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Bacterial contamination causes various problems ranging from bacterial infection to biofouling. As an effective and non-toxic agent for bacterial de-contamination, glucose oxidase (GOx)-copper hybrid nanoflowers embedded with amine-functionalized magnetic nanoparticles (NH 2 -MNPs), called 'MNP-GOx NFs', are developed. Positively-charged NH 2 -MNPs and negatively-charged GOx molecules are first interacted via electrostatic attraction which can be controlled by changing the buffer pH, and the follow-up addition of copper(II) sulfate leads to blooming of nanoflowers (MNP-GOx NFs) after incubation at room temperature for 3 days. MNP-GOx NFs show effective antibacterial activity by generating H 2 O 2 from GOx-catalyzed glucose oxidation. For example, 99.9% killings of Staphylococcus aureus and Escherichia coli are achieved after 3 h treatment of 10 6 /mL cells with 0.2 and 3.0 mg/mL MNP-GOx NFs, respectively, revealing that Gram-positive S. aureus with mono-layer membrane system is more vulnerable to the treatment of MNP-GOx NFs than Gram-negative E. coli with two-layer membrane system. MNP-GOx NFs can maintain 97% of bactericidal activity even after recycled uses by magnetic separation for eight times iterative bacterial killings. Finally, MNP-GOx NFs are employed for the fabrication of antibacterial gauzes. MNP-GOx NFs have also opened up a great potential for their applications in biosensors, biofuel cells and bioconversion as well as bacterial de-contamination., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Rosette-shaped graphitic carbon nitride (rosette-GCN) is described as a promising alternative to natural peroxidase for its application to fluorescence-based glucose assays. Rosette-GCN was synthesized via a rapid reaction between melamine and cyanuric acid for 10 min at 35 °C, followed by thermal calcination for 4 h. Importantly, rosette-GCN possesses a peroxidase-like activity, producing intense fluorescence from the oxidation of Amplex UltraRed in the presence of H 2 O 2 over a broad pH-range of, including neutral pH; the peroxidase activity of rosette-GCN was ~ 10-fold higher than that of conventional bulk-GCN. This enhancement of peroxidase activity is presumed to occur because rosette-GCN has a significantly larger surface area and higher porosity while preserving its unique graphitic structure. Based on the high peroxidase activity of rosette-GCN along with the catalytic action of glucose oxidase (GOx), glucose was reliably determined down to 1.2 μM with a dynamic linear concentration range of 5.0 to 275.0 μM under neutral pH conditions. Practical utility of this strategy was also successfully demonstrated by determining the glucose levels in serum samples. This work highlights the advantages of GCNs synthesized via rapid methods but with unique structures for the preparation of enzyme-mimicking catalysts, thus extending their applications to the diagnostics field and other biotechnological fields. Graphical abstract.

To understand the protein functions within a cell, where proteins exist in an extremely crowded and confined state, various modeling and experimental methods have been proposed. Here, we propose a new experimental approach to modulate the macromolecular crowding and/or confinement effects by using mesoporous silicas with two different pore structures. SBA-15 and MSU-F with linear and mesocellular pore structures, respectively, were used to adsorb a model enzyme, glucose oxidase (GOx), in various concentrations ranging from 3 to 430 mg ml -1 . The concentration of adsorbed GOx in the mesopores, representing the degree of crowding, showed a good correlation with thermal enzyme stability. Interestingly, the increase of thermal stability as a function of macromolecular crowding showed different correlations depending on the pore structure of mesoporous silicas. It represents that combination of crowding and confinement effects can promote different microenvironments for enzyme molecules, while mesoporous silicas can impose controlled crowding and confinement effects on enzymes due to their uniform and tunable pore structures. It is anticipated that this new and simple approach can provide a tool to elucidate crowding and confinement effects on the protein functions, including its stability in vivo, because the mesopore environments could mimic the real macromolecular cell system under crowding., (Copyright © 2019. Published by Elsevier B.V.)

A reagent-free colorimetric detection method using mesoporous cerium oxide with a large pore size trapping an oxidative enzyme has been developed and glucose is sensitively detected with a limit of detection of 10 μM by supporting glucose oxidase on mesoporous cerium oxide.

