Novel Ce-based coordination polymer nanoparticles with excellent oxidase mimic activity applied for colorimetric assay to organophosphorus pesticides

Iron/phosphorus co-doped carbon nanozyme for colorimetric sensing of organophosphorus pesticides in food

In this work, a peroxidase-like (POD-like) nanozyme of Fe/P-NC was synthesized by doping phosphorus (P) and nitrogen (N) to manipulate iron (Fe) activity centers, which showed catalytic activity and kinetics comparable to those of natural HRP. Based on the efficient POD-like activity of the Fe/P-NC nanozyme and cascaded catalytic reactions with acetylcholinesterase (AChE), we constructed a colorimetric, affordable and sensitive sensing platform to detect organophosphorus pesticides (OPs). In the presence of AChE, the POD-like activity of the prepared Fe/P-NC was suppressed, which weakened the Fe/P-NC-catalyzed oxidation of TMB. After the introduction of OPs, the catalytic activity of the Fe/P-NC nanozyme was restored, resulting in efficient oxidation of TMB and an increasing blue color. By monitoring the variation in UV-vis absorbance, OPs could be quantitatively analyzed. The proposed colorimetric method exhibited superior analytical performance, with a wide detection range of 0.5-100 ng mL-1 and a low detection limit of 0.13 ng mL-1 for OPs. The assay was successfully employed to detect methyl parathion in fruit and vegetable samples. This work provides new insights into the design of new efficient nanozymes for the rapid and low-cost detection of OPs in real samples.

Apple polysaccharide stabilized palladium nanoparticles for sensitive detection of organophosphorus pesticide

The widespread application of organophosphorus pesticides (OPs) has inflicted significant damage on human well-being and food security. Hence, it is imperative to develop a friendly and accessible biosensor for the detection of OPs. Herein, apple polysaccharide (AP) stabilized palladium nanoparticles (AP-PdnNPs) with a particle size of 2.75-5.95 nm were prepared using AP as a stabilizer and reducing agent. AP-Pd30NPs exhibited good peroxidase-like activity and effectively decomposed H2O2 to ·OH, which catalyzed the 3,3',5,5'-tetramethylbenzidine system to become blue. The catalytic kinetics of AP-Pd30NPs conformed to the typical Michelis-Menten equation. Furthermore, OPs directly inhibited the peroxidase-like activity of AP-Pd30NPs. Thus, a highly effective colorimetric biosensor was developed for the detection of OPs. The detection range of the biosensor was 0.050 μg/L - 200 mg/L, and the limit of detection was extremely low to 0.010 μg/L. Compared with other nanomaterials, the detection platform based on AP-Pd30NPs can effectively detect organophosphorus pesticides without coupling natural enzymes；this method is more economical and practical. Therefore, this established method explores good perspective for the detection of OPs.

Applications of nanomaterials with enzyme-like activity for the detection of phytochemicals and hazardous substances in plant samples

Plants such as herbs, vegetables, fruits, and cereals are closely related to human life. Developing effective testing methods to ensure their safety and quantify their active components are of significant importance. Recently, nanomaterials with enzyme-like activity (known as nanozymes) have been widely developed in various assays, including colorimetric, fluorescence, chemiluminescence, and electrochemical analysis. This review presents the latest advances in analyzing phytochemicals and hazardous substances in plant samples based on nanozymes, including some active ingredients, organophosphorus pesticides, heavy metal ions, and mycotoxins. Additionally, the current shortcomings and challenges of the actual sample analysis were discussed.

Applications of cerium-based materials in food monitoring

With the rapid development of society, food safety to public health has been a topic that cannot be ignored. In recent years, lanthanide-based materials are studied to be potential candidates in the detection of food samples. Cerium (Ce)-based materials (such as Ce ions, CeO2, Ce-metal organic framework (Ce-MOF), etc.) have also attracted more attention in food detection by virtue of colorimetric, fluorescence, sensing, and other methods. This is because the mixed valence of Ce (Ce3+ and Ce4+), the formation of oxygen vacancies, and their optical and electrochemical properties. In this review, Ce-based materials will be introduced and discussed in the field of food detection, including biogenesis, construction, catalytic mechanisms, combination, and applications. In addition, the current challenges and future development trend of these Ce-based materials in food safety detection are also proposed and discussed. Therefore, it is meaningful to explore the Ce-based materials for detection of biomarkers in food samples.

