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For the first time a novel fluorescent La@ZrMOF nanomaterial was synthesized for the convenient and visual detection of ethephon (ETH) based on the ligand–metal charge transfer process. The fluorescence signal gradually enhanced as the concentration of ETH increased, accompanied by a change in the color from colorless to blue. The assay can be completed within 75 min with a detection limit of 0.03 mg/L. A paper-based approach for the rapid and visual determination of ETH has also been devised, enabling the efficient used in a variety of actual products, with apples, pears, and tomatoes as examples. It proved to be simple, easy to use, and sensitive, and has the potential for further uses of ETH detection. [ABSTRACT FROM AUTHOR]

A covalent organic framework–based strategy was designed for label-free colorimetric detection of pesticides. Covalent organic framework–based nanoenzyme with excellent oxidase-like catalytic activity was synthesized. Unlike other artificial enzymes, porphyrin-based covalent organic framework (p-COF) as the oxidase mimic showed highly catalytic chromogenic activity and good affinity toward TMB without the presence of H2O2, which can be used as substitute for peroxidase mimics and H2O2 system in the colorimetric reaction. Based on the fact that the pesticide-aptamer complex can inhibit the oxidase activity of p-COF and reduced the absorbance at 650 nm in UV–Vis spectrum, a label-free and facile colorimetric detection of pesticides was designed and fabricated. Under the optimized conditions, the COF-based colorimetric probe for pesticide detection displayed high sensitivity and selectivity. Taking fipronil for example the limit of detection was 2.7 ng/mL and the linear range was 5 –500,000 ng/mL. The strategy was successfully applied to the detection of pesticides with good recovery , which was in accordance with that of HPLC–MS/MS. The COF-based colorimetric detection was free of complicated modification H2O2, which guaranteed the accuracy and reliability of measurements. The COF-based sensing strategy is a potential candidate for the sensitive detection of pesticides of interests. [ABSTRACT FROM AUTHOR]

A novel electrochemical method has been developed, based on a covalent organic framework (COF) and reduced graphene oxide (rGO), to detect fentanyl and alfentanil. COF nanomaterials with chrysanthemum morphology obtained by solvothermal reaction contain rich active sites for electrochemical catalytic reaction, thus improving the detection performance of the designed sensor. Reduced graphene oxide improves the sensor's sensitivity due to enhanced electron transfer. Under optimized experimental conditions, the fabricated electrode presents a linear range of 0.02 to 7.26 μM for alfentanil and 0.1 to 6.54 μM for fentanyl, with detection limits of 6.7 nM and 33 nM, respectively. In addition, the sensor possesses excellent selectivity, outstanding reproducibility, and acceptable stability. The proposed sensor is feasible for the reliable monitoring of fentanyl and alfentanil in human serum samples, with acceptable reliability and high potential in real-world applications. Finally, the electrochemical characteristic fingerprint of fentanyl is investigated by studying the electrochemical behavior of alfentanil and fentanyl on the electrode surface. [ABSTRACT FROM AUTHOR]

Terbium-based metal–organic frameworks (Tb-MOF) prepared under mild conditions was utilized to construct a fluorescence probe for determination of organophosphorus pesticides (OPs) coupled with acetylcholinesterase (AChE), acetylcholine chloride (Ach), and choline oxidase (CHO). Since OPs have obvious inhibition on the activity of AChE in the Tb-MOF/ACh/CHO/AChE system, the detection of OPs was accomplished by restoring the fluorescence of Tb-MOF resulting from reduced production of H2O2. By taking chlorpyrifos (CPF) as a pesticide model, the method exhibits high sensitivity in the linear range 0.1–4.0 μg·L−1 with the limit of detection (LOD) of 0.04 μg·L−1 under optimum conditions (λex = 280 nm, λem = 544 nm). The Tb-MOF/ACh/CHO/AChE fluorescence system has high selectivity for CPF. The method was successfully applied to the detection of CPF in tap water and strawberry samples (recovery of 87.36–115.60% for tap water and 95.04–103.20% for strawberry). Free from complicated fabrication operation, the Tb-MOF-based system is rapid, simple, and stable, which provides a reference and new way for the design of OPs fluorescent probes in the future. [ABSTRACT FROM AUTHOR]

