 11 nm have been successfully synthesized and they are uniformly assembled on the surface of rGONRs. The electrochemical measurements demonstrated that the PtPd-rGONRs composite-modified glassy carbon electrode (GCE) shows much enhanced current signals for TNT reduction, which is 4 and 12-fold higher than rGONRs and bare glassy carbon electrode, respectively. The PtPd-rGONRs exhibited a wide linear range for TNT detection from 0.01 to 3 ppm with the sensing limit of 0.8 ppb. Moreover, the PtPd-rGONRs showed excellent detection stability for the determination of TNT. Most importantly, the PtPd-rGONRs-based electrochemical detection platform can be successfully applied to TNT detection in tap water and real lake water samples. The present study indicates that graphene nanoribbon-supported nanocrystals are promising in designing high performance electrochemical sensors for explosives detection.

Advances in explosives analysis--part I: animal, chemical, ion, and mechanical methods

The number and capability of explosives detection and analysis methods have increased substantially since the publication of the Analytical and Bioanalytical Chemistry special issue devoted to Explosives Analysis (Moore and Goodpaster, Anal Bioanal Chem 395(2):245-246, 2009). Here we review and critically evaluate the latest (the past five years) important advances in explosives detection, with details of the improvements over previous methods, and suggest possible avenues towards further advances in, e.g., stand-off distance, detection limit, selectivity, and penetration through camouflage or packaging. The review consists of two parts. This part, Part I, reviews methods based on animals, chemicals (including colorimetry, molecularly imprinted polymers, electrochemistry, and immunochemistry), ions (both ion-mobility spectrometry and mass spectrometry), and mechanical devices. Part II will review methods based on photons, from very energetic photons including X-rays and gamma rays down to the terahertz range, and neutrons.

A porous elastomeric polyurethane monolith synthesized by concentrated emulsion templating and its pressure-sensitive conductive property

The spontaneous distribution of acid-treated MWCNTs in the concentrated emulsion leads to the press-sensitive conductivity of the porous PU.

Removal of multi-substituted nitroaromatic pollutants by zero valent iron: a comparison of performance, kinetics, toxicity and mechanisms

Reductive degradation of three typical multi-substituted nitroaromatic pollutants by zero valent iron was comprehensively compared in terms of performance, kinetics, toxicity and mechanisms in this study.

Nanomaterials-based electrochemical detection of chemical contaminants

Recent advances in the development of nanomaterials-based electrochemical sensors for environmental monitoring and food safety applications are assessed.