A portable colorimetric sensing platform for rapid and sensitive quantification of dichlorvos pesticide based on Fe-Mn bimetallic oxide nanozyme-participated highly efficient chromogenic catalysis

BACKGROUND

Dichlorvos (DDVP), as a highly effective insecticide, is widely used in agricultural production. However, DDVP residue in foodstuffs adversely affects human health. Conventional instrumental analysis can provide highly sensitive and accurate detection of DDVP, while the need of bulky and expensive equipment limits their application in resource-poor areas and on-site detection. Therefore, the development of easily portable sensing platforms for convenient, rapid and sensitive quantification of DDVP is very essential for ensuring food safety.

RESULT

A portable colorimetric sensing platform for rapid and sensitive quantification of DDVP is developed based on nanozyme-participated highly efficient chromogenic catalysis. The Fe-Mn bimetallic oxide (FeMnOx) nanozyme possesses excellently oxidase-like activity and can efficiently catalyze oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) into a blue oxide with a very low Michaelis constant (Km) of 0.0522 mM. The nanozyme-catalyzed chromogenic reaction can be mediated by DDVP via inhibiting the acetylcholinesterase (AChE) activity. Thus, trace DDVP concentration-dependent color evolution is achieved and DDVP can be sensitively detected by spectrophotometry. Furthermore, a smartphone-integrated 3D-printed miniature lightbox is fabricated as the colorimetric signal acquisition and processing device. Based on the FeMnOx nanozyme and smartphone-integrated lightbox system, the portable colorimetric sensing platform of DDVP is obtained and it has a wide linear range from 1 to 3000 ng mL-1 with a low limit of detection (LOD) of 0.267 ng mL-1 for DDVP quantification.

SIGNIFICANCE

This represents a new portable colorimetric sensing platform that can perform detection of DDVP in foodstuffs with simplicity, sensitivity, and low cost. The work not only offers an alternative to rapid and sensitive detection of DDVP, but also provides a new insight for the development of advanced sensors by the combination of nanozyme, 3D-printing and information technologies.

Electrochemiluminescence enhanced by isolating ACQphores in imine-linked covalent organic framework for organophosphorus pesticide assay

Most of covalent organic frameworks (COFs) are non or weakly emissive due to either the molecular thermal motion-mediated energy dissipation or the aggregation-caused quenching (ACQ) effect. Herein, we synthesize an imine-linked COF (TFPPy-TPh-COF) with high electrochemiluminescence (ECL) emission and the capability of eliminating the ACQ effect and further construct an ECL sensor for malathion detection. The imine-linked COF is obtained by the condensation reaction of (1,1':3',1″-terphenyl)-4,4″-diamine (TPh) and 1,3,6,8-tetrakis(p-formylphenyl)pyrene (TFPPy), and it has higher ECL efficiency than TFPPy aggregates due to the separation of ACQ luminophores (i.e., TFPPy) from each other by TPh and the restriction of intramolecular motions of TFPPy and TPh to reduce the nonradiative decay. The efficient quenching of ECL is achieved by electrochemiluminescence resonance energy transfer (ERET) from the excited state of the TFPPy-TPh-COF to zeolite imidazolate framework-8 (ZIF-8) and the steric hindrance of ZIF-8. Acetylcholinesterase (AChE) can enzymatically hydrolyze acetylcholine (ACh) to generate acetic acid. The resultant acetic acid can trigger the dissolution of ZIF-8 to produce an enhanced ECL signal. Malathion as an organophosphorus pesticide serves as an AChE inhibitor to prevent the production of acetic acid, inducing the decrease of ECL signal. This sensor displays a limit of detection (LOD) of 2.44 pg/mL and a wide dynamic detection range of 0.01-1000 ng/mL. Furthermore, it can be used to detect other organophosphates pesticides (e.g., methidathion, chlorpyrifos, and paraoxon) and measure malathion in real samples (i.e., pakchoi, lettuce, and apples).

