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This paper reports a flexible glucose biosensor which is modified by a reduced-swelling and conductive zwitterionic hydrogel enzyme membrane that contains two forms of chemical cross-links. One chemical cross-linking is induced by thermal initiators and forms the basal network of the hydrogel. Another cross-linking is achieved by the coordination interactions between the multivalent metal ion Al3+ and anionic group -COO− of zwitterionic poly-carboxy betaine (pCBMA), which significantly increase the cross-linking density of the zwitterionic hydrogel, improving the reduced-swelling property and reducing the pore size. The better reduced-swelling property and reduced diameters of pores within the zwitterionic hydrogel make less glucose oxidase (GOx) leakage, thus significantly improving the enzyme membrane's service life. By introducing the Al3+ and Cl−, the conductivity of the zwitterionic hydrogel is enhanced approximately 10.4-fold. According to the enhanced conductivity, the reduced-swelling property, and the high GOx loading capacity of the zwitterionic hydrogel, the sensitivity of the biosensor with GOx/pCBMA-Al3+ is significantly improved by 5 times and has a long service life. Finally, the proposed GOx/pCBMA-Al3+ biosensor was applied in non-invasive blood glucose detection on the human body, verifying the capability in practice. [ABSTRACT FROM AUTHOR]

A highly efficient ratiometric electrochemiluminescence (ECL) immunoassay was explored by bidirectionally regulating the ECL intensity of two luminophors. The immunoassay was conducted in a split-type mode consisting of an ECL detection procedure and a sandwich immunoreaction. The ECL detection was executed using a dual-disk glassy carbon electrode modified with two potential-resolved luminophors (g-C3N4-Ag and Ru-MOF-Ag nanocomposites), and the sandwich immunoreaction using glucose oxidase (GOx)-modified SiO2 nanospheres as labels was carried out in a 96-well plate. The Ag nanoparticles (NPs) acted as bifunctional units both for triggering the resonance energy transfer (RET) with g-C3N4 and for accelerating the electron transfer rate of the Ru-MOF-Ag ECL reaction. When the H2O2 catalyzed by GOx in the 96-well plate was transferred to the dual-disk glass carbon electrode, the doped Ag NPs in the two luminophors could be etched, thus destroying the RET between C3N4 and the accelerated reaction to Ru-MOF, resulting in an opposite trend in the ECL signal outputted from the dual disks. Using the ratio of the two signals for quantification, the constructed immunosensor for a model target, i.e. myoglobin, exhibited a low detection limit of 4.7 × 10–14 g/mL. The ingenious combination of ECL ratiometry, bifunctional Ag NPs, and a split-type strategy effectively reduces environmental and human errors, offering a more precise and sensitive analysis for complex samples. [ABSTRACT FROM AUTHOR]

An innovative supramolecular architecture is reported for bienzymatic glucose biosensing based on the use of a nanohybrid made of multi-walled carbon nanotubes (MWCNTs) non-covalently functionalized with a Schiff base modified with two phenylboronic acid residues (SB-dBA) as platform for the site-specific immobilization of the glycoproteins glucose oxidase (GOx) and horseradish peroxidase (HRP). The analytical signal was obtained from amperometric experiments at − 0.050 V in the presence of 5.0 × 10−4 M hydroquinone as redox mediator. The concentration of GOx and HRP and the interaction time between the enzymes and the nanohybrid MWCNT–SB-dBA deposited at glassy carbon electrodes (GCEs) were optimized through a central composite design (CCD)/response surface methodology (RSM). The optimal concentrations of GOx and HRP were 3.0 mg mL−1 and 1.50 mg mL−1, respectively, while the optimum interaction time was 3.0 min. The bienzymatic biosensor presented a sensitivity of (24 ± 2) × 102 µA dL mg−1 ((44 ± 4) × 102 µA M−1), a linear range between 0.06 mg dL−1 and 21.6 mg dL−1 (3.1 µM–1.2 mM) (R2 = 0.9991), and detection and quantification limits of 0.02 mg dL−1 (1.0 µM) and 0.06 mg dL−1 (3.1 µM), respectively. The reproducibility for five sensors prepared with the same MWCNT–SB-dBA nanohybrid was 6.3%, while the reproducibility for sensors prepared with five different nanohybrids and five electrodes each was 7.9%. The GCE/MWCNT–SB-dBA/GOx-HRP was successfully used for the quantification of glucose in artificial human urine and commercial human serum samples. [ABSTRACT FROM AUTHOR]

This study reports a micromachined parylene-C-coated integrated electrode (IDE) sensor fabricated on a polyimide film. Glucose and uric acid within the human sweat concentration range were tested using hydrothermally grown ZnO nanoparticles (NPs) immobilized on the IDE regions of sensors and modified with urate oxidase and glucose oxidase enzymes. Four important sensing parameters, including capacitance, impedance, resistance, and phase, were simultaneously investigated during the dynamic test. The sensor fabrication and characterization of ZnO NPs and ZnO NP formed sensing film were described in detail. The experimental results show that the amount of capacitance change and phase change vs. the concentration variation of glucose and uric acid exhibits an excellent linear regression relationship. On the other hand, the amount of impedance change vs. concentration variation of glucose and uric acid exhibits a power regression relationship. Sensitivities of uric acid and glucose detection based on capacitance changes were 0.1131 pF/µM and 0.7875 pF/µM, respectively. Limits of detection of uric acid and glucose were 1.23 µM and 0.311 µM, respectively. Thus, the developed sensor can be applied to wearable devices for the quantitative analysis of sweat composition in the future. [ABSTRACT FROM AUTHOR]

