Search

Sample preparation, including extraction, separation, and purification, is a vital process for natural product analysis. As an attractive sample pretreatment method, magnetic solid‐phase extraction (MSPE) has gained plenty of attention, mainly due to its simpler operation, less consumption of organic solvents, and shorter processing time than traditional SPE. This updated review is devoted to summarizing the applications of MSPE based on different magnetic nanomaterials in the analysis of various natural products in complex matrixes, such as biological samples, plants, and Chinese herbal preparations in the past four years (2020–2023). The preparation and fabrication of different materials are briefly introduced. Furthermore, the extraction mechanism and interaction forces between adsorbent and analytes are elaborated, and the advantages and disadvantages of different adsorbents coupled with various analytical methods for MSPE of different natural products are summarized. Moreover, the future trends and opportunities for MSPE in the natural product analysis are discussed. It is expected that this work can provide updated information for future research on the applications of MSPE in such fields. [ABSTRACT FROM AUTHOR]

Colorimetric sensors are widely used for various sensing applications due to their specificity, sensitivity, cost-effectiveness, and ease of use. They have been developed to detect a range of substances including metal and non-metal ions, proteins, small molecules, gases, viruses and bacteria, DNA/RNA, acidity/base, and biomarkers in clinical diagnostics. Recent advancements in nanomaterials have played a significant role in the development of colorimetric sensors. This article provides an overview of the field, discussing the design and fabrication of sensors for various applications such as alkaline vapors, dopamine detection, uric acid detection, organic thiol analysis, H2O2 and glucose detection, HPV detection, metal ion detection, protein identification, synthetic food dye detection, and phenolic compound detection. These sensors offer promising applications in different fields, providing rapid, low-cost, and portable solutions for detection. The article also highlights the development of multifunctional sensors and the integration of colorimetric sensors with smartphones, color-recording devices, and optical sensing arrays, which have improved the portability, sensitivity, and specificity of detection. The article concludes that with further advancements in materials and analytical chemistry, colorimetric sensors will continue to contribute to the fields of chemical and biological sensing. [Extracted from the article]

With the increase of obesity incidence, the development of antiobesity drugs has aroused extensive interest. In this study, a simple and portable personal glucose meter (PGM) method based on the lipase-mediated reaction combined with molecular docking was developed for the screening of lipase inhibitors. Lipase can catalyse the hydrolysis of 4-acetamidophenyl acetate to form acetaminophen, which can directly trigger the reduction of K3[Fe(CN)6] to K4[Fe(CN)6] in the glucose test strips and generate an electrical signal that can be detected by the PGM. When lipase inhibitors exist, the yield of acetaminophen will be reduced and results in a corresponding decrease of the PGM signal. Therefore, the activity of lipase can be measured by the PGM. After optimization of the experimental conditions, the inhibitory activity of fourteen small-molecule compounds and fifteen natural product extracts on lipase were evaluated by the developed PGM method. The results indicate that tannic acid, (-)-epigallocatechin gallate, (-)-epigallocatechin, (-)-epicatechin gallate, and epicatechin have good inhibitory effect on lipase (% of inhibition higher than 40.0%). Besides, the natural product extracts of Galla Chinensis, lemon, and Rhei Radix et Rhizoma have a good inhibitory effect on lipase with % of inhibition of (97.5 ± 0.6)%, (88.1 ± 0.7)%, and (79.1 ± 1.6)%, respectively. Finally, the binding sites and modes of six small-molecule compounds on lipase were investigated by the molecular docking study. The results show that the developed PGM method is an effective approach for the discovery of potential lipase inhibitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • A paper-based lateral flow sensor is developed for the detection of PG. • Detection of PG is achieved based on enzyme-mediated pectin viscosity change. • Combination of paper-based lateral flow sensor and smartphone method for PG detection. • The method exhibits good performance in high portability and label-free detection. In this study, a simple, convenient, and cost-effective paper-based lateral flow strip sensor combined with a smartphone was developed for the determination of polygalacturonase (PG) activity based on the modulation of viscosity of pectin solution, which can be visualized by the difference in the average diffusion distance on the pH indicator strips. Effects of the pectin concentration, enzymatic reaction time, the volume of diffusion liquid, and the diffusion time on the average diffusion distance were systematically investigated. For quantitative analysis of PG activity, the images of the pH indicator strips after lateral flow diffusion were collected by a smartphone and processed through Adobe Photoshop CS 5.1 software. Under the optimal conditions, the average lateral flow diffusion distance shows a good linear relationship with PG activity in the range of 0.025–0.80 U/mL, and the limit of quantification is 0.025 U/mL. Finally, the applicability of the proposed strategy was successfully verified by measuring PG activity in cucumber sample. The recoveries are in the range of 87.4%–96.7%. In short, the present study developed a convenient, low-cost, and accurate approach for on-site detecting of PG activity, especially in remote or resource-limited regions. [ABSTRACT FROM AUTHOR]

A polyhedral MIL-125-NH2@Pd nanoparticle with light-responsive oxidase-like activity was synthesized through a simple solvothermal method and was characterized by field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer–Emmett–Teller analysis, etc. MIL-125-NH2@Pd can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) under light radiation without H2O2, indicating its intrinsic light-responsive oxidase-like characteristic. MIL-125-NH2@Pd shows a superior catalytic activity and higher affinity to TMB, compared to MIL-125-NH2, owing to the presence of homogenously distributed palladium (Pd) nanoparticles. The results of the mechanism study indicate the existence of ˙O2− and electron holes during the catalytic reaction of MIL-125-NH2@Pd. Furthermore, based on the excellent light-responsive oxidase-like activity and specific recognition capacity for casein phosphopeptides (CPP) of titanium ions (Ti4+) in MIL-125-NH2@Pd, a simple colorimetric sensing platform was developed for the determination of CPP in a linear range of 10–100 μg mL−1 with a limit of detection as low as 2.9 μg mL−1. Finally, the developed method was successfully employed in the sensitive and selective detection of CPP in spiked rabbit and rat plasma samples. This study may provide a reliable and highly efficient strategy to realize the excitation-responsive sensing applications of materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Quantitation of urea by urease-mediated chitosan viscosity change on paper-based sensor. • Chitosan solution viscosity is converted to distance-readout on paper-based sensor. • Combination of paper-based sensor and distance-readout method for urea POCT. In this study, a paper-based sensor combined with visual distance-readout technique for point of-care testing (POCT) of urea was developed by urease-mediated chitosan viscosity change. A series of factors that affect the performance of the sensor were investigated, including the type of filter paper, chitosan concentration, acetic acid concentration and enzymatic reaction conditions. Under optimal conditions, the proposed method for urea determination has good linearity between 3.8–15.1 mM. The limit of quantitation is 3.8 mM. Finally, the paper-based sensor was successfully applied to the determination of urea in two diesel exhaust fluid (DEF) samples. The recoveries of urea were 91.4 % and 109.9 % in DEF-1 and DEF-2, respectively. The present study provides a novel approach, which integrates paper-based sensor and visual distance-readout technique, for monitoring urea in POCT application, especially in remote or resource-limited regions. [ABSTRACT FROM AUTHOR]

The development of a facile and reliable assay for arsenic (As) detection is crucial for its pollution control, which is a well-known heavy-metal pollutant in the environment. In this work, an efficient colorimetric method was established for As(V) detection based on a novel cuboid-shape Mn-Urea nanozyme (UMnzyme) with arsenic-enhanced oxidase-like activity. The UMnzyme was prepared through the coordination of Mn ions and carbonyl groups in urea, which possesses outstanding oxidase-like activity that can generate the superoxide anion free radical (O2˙−) by catalyzing the dissolved O2, triggering the 3,3′,5,5′-tetramethylbenzidine (TMB) chromogenic reaction. Furthermore, the free oxygen atoms in UMnzyme provide potential sites to bind with As, in which the formation of As–O will not destroy the morphology and structure of UMnzyme. The capture of As by UMnzyme results in the improvement of its oxidase-like activity; therefore, a colorimetric method for As(V) detection was developed with a linear range of 12.5–250 μg L−1. The limit of detection was determined to be 2.4 μg L−1 (S/N = 3), which is lower than the threshold (10 ppb) recommended by the World Health Organization. Moreover, the developed method was applied in the detection of As(V) in environmental water, and the recoveries are 89.5–103.6%. In short, this study provides an efficient and reliable strategy for As(V) detection based on a novel Mn-based nanozyme and a new idea for the reasonable design of Mn-based nanozymes with enhanced catalytic performance. [ABSTRACT FROM AUTHOR]