Highly effective and minimally toxic antimicrobial agents have been prepared by immobilizing glucose oxidase (GOx) onto biocompatible chitosan nanoparticles (CS-NPs). CS-NPs were prepared via ionotropic gelation and used for the immobilization of GOx via approaches of covalent attachment (CA), enzyme coating (EC), enzyme precipitate coating (EPC), and magnetic nanoparticle-incorporated EPC (Mag-EPC). EPC represents an approach consisting of enzyme covalent attachment, precipitation, and cross-linking, with CA and EC being control samples while Mag-EPC was prepared by mixing magnetic nanoparticles (Mag) with enzymes during the preparation of EPC. The GOx activities of CA, EC, EPC, and Mag-EPC were 8.57, 17.7, 219, and 247 units/mg CS-NPs, respectively, representing 26 and 12 times higher activity of EPC than those of CA and EC, respectively. EPC improved the activity and stability of GOx and led to good dispersion of CS-NPs, while Mag-EPC enabled facile magnetic separation. To demonstrate the expandability of the EPC approach to other enzymes, bovine carbonic anhydrase was also employed to prepare EPC and Mag-EPC samples for their characterizations. In the presence of glucose, EPC of GOx generated H 2 O 2 in situ, which effectively inhibited the proliferation of Staphylococcus aureus in both suspended cultures and biofilms, thereby demonstrating the potential of EPC-GOx as environmentally friendly and highly effective antimicrobial materials.

In this study, a microscale well-plate colorimetric assay for the multiplexed detection of glucose and cholesterol in clinical human blood samples has been developed. This system utilized one-pot nanocomposite entrapping Fe3O4 magnetic nanoparticles (MNPs) as peroxidase mimetics and glucose oxidase (GOx)/cholesterol oxidase (ChOx) in mesoporous silica to detect glucose and cholesterol in blood samples. The sensing mechanism involves the generation of H2O2 by the catalytic action of an immobilized oxidase on the target molecules in the sample. This subsequently activates the MNPs in the mesopores, thereby leading to the conversion of the substrate into a colored end product. This strategy is used to detect the target glucose or cholesterol molecules in the concentration range of 15-250 mg/dL. The response is highly linear and the lower detection limit is 7.5 mg/dL. The aforementioned colorimetric assay is extremely convenient, and it exhibits a high degree of linearity, precision, and reproducibility when employing real human blood samples. Therefore, this assay can be used in clinical practice for the multiplexed and reliable quantification of glucose and cholesterol.

We have developed a mediatorless glucose biofuel cell based on hybrid nanoflowers incorporating enzymes including glucose oxidase (GOx), laccase, or catalase with copper phosphate, which were further mixed and compressed with conductive multi-walled carbon nanotube (CNT). The nanoflowers were simply synthesized within 5 min at room temperature using sonication method but yielded greatly improved stability as well as highly retained activity by the proper incorporation of enzyme molecules inside the flower-like structure. With glucose as biofuel, GOx and laccase nanoflowers were applied to form enzyme anode and cathode, respectively, and catalase nanoflowers were additionally employed to catalyze the decomposition of hydrogen peroxide, which may be deleterious for GOx, into oxygen and water. Using the enzyme nanoflowers-based biofuel cell system without any involved mediator, a high power density up to 200 μW cm −2 were obtained, which was approximately 80% to that from the biofuel cell system prepared with the corresponding free enzymes. Importantly, the enzyme nanoflowers-based biofuel cell maintained their initial power density over 90% during storage for two months at 4 °C, while most of the glucose biofuel cells in the literature present meaningful stability only in the range of one or two weeks. Based on this result, we expect that this simple but efficient strategy to prepare highly stable glucose biofuel cell using the rapidly-synthesized enzyme-inorganic hybrid nanoflowers can be readily extended to diverse applications in medical and environmental chemistry. [ABSTRACT FROM AUTHOR]