A novel biofuel cell (BFC)-based self-powered electrochemical immunosensing platform was developed by integrating the target-induced biofuel release and biogate immunoassay for ultrasensitive 17β-estradiol (E2) detection. The carbon nanocages/gold nanoparticle composite was employed in the BFCs device as the electrode material, through which bilirubin oxidase and glucose oxidase were wired to form the biocathode and bioanode, respectively. Positively charged mesoporous silica nanoparticles (PMSN) were encapsulated with glucose molecules as biofuel and subsequently coated by the negatively charged AuNPs-labelled anti-E2 antibody (AuNPs-Ab) serving as a biogate. The biogate could be opened efficiently and the trapped glucose released once the target E2 was recognized and captured by AuNPs-Ab due to the decreased adhesion between the antigen–antibody complex and PMSN. Then, glucose oxidase oxidized the glucose to produce a large number of electrons, resulting in significantly increased open-circuit voltage (EOCV). Promisingly, the proposed BFC-based self-powered immunosensor demonstrated exceptional sensitivity for the detection of E2 in the concentration range from 1.0 pg mL−1 to 10.0 ng mL −1, with a detection limit of 0.32 pg mL−1 (S/N = 3). Furthermore, the prepared BFC-based self-powered homogeneous immunosensor showed significant potential for implementation as a viable prototype for a mobile and an on-site bioassay system in food and environmental safety applications. [ABSTRACT FROM AUTHOR]

An intelligent nanodrug delivery system (Cu/ZIF-8@GOx-DOX@HA, hereafter CZGDH) consisting of Cu-doped zeolite imidazolate framework-8 (Cu/ZIF-8, hereafter CZ), glucose oxidase (GOx), doxorubicin (DOX), and hyaluronic acid (HA) was established for targeted drug delivery and synergistic therapy of tumors. The CZGDH specifically entered tumor cells through the targeting effect of HA and exhibited acidity-triggered biodegradation for subsequent release of GOx, DOX, and Cu2+ in the tumor microenvironment (TME). The GOx oxidized the glucose (Glu) in tumor cells to produce H2O2 and gluconic acid for starvation therapy (ST). The DOX entered the intratumoral cell nucleus for chemotherapy (CT). The released Cu2+ consumed the overexpressed glutathione (GSH) in tumor cells to produce Cu+. The generated Cu+ and H2O2 triggered the Fenton-like reaction to generate toxic hydroxyl radicals (·OH), which disrupted the redox balance of tumor cells and effectively killed tumor cells for chemodynamic therapy (CDT). Therefore, synergistic multimodal tumor treatment via TME-activated cascade reaction was achieved. The nanodrug delivery system has a high drug loading rate (48.3 wt%), and the three-mode synergistic therapy has a strong killing effect on tumor cells (67.45%). [ABSTRACT FROM AUTHOR]

This study demonstrated a unique method for quantifying β-glucan in edible mushrooms by immobilizing glucose oxidase (GOx) and β-glucanase (βg) on Multi-Walled Carbon Nanotubes (MWCNTs) modified glassy carbon electrode (GCE)-Nafion composite. Utilizing the special qualities of MWCNTs and Nafion, the electrochemical sensor's performance was improved. A sensitive and precise measurement of β-glucan was made possible by the sensor's design, which made use of βg and GOx. βg-GOx/MWCNTs/Nafion/GCE were evaluated for their efficacy in determining β-glucan. The findings indicated that the βg-GOx/MWCNTs/Nafion/GCE reacted only to β-glucan determination and not to other substances that could interfere. Peak current changed in a manner that was exactly proportional to β-glucan concentration in the 1–181 µg/mL range; this suggests a sensitivity of 2.14808 µA/µg mL− 1 and a detection limit of 0.7 ng/mL. By comparing seven identical biosensors made under the same circumstances, the suggested biosensor's homogeneity was assessed. The biosensor's repeatability was verified with a 4.40% relative standard deviation (RSD). Using edible mushroom samples, the βg-GOx/MWCNTs/Nafion/GCE was utilized and verified as a β-glucan sensor. Relative standard deviations of less than 4.88% and excellent recoveries ranging from 97.00 to 99.70% were obtained from the amperometric study. This confirmed that the results of βg-GOx/MWCNTs/Nafion/GCE for determining β-glucan concentration in edible mushroom samples were adequate and validated. The results of this study have the potential to greatly improve our knowledge of polysaccharides and how to use them in food science and agriculture. [ABSTRACT FROM AUTHOR]

This study synthesized Fe-doped dopamine carbon dots (Fe-DACDs) as a reducing agent and template hybrid Au and Pt nanoparticles (Au@Pt/Fe-DACDs). Au@Pt/Fe-DACDs with core–shell structures show strong peroxidase (POD)-like activity at physiological pH. A colorimetric and surface-enhanced Raman scattering (SERS) dual-mode detection system for glucose in human serum was constructed by combining Au@Pt/Fe-DACDs with natural glucose oxidase (GOx). The cascade catalysis reactions convert glucose into hydrogen peroxide (H2O2), and then, the Au@Pt/Fe-DACDs as both POD-like nanozyme and Raman-enhancers oxidize colorless and weak Raman-active 3,3′,5,5′-tetramethylbenzidine (TMB) into blue and strong Raman-active ox-TMB. The linear response ranges of glucose are from 0.02 to 1 mM, with a detection limit of 2.3 μM for colorimetric detection and 0.01 mM to 0.7 mM with a detection limit of 1.4 μM for SERS sensors. Glucose content in human serum samples was successfully assayed with a good recovery from 97.6 to 105.3%. Overall, these results demonstrate a new way of designing biological detection systems based on SERS and colorimetric dual-mode sensing. [ABSTRACT FROM AUTHOR]