The high toxicity of arsenic (As) can cause irreversible harm to the environment and human health. In this study, the chlorin e6 (Ce6), which emits fluorescence in the infrared region, was introduced as the luminescence center, and the addition of copper ion (Cu2+) and As(V) provoked a regular change in fluorescence at 652 nm, whereas that of As(III) was 665 nm, which was used to optionally detect Cu2+, arsenic (As(III), and As(V)). The limit of detection (LOD) values were 0.212 μM, 0.089 ppm, and 1.375 ppb for Cu2+, As(III), and As(V), respectively. The developed method can be used to determine Cu2+ and arsenic in water and soil with good sensitivity and selectivity. The 1:1 stoichiometry of Ce6 with Cu2+ was obtained from the Job plot that was developed from UV–visible spectra. The binding constants for Cu2+ and As(V) were established to be 1.248 × 105 M−1 and 2.35 × 1012 M−2, respectively, using B–H (Benesi–Hildebrand) plots. Fluorescence lifetimes, B–H plots, FT–IR, and 1H-NMR were used to postulate the mechanism of Cu2+ fluorescence quenching and As(V) fluorescence restoration and the interactions of the two ions with the Ce6 molecule. [ABSTRACT FROM AUTHOR]

Phenolic compounds are one of the main organic pollutants in the environment that can seriously affect ecosystems, even at very low concentrations. Due to the resistance of phenolic compounds to microorganisms, conventional biological treatment methods face challenges in effectively addressing this pollution problem. In this study, a novel laccase mimic (Tris-Cu nanozyme) is prepared using a simple and rapid synthesis strategy based on the coordination of copper ions and amino groups in Tris(hydroxymethyl)aminomethane (Tris). It is found that the Tris-Cu nanozyme exhibits good catalytic activity against a variety of phenolic compounds, the Km, Vmax and Kcat are determined to be 0.18 mM, 15.62 μM·min−1 and 1.57 × 107 min−1 using 2,4-dichlorophenol (2,4-DP) as the substrate, respectively. Then, based on the laccase-like activity of the Tris-Cu nanozyme, a novel colorimetric method for 2,4-DP (the limit of detection (LOD) = 2.4 μM, S/N = 3) detection in the range of 10–400 μM was established, and its accuracy was verified by analyzing tap and lake water samples. In addition, the Tris-Cu nanozyme shows excellent removal abilities for six phenolic compounds in experiments. The removal percentages for 2,4-DP, 2-chlorophenol (2-CP), phenol, resorcinol, 2,6-dimethoxyphenol (2,6-DOP), and bisphenol A (BPA) are 100%, 100%, 100%, 100%, 87%, and 81% at 1 h, respectively. In the simulated effluent, the Tris-Cu nanozyme maintains its efficient catalytic activity towards 2,4-DP, with a degradation percentage of 76.36% at 7 min and a reaction rate constant (k0) of 0.2304 min−1. Therefore, this metal–organic complex shows promise for applications in the monitoring and degrading of environmental pollutants. [ABSTRACT FROM AUTHOR]

A core–shell-derived structural magnetic zeolite imidazolate framework-67 (Fe3O4-COOH@ZIF-67) nanocomposite was fabricated through a single-step coating of zeolite imidazolate framework-67 on glutaric anhydride-functionalized Fe3O4 nanosphere for the magnetic solid-phase extraction (MSPE) of theophylline (TP). The Fe3O4-COOH@ZIF-67 nanocomposite was characterized through scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectrometry, Fourier transform infrared spectroscopy, Zeta potential analysis, X-ray diffraction, Brunauer–Emmett–Teller, and vibrating sample magnetometer. The material has a high specific surface area and good magnetism, which maintains the regular dodecahedron structure of ZIF-67 without being destroyed by the addition of Fe3O4-COOH nanospheres. The Fe3O4-COOH@ZIF-67 can rapidly adsorb TP mainly through the strong coordination interaction between undercoordinated Co2+ on ZIF-67 and –NH from imidazole of TP. The adsorption and desorption conditions, such as the amount of adsorbent, adsorption time, pH value, and elution solvent, were optimized. The kinetics of TP adsorption on Fe3O4-COOH@ZIF-67 was found to follow pseudo-second-order kinetics. The Langmuir model fits the adsorption data well and the maximum adsorption capacity is 1764 mg/g. Finally, the developed MSPE-HPLC method was applied in the enrichment and analysis of TP in four tea samples and rabbit plasma. TP was not detected in oolong tea and rabbit plasma, and its contents in jasmine tea, black tea, and green tea are 5.80, 4.31, and 1.53 μg/g, respectively. The recoveries of spiked samples are between 74.41% and 86.07% with RSD in the range of 0.81–3.83%. The adsorption performance of Fe3O4-COOH@ZIF-67 nanocomposite was nearly unchanged after being stored at room temperature for at least 80 days and two consecutive adsorption–desorption cycles. The results demonstrate that Fe3O4-COOH@ZIF-67 nanocomposite is a promising magnetic adsorbent for the preconcentration of TP in complex samples. [ABSTRACT FROM AUTHOR]

A biomimetic mineralization method was used in the facile and rapid preparation of nanoflowers for immobilizing alcohol dehydrogenase (ADH). The method mainly uses ADH as an organic component and zinc phosphate as an inorganic component to prepare flower-like ADH/Zn3(PO4)2 organic-inorganic hybrid nanoflowers (HNFs) with the high specific surface area through a self-assembly process. The synthesis conditions of the ADH HNFs were optimized and its morphology was characterized. Under the optimum enzymatic reaction conditions, the Michaelis-Menten constant (Km) of ADH HNFs (β-NAD+ as substrate) was measured to be 3.54 mM, and the half-maximal inhibitory concentration (IC50) of the positive control ranitidine (0.2–0.8 mM) was determined to be 0.49 mM. Subsequently, the inhibitory activity of natural medicine Penthorum chinense Pursh and nine small-molecule compounds on ADH was evaluated using ADH HNFs. The inhibition percentage of the aqueous extract of P. chinense is 57.9%. The vanillic acid, protocatechuic acid, gallic acid, and naringenin have obvious inhibitory effects on ADH, and their percentages of inhibition are 55.1%, 68.3%, 61.9%, and 75.5%, respectively. Moreover, molecular docking analysis was applied to explore the binding modes and sites of the four most active small-molecule compounds to ADH. The results of this study can broaden the application of immobilized enzymes through biomimetic mineralization, and provide a reference for the discovery of ADH inhibitors from natural products. [ABSTRACT FROM AUTHOR]

Herein, a Co–Fe Prussian blue analogue nanocube (Co–Fe PBA NC) was prepared in situ via a simple and rapid coprecipitation method at room temperature, and the synthesized nanocube was systematically characterized. The Co–Fe PBA NC was proven to have intrinsic oxidase-like activity, which can catalyze the production of reactive oxygen species, such as superoxide anions (O2˙−), hydroxyl radicals (˙OH), and singlet oxygen (1O2), in a dissolved oxygen system without the presence of hydrogen peroxide (H2O2). By making full use of the oxidase-like activity of the Co–Fe PBA NC and using the chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB), a colorimetric sensor was fabricated for the detection of ascorbic acid (AA) and its related biological enzymes' activities, including alkaline phosphatase (ALP), α-glucosidase (α-Glu), and ascorbic acid oxidase (AAO), in human serum. This study presents an oxidase mimic that can be synthesized via a simple, rapid, and low-cost method, which overcomes the defects of cumbersome and time-consuming synthetic process, dependence on professional instruments and high cost of some previously reported nanozymes. In addition, this study provides a new multifunctional colorimetric sensing platform for AA and its related biological enzymes, showing great potential in biological assays. [ABSTRACT FROM AUTHOR]