Triethylamine (TEA) possesses an irritating odor and potential hazards. It is therefore imperative to develop a highly sensitive, rapid, and accurate sensing material for the detection of TEA gas. In this work, metal-organic frameworks (MOFs)-derived ZnO/In 2 O 3 composites were prepared using a simple one-pot oil bath method for ultra sensitivity, rapid, and accurate detection of TEA gas. The prepared samples were characterized by XRD, SEM, TEM, XPS, and BET. The results indicate that the ZnO/In 2 O 3 composites with a Zn: In molar ratio of 1:9 (ZIO-9) consist of hexagonal tubes assembled from nanoparticles, exhibiting the specific surface area of the material is as high as 45.27 m2/g. Due to the unique tubular structure, abundant mesopores, and more generation of chemical adsorbed oxygen, the ZIO-9 sensor exhibited excellent gas properties, including a response as high as 2480–5 ppm TEA gas at an optimal operating temperature of 100 ℃, which is about 10 times that of In 2 O 3 and 26 times of ZnO. Furthermore, the ZIO-9 sensor offers several advantages, including excellent selectivity, good repeatability, long-term stability, and a rapid response/recovery time (229/32 s) to TEA gas. Therefore, the ZnO/In 2 O 3 composite material is an ideal candidate for fabricating high-performance sensors for detecting TEA gas. [Display omitted] • A porous ZnO/In 2 O 3 composites derived from Zn/In bimetallic organic frameworks were prepared. • The ZIO-9 sensor has a response value of 2480–5 ppm TEA at the low optimal operating temperature of 100 °C, which is better than most TEA sensors. • The ZIO-9 sensor's detection limit is as low as 140 ppb, enabling the detection of lower concentrations. • The ZIO-9 sensor has a 625 response at humidity levels of up to 85 %, allowing it to adapt to high-humidity environments. [ABSTRACT FROM AUTHOR]

Ketamine is an organic drug with weak electrochemical activity, which makes it difficult to directly detect by electrochemical methods. Herein, an electrochemical sensor, with excellent detection sensitivity, is proposed for direct detection of ketamine based on a weakly conductive poly-L-cysteine molecularly imprinted membrane. Poly-L-cysteine molecularly imprinted membrane sensor (poly-L-Cys-KT-MIM/GCE) is obtained using L-cysteine as a functional monomer and ketamine as a template molecule based on electropolymerization. The green and highly active cysteine is selected as a functional monomer during electropolymerization, which cannot only achieve specific recognition but also improve detection sensitivity. Furthermore, the oxidation mechanism and fingerprint of ketamine on the electrode surface are established by analyzing the corresponding oxidation products using high/resolution mass spectrometry, which will help to promote the application of electrochemistry in the rapid detection of drugs. Under optimal conditions, the as-designed sensor demonstrated a linear response to ketamine within the range of 5.0 × 10−7 to 2.0 × 10−5 mol L−1 and a detection limit of 1.6 × 10−7 mol L−1. The proposed method exhibited excellent performance from the viewpoints of selectivity, sensitivity and stability. Notably, the sensor rendered excellent reliability and could be used for the detection of target analytes in hair and urine samples with high recovery rates. [ABSTRACT FROM AUTHOR]

• The sensor based on H-SnO 2 @1.2%rGO has extremely high selectivity coefficients (>50) to the other interfering gases. • The sensor based on H-SnO 2 @1.2%rGO exhibits an ultrahigh response (435) to 10 ppm formaldehyde, which is more than 17 times higher compared to the pristine SnO 2. • Optimal temperature of the sensor is ultralow and 130 °C. • The preparation method is convenient, simple and cost-effective. In addition, the best ratio of SnO 2 and rGO was determined. • Excellent super-low theoretical detection limits (1 ppb) for sensors. Incorporating of semiconducting metal oxides and carbonaceous materials reasonably has been proven to be an effective method to improve the sensing properties for gas sensors. In this work, the novel reduced graphene oxide-wrapped hollow SnO 2 nanospheres (H-SnO 2 @rGO) composites are successfully synthesized via a simple hydrothermal method without any templates added. This unique hybrid structure is demonstrated to show significantly enhanced formaldehyde sensing performance compared to the pristine SnO 2 nanospheres. At an optimal temperature of 130°C, H-SnO 2 @1.2%rGO sensor exhibits an ultrahigh response (435) to 10 ppm formaldehyde, which is more than 17 times higher compared to the pristine SnO 2. Besides, it delivers excellent selectivity, low detection limit and fast response/recovery time. The synergistic effect of SnO 2 and rGO plays an important role in improving the sensing behavior. The enhancement mechanism responsible for the superior sensing properties of the nanocomposite is also discussed. [ABSTRACT FROM AUTHOR]