A cancer-targeted glutathione (GSH)-gated theranostic probe (CGT probe) for intracellular miRNA imaging and combined treatment of self-sufficient starvation therapy (ST) and chemodynamic therapy (CDT) was developed. The CGT probe is constructed using MnO2 nanosheet (MS) as carrier material to adsorb the elaborately designed functional DNAs. It can be internalized by cancer cells via specific recognition between the AS1411 aptamer and nucleolin. After CGT probe entering the cancer cells, the overexpressed GSH, as gate-control, can degrade MS to Mn2+ which can be used for CDT by Fenton-like reaction. Simultaneously, Mn2+-mediated CDT can further cascade with the enzyme-like activities (catalase-like activity and glucose oxidase-like activity) of CGT probe, achieving self-sufficient ST/CDT synergistic therapy. Meanwhile, the anchored DNAs are released, achieving in situ signal amplification via disubstituted-catalytic hairpin assembly (DCHA) and FRET (fluorescence resonance energy transfer) imaging of miR-21. The in vitro and in vivo experiments demonstrated that accurate and sensitive miRNA detection can be achieved using the CGT probe. Overall, the ingenious CGT probe opens a new avenue for the development of early clinical diagnosis and cancer therapy. [ABSTRACT FROM AUTHOR]

Sensors play a critical role in the detection and monitoring of various substances present in our environment, providing us with valuable information about the world around us. Within the field of sensor development, one area that holds particular importance is the detection of small molecules. Small molecules encompass a wide range of organic or inorganic compounds with low molecular weight, typically below 900 Daltons including gases, volatile organic compounds, solvents, pesticides, drugs, biomarkers, toxins, and pollutants. The accurate and efficient detection of these small molecules has attracted significant interest from the scientific community due to its relevance in diverse fields such as environmental pollutants monitoring, medical diagnostics, industrial optimization, healthcare remedies, food safety, ecosystems, and aquatic and terrestrial life preservation. To meet the demand for precise and efficient monitoring of small molecules, this summary aims to provide an overview of recent advancements in sensing and quantification strategies for various organic small molecules including Hydrazine, Glucose, Morpholine, Ethanol amine, Nitrosamine, Oxygen, Nitro-aromatics, Phospholipids, Carbohydrates, Antibiotics, Pesticides, Drugs, Adenosine Triphosphate, Aromatic Amine, Glutathione, Hydrogen Peroxide, Acetone, Methyl Parathion, and Thiophenol. The focus is on understanding the receptor sensing mechanism, along with the electrical, optical, and electrochemical response. Additionally, the variations in UV–visible spectral properties of the ligands upon treatment with the receptor, fluorescence and absorption titration analysis for limit of detection (LOD) determination, and bioimaging analysis are discussed wherever applicable. It is anticipated that the information gathered from this literature survey will be helpful for the perusal of innovation regarding sensing strategies. [ABSTRACT FROM AUTHOR]

In this study, 3,4-ethylenedioxythiophene derivative conjugated monomer 4-(dihexylamino)-9,12-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-7H-benzo [de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (EDOTBN) was synthesized and electropolymerized on pencil graphite electrode (PGE) to fabricate a highly stable and sensitive sensor for glucose detection for the first time. The structurally high conjugation of the monomer and the effect of increasing the conductivity of the gold nanoparticles increased the covalent bonding ability of the enzyme to the modified electrode surface and provided an excellent immobilization. PGE/p(EDOTBN)/AuNPs/GOx designed biosensor was characterized by a wide linear glucose determination range between 1.169 × 10–2 and 10 mM with a limit of detection of 0.008461 mM and a sensitivity of 38.365 µA/mMcm2. Furthermore, the prepared bioelectrode showed storage stability for 4 weeks. Recovery studies were also carried out to check the accuracy of the developed bioelectrode and the glucose concentration in commercial samples was determined accurately. [ABSTRACT FROM AUTHOR]

Mesoporous silica materials (MSMs) are widely used materials in many applications due to their diverse pore structures. However, the electrical conductivity of MSMs is poor which limits their use in electrochemical applications. In this study, widely used MSMs of different structural properties such as MCM-41, MCM-48, SBA-15, and SBA-16 were synthesized and reinforced with graphene oxide (GO) to obtain conductive composite supports for enzyme immobilization. MSMs were first synthesized using a hydrothermal method and characterized by Fourier-transform infrared spectroscopy, X-ray crystallography, scanning electron microscopy/energy dispersive X-ray, and MAPPING techniques. Aqueous dispersion of GO:MSM composites were prepared with as-synthesized materials and coated on screen-printed electrodes (SPE). The best composites were chosen based on their electroanalytical performance. Glucose oxidase (GOx) was then immobilized on modified SPEs using a simple drop-casting method to produce enzymatic electrodes. The electroanalytical performance of the enzymatic electrodes was investigated using different glucose concentrations to demonstrate biocatalytic activity. Stability tests were performed using intraday and interday measurements which revealed that SPE/GO:MCM-41/GOx electrode showed a more stable performance (3-folds) than SPE/GO/GOx electrode. This study presents an investigation of MSM mixed with GO in enzymatic electrochemical systems providing insight into the use of such materials to preserve enzyme activity. [ABSTRACT FROM AUTHOR]