In this study, 3,3′,5,5′-tetramethylbenzidine (TMB) was selected as a chromogenic substrate to evaluate the light-responsive oxidase-like activity of different zeolitic imidazolate frameworks (ZIFs). The synthesized ZIFs were systematically characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. Several main operational parameters, including ZIFs and TMB concentrations, pH value, radiation time, and working current, in the reaction process were optimized. The kinetic measurement results show that ZIF-90 exhibits higher affinity to the substrate than horseradish peroxidase. Furthermore, given that adenosine triphosphate (ATP) can specifically combine with Zn2+ binding site and destroy the structure of ZIF-90, a specific and sensitive colorimetric method was established for the quantitative detection of ATP within the range 10 − 240 μM. In addition, on the basis that phenolic pollutants can impact the reaction kinetics diversely on different ZIFs, a sensor array was constructed and successfully applied to differentiate five phenolic pollutants in lake water samples. This work is expected to shed light on the establishment of ZIF-based light-responsive oxidase-like nanozymes for the highly selective colorimetric detection and sensor array. [ABSTRACT FROM AUTHOR]

A magnetic porous carbon NH2‐MIL‐101‐C was synthesized through a one‐step carbonization process using NH2‐MIL‐101(Fe) as the precursor. The morphology, structure, magnetic behavior, and porosity of the as‐prepared NH2‐MIL‐101‐C were characterized. The results show that NH2‐MIL‐101‐C has a high Brunauer‐Emmett‐Teller surface area (213.7 m2/g), a large pore volume (0.2 m3/g), and a good magnetic property (23.4 emu/g). The NH2‐MIL‐101‐C was first used as a magnetic solid‐phase extraction adsorbent for the extraction of five anthraquinones from rhubarb. The main parameters that will affect the extraction efficiency were investigated. Under the optimized conditions, good linearity for the five anthraquinones was obtained with the R2 higher than 0.9910. The limits of detection and limits of quantitation for the analytes are 0.018−0.042 and 0.050−0.140 μg/mL, respectively. [ABSTRACT FROM AUTHOR]

In this study, a simple colorimetric method was established to detect copper ion (Cu2+), sulfathiazole (ST), and glucose based on the acetylcholinesterase (AChE)-like activity of zeolitic imidazolate framework-8 (ZIF-8). The AChE-like activity of ZIF-8 can hydrolyze acetylthiocholine chloride (ATCh) to thiocholine (TCh), which will further react with 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB) to generate 2-nitro-5-thiobenzoic acid (TNB) that has a maximum absorption peak at 405 nm. The effects of different reaction conditions (buffer pH, the volume of ZIF-8, reaction temperature and time, and ATCh concentration) were investigated. Under the optimized conditions, the value of the Michaelis-Menten constant (Km) is measured to be 0.83 mM, which shows a high affinity toward the substrate (ATCh). Meanwhile, the ZIF-8 has good storage stability, which can maintain more than 80.0% of its initial activity after 30 days of storage at room temperature, and the relative standard deviation (RSD) of batch-to-batch (n = 3) is 5.1%. The linear dependences are obtained based on the AChE-like activity of ZIF-8 for the detection of Cu2+, ST, and glucose in the ranges of 0.021–1.34 and 5.38–689.66 µM, 43.10–517.24 µM, and 0.0054–1.40 mM, respectively. The limit of detections (LODs) are calculated to be 20.00 nM, 9.25 µM, and 5.24 µM, respectively. Moreover, the sample spiked recoveries of Cu2+ in lake water, ST in milk, and glucose in strawberry samples were measured, and the results are in the range of 98.4–115.4% with the RSD (n = 3) lower than 3.3%. In addition, the method shows high selectivity in the real sample analysis. [ABSTRACT FROM AUTHOR]

An effective, selective, and multicolor colorimetric assay for Cu2+ detection based on the regulation of peroxidase-like nanozyme-mediated etching of gold nanorods (Au NRs) is proposed. Cu2+-creatinine complex is selected as the nanozyme that exhibits excellent peroxidase-like activity even in the case of low concentration of Cu2+, which can catalyze 3,3,5,5-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB+) in the presence of hydrogen peroxide, and TMB+ is oxidized to generate TMB2+ after adding H+, and the TMB2+ can etch Au NRs. The determination of Cu2+ is achieved based on the blue shift of the longitudinal localized surface plasmon resonance peak of Au NRs. Under the optimal conditions, the developed colorimetric assay exhibits high sensitivity for the detection of Cu2+ (limit of detection is 0.034 μM) with a wide linear range of 0.05–4.0 μM (R2 = 0.987). The solution shows a rainbow-like color in response to the increase of Cu2+ concentration, which can realize the semi-quantitative detection of Cu2+ by naked eyes. In addition, the developed method exhibits excellent selectivity for Cu2+-detection. The established method was used for the determination of Cu2+ in lake water, soil, and normal human serum with satisfactory recovery of spiked samples. [ABSTRACT FROM AUTHOR]

This work describes a simple and reliable colorimetric method based on the gold nanoparticles without any modification, which can realize the rapid, sensitive, and quantitative detection of lead (Pb2+) and copper (Cu2+) ions, providing a reference for monitoring metal ions in the environmental water. When Pb2+ was added to the gold nanoparticles solution containing a low concentration of L‐Cysteine, the combination of Pb2+ and L‐Cysteine can induce the aggregation of gold nanoparticles. On the contrary, Cu2+ can catalyze the oxidation of L‐Cysteine and destroy the formation of the Au‐S bond between L‐Cysteine and gold nanoparticles, thereby preventing the aggregation of gold nanoparticles. As the ultraviolet‐visible spectrum of gold nanoparticle solution is closely related to their aggregation status, the Cu2+ and Pb2+ can be determined. The calibration curves, which are constructed based on ratios of the absorbance at 650 nm and 520 nm of gold nanoparticles, display good linearity in the range of 50.0−2.5 × 103 nM for Pb2+ and 25.0−300.0 nM for Cu2+, respectively. The limits of quantitation of Pb2+ and Cu2+ are determined to be 50.0 and 25.0 nM, respectively. In addition, the spiked recoveries of Pb2+ and Cu2+ in real water samples are 94.6−112.5 and 87.3−114.7% with a relative standard deviation of less than 6.3%, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mild-condition synthesized metal-complex nanozymes in the colorimetric and fluorescence analysis are reviewed. • The mild-condition synthesis processes of metal-complex nanozymes are discussed. • Strategy in developing colorimetric and fluorescent assays with high performance and specificity are summarized. The metal complexes, which are prepared through the coordination of metal ions with organic ligands, have various characteristics such as high porosity and specific surface area. In recent years, the metal complexes with enzyme-like activities have been widely used in colorimetric and fluorescence analysis. The synthesis process of metal complexes under mild conditions is particularly significant as it is not only easy to operate but also safe. In this article, the synthesis processes, catalytic mechanisms, activity regulation methods, and recent research progress of metal-complex nanozymes in the past years (2018 to present) have been summarized. Furthermore, the applications of metal-complex nanozymes-based biosensors in colorimetric and fluorescence detection of various analytes, such as antibiotics, metal ions, mycotoxins, pathogens, pesticides, and proteins, have been summarized and discussed. This review is prospective to promote the further applications of metal complexes with enzyme-like activity synthesized under mild conditions. [ABSTRACT FROM AUTHOR]

A Mn decorated zeolitic imidazolate framework-90 (ZIF-90) nanozyme (Mn/ZIF-90) was constructed through an effective and rapid post-synthetic strategy for the first time. The Mn in Mn/ZIF-90 exists in mixed valence states, which is doped to the ZIF-90 through the formation of Mn–O bond. The Zn–N coordination structure of ZIF-90 may change the electronic arrangement of oxygen atoms in the free carbonyl groups (–CHO), allowing the coordination of Mn with O. The prepared Mn/ZIF-90 possesses outstanding oxidase-like activity and remarkable stability. Besides, the catalytic activity of Mn/ZIF-90 can be inhibited in the presence of H 2 O 2. Therefore, using the Mn/ZIF-90-triggered chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) as an amplifier, a versatile enzyme cascade-based colorimetric method for the detection of glucose and choline with good sensitivity and selectivity was developed. The linear ranges for glucose and choline are 6.25–500 μM and 5–1000 μM, respectively. Furthermore, the developed method was applied in the detection of glucose and choline in rabbit plasma samples, and the recoveries are 89.5–107.3 % and 96.0–109.3 %, respectively. In short, the simple and efficient post-synthetic doping method may provide a new thought for the rational designs of enzyme mimics with improved catalytic performance. Moreover, the colorimetric method based on the excellent catalytic activity of Mn/ZIF-90 may be extended to detect other H 2 O 2 -generating or consuming molecules and evaluate the activity of bio-enzymes that can catalyze the generation of glucose or choline. [Display omitted] • A novel and efficient post-synthetic strategy for Mn doping is presented. • Mn-decorated ZIF-90 (Mn/ZIF-90) with excellent oxidase-like activity is prepared. • The mixed valence state Mn endows the excellent oxidase-like activity to Mn/ZIF-90. • A colorimetric method for glucose and choline detection is developed based on Mn/ZIF-90. • The colorimetric method has potential to detect H 2 O 2 generating or consuming molecules. [ABSTRACT FROM AUTHOR]

