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An electrochemical sensor for detection of three monohydroxylated polycyclic aromatic hydrocarbons (OH−PAHs) was fabricated by electrochemical reduction of graphene oxide (E‐rGO) on screen‐printed electrode (SPE). The E‐rGO film presents typical wrinkled structure with porous and cavity‐like nanostructure, providing large surface area, effective π‐electron system and high electrical conductivity. The developed E‐rGO/SPE sensor exhibits outstanding sensing performance for the target OH−PAHs, 2‐hydroxynaphthalene, 3‐hydroxyphenanthrene, and 1‐hydroxypyrene, within a linear range varying from 50–800 nM, 50–1150 nM, and 100–1000 nM, and with a limit of detection (LOD) of 10.1 nM, 15.3 nM, and 20.4 nM (S/N=3), respectively. The electrochemical sensor possesses excellent stability, acceptable reproducibility, and good anti‐interference ability. Additionally, the proposed sensor can be applied to the analysis of OH−PAHs in the urine samples with recoveries of 98.1–105.9 %. [ABSTRACT FROM AUTHOR]

• A reliable assay of rolling circle amplification combined with DNAzyme. • The method detection limit as low as fM. • Colorimetric semi-quantitative sensing of CaMV35S promoter. The cauliflower mosaicvirus 35S (CaMV35S), as the most common promoter, has a usage rate of 70 % in transgenic crops, especially in dicots. Herein, a visual detection method of rolling circle amplification (RCA) combined with DNAzyme technology was developed for the determination of CaMV35S gene. A template sequence of the G-quadruple gene was designed for combining with the target gene CaMV35S. When the target gene existed, the RCA reaction occurred through the action of the enzyme, and the product combined with hemin to generate DNAzyme, which catalyzed the color reaction of 2′-hydrazine-bis-3-ethylbenzothiazolin-6-sulfonic acid (ABTS). Under the optimal experimental conditions, the linear range is 1 × 10−13∼1 × 10-8 mol/L, and the detection limit is 3 × 10-14 mol/L (S/N = 3). The method has been successfully applied to standard samples and practical samples (soybean and tofu). For verifying the feasibility and reliability, real-time fluorescent quantitative PCR method was used to detect the target gene CaMV35S, and the results were in good agreement with those of our method, indicating that our developed method can be used for the determination of actual samples. [ABSTRACT FROM AUTHOR]

• A simple and efficient method based on free-complementary DNA was developed to detect ochratoxin A. • A lower detection limit and a higher sensitivity of the method were achieved due to the optimization of detection conditions. • The assay showed the potential and practical application for OTA detection in real food samples. An ultrasensitive, rapid, and specific method for Ochratoxin A (OTA) detection was designed using complementary sequence to aptamer as a target of molecular beacon (MB). The designed loop structure of the MB has the same sequence as the aptamer with a complementary DNA (cDNA) which translates the level of the target into a measurable response. The presence of the target holds aptamer at the corresponding amount and the additional cDNAs are consumed by unbound aptamers which avails free cDNAs that resulting in fluorescence rising due to unfolding of MBs. Under the optimized conditions, the fluorescence intensity increased linearly with OTA concentration over the range of 10 pg mL−1–1 µg mL−1 with the detection limit of 0.247 pg mL−1. The application of this assay in wheat sample in comparison with HPLC-MS/MS method, demonstrated that the new assay could be a potential sensing platform for OTA detection. [ABSTRACT FROM AUTHOR]

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), a type of fatty acid that has many health benefits, are of increasing concern. Herein, we developed a method for the rapid esterification and enrichment of ω-3 PUFAs in eggs, which includes microwave-assisted esterification (MAE) and electrically enhanced solid-phase microextraction (EE-SPME). Combined with gas chromatographic, efficient detection of ω-3 PUFAs was achieved in eggs. Under microwave radiation, the esterification efficiency exhibited a significant increase ranging from 5.06 to 10.65 times. The EE-SPME method reduced extraction time from 50 to 15 min. In addition, improvements in extractive fiber coating materials were explored, which ensured efficient extraction of ω-3 PUFAs. Under the optimal conditions, the method displayed a low detection limit (1.01–1.54 μg L−1), good recoveries (85.82%–106.01%), and wide linear range (7.5–1000 μg L−1), which was successfully applied to determine ω-3 PUFAs in real egg samples. • The modified coating material (HLB-An) had good electrical and thermal properties. • Microwave method significantly reduced esterification time. • The introduction of electric field accelerated the extraction of omega-3 fatty acids. • A rapid and efficient method was developed to detect omega-3 fatty acids in eggs. [ABSTRACT FROM AUTHOR]