The growing need in the current market for innovative solutions to obtain lactose-free (L-F) milk is caused by the annual increase in the prevalence of lactose intolerance inside as well as the newborn, children, and adults. Various configurations of enzymes can yield two distinct L-F products: sweet (β-galactosidase) and unsweet (β-galactosidase and glucose oxidase) L-F milk. In addition, the reduction of sweetness through glucose decomposition should be performed in a one-pot mode with catalase to eliminate product inhibition caused by H2O2. Both L-F products enjoy popularity among a rapidly expanding group of consumers. Although enzyme immobilization techniques are well known in industrial processes, new carriers and economic strategies are still being searched. Polymeric carriers, due to the variety of functional groups and non-toxicity, are attractive propositions for individual and co-immobilization of food enzymes. In the presented work, two strategies (with free and immobilized enzymes; β-galactosidase NOLA, glucose oxidase from Aspergillus niger, and catalase from Serratia sp.) for obtaining sweet and unsweet L-F milk under low-temperature conditions were proposed. For free enzymes, achieving the critical assumption, lactose hydrolysis and glucose decomposition occurred after 1 and 4.3 h, respectively. The tested catalytic membranes were created on regenerated cellulose and polyamide. In both cases, the time required for lactose and glucose bioconversion was extended compared to free enzymes. However, these preparations could be reused for up to five (β-galactosidase) and ten cycles (glucose oxidase with catalase). [ABSTRACT FROM AUTHOR]

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Directed toward the limitations of natural enzymes in diabetes management, it is possible to design nano-enzymatic structures and modulate the activity as needed to obtain superior materials that are more suitable for the specific application environment. In this work, noble metal–semiconductor composite nanozymes [Te–Au nanowires (NWs)] were designed and their enzyme-like activities were systematically investigated for diabetes management. The results indicated that Te–Au NWs exhibited pH-switching multi-enzyme-like activities and adapted to a wider range of reaction conditions than natural enzymes. The kinetics of their enzyme-catalyzed reactions followed the Michaelis–Menten model, showing their substrate affinity similar to that of natural enzymes. Actually, the nanozymes showed reliable application stability, maintaining more than 80% of various enzyme activities under prolonged or extreme storage conditions. Furthermore, the nanozymes can be flexibly applied to various paths of glucose detection. For example, we constructed three different colorimetric detection methods to achieve the detection of glucose in saliva and blood. All three detection methods showed a wider linear range and lower limit of detection (LOD), among which the most optimal method was the combination of Te–Au NWs and glucose oxidase (GOx), with a linear range of 0.05–4 mM and a LOD of 2.11 μM. In summary, nanozymes with multiple enzyme-like activities have significant advantages and effectively address the limitations of natural enzymes in the application of diabetes management. [ABSTRACT FROM AUTHOR]

Oxidative stress from excess H2O2 activates transcription factors that restore redox balance and repair oxidative damage. Although many transcription factors are activated by H2O2, it is unclear whether they are activated at the same H2O2 concentration, or time. Dose-dependent activation is likely as oxidative stress is not a singular state and exhibits dose-dependent outcomes including cell-cycle arrest and cell death. Here, we show that transcription factor activation is both dose-dependent and coordinated over time. Low levels of H2O2 activate p53, NRF2 and JUN. Yet under high H2O2, these transcription factors are repressed, and FOXO1, NF-κB, and NFAT1 are activated. Time-lapse imaging revealed that the order in which these two groups of transcription factors are activated depends on whether H2O2 is administered acutely by bolus addition, or continuously through the glucose oxidase enzyme. Finally, we provide evidence that 2-Cys peroxiredoxins control which group of transcription factors are activated. H2O2 stress is known to activate a slew of transcription factors that restore redox balance. Here, the authors use live-cell imaging and single-cell analysis to reveal that the transcription factors that are activated and their timing of activation is dose dependent. [ABSTRACT FROM AUTHOR]

Considering the application prospects of a cascade catalytic system in biomedical analysis, it remains significant to develop a cascade catalytic system for one-step rapid colorimetric detection. Herein, PVP/NH2-MIL-101(Fe) possessing enhanced peroxidase (POD)-like activity was successfully synthesized by microwave-assisted and polyvinylpyrrolidone (PVP) modification strategies. Then, PVP/NH2-MIL-101(Fe) and glucose oxidase (GOx) were covalently coupled via the bifunctional cross-linker glutaraldehyde, the GOx@PVP/NH2-MIL-101(Fe) with dual enzymatic functional activities (POD-like and GOx activities) was subsequently synthesized. GOx@PVP/NH2-MIL-101(Fe) had strong affinities for the substrates glucose, 3,3',5,5'-tetramethylbenzidine, and hydrogen peroxide. Based on this specific nanozyme GOx@PVP/NH2-MIL-101(Fe), a one-step colorimetric assay for rapid glucose determination was built. This detection method not only took 20 min to analyze but also possessed a linear range of 10–250 µM with a detection limit of 1.05 µM. Furthermore, the cascade catalytic system was applied to determine glucose concentrations in human serum samples. Compared with commercial blood glucose meters, the proposed method was also accurate and effective, making it a candidate method for determining blood glucose. [ABSTRACT FROM AUTHOR]

Wearable glucose biosensors enable noninvasive glucose monitoring, thereby enhancing blood glucose management. In this work, we present a wearable biosensor based on carbon black nanoparticles (CBNPs) for glucose detection in human sweat. The biosensor consists of CBNPs, Prussian blue (PB), glucose oxidase, chitosan, and Nafion. The fabricated biosensor has a linear range of 5 µM to 1250 µM, sensitivity of 14.64 µA mM−1 cm−2, and a low detection potential (−0.05 V, vs. Ag/AgCl). The detection limit for glucose was calculated as 4.83 µM. This reusable biosensor has good selectivity and stability and exhibits a good response to glucose in real sweat. These results demonstrate the potential of our CBNP-based biosensor for monitoring blood glucose in human sweat. [ABSTRACT FROM AUTHOR]