A rapid, portable, and cost-effective method using personal glucose meter (PGM) for quantitative analysis of hydrogen peroxide (H 2 O 2) was established based on ascorbate oxidase (AAO)-catalyzed reaction for the first time. Ascorbic acid (AA) can rapidly reduce ferricyanide (K 3 [Fe(CN) 6 ]) to ferrocyanide (K 4 [Fe(CN) 6 ]) in the glucose test strip and transfer electron to the electrode to generating a PGM detectable signal. Thus, the concentration of AA can be directly determined by the PGM as simple as measuring the blood glucose. On the other hand, AAO can catalyze the reduction of H 2 O 2 and produce an enzyme-peroxide complex, which decreases the yields of dehydroascorbic acid formed by the oxidation of AA, resulting in the increase in PGM detectable signal of residual ascorbic acid (re-AA). Therefore, the concentration of H 2 O 2 is proportional to the concentration of re-AA. After optimization of the experimental conditions, the developed method can be used to detect H 2 O 2 at linear range of 2.5–5 × 103 μM with the quantification limit of 2.5 μM. In addition, the satisfactory spiked recoveries (95.3–108.9 %) of real samples (i.e., tap water, contact lens solution, medical hydrogen peroxide, and normal human serum) confirm its feasibility for practical applications. In short, this study provides a feasible PGM-based method for H 2 O 2 detection with simple operations. [Display omitted] • A simple, rapid and portable assay for quantitation of hydrogen peroxide. • The method based on the reduction of K 3 [Fe(CN) 6 ] to K 4 [Fe(CN) 6 ] via AA-triggered reaction. • The developed method expands the application of PGM in non-glucose target analysis. [ABSTRACT FROM AUTHOR]

In this work, a magnetic octahedral metal‐organic framework (Fe3O4@NH2‐MIL‐101(Fe)) was synthesized for the magnetic solid‐phase extraction of three anthraquinones, including aloe‐emodin, emodin, and physcion, in rhubarb. The Fe3O4@NH2‐MIL‐101(Fe) exhibits a high specific surface area of 259.2 m2/g with an average pore size of 6.0 nm and high magnetic responsivity of 23.4 emu/g, which may be used as an adsorbent for rapid preconcentration and separation of target analytes. The main parameters for magnetic solid‐phase extraction of anthraquinones, including the amount of adsorbent, extraction time, extraction temperature, extraction pH, elution solvent, and elution time, were systematically optimized. The whole extraction process requires a very low amount of adsorbent and a small volume of the sample. Besides, under the optimized conditions, the method shows satisfactory spiked recovery for anthraquinones in the range of 93.3–109.1% and the limits of detection are 1.7–3.4 ng/mL. The relative standard deviations for intra‐ and inter‐day precision are 0.2–1.3% and 0.2–0.6%, respectively. The experimental results indicate that the developed method is feasible for the analysis of anthraquinones in rhubarb. [ABSTRACT FROM AUTHOR]

The peroxidase-like activity of vitamin B6 (VB6) was firstly demonstrated by catalyzing the peroxidase chromogenic substrate 3,3′,5,5′-tetramethylbenzidine (TMB) at the existence of H2O2. The influence of different factors on the catalytic property of VB6, including pH, temperature, VB6 concentration, and incubation time, were investigated. The steady-state kinetic study results indicate that VB6 possesses higher affinity to H2O2 than natural horseradish peroxidase and some other peroxidase mimics. Besides, the radical quenching experiment results confirm that hydroxyl radical (•OH) accounts for the catalytic process. Based on the excellent peroxidase-like catalytic activity of VB6, the colorimetric methods for H2O2 and gallic acid (GA) detection were developed by measuring the absorbance variance of the catalytic system. Under the optimal conditions, the linear ranges of the methods for H2O2 and GA determination with good selectivity are 50.0–600.0 μM and 10.0–50.0 μM, respectively. In addition, the developed method was applied in the detection of H2O2 in milk samples and evaluation of total antioxidant capacity of different tea infusions. This study may broaden the application prospect of VB6 in environmental and biomedical analysis fields, contribute to profound insight of the physiological functions of VB6, as well as lay foundation for further excavation of small-molecule peroxidase mimics. [ABSTRACT FROM AUTHOR]

A novel MOF@HOF composite that can serve as a matrix for analysis of small molecules by MALDI-TOF-MS was fabricated through a simple solvothermal method. Taking falvonoids as an example, this composite/matrix presents high desorption/ionization efficiency, low background interference, high salt tolerance, and satisfactory signal reproducibility for MALDI-TOF-MS analysis. [ABSTRACT FROM AUTHOR]

In this study, the poly (sodium 4‐styrenesulfonate)‐mediated calcium carbonate magnetic microspheres were prepared by a simple spontaneous biomimetic mineralization method to immobilize kallikrein. The immobilized kallikrein can be easily separated from the reaction mixture by an external magnet. The structural properties of the materials were studied by several characterization techniques. Subsequently, the immobilized kallikrein enzyme activity and stability were studied. Moreover, the inhibitory potency of ten natural compounds on kallikrein was evaluated by combining with capillary electrophoresis analysis. The immobilized kallikrein exhibited optimum pH and temperature at 7.5 and 75°C, respectively. After seven successive cycles, the immobilized kallikrein retained 82% of its initial activity. Furthermore, the Michaelis–Menten constant (Km) and the half‐maximal inhibitory concentration (IC50) of serine protease inhibitor on the immobilized kallikrein were determined to be 3.30 mM and 67.04 μM, respectively. In addition, berberine, evodine, coptisine, and jatrorrhizine among the ten natural compounds showed good inhibitory activity on the immobilized kallikrein, and their % of inhibition were (43.1 ± 1.7), (34.4 ± 1.9), (38.0 ± 1.7), and (28.5 ± 1.0)%, respectively. These results indicate that the biomimetic mineralization synthetic magnetic microsphere is an efficient method for kallikrein immobilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • New Mn coordination polymer nanoparticles (Mn-IMZs CPNs) with oxidase-like activity. • Mixed valence state of Mn endows excellent oxidase-like activity to Mn-IMZs CPNs. • Colorimetric method for glutathione detection with a wide linear range is developed. • A discriminative detection strategy of glutathione from cysteine is developed. Novel kinds of manganese coordination polymer nanoparticles (Mn-IMZs CPNs) were fabricated through self-assemble of imidazole with Mn2+ ions in aqueous solution. The prepared Mn-IMZs CPNs, with remarkable stability, exhibit excellent oxidase-like activity that can effectively catalyze the conversion of the dissolved O 2 to O 2 •−, turning the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). Based on the inhibitory effect of glutathione (GSH) on the TMB oxidation, a rapid and highly sensitive colorimetric method for the detection of GSH was developed, and the linear ranges are 1.25–50 μM and 50–112.5 μM. Besides, the discriminative detection of GSH from cysteine was achieved by using the time lag between N-ethylmaleimide on the destruction of thiol compounds. Finally, the developed method was successfully applied in the quantification of GSH in tablets and rabbit plasma with high accuracy and good recovery. [ABSTRACT FROM AUTHOR]