A sensitive, selective and high-throughput electrochemical enzyme-linked immunosorbent assay (EC-ELISA) platform was constructed for determination of alfatoxin M1 (AFM1). Rolling circle amplified (RCA) DNAzyme coupled with covalent organic frameworks (COFs) modified electrode was used as signal amplification strategies. The immunoreaction was performed on a microplate via specific recognition of AFM1 by primer-AuNPs-aptamer and anti-AFM1 antibody. The primer triggered RCA reaction produced a long single-stranded DNA, which can fold into a peroxidase-mimicking DNAzyme with the presence of hemin and K+. In the presence of H 2 O 2 , DNAzyme catalyzed the oxidation of 2-aminophenol and the oxidation product 3-aminophenylhydrazine was enriched as a signal molecule on the TpBD modified electrode with a significant current response. Under optimized conditions, the sensor exhibited high selectivity and sensitivity towards AFM1 with a detection limit of 0.15 ng/mL. In addition, the AFM1 can also be quantified by the naked eye. This EC-ELISA platform was successfully applied for the determination of AFM1 in milk samples with recoveries from 93.37% to 104.01%. [ABSTRACT FROM AUTHOR]

Phthalate esters (PAEs), a category of widely used plasticizers, are tend to migrate from plastic packaging to drinks. In this paper, we develop a simple and rapid coprecipitation method for synthesis of a magnetic covalent organic framework (COF) adsorbent. The fabricated COF-(TpBD)/Fe 3 O 4 was applied to magnetic solid phase extraction (MSPE) of 15 phthalate esters (PAEs) for subsequent GC-MS/MS determination in beverage samples. The as-synthesized magnetic adsorbent exhibited great potential in PAEs analysis with a limit of detection of 15 PAEs ranged from 0.005 to 2.748 μg L−1 (S/N = 3). The intra-day and inter-day relative standard deviations (RSD) value of the PAEs were less than 8.8% and 9.9%, respectively. The adsorbent can be reused after washing with methanol. The developed method was successfully applied for the determination of trace PAEs in eight beverages with recoveries ranging from 79.3% to 121.8% and RSDs were less than 11.9%. This work provides a simple magnetization process, which facilitates the application of COFs for enrichment and separation of PAEs in beverages with different matrices. Image 1 • A simple and rapid coprecipitation method for the preparation of a magnetic covalent organic framework. • COF-based magnetic solid phase extraction efficiently enrich 15 phthalate esters in beverage samples. • Method development for the simultaneous analysis of 15 phthalate esters by GC-MS/MS. [ABSTRACT FROM AUTHOR]

Levodopa and uric acid are important neurotransmitters associated with many neurological diseases. Abnormal concentrations of levodopa and uric acid in biological fluids can be used for the evaluation of such diseases. In this work, three-dimensional graphene foam (3D GF) was prepared by chemical vapor deposition. ZnS nanoparticles were in-situ grown on the surface of 3D GF (ZnS NPs/3D GF) using a simple hydrothermal method, which was used to simultaneously determinate levodopa and uric acid. The results show that a porous mesh film made up of ZnS NPs with the diameter of 200 nm is evenly covered on the surface of 3D GF. The ZnS NPs/3D GF electrode exhibits a high sensitivity of 2.34 and 2.39 μA·μM−1·cm−2 for the detection of levodopa and uric acid, respectively. Also, it shows a low limit of detection, excellent selectivity, good anti-interference ability and stability. Moreover, the electrode was successfully used in human plasma samples. Unlabelled Image • A porous mesh film made up of ZnS nanoparticles is grown on the GF (ZnS NPs/3D GF) by a hydrothermal process. • The ZnS NPs/3D GF demonstrates a high sensitivity and low detection limits for simultaneous detection of levodopa and uric acid. [ABSTRACT FROM AUTHOR]

An electrochemical sensor is described for simultaneous voltammetric determination of dopamine (DA) and uric acid (UA). It is based on the use of a nanomaterial composed of gold nanoparticles and 3-dimensional graphene (Au NP@3D GR). The 3D GR was prepared by chemical vapor deposition using nickel nanoparticles as the template at a temperature of around 900 °C. The surface of 3D GR contains oxygen-functional groups after treatment with acid. Carboxylated Au NP were self-assembled and anchored onto the surface of 3D GR. The nanomaterial was placed on a ITO electrode. The few-layer graphene on the ITO glass has a porous structure and the distribution of Au NP is uniform. The electrode shows a high sensitivity and a low detection limit for DA and UA. Figures of merit include detection limits of 0.1 M for DA and of 0.1 μM for UA, and well separated peaks at potentials of 0.18 and 0.30 V (vs. Ag/AgCl), respectively, at pH 7.0. The electrode has good repeatability and stability. [ABSTRACT FROM AUTHOR]