In this study, glucose oxidase (GOD) was fixed on ferrimagnetic vortex-domain iron oxide nanorings (FVIOs) using the covalent bond crosslinking method to create FVIOs-GOD compounds. The activity of surface-conjugated enzymes can be effectively and selectively enhanced by utilizing FVIOs to induce magnetothermal effects under the influence of alternating magnetic fields. GOD can further catalyze the oxidation of glucose to hydrogen peroxide (H2O2), which possesses bactericidal properties. This study presents a comprehensive technique for controlling the activity of enzymes by nano-magnetothermal stimulation, which was utilized in Escherichia coli antibacterial studies. In comparison to the control group, the enzyme activity of the FVIOs-GOD immobilized enzymes rose by 50 % due to the nano-magnetothermal stimulation, and the enzyme activity could be controlled by varying the magnetic field intensity. The antibacterial experiments indicated that the survival rate of Escherichia coli decreased by 55 % after exposure to a magnetic field. [ABSTRACT FROM AUTHOR]

A novel strategy based on gradient porous hollow fiber membrane (GPF) is proposed for the modular assembly of enzyme-nanozyme cascade systems. The porous structure of GPF provided sufficient specific surface area, while the gradient structure effectively minimized the leaching of enzymes and nanozymes. To enhance stability, we prepared and immobilized metal–organic framework (MOF) nanozymes, resulting in the fabrication of GPF-MOF with excellent stability and reusability for colorimetric H2O2 detection. To improve specificity and expand the detection range, micro-crosslinked natural enzymes were modularly assembled, using glucose oxidase as the model enzyme. The assembled system, GPF-mGOx@MOF, achieved a low detection limit of 0.009 mM and a linear range of 0.2 to 11 mM. The sensor retained 87.2% and 80.7% of initial activity after being stored for 49 days and 9 recycles, respectively. Additionally, the reliability of the biosensor was validated through glucose determination of human blood and urine samples, yielding comparable results to a commercial glucose meter. [ABSTRACT FROM AUTHOR]

Oxygen is crucial for converting glucose to gluconic acid catalyzed by glucose oxidase (Gox). However, industrial gluconic acid production faces oxygen supply limitations. To enhance Gox efficiency, Vitreoscilla hemoglobin (VHb) has been considered as an efficient oxygen transfer carrier. This study identified GoxA, a specific isoform of Gox in the industrial gluconic acid-producing strain of Aspergillus niger. Various forms of VHb expression in A. niger were tested to improve GoxA's catalytic efficiency. Surprisingly, the expression of free VHb, both intracellularly and extracellularly, did not promote gluconic acid production during shake flask fermentation. Then, five fusion proteins were constructed by linking Gox and VHb using various methods. Among these, VHb-GS1-GoxA, where VHb's C-terminus connected to GoxA's N-terminus via the flexible linker GS1, demonstrated a significantly higher Kcat/Km value (96% higher) than GoxA. Unfortunately, the expression of VHb-GS1-GoxA in A. niger was limited, resulting in a low gluconic acid production of 3.0 g/L. To overcome the low expression problem, single- and dual-strain systems were designed with tools of SpyCatcher/SpyTag and SnoopCatcher/SnoopTag. In these systems, Gox and VHb were separately expressed and then self-assembled into complex proteins. Impressively, the single-strain system outperformed the GoxA overexpression strain S1971, resulting in 23% and 9% higher gluconic acid production under 0.6 vvm and 1.2 vvm aeration conditions in the bioreactor fermentation, respectively. The successful construction of Gox and VHb fusion or complex proteins, as proposed in this study, presents promising approaches to enhance Gox catalytic efficiency and lower aerodynamic costs in gluconic acid production. Key points: • Overexpressing free VHb in A. niger did not improve the catalytic efficiency of Gox • The VHb-GS1-GoxA showed an increased Kcat/Km value by 96% than GoxA • The single-strain system worked better in the gluconic acid bioreactor fermentation [ABSTRACT FROM AUTHOR]

In this work the green synthesis of gold nanoparticles (Au-NPs) using the oxidoreductive enzymes Myriococcum thermophilum cellobiose dehydrogenase (Mt CDH), Glomerella cingulata glucose dehydrogenase (Gc GDH), and Aspergillus niger glucose oxidase (An GOX)) as bioreductants was investigated. The influence of reaction conditions on the synthesis of Au-NPs was examined and optimised. The reaction kinetics and the influence of Au ions on the reaction rate were determined. Based on the kinetic study, the mechanism of Au-NP synthesis was proposed. The Au-NPs were characterized by UV–Vis spectroscopy and transmission electron microscopy (TEM). The surface plasmon resonance (SPR) absorption peaks of the Au-NPs synthesised with Mt CDH and Gc GDH were observed at 535 nm, indicating an average size of around 50 nm. According to the image analysis performed on a TEM micrograph, the Au-NPs synthesized with Gc GDH have a spherical shape with an average size of 2.83 and 6.63 nm after 24 and 48 h of the reaction, respectively. Key points: • The Au NPs were synthesised by the action of enzymes CDH and GDH. • The synthesis of Au-NPs by CDH is related to the oxidation of cellobiose. • The synthesis of Au-NPs by GDH was not driven by the reaction kinetic. [ABSTRACT FROM AUTHOR]