Yolk-shell structure magnetic metal–organic framework nanoparticles were prepared via post solvothermal method and employed as a magnetic solid-phase extraction adsorbent for selective pre-concentration of 5′-ribonucleotides by π stacking interaction, hydrogen bonding, and the strong interaction between titanium ions (Ti4+) and phosphate group. The properties of the materials were confirmed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, vibrating sample magnetometer, infrared spectroscopy, thermogravimetric analysis, and Brunauer–Emmett–Teller analysis. The main parameters affecting the adsorption–desorption process, including adsorbent amount, incubation time, incubation temperature, sample pH, shaking speed, elution solution, and elution time, were systematically optimized. Finally, 1.0 mg of adsorbent mixed with 1.0 mL sample solution (10.0 mmol⋅L−1 NaCl, pH 3.0) and shaken at 135 rpm for 5 min at 40 °C, washed with 1.0 mL Na3PO4-NH3∙H2O under vortex for 5 min were selected as optimized adsorption–desorption conditions. The binding performance of adsorbent towards five nucleotides was evaluated by static adsorption experiments. The data are well-fitted to the Langmuir isotherm model and the maximum adsorption capacity is 27.8 mg g−1 for adenosine 5′-monophosphate. The limit of detection of the method is 19.44–38.41 ng mL−1. Under the optimal conditions, the adsorbent was successfully applied to magnetic solid-phase extraction and high performance liquid chromatography determination of five nucleotides in octopus, chicken, fish, and pork samples. [ABSTRACT FROM AUTHOR]

In this study, a magnetic yolk-shell structured metal-organic framework material (Fe3O4@YS-UiO-66-NH2) is prepared by the directional etching of Co2+/peroxymonosulfate and in situ magnetization. The characteristic properties of the material were investigated by using field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometer, Brunauer-Emmett-Teller, and contact angle test. The Fe3O4@YS-UiO-66-NH2 shows the advantages of large surface area, good magnetic property, and satisfactory stability, as well as giving high affinity to alkaloids (ALs) via hydrophilic interaction, hydrogen bonding, and π-π interaction. The results of static adsorption experiment indicate that the Fe3O4@YS-UiO-66-NH2 possesses high adsorption capacity towards ALs and the adsorption behaviors are fitted with Langmuir adsorption isotherm model. Furthermore, a magnetic solid-phase extraction using Fe3O4@YS-UiO-66-NH2 and HPLC method was developed for the analysis of ALs in spiked samples with the recovery of 89.6–100.8%. In addition, the proposed method was successfully applied in the pharmacokinetics study of berberine, coptisine, and palmatine in the rat. In short, the developed method might be used for high-efficient recognition and determination of ALs in plasma sample, which would also provide a new way to fabricate magnetic functionalized metal-organic framework in separation science. [ABSTRACT FROM AUTHOR]

• PA/Cu 3 (PO 4) 2 ·3H 2 O nanozyme is prepared using a facile co-precipitation method. • The peroxidase-like activity of PA/Cu 3 (PO 4) 2 ·3H 2 O is firstly demonstrated. • A method is developed for improving the peroxidase-like activity of metal phosphate. The Cu 3 (PO 4) 2 ·3H 2 O was modified by hydrophilic phytic-acid (PA/Cu 3 (PO 4) 2 ·3H 2 O) using a facile co-precipitation method. The peroxidase-like activities of Cu 3 (PO 4) 2 ·3H 2 O and PA/Cu 3 (PO 4) 2 ·3H 2 O were demonstrated by catalyzing the peroxidase substrate 3,3,5,5-tetramethylbenzidine in the presence of hydrogen peroxide. The catalytic activity of PA/Cu 3 (PO 4) 2 ·3H 2 O is about four times than that of Cu 3 (PO 4) 2 ·3H 2 O, indicating that the peroxidase activity can be enhanced by the introduction of PA. Then, the as-prepared PA/Cu 3 (PO 4) 2 ·3H 2 O was used to develop a colorimetric method for hydrogen peroxide detection with linear range of 0.1–5.0 mM and detection limit of 0.079 mM. Finally, the applicability of PA/Cu 3 (PO 4) 2 ·3H 2 O-based assay was validated by the detection of hydrogen peroxide in milk samples, and the recoveries were 92.4%-101.7%. The developed strategy highlights opportunity for the design of inorganic materials with enhanced inherently peroxidase-mimicking performance using PA. [ABSTRACT FROM AUTHOR]

In drug discovery, one of the most important tasks is to find novel and biologically active molecules. Given that only a tip of iceberg of drugs was founded in nearly one-century's experimental exploration, it shows great significance to use in silico methods to expand chemical database and profile drug-target linkages. In this study, a web server named ChemGenerator was proposed to generate novel activates for specific targets based on users' input. The ChemGenerator relies on an autoencoder-based algorithm of Recurrent Neural Networks with Long Short-Term Memory by training of 7 million of molecular Simplified Molecular-Input Line-Entry System as the basic model, and further develops target guided generation by transfer learning. As results, ChemGenerator gains lower loss (<0.01) than existing reference model (0.2~0.4) and shows good performance in the case of Epidermal Growth Factor Receptor. Meanwhile, ChemGenerator is now freely accessible to the public by http://smiles.tcmobile.org. In proportion to endless molecular enumeration and time-consuming expensive experiments, this work demonstrates an efficient alternative way for the first virtual screening in drug discovery. [ABSTRACT FROM AUTHOR]

Nanomaterials with enzyme-like activity have been widely used in the construction of colorimetric and fluorescence sensors due to their advantages of cost-effectiveness, high stability, good biocompatibility, and ease of modification. Furthermore, the colorimetric and fluorescence sensors, which are effective approaches for detecting bioactive small-molecule compounds, have been extensively explored due to their simple operation and high sensitivity. Recent significant researches have focused on designing various sensors based on nanozymes with peroxidase- and oxidase-like activity for the colorimetric and fluorescence analysis of different analytes. In this review, recent developments (from 2018 to present) in the colorimetric and fluorescent analysis of bioactive small-molecule compounds based on the enzyme-like activity of nanomaterials were summarized. In addition, the challenges and design strategies in developing colorimetric and fluorescent assays with high performance and specific sensing were discussed. • Colorimetric and fluorescent analysis of bioactive small-molecule compounds are reviewed. • Nanomaterials with POD- and OXD-like activities are commonly used in the detections. • Strategy in developing high performance colorimetric and fluorescent assays are discussed. [ABSTRACT FROM AUTHOR]

With the development of nanotechnology, various nanomaterials with enzyme-like activity (nanozymes) have been reported. Due to their superior properties, nanozymes have shown important application potential in the fields of bioanalysis, disease detection, and environmental remediation. However, only a few nanomaterials with multi-enzyme mimicry activity have been reported. In this study, a novel multienzyme mimic was synthesized through a simple and rapid preparation protocol by coordinating copper ions with N3, N6 (amino), N7, and N9 on adenine phosphate. The prepared adenine phosphate-Cu complex exhibits significant peroxidase, laccase, and oxidase mimicking activities. The Michaelis-Menten constant (K m) and the maximal velocity (V max) values of the peroxidase, laccase, and oxidase mimicking activities of AP-Cu nanozyme are 0.052 mM, 0.14 mM, and 2.49 mM; and 0.552 μM min−1, 6.70 μM min−1, and 2.24 μM min−1, respectively. Then, based on its laccase mimicking activity, the nanozyme was applied in the degradation of phenolic compounds. The calculated kinetic constant for the degradation of 2,4-dichlorophenol is 0.468 min−1 and the degradation efficiency of 2,4-dichlorophenol (0.1 mM) reaches 96.14% at 7 min. Finally, based on the multienzyme mimicking activity of adenine phosphate-Cu nanozyme, simple colorimetric sensing methods with high sensitivity and good selectivity were developed for the detection of hydrogen peroxide, epinephrine, and glutathione in the ranges of 20.0–200.0 μM (R2 = 0.9951), 5.0–100.0 μM (R2 = 0.9970), and 5.0–200.0 μM (R2 = 0.9924) with the limits of quantitation of 20.0 μM, 5.0 μM, and 5.0 μM, respectively. In short, the synthesis of nanozymes with multi-enzyme mimicry activity through coordination between copper ions and small molecule mimicry enzymes provides new ideas for the design and research of multi-enzyme mimics. • Adenine phosphate-Cu nanozyme is synthesized via simple coordination reaction. • It exhibits significant peroxidase, laccase, and oxidase mimicking activities. • Adenine phosphate-Cu nanozyme can efficiently degrade phenolic compounds. • It has excellent performance in detecting H 2 O 2 , epinephrine, and glutathione. [ABSTRACT FROM AUTHOR]