[Display omitted] • A single Fe-site-containing hydrogel nanozyme was synthesized via an ionic gelation. • Fe-N sites function as active sites, yielding a significant peroxidase-like activity. • Foldable paper microfluidic device integrating two pH systems was developed. • Foldable device showed excellent analytical performances for detecting glucose. Peroxidase-mimicking nanozymes have been extensively studied, but their real utilization is limited by their working conditions limited to acidic pH, which makes it difficult to couple with oxidative enzymes operating at near-neutral pH. Here, we have developed a foldable paper microfluidic device that enables a highly convenient cascade reaction between peroxidase-mimicking nanozymes and oxidative enzymes to visually identify the target molecules. A single-atom iron-site-containing poly-γ-glutamic acid/chitosan hydrogel nanoparticle (PGA-Fe/CS NP) was developed, as a model peroxidase-like nanozyme, via rapid ionic gelation. Glucose oxidase (GOx) was used as a model oxidative enzyme. The paper device was constructed by simple wax-printing, including two parts with a foldable configuration: the first is for glucose oxidation under neutral pH and the second is for H 2 O 2 reduction to produce a colorimetric signal under acidic pH. By dropping the sample solution in the first part, the device allowed efficient glucose oxidation by the immobilized GOx at neutral pH. On merely folding the device, the produced H 2 O 2 from the glucose oxidation easily transfers to the second part of the device where PGA-Fe/CS NP was immobilized, inducing the peroxidase-like catalytic reaction at acidic pH. Using the foldable paper microfluidic device, the target glucose was successfully determined with excellent selectivity, sensitivity, stability, and reliability, using an image acquired by a smartphone. Since any oxidative enzymes could be incorporated into the device with the peroxidase-like PGA-Fe/CS NP, we expect that the foldable paper microfluidic device, which conveniently allows the cascade reaction under different pH environments, would be highly beneficial for the detection of various clinically important target molecules, thus laying the groundwork for future biosensing applications of nanozymes in point-of-care testing environments. [ABSTRACT FROM AUTHOR]

• Hybrid nanoflowers are in situ grown on activated carbon fibers. • The hybrid structure is more active and stable than enzymes adsorbed physically. • Power retention of cells prepared from the hybrid structures is 80% after one month. Hybrid nanoflowers (HnFs) are novel structures that comprise enzymes (laccase, glucose oxidase, or catalase) and Cu 3 (PO 4) 2 -based crystals, which can directly in situ grow on activated carbon fibers (ACFs) for the preparation of electrodes (HnF/ACF) used in glucose biofuel cells. The HnF/ACF structures perform higher enzymatic activities (~4 times) and stability (~2 times) than the enzymes physically adsorbed on ACFs in distinct analyses such as epinephrine oxidation, H 2 O 2 decomposition, and glucose oxidation. The power density of an HnF/ACF-based cell (50 µW cm−2 for a glucose concentration of 50 mM) is 3–5 times higher than that of a cell prepared from conventional enzyme immobilization routes, which can be sustained at up to 80% after one month of operation. [ABSTRACT FROM AUTHOR]

• Ultrarapid, size-controlled, and high-crystalline synthetic protocol for ceria nanoparticles were developed. • Plasma-mediated ceria nanoparticles exhibited an efficient color-changing activity toward H 2 O 2. • The ceria nanoparticles-embedded paper strip showed high selectivity, sensitivity, reusability, and stability for glucose detection. • Diverse glucose levels in human blood were successfully determined with excellent reproducibility and reliability. We describe an ultrarapid (within several minutes), size-controlled (<100 nm in diameter), and high-crystalline plasma-mediated synthesis of ceria nanoparticles and their application in reagent-free colorimetric test strips. Glucose oxidase (GOx) incorporated onto the paper matrix generates H 2 O 2 with glucose, subsequently inducing color changes of the embedded ceria nanoparticles from white/yellow to yellow/orange without any involvement of colorimetric substrate or dye. The optimized protocol yielded ∼2-fold higher color intensity compared to that of commercially available ceria nanoparticles, presumably due to its much larger surface area and higher Ce3+ content, facilitating the oxidation from Ce3+ to Ce4+ and formation of peroxide complexes at the nanoparticle surfaces. Using the colorimetric test strip, glucose was specifically detected over a wide linear range (0.1−10 mM), with excellent reusability, storage stability, precision, and reproducibility. The innovative plasma-mediated ultrarapid synthesis of size-controlled and high-crystalline ceria nanoparticles and their utilization on reagent-free colorimetric test strip allow for a straightforward sensing platform for the point-of-care detection of glucose and can be expanded to other oxidative enzymes for facile colorimetric detection of various clinically important target molecules. [ABSTRACT FROM AUTHOR]