In this work, the β-cyclodextrins (βCD) grafted on magnetite@polynorepinephrine (Fe3O4@PNE) nanomaterial with glucose oxidase (GOx) from Aspergillus niger was presented. The electroactive nanoplatform was used to construct rapid response and long-live time biosensor for qualitative and quantitative glucose determination. The nanomaterial was deposited on the screen-printed electrode (SPE) and integrated with the potentiostat in tandem with a portable devices. The methodology may affect its relatively low unit cost, miniaturization aspect, and electrode system integrity. The potential usage is intended for advanced diabetes care with a focus on the point-of-care testing idea. The cyclic voltammetry and amperometry were used for electrochemical characterization. The presented SPE/Fe3O4@PNE@βCD-GOx biosensor enabled measurements in a wide range of concentrations (0.1–30.0 mM), an enhanced sensitivity (204.82 µA mM− 1 cm− 2), a low limit of detection (3.2 µM), and a rapid response (2.6 s). Moreover, the proposed sensor achieved long-term stability, up to 11 months. Testing on real samples (human blood, human serum, infusion fluids) showed recovery in range from 95.5 to 98.6%. The outcomes demonstrated that this biosensor has great potential for use in determining the amount of glucose in a biological fluids and commercial products. The novelty of this work would largely consist of the possibility of qualitative and quantitative measurements of glucose in real human samples with a long time stability. This portable system enables mobile diagnostics tests including point-of-care testing idea. Due to the applied β-cyclodextrins on the surface of the novel polynorepinephrine biopolymer coating, selectivity, stability, and sensitivity were improved. [ABSTRACT FROM AUTHOR]

A novel and self referenced multi-analyte Hybrid Plasmonic Dual Grating Biosensor is proposed. The grating structure is composed of gold and corrugations are filled with dielectric ZnS. A thin layer of ZnS with slit is spread over grating thus making it dual grating structure. The influence of convexing of slit walls is modeled by parameter alpha in analytical equation. The reflectance characteristics are rigorously investigated using wavelength interrogation method for different values of parameter alpha, it is observed that wavelength varies from 722.2 to 729.6 nm for surface refractive index in the slit varying from 1.3 to 1.4 respectively at alpha equal to 0. The surface sensitivity obtained is about 74 nm/RIU. The surface sensitivity is also investigated by intensity interrogation and is equal to 0.2637 R/RIU or 26.37% R/RIU. It is observed that for higher values of alpha, the sensor is ideal for sensing gaseous analytes while at lower values of alpha can be used for liquid analytes. Refractive index range of surface analyte is correlated with the refractive index of blood by using linear refractive index model and Gladstone-Dale law for blood. It is observed that for alpha equal to 0, the grating biosensor can be used for invasive blood glucose monitoring with very high sensitivity of about 0.02641 nm/mg/dl. Linear regression model relating blood glucose and salivary glucose is used. The proposed sensor can also be used for noninvasive salivary glucose monitoring with surface sensitivity of 0.7410 nm/mg/dl. [ABSTRACT FROM AUTHOR]

Two-dimensional polymeric cobalt phthalocyanine (poly-CoPc) was synthesized using a microwave-assisted process, and its feasibility for use in continuous glucose monitoring (CGM) was investigated. The poly-CoPc/CNT composite showed 18% higher Co content than using commercial CoPc (c-CoPc/CNT) and synthesized CoPc (s-CoPc/CNT) composites, due to its intrinsic polymeric structure. In the cyclic voltammetry test, the bioelectrode incorporating glucose oxidase (GOx) based upper enzyme layer ([poly-CoPc/CNT]/PEI/[GOx-TPA]) demonstrated 1.51 times higher current densities than monomeric CoPc used bioelectrode ([CoPc/CNT]/PEI/[GOx-TPA]). This improvement is attributed to the higher biocompatibility with the enzyme layer of poly-CoPc, which prevents the blocking of hydrophobic sites near the co-factor of GOx. As a glucose sensor, [poly-CoPc/CNT]/PEI/[GOx-TPA] exhibits a sensitivity of 50.5 µA mM−1 cm−2 and a response time of 2.4 s in the chronoamperometric response test. Furthermore, the proposed bioelectrode showed 95.6% performance maintenance during 24 h and 81.4% stability over 20 days. These findings demonstrate the suitability of [poly-CoPc/CNT]/PEI/[GOx-TPA] for implantable and low-invasive patch-type glucose sensors offering high sensitivity, durability, and a linear response within the physiological glucose concentration range (0.1–20.0 mM) of both average individuals and diabetic patients. [ABSTRACT FROM AUTHOR]

Artificial actuators have been extensively studied due to their wide range of applications from soft robotics to biomedicine. Herein we introduce an autonomous bi-enzymatic system where reversible motion is triggered by the spontaneous oxidation and reduction of glucose and oxygen, respectively. This chemo-mechanical actuation is completely autonomous and does not require any external trigger to induce self-sustained motion. The device takes advantage of the asymmetric uptake and release of ions on the anisotropic surface of a conducting polymer strip, occurring during the operation of the enzymes glucose oxidase and bilirubin oxidase immobilized on its surface. Both enzymes are connected via a redox polymer at each extremity of the strip, but at the opposite faces of the polymer film. The time-asymmetric consumption of both fuels by the enzymatic reactions produces a double break of symmetry of the film, leading to autonomous actuation. An additional break of symmetry, introduced by the irreversible overoxidation of one extremity of the polymer film, leads to a crawling-type motion of the free-standing polymer film. These reactions occur in a virtually unlimited continuous loop, causing long-term autonomous actuation of the device. Owing to their interesting applications from soft robotics to biomedicine, methodologies to produce artificial actuators are desirable. Herein the authors develop an autonomous soft bioelectrochemical actuator with self-sustained motion triggered by spontaneous enzymatic reactions. [ABSTRACT FROM AUTHOR]