[Display omitted] • The silver nanocomposite is in situ synthesized on paper substrate. • Detection of Fe3+ is based on the aggregation of silver nanocomposite. • The sensitivity for Fe3+ detection can be tuned by the pre-concentration steps. • On site detection of Fe3+ can be realized with the aid of a smartphone. In this study, a green and novel method for in situ synthesis of silver nanocomposites on paper substrate was developed and used for the pre-concentration and determination of Fe3+. Silver nanocomposites were in situ synthesized using tannic acid as reducing and capping agent under a mildly alkaline condition. The mechanism for the Fe3+ detection is based on its coordination with the tannic acid present on the surface of the silver nanocomposites and the formation of aggregates. The colorimetric response between Fe3+ and tannic acid modified silver nanocomposites deposited on the surface of the paper substrate was collected by a smartphone followed by processing with Adobe Photoshop CS 5.1 software. Under the optimal conditions, the color response showed a good linear relationship with Fe3+ concentration in the range of 25.0–500.0 μM. The limit of detection for Fe3+ was calculated to be 10.0 μM. Finally, the developed smartphone assisted paper-based chemical sensor was used to detect Fe3+ in two lake water samples, and the recoveries are in the range of 83.5 %−106.7 %. The sensitivity for Fe3+ detection can be tuned through the pre-concentration steps based on the porous nature of the filter paper. The platform highlights the advantage of simplicity, ease of synthesis, fast response time, and low reagent/analyte volume requirement, which is suitable for point-of-use application in iron ions contamination, especially in the remote or resource-limited regions. [ABSTRACT FROM AUTHOR]

A bisubstrate colorimetric system was developed for rapid and multi-color assay of copper ion (Cu2+). Cu2+-triethylamine (Cu2+-TEA) complex with the peroxidase-like activity can catalyze the 3,3′,5,5′-tetramethylbenzidine (TMB) to produce oxidized TMB (TMB+, color in blue) and dopamine (DA) to oxidized DA (oxDA, color in orange) in the presence of hydrogen peroxide, which can obtain a three-color colorimetric result due to the couple of complementary colors of blue and orange. The determination of Cu2+ is achieved based on the absorbance value at 460 nm of the composite peak of TMB+ and oxDA. After systematically optimizing the reaction conditions, the developed bisubstrate colorimetric method exhibits high sensitivity for the detection of Cu2+ (limit of quantitation (LOQ) is 0.0625 μM) with a wide linear range of 0.0625–8.0 μM (R2 = 0.991). Meanwhile, the reaction solution shows an orange, brown, and green color change with the increase in Cu2+ concentration, which can realize the semi-quantitatively detection by the naked eyes. Furthermore, TMB was also used as a single substrate for Cu2+ detection with a linear range of 0.5–9.0 μM (R2 = 0.994), and the LOQ is determined to be 0.5 μM. The LOQ of bisubstrate system is 8 times lower than that of single substrate system, indicating a higher sensitivity for the detection of Cu2+ using the bisubstrate colorimetric system. In addition, the developed bisubstrate colorimetric method exhibits excellent selectivity for Cu2+ detection, which was applied in the determination of Cu2+ in lake water and soil samples, and satisfactory spiked recoveries were obtained. [Display omitted] • Cu2+-triethylamine (TEA) complex exhibits excellent peroxidase-like activity. • A bisubstrate (TMB + dopamine) colorimetric sensor is developed based on Cu2+-TEA complex. • The developed senor displays three-color change for the detection of Cu2+. • The bisubstrate sensor shows a higher sensitivity than that of single substrate. [ABSTRACT FROM AUTHOR]

In this study, the cobalt carbonate (CoCO 3) was in situ prepared using cobalt (Ⅱ) and carbonate at room temperature, and the intrinsic peroxidase-like activity of CoCO 3 was demonstrated for the first time through the oxidation of chromogenic substrate 3, 3', 5, 5' - tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2). The effects of pH, reaction temperature, and incubation time on the catalytic activity of CoCO 3 were studied. Under the optimal reaction conditions, the Michaelis constant (K m) of CoCO 3 to H 2 O 2 is 0.443 mM, which is lower than that of natural horseradish peroxidase and the previously reported peroxidase mimics. Furthermore, the mechanism exploration experiments confirm that the catalytic activity of CoCO 3 is mainly attributed to the hydroxyl radical (•OH). Finally, based on the outstanding peroxidase-like activity of CoCO 3 , a colorimetric sensor for the detection of H 2 O 2 , glucose, and ascorbic acid (AA) was developed, which shows satisfactory selectivity and recovery. In addition, the total antioxidant capacity of three types of tea, dried lemon, three kinds of fresh fruit juice, and vitamin C tablet were determined. In short, this study reports a novel in situ generated CoCO 3 , which can be prepared rapidly at room temperature, eliminating the harsh, cumbersome, and time-consuming synthesis and purification process. The developed sensor based on the newly found excellent peroxidase-like activity of in situ prepared CoCO 3 for the determination of H 2 O 2 , glucose, and AA is fast, simple, low cost, and high sensitivity. [Display omitted] • The excellent peroxidase-like activity of CoCO 3 is firstly investigated. • The CoCO 3 is in situ prepared of rapidity and simplicity. • The hydroxyl radical (•OH) is the major active specie in the catalytic reaction. • The nanozyme has preferable kinetics with a low K m value towards substrate H 2 O 2. • A colorimetric detection platform for H 2 O 2 , glucose, and ascorbic acid is developed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Products of urease catalyzes urea induce color change of Prussian blue nanoparticles. • A paper-based sensor depending on the Prussian blue pH sensitivity is developed. • Smartphone captures color signals of the sensor to achieve rapid detection of urea. Depending on the pH sensitivity of Prussian blue nanoparticles (PB NPs) and the specificity of urease-catalyzed urea, a paper-based colorimetric sensor was developed using urease, PB NPs, and cellulose filter paper. With the assistance of a smartphone, the rapid detection of urea can be realized. Under the optimal conditions, the linear range of the paper-based sensor for detection of urea is 0.5–5.0 mM, and the limit of detection is 0.27 mM. The RSD values of within-batch and between-batch repeatability are 2.5 % and 0.9 %, respectively. The method was successfully applied to the detection of urea in spiked milk samples and artificial urine sample, and the recoveries are in the range of 91.8–107.9%. The developed paper-based colorimetric sensor is a simple, economic, and rapid method that can be used for the determination of urea in real samples, particularly in resource-poor regions. [ABSTRACT FROM AUTHOR]

The formation of Pb-O bond between Pb SP 2+ sp and L-Cysteine can induce significant aggregation of Au NPs (blue color), conversely, Cu can catalyze the oxidation of Cysteine and prevent the aggregation of Au NPs (pink color). DOI: 10.1002/sscp.202200019 The cover picture shows that the lead ion (Pb SP 2+ sp ) and copper ion (Cu SP 2+ sp ) in lake water are detected by UV-Vis analysis using gold nanoparticles (Au NPs) as the colorimetric probe. [Extracted from the article]

A simple and time-saving colorimetric method was developed to quantify sulfonamides (SAAs) in milk via inhibition of the human carbonic anhydrase II (hCAII)-like activity of ZIF-8 that can hydrolyze p -nitrophenyl acetate (p NPA) to p -nitrophenol (p NP), following the color change from yellow to colorless. Effects of different reaction conditions, including pH, temperature, amount of ZIF-8, and incubation time, were investigated. The value of Michaelis-Menten constant (K m) is measured to be 0.15 mM, which exhibits high affinity to p NPA. The IC 50 (0.17, 0.24, and 0.60 mM) and inhibition constant (K i) (0.09, 0.13, and 0.33 mM) of sulfamethazine (SD), sulfadimethoxine (SDM), and sulfathiazole (ST) on ZIF-8 were measured, respectively. Moreover, the activity of ZIF-8 remains more than 90.0% of its initial activity after 30 days' storage. The colorimetric method for SD, SDM, and ST determination was established at the linear ranges of 6.3–750.0 μM (1.75–208.75 mg/kg), 6.3–750.0 μM (1.96–232.75 mg/kg), and 5.0–1250.0 μM (1.28–319.15 mg/kg) with limit of detection of 4.3, 3.2, and 3.9 μΜ (1.2, 0.99, and 0.96 mg/kg), respectively. In addition, the spiked recoveries of SAAs in milk sample are in the range of 81.6%–106.7% with RSD less than 6.5%. In short, the developed colorimetric method can achieve rapid analysis of SAAs in milk with simple operations. [Display omitted] • A simple colorimetric method is developed for sulfonamides detection. • The method is based on the human carbonic anhydrase II-like activity of ZIF-8. • The method can achieve rapid analysis of sulfonamides with simple operation. • It provides a possible strategy for the detection of sulfonamides in milk. [ABSTRACT FROM AUTHOR]