Smartphone-assisted colorimetric aptasensor for rapid detection of carbendazim residue in agriculture products based on the oxidase-mimicking activity of octahedral Ag2O nanoparticles

Carbendazim (CBZ) is a widely used pesticides, and its excessive intake is serious damage to humans and animals. Herein, a stable and sensitive colorimetric aptasensor for rapid detection of CBZ residue has been established based on the enhancement of CBZ-specific aptamer (CZ-13) on oxidase-mimicking activity of octahedral Ag2O nanoparticles (NPs). The CZ-13 aptamer can significantly increase the catalytic activity by promoting the production of superoxide anion (·O2-) on the surface of Ag2O NPs and enhancing the affinity of octahedral Ag2O NPs to 3,3',5,5'-tetramethylbenzidine (TMB) molecules. In the presence of CBZ, the quantity of CZ-13 aptamer will be exhausted due to the specific binding to CBZ pesticide. Thus, the rest CZ-13 aptamer no longer enhanced the catalytic activity of octahedral Ag2O NPs, which leads to the change in color of sensing solution. The color change of sensing solution can be easily converted to the corresponding RGB value by a smartphone for quantitative and rapid detection of CBZ. The designed aptasensor has excellent sensitivity and specificity, and the limit of detection was determined as low as 7.35 μg L-1 for CBZ assay. Besides, the aptasensor exhibited good recoveries in the spiked cabbage, apple and cucumber, showing that it may have broad application prospects for detecting CBZ residues in agriculture products.

Organophosphorus and carbamate pesticides: Molecular toxicology and laboratory testing

Population and food requirements are increasing daily throughout the world. To fulfil these requirements application of pesticides is also increasing. Organophosphorous (OP) and Organocarbamate (OC) compounds are widely used pesticides. These pesticides are used for suicidal purposes too. Both inhibit Acetylcholinesterase (AChE) and cholinergic symptoms are mainly used for the diagnosis of pesticide poisoning. Although the symptoms of the intoxication of OP and OC are similar, recent research has described different targets for OP and OC pesticides. Researchers believe the distinction of OP/OC poisoning will be beneficial for the management of pesticide exposure. OP compounds produce adducts with several proteins. There is a new generation of OP compounds like glyphosate that do not inhibit AChE. Therefore, it's high time to develop biomarkers that can distinguish OP poisoning from OC poisoning.

A high-throughput dual system to screen polyphosphate kinase mutants for efficient ATP regeneration in L-theanine biocatalysis

ATP, an important cofactor, is involved in many biocatalytic reactions that require energy. Polyphosphate kinases (PPK) can provide energy for ATP-consuming reactions due to their cheap and readily available substrate polyphosphate. We determined the catalytic properties of PPK from different sources and found that PPK from Cytophaga hutchinsonii (ChPPK) had the best catalytic activity for the substrates ADP and polyP6. An extracellular-intracellular dual system was constructed to high-throughput screen for better catalytic activity of ChPPK mutants. Finally, the specific activity of ChPPKD82N-K103E mutant was increased by 4.3 times. Therefore, we focused on the production of L-theanine catalyzed by GMAS as a model of ATP regeneration. Supplying 150 mM ATP, GMAS enzyme could produce 16.8 ± 1.3 g/L L-theanine from 100 mM glutamate. When 5 mM ATP and 5 U/mL ChPPKD82N-K103E were added, the yield of L-theanine was 16.6 ± 0.79 g/L with the conversion rate of 95.6 ± 4.5% at 4 h. Subsequently, this system was scaled up to 200 mM and 400 mM glutamate, resulting in the yields of L-theanine for 32.3 ± 1.6 g/L and 62.7 ± 1.1 g/L, with the conversion rate of 92.8 ± 4.6% and 90.1 ± 1.6%, respectively. In addition, we also constructed an efficient ATP regeneration system from glutamate to glutamine, and 13.8 ± 0.2 g/L glutamine was obtained with the conversion rate of 94.4 ± 1.4% in 4 h after adding 6 U/ mL GS enzyme and 5 U/ mL ChPPKD82N-K103E, which further laid the foundation from glutamine to L-theanine catalyzed by GGT enzyme. This proved that giving the reaction an efficient ATP supply driven by the mutant enzyme enhanced the conversion rate of substrate to product and maximized the substrate value. This is a positively combination of high yield, high conversion rate and high economic value of enzyme catalysis. The mutant enzyme will further power the ATP-consuming biocatalytic reaction platform sustainably.