Caterpillar salivary glucose oxidase (GOX) can function as both an elicitor or as an effector of plant defense responses depending upon the system. Treatment with GOX reduces the stomatal aperture of tomato and soybean leaves, thereby reducing the emission of volatile organic compounds (VOCs), that are important indirect defense responses of plants by attracting natural enemies of the caterpillars. Here we examined the effect of fungal GOX (fungal glucose oxidases have been used to determine specificity in defense response elicitation) on stomatal closure of maize leaves and on the volatile emission pattern whole maize plants. We also used salivary gland homogenate from wild-type and CRISPR-Cas9 Helicoverpa zea mutants deficient in GOX activity to determine the effect caterpillar saliva with and without GOX had on maize volatile emission. Collecting volatiles at 2-hour intervals allowed us to examine the changes in emission over time. Fungal GOX reduced the stomatal aperture in maize leaves, which may have influenced the observed significant reduction in total green leaf volatile (GLV) emission. Furthermore, fungal GOX significantly increased the emission of several key terpenes: linalool, DMNT, and Z-β-farnesene from maize, while salivary gland homogenate from wild type (WT; GOX+) H. zea increased the emission of α-pinene, β-pinene, and ocimene compared to H. zea unable to synthesize GOX. This study addressed a significant knowledge gap about the effect of GOX on maize volatiles and provides a baseline for further research on the effect of GOX on the regulation of terpene synthase genes and their relation to terpene volatile emission. [ABSTRACT FROM AUTHOR]

The ability of shape-controlled octahedral Pt nanoparticles to act as nanozyme mimicking glucose oxidase enzyme is reported. Extended {111} particle surface facets coupled with a size comparable to natural enzymes and easy-to-remove citrate coating give high affinity for glucose, comparable to the enzyme as proven by the steady-state kinetics of glucose electrooxidation. The easy and thorough removal of the citrate coating, demonstrated by X-ray photoelectron spectroscopy analysis, allows a highly stable deposition of the nanozymes on the electrode. The glucose electrochemical detection (at −0.2 V vs SCE) shows a linear response between 0.36 and 17 mM with a limit of detection of 110 μM. A good reproducibility has been achieved, with an average relative standard deviation (RSD) value of 9.1% (n = 3). Similarly, a low intra-sensor variability has been observed, with a RSD of 6.6% (n = 3). Moreover, the sensor shows a long-term stability with reproducible performances for at least 2 months (RSD: 7.8%). Tests in saliva samples show the applicability of Pt nanozymes to commercial systems for non-invasive monitoring of hyperglycemia in saliva, with recoveries ranging from 92 to 98%. [ABSTRACT FROM AUTHOR]

Receptor-mediated drug delivery systems are a promising tool for targeting malignant cells to suppress/inhibit the malignancy without disturbing healthy cells. Protein-based nanocarrier systems possess numerous advantages for the delivery of variety of chemotherapeutics, including therapeutic peptides and genes. In the present work, glucose-conjugated camptothecin-loaded glutenin nanoparticles (Glu-CPT-glutenin NPs) were fabricated to deliver camptothecin to MCF-7 cells via GLUT-1 transporter protein. Initially, Glu-conjugated glutenin polymer was successfully synthesized through reductive amination reaction, and this was confirmed by FTIR and 13C-NMR. Then, camptothecin (CPT) was loaded into Glu-conjugated glutenin polymer forming Glu-CPT-glutenin NPs. The nanoparticles were studied for their drug releasing capacity, morphological shape, size, physical nature, and zeta potential. The fabricated Glu-CPT-glutenin NPs were found to be spherical in shape and amorphous in nature with 200-nm size range and a zeta potential of − 30 mV. Furthermore, MTT assay using Glu-CPT-glutenin NPs confirmed concentration-dependent cytotoxicity against MCF-7 cells after 24-h treatment, and IC50 was found to be 18.23 μg mL−1. In vitro cellular uptake study demonstrated that the Glu-CPT-glutenin NPs had enhanced endocytosis and delivered CPT in MCF-7 cells. A typical apoptotic morphological change of condensed nuclei and distorted membrane bodies was found after treatment with IC50 concentration of NPs. The released CPT from NPs also targeted mitochondria of MCF-7 cells, significantly increasing the level of reactive oxygen species and causing the damage of mitochondrial membrane integrity. These outcomes confirmed that the wheat glutenin can positively serve as a significant delivery vehicle and enhance the anticancer potential of this drug. [ABSTRACT FROM AUTHOR]

In this work, a novel amperometric biosensor for the determination of adenosine triphosphate (ATP) was developed. The biosensor was based on two enzymes (glucose oxidase and hexokinase) that were entrapped in the electrospun nanofibers. The biosensor was prepared by direct electrospinning of the enzymes/polymer mixture on the surface of platinum disc electrodes with subsequent UV cross-linking of the obtained nanofibers. Photocrosslinkable polymer (polyvinyl alcohol containing styrylpyridinium groups, PVA-SbQ) was chosen as matrix, while gold nanoparticles (GNPs) were added to the enzymes/polymer mixture to improve analytical characteristics of the biosensor. For the first time, incorporation of several enzymes in the nanofibers during electrospinning was demonstrated. Composition of the mixture for electrospinning was optimized. The obtained biosensors enabled successful detection of ATP by chronoamperometry, linear range was 25–200 μM. The analytical characteristics of the biosensors were compared with the biosensors prepared by manual drop-casting of the enzymes/polymer/GNP mixture. The biosensor can be also used to detect glucose in samples with known or very low (< 10 μM) ATP concentration; linear range of the glucose determination was 0.01–3 mM. The described approach for one-step electrospinning of several enzymes is fast and simple and can be easily modified for immobilization of other multi-enzyme systems, which opens possibilities to enlarge the range of the targets that can be determined by the biosensors produced using electrospinning. [ABSTRACT FROM AUTHOR]