The Co 3 (PO 4) 2.8 H 2 O nanozyme was in situ synthesized through direct reaction between cobalt (Ⅱ) and phosphate, and its peroxidase-like activity was studied in the presence of hydrogen peroxide (H 2 O 2) using a chromogenic substrate 3, 3′, 5, 5′ - tetramethylbenzidine (TMB). The effects of pH value, temperature, and incubation time on the conversion of TMB to oxidized TMB (oxTMB) catalyzed by Co 3 (PO 4) 2.8 H 2 O in the presence of H 2 O 2 were optimized. The peroxidase-like activity of Co 3 (PO 4) 2.8 H 2 O conforms to the Michaelis-Menten kinetics, and its Michaelis constant (K m) is 0.073 mM, showing a higher H 2 O 2 affinity than natural horseradish peroxidase (HRP) and some other peroxidase nanozymes. The mechanism exploration experiment confirmed that the hydroxyl radical (•OH) is the main active species in the catalytic reaction of Co 3 (PO 4) 2.8 H 2 O. Finally, based on the inherent peroxidase-like activity of Co 3 (PO 4) 2.8 H 2 O, a simple colorimetric detection method for H 2 O 2 was established, with a linear range of 15.0 − 100.0 μM and a detection limit of 4.385 μM. The method was applied to the determination of H 2 O 2 in milk samples with the spiked recovery of 90.2%− 106.2%. This study reports a novel nanozyme that can be easily produced in situ, which is exempt from the harsh, cumbersome, and time-consuming synthesis and purification procedures. In addition, the H 2 O 2 colorimetric detection method based on the nanozyme has the advantages of low cost, convenient, high sensitivity, and good selectivity. [Display omitted] • A novel nanozyme Co 3 (PO 4) 2.8 H 2 O of excellent catalytic activity is discovered. • This peroxidase-mimic nanozyme is in situ synthesized rapidly. • The hydroxyl radical is the major active specie in the catalytic reaction. • A sensitive colorimetric method for hydrogen peroxide determination is established. [ABSTRACT FROM AUTHOR]

Salvia miltiorrhiza (Danshen, DS), the dried root and rhizome of Salvia miltiorrhiza Bunge and Ligusticum chuanxiong (Chuanxiong, CX), the dried rhizomes of Ligusticum striatum DC are effective in invigorating blood circulation and eliminating stasis which is highly related with cardiovascular disease (CVD). The identification of activity-based chemical markers is very important, but the complex mechanism of "multi-component, multi-target, and multi-effect" within traditional Chinese medicine (TCM) poses a great challenge to this work. In this study, we combined network pharmacological prediction with experimental validation of the DS and CX to explore an effective method for discovering quality control (QC) of antithrombotic herbs by clarifying the intermediate layer "module/cluster" between the whole complex system and a single component. Based on structural similarity analysis of compound and the thrombosis network published before, we firstly modularized two layers called chemical cluster (CC) network and functional module (FM) network respectively and linked them into one bilayer modularized compound target (BMCT) network. "Two-step" calculation was applied on identifying the significant compounds as the potential QC markers from CC. The in vitro inhibitory activity of selected QC marker compounds on thrombin was evaluated to partially verify their pharmacological activities. HPLC was used to determine contents. According to the network-based analysis, nine compounds with great importance in the BMCT network were identified as QC markers of DS-CX, including tanshinone I, tanshinone IIA, cryptotanshinone, salvianolic acid B, ferulic acid, salvianolic acid A, rosmarinic acid, chlorogenic acid, and coniferyl ferulate. Enzyme inhibitory test partially verified the activity of tanshinone I and tanshinone IIA. Chemical profiling indicated that the nine marker compounds are the main components in the herbal pair. This study identified activity-based QC markers of DS-CX herbal pair and provided a new methodology that can be used in the QC of other herbs, herbal pairs, or formulas. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A sensitive visual colorimetric sensor is developed for the detection of trichlorfon. • The sensor is based on inhibition of enzyme-induced metallization of gold nanorods. • The method is able to achieve rapid analysis of trichlorfon with simple operation. • It provides a possible strategy for the detection of pesticides i.e. trichlorfon. In this study, a highly sensitive visual colorimetric sensor was designed for the detection of trichlorfon based on inhibiting ascorbate oxidase (AAO)-induced metallization of gold nanorods (Au NRs). Ascorbic acid (AA) can reduce silver ion (Ag+) to metal silver (Ag) that will be deposited on the surface of Au NRs, which results in the blue shift of longitudinal localized surface plasmon resonance (LSPR) peak of Au NRs, accompanying by perceptible color changes from red to cyan to red to yellow. In the presence of trichlorfon, the activity of AAO will be inhibited, resulting in less AA is hydrolyzed to dehydroascorbic acid (DHA), and therefore more Ag+ is reduced to Ag by AA. Under the optimized conditions, detection of trichlorfon has a wide linear range of 27.8–11111.1 μg/L with a limit of detection as low as 132.6 ng/L. Moreover, the sensor has a good sample spiked recovery (84.7–96.8%) for the determination of trichlorfon in lake water samples. The proposed method can achieve rapid analysis (about 10 min) of trichlorfon with simple operation when there are no other types of organophosphorus pesticides in the real samples. [ABSTRACT FROM AUTHOR]

A convenient and green method was developed using a personal glucose meter (PGM) for direct determination of hydrogen peroxide and hypochlorite in household disinfectants based on the acetylthiocholine iodide (ATCI)-mediated reaction. In this method, acetylcholinesterase catalyzes the hydrolysis of ATCI to generate thiocholine iodide, which can trigger the reduction of K 3 [Fe(CN) 6 ] to K 4 [Fe(CN) 6 ] and generate a PGM detectable signal. When the hydrogen peroxide or hypochlorite is pre-incubated with the ATCI, the yield of thiocholine will be decreased because the iodine molecules can initiate the oxidation of thiocholine to disulphides, leading to a lower PGM readout. Thus, the hydrogen peroxide or hypochlorite can be directly quantified by PGM as simple as detecting glucose in blood. After being systematically investigated, the optimum conditions of the PGM method are as follows: 5.0 min of enzymatic reaction time, 6.0 mM final concentration of ATCI solution, and 10.0 min of reaction time between ATCI/H 2 O 2 and thiocholine. Moreover, the recoveries of hydrogen peroxide in real sample spiked with three different concentrations (final concentrations of 5.0, 10.0, and 20.0 mM) are in the range of 96.3–108.4%. The recoveries of hypochlorite in real sample spiked with three different concentrations (final concentrations of 1.0, 5.0, and 10.0 mM) are in the range of 99.4–117.0%. These results indicate that the developed method can be employed for the detection of hydrogen peroxide and hypochlorite in household disinfectants. [Display omitted] • A simple and green method for direct detection of hydrogen peroxide and hypochlorite. • Generating personal glucose meters detectable signals based on acetylthiocholine iodide-mediated reaction. • The user-friendly detection process is as simple as detection of glucose in blood. [ABSTRACT FROM AUTHOR]