Arrays of molybdenum(IV) disulfide nanosheets resembling the shape of golf balls (MoS2 NSBs) were deposited on carbon nanofibers (CNFs), which are shown to enable superior electrochemical detection of dopamine without any interference by uric acid. The MoS2 NSBs have a diameter of ∼ 2 μm and are made up of numerous bent nanosheets. MoS2 NSBs are connected by the CNFs through the center of the balls. Figures of merit for the resulting electrode include (a) a sensitivity of 6.24 μA·μM−1·cm−2, (b) a low working voltage (+0.17 V vs. Ag/AgCl), and (c) a low limit of detection (36 nM at S/N = 3). The electrode is selective over uric acid, reproducible and stable. It was applied to the determination of dopamine in spiked urine samples. The recoveries at levels of 10, 20 and 40 μM of DA are 101.6, 99.8 and 107.8%. [ABSTRACT FROM AUTHOR]

Organophosphorus pesticides (OPs) are of great concern due to its potential harms on human health and the environment. Herein, a budget-friendly, rapid and convenient colorimetric sensing platform is developed for detection of OPs in the environmental and food samples. The sensing element, PANI-MnO 2 nanozyme with excellent oxidase mimetic activity is synthesized at room temperature, which is able to directly oxidize 3,3,5,5-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB (OxTMB) within 2 min. Ascorbic acid (AA) can inhibit the oxidization reaction of TMB, consequently causing the blue color fading. Ascorbic acid 2-phosphate (AAP) could be hydrolyzed to produce AA by alkaline phosphatase (ALP). In the presence of OPs can effectively decrease ALP activity, resulting in the recovery of catalytic activity of PANI-MnO 2. Therefore, sensitive and selective OPs detection is achieved. Under the optimal conditions, excellent detection performance in term of glyphosate as a model is achieved with a linear range from 0.50 to 50 μM, the detection limit is 0.39 μM (S/N = 3). The utility of method is further improved by combining a portable smartphone platform with a color picking application. The colorimetric platform achieves instrument-free detection of OPs and overcomes the uneven color distribution of traditional paper-based chip, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of OPs on-site. [Display omitted] • PANI-MnO 2 with mild preparation conditions exhibits excellent oxidase-like activity. • PANI-MnO 2 -based colorimetry was established for organophosphorus pesticide detection. • A colorimetric platform was fabricated for instrument-free detection. • This proposed method can be applied in environment and food samples. [ABSTRACT FROM AUTHOR]

An in situ growth strategy for construction of covalent organic frameworks (COFs) TpBD on glassy carbon electrode using p-aminobenzoic acid and ethylenediamine as connector is introduced. The fabricated electrode was used for electrochemical biosensing of aflatoxin M1 in milk samples combined with magnetic nanoparticles, which acted as probe carriers. The developed electrochemical biosensor exhibited high selectivity and sensitivity toward aflatoxin M1 with a detection limit of 0.15 ng/mL (S/N = 3). Moreover, the covalent bonding of TpBD on the glassy carbon electrode has good stability, which retained 76% of the initial signal after 15 days storage at room temperature. This work provides a valuable case for in situ growth of COFs TpBD on the electrode, and the proposed synthetic route is expected to provide a powerful tool for the wide application of other functional COFs in electrochemical biosensor. • Covalent organic frameworks TpBD was grown in situ on the electrode. • The modified TpBD electrode possesses an excellent stability. • The electrochemical biosensor was developed for the determination of aflatoxin M1 in milk. [ABSTRACT FROM AUTHOR]

A colorimetric-electrochemical dual-mode analytical method based on bismuth metal-organic framework nanozyme was developed for label-free and trace/ultra-trace Cr6+ detection. 3D ball-flower shaped bismuth oxide formate (BiOCOOH) was used as the precursor and template to facilely construct the metal-organic framework nanozyme BiO-BDC-NH 2 , which possesses intrinsic peroxidase-mimic activity to effectively catalyze the colorless 3,3′,5,5′-tetramethylbenzidine into blue oxidation products in the presence of hydrogen peroxide. Based on Cr6+ to promote the peroxide-mimic activity of BiO-BDC-NH 2 nanozyme, a colorimetric method for Cr6+ detection was developed with the detection limit of 0.44 ng mL−1. Cr6+ can be electrochemically reduced to Cr3+ that would specifically inhibit the peroxidase-mimic activity of BiO-BDC-NH 2 nanozyme. Thus, the colorimetric system for Cr6+ detection was converted into a low-toxic and signal-off electrochemical sensor. The electrochemical model showed upgraded sensitivity and a lower detection limit of 9.00 pg mL−1. The dual-model method was developed for selective appropriate sensing instruments in different detection scenarios, which can provide built-in correction for environmental effects, as well as the development and utilization of dual-signal sensing platforms for trace to ultra-trace Cr6+ rapid assay. [Display omitted] • A bismuth-based MOF nanozyme with 3D ball-flower shape was constructed. • The MOF showed Cr6+-promoted and Cr3+-inhibited peroxidase-mimic activity. • A dual-model colorimetric-electrochemical sensor for trace to ultra-trace Cr6+ detection. • The colorimetric model can convert into sensitive electrochemical model. [ABSTRACT FROM AUTHOR]