• The covalently bonded liposome capillary column is prepared by a new three-step method. • The immobilized liposome capillary column (ILCC) has good repeatability and stability. • Retention factors of seventeen drugs are determined using ILCC and compared with other systems. • Partitions of drugs in ILCC are explained by linear free energy relationship analysis with seven solute descriptors. • This study provide reference information for evaluating the membrane permeability of drugs [Display omitted] Two liposomes, including 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) + 1,2-dimyristoyl- sn -glycero-3-phosphoethanolamine (PE) + cholesterol (Chol) (DSPC/PE/Chol liposomes) and soybean lecithin (SPC) + PE + Chol (SPC/PE/Chol liposomes), were prepared and fixed on the inner wall of capillary column by using the adhesion of polydopamine (PDA) membrane and the cross-linking property of glutaraldehyde (GA). The immobilized liposome capillary column (ILCC) has good repeatability and stability based on the electrophoretic mobility of analyte. A CE method based on the immobilized liposome capillary column chromatography (ILCCC) was successfully developed to study the retention behavior of drugs on ILCC, and the logarithm of retention factor (log k) of neutral and ionic drugs were determined. The results show that the log k measured by the ILCCC based on two liposomes have a good linear fitting (R2 = 0.86). Moreover, the linear relationship between ILCCC system and other related research systems (octanol-water system and immobilized artificial membrane (IAM)) was analyzed, and the results indicate that SPC/PE/Chol ILCCC, DSPC/PE/Chol ILCCC and IAM systems have good fitting results, R2 values are 0.86 and 0.78, respectively. In addition, the normalization coefficients of ILCCC and IAM systems obtained by the linear free energy relationship (LFER) analysis are close and the d value is small. In short, the ILCCC is a simple and feasible method for studying drug membrane permeability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adenine phosphate (AP) is first found exhibiting intrinsic peroxidase-like activity. • The hydroxyl radical (•OH) is the active specie of catalytic reaction of AP. • A sensitive colorimetric method for hydrogen peroxide and ascorbic acid detection is established. • The findings facilitate the development of new small-molecule enzyme mimics. The peroxidase-like activity of adenine phosphate (AP) was investigated for the first time using chromogenic substrate 3, 3′, 5, 5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2. Effects of different reaction conditions, including pH, temperature, AP concentration and incubation time on the catalytic property of AP, were investigated. The peroxidase-like activity of AP complies with Michaelis-Menten kinetics, and the calculated kinetic parameter (K m , 0.038 mM) of AP catalysis exhibits higher affinity to H 2 O 2 than natural horseradish peroxidase and some of the other small-molecule peroxidase mimics. The radical scavenging results confirm that hydroxyl radical (•OH) is the active specie of catalytic process. Based on the excellent catalytic performance of AP, a facile colorimetric method for the H 2 O 2 and ascorbic acid detection with good sensitivity and selectivity was established at the linear ranges of 2.0–50.0 μM and 20.0–70.0 μM, respectively. In addition, the developed method was applied to detect H 2 O 2 and ascorbic acid in practical samples. In short, this work will not only broaden the understanding of biological function of AP, but also facilitate the development of new category of small-molecule enzyme mimics. [ABSTRACT FROM AUTHOR]

In this study; a spectrum–effect relationship analysis combined with a high-performance liquid chromatography–mass spectrometry (LC–MS) analysis was established to screen and identify active components that can inhibit thrombin and factor Xa (THR and FXa) in Salviae Miltiorrhizae Radix et Rhizoma–Chuanxiong Rhizoma (Danshen–Chuanxiong) herbal pair. Ten potential active compounds were predicted through a canonical correlation analysis (CCA), and eight of them were tentatively identified through an LC–MS analysis. Furthermore; the enzyme inhibitory activity of six available compounds; chlorogenic acid; Z-ligustilide; caffeic acid; ferulic acid; tanshinone I and tanshinone IIA; were tested to verify the feasibility of the method. Among them; chlorogenic acid was validated to possess a good THR inhibitory activity with IC50 of 185.08 µM. Tanshinone I and tanshinone IIA are potential FXa inhibitors with IC50 of 112.59 µM and 138.19 µM; respectively. Meanwhile; molecular docking results show that tanshinone I and tanshinone IIA; which both have binding energies of less than −7.0 kcal·mol−1; can interact with FXa by forming H-bonds with residues of SER214; GLY219 and GLN192. In short; the THR and FXa inhibitors in the Danshen–Chuanxiong herbal pair have been successfully characterized through a spectrum–effect relationship analysis and an LC–MS analysis. [ABSTRACT FROM AUTHOR]

As a key enzyme regulating postprandial blood glucose, α-Glucosidase is considered to be an effective target for the treatment of diabetes mellitus. In this study, a simple, rapid, and effective method for enzyme inhibitors screening assay was established based on α-glucosidase catalyzes reactions in a personal glucose meter (PGM). α-glucosidase catalyzes the hydrolysis of maltose to produce glucose, which triggers the reduction of ferricyanide (K3[Fe(CN)6]) to ferrocyanide (K4[Fe(CN)6]) and generates the PGM detectable signals. When the α-glucosidase inhibitor (such as acarbose) is added, the yield of glucose and the readout of PGM decreased accordingly. This method can achieve the direct determination of α-glucosidase activity by the PGM as simple as the blood glucose tests. Under the optimal experimental conditions, the developed method was applied to evaluate the inhibitory activity of thirty-four small-molecule compounds and eighteen medicinal plants extracts on α-glucosidase. The results exhibit that lithospermic acid (52.5 ± 3.0%) and protocatechualdehyde (36.8 ± 2.8%) have higher inhibitory activity than that of positive control acarbose (31.5 ± 2.5%) at the same final concentration of 5.0 mM. Besides, the lemon extract has a good inhibitory effect on α-glucosidase with a percentage of inhibition of 43.3 ± 3.5%. Finally, the binding sites and modes of four active small-molecule compounds to α-glucosidase were investigated by molecular docking analysis. These results indicate that the PGM method is feasible to screening inhibitors from natural products with simple and rapid operations. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enzyme-mediated sodium alginate gelation on paper-based sensor for glucose detection. • The sodium alginate viscosity is converted to distance-readout on paper-based sensor. • Combination of paper-based sensor and distance-readout method for glucose detection. In this study, a paper-based sensor, combined with a visual distance-readout method, was developed to determine glucose in fruit samples based on the glucose oxidase-mediated sodium alginate gelation. The type of filter paper, the concentration of sodium alginate and the enzymatic reaction conditions were systematically investigated. Under optimal conditions, the increase in diffusion diameter showed a good linear relationship with glucose concentration between 1.4–7.0 mM, and the limit of quantification was 1.4 mM. Finally, the applicability of the proposed strategy was successfully verified by measuring glucose concentrations in fruit samples. The results generated by the developed paper-based sensor were in good agreement with the results obtained from a glucose assay kit. The recoveries were 91.8%–99.1%. In short, the present study developed a simple, low-cost and efficient method for assessing fruit quality and for guiding fruit intake for diabetic patients, especially in remote or resource-limited regions. [ABSTRACT FROM AUTHOR]

In this study, a polydopamine (PDA)-modified hollow fiber-immobilized xanthine oxidase (XOD) was prepared for screening potential XOD inhibitors from flavonoids. Several parameters for the preparation of PDA-modified hollow fiber-immobilized XOD, including the dopamine concentration, modification time, XOD concentration and immobilization time, were optimized. The results show that the optimal conditions for immobilized XOD activity were a dopamine concentration of 2.0 mg/mL in 10.0 mM Tris-HCl buffer (pH 8.5), a modification time of 3.0 h, an XOD concentration of 1000 μg/mL in 10.0 mM phosphate buffer (pH 7.5) and an immobilization time of 3.0 h. Subsequently, the enzymatic reaction conditions such as the pH value and temperature were investigated, and the enzyme kinetics and inhibition parameters were determined. The results indicate that the optimal pH value (7.5) and temperature (37 °C) of the PDA-modified hollow fiber-immobilized XOD were consistent with the free enzyme. Moreover, the PDA-modified hollow fiber-immobilized XOD could still maintain above 50% of its initial immobilized enzyme activity after seven consecutive cycles. The Michaelis–Menten constant (Km) and the half-maximal inhibitory concentration (IC50) of allopurinol on the immobilized XOD were determined as 0.25 mM and 23.2 μM, respectively. Furthermore, the PDA-modified hollow fiber-immobilized XOD was successfully applied to evaluate the inhibitory activity of eight flavonoids. Quercetin, apigenin, puerarin and epigallocatechin showed a good inhibition effect, and their percentages of inhibition were (79.86 ± 3.50)%, (80.98 ± 0.64)%, (61.15 ± 6.26)% and (54.92 ± 0.41)%, respectively. Finally, molecular docking analysis further verified that these four active compounds could bind to the amino acid residues in the XOD active site. In summary, the PDA-modified hollow fiber-immobilized XOD is an efficient method for the primary screening of XOD inhibitors from natural products. [ABSTRACT FROM AUTHOR]