The nanoscale thermal effect of ferrimagnetic vortex-domain iron oxide nanorings (FVIOs) was measured when exposed to an alternating magnetic field. A molecular temperature probe (fluorescein isomer I, FI) was attached to a thermo-sensitive molecule (4,4′-Azobis (4-cyanovaleric acid, AZO), then the molecule was bound to the nanoparticle surface through poly (ethylene glycol) (PEG, Mw = 1000, 2000, 5000 Da) spacers of different molecular weights. The magnetothermal effect induced the thermal decomposition of AZO driving the release of FI which was monitored by the photoluminescence method. It was found that the effective local temperature (Teff) decreased with the increase of Mw (PEG) and increased with the rise in field amplitudes B, and the temperature was found in a linear relationship with the applied magnetic field at all distances. The significant local heating temperature (T) rose to 60.3 °C when d = 0 of FVIOs, where d is the distance of the AZO-FI end group to the surface, while it fell exponentially with the increasing distance. The nanoscale thermal effect of the 20 nm superparamagnetic iron oxide nanoparticles (SPIOs) was also studied. The results revealed that FVIOs have much higher nanometer local heat than SPIOs for all the applied magnetic field amplitudes. These findings were then applied in the enzyme activity regulation experiment of FVIOs and SPIOs. The results indicated that glucose oxidase (GOD) had higher enzyme activity after nano-magnetothermal stimulation of FVIOs. [ABSTRACT FROM AUTHOR]

Bacterial cellulose (BC) has become attractive for biomedical applications owing to its excellent properties. However, it is necessary to use bioactive substances to compensate for the lack of antibacterial activity of BC. In this study, the l-arginine (Arg) Schiff base was introduced into the oxidized BC (OxBC). Glucose oxidase (GOD) and Schiff base were selected to endow the cellulose composites with suitable antibacterial properties. These composites were tested as potential antibacterial bioactive materials. SEM, FTIR, XPS, and XRD analyses confirmed the structures of the prepared composites. In addition, H2O2-releasing behavior was also tested. The antibacterial potential of those composites was tested against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. Antibacterial tests indicated that the antibacterial activity of OxBC–GOD/Arg was higher than that of OxBC–GOD. Under low concentrations of GOD, the bacteriostatic rates of OxBC–GOD/Arg complex against E. coli, S. aureus, and P. aeruginosa were 95.8%, 95.7%, and 89.1%, respectively. Collectively, this work provides cellulose composite membranes with antibacterial activity as promising candidates for biomedical applications. [ABSTRACT FROM AUTHOR]

A procedure for the synthesis of a highly selective adsorbent based on an imprinted protein (IP), glucose oxidase (GO), and commercially available SiO2 microparticles for the sorption of mycotoxin zearalenone produced by fungi of the Fusarium species is developed. The use of 3D fluorescence spectroscopy for the control of the process of IP purification is proposed for the first time. A possibility of replacing the zearalenone molecule as a template molecule with structural analogues with lower toxicity is assessed. The analytical characteristics of the determination of zearalenone using imprinted GO as a receptor element in enzyme immunoassay are determined: the limit of detection is 5 ng/mL, the linear analytical range is 11–112 ng/mL. High sorption characteristics of the synthesized adsorbent based on IP (sorption capacity—7.6 μg/mg sorbent; imprinting factor—2.5) are shown. [ABSTRACT FROM AUTHOR]

Purpose: This study aims at chemotherapy and starvation therapy of HCC via starvation and apoptosis. Methods: Hollow mesoporous organosilica nanoparticles (HMONs) with the thioether-hybrid structure were developed using an organic/inorganic co-templating assembly approach. Hydrofluoric acid was used to remove the internal MSN core for yielding large radial mesopores for loading drug cargos. The morphology and structure of NPs were determined using TEM and SEM. HMONs were stepwise surface modified with glucose oxidase (GOx), oxygen (O2) and Doxorubicin (DOX), and cancer cell membrane (CCM) for yielding CCM-coated HMONs (targeted stealth biorobots; TSBRs) for starvation, apoptotic, and enhanced cell uptake properties, respectively. The surface area and pore size distribution were determined via BET and BJH assays. The catalytic ability of GOx-modified NPs was measured using in vitro glucose conversion approach authenticated by H2O2 and pH determination assays. MTT assay was used to determine the cytotoxicities of NPs. Cell uptake and apoptotic assay were used for the NPs internalization and apoptosis mechanisms. The subcutaneous HepG2 tumor model was established in mice. The long-term in vivo toxicity was determined using blood assays. Results: The prepared NPs were spherical, hollow and mesoporous with excellent surface area and pore size distribution. The GOx-modified NPs exhibited excellent catalytic activity. The TSBRs showed better cytotoxicity and reduce the tumor size and weight. The NPs showed long-term safety in vivo. Conclusion: TSBRs destroyed cancer cells by starvation and chemotherapy in both in-vitro and in-vivo settings which demonstrates its anti-cancer potential. [ABSTRACT FROM AUTHOR]

A novel magnetic nanozyme Fe3O4@MXene-Au nanocomposite, which possessed higher peroxidase-like activity than that of Fe3O4 nanoparticles and Fe3O4@MXene nanocomposites, was developed. The outstanding magnetic properties of the nanozyme endowed it with the ability of simple and rapid separation, achieving great recyclability. Based on Fe3O4@MXene-Au nanocomposites and glucose oxidase (Glu Ox), a highly selective colorimetric biosensor for glucose detection was developed. Fe3O4@MXene-Au nanocomposites can catalyze H2O2 produced from glucose catalyzed by glucose oxidase to ·OH and oxidize colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) with a significant absorbance at 652 nm. The linear range of glucose was 0–1.4 mM under optimal conditions, with a limit of detection (LOD) of 0.11 mM. Glucose in human whole blood was successfully detected with satisfactory recoveries. Furthermore, a facile agarose hydrogel detection platform was designed. With smartphone software, glucose detection can be realized by the agarose hydrogel platform, demonstrating the potential in on-site and visual detection of glucose. [ABSTRACT FROM AUTHOR]

Selective and sensitive quantification of xanthine (XA) in food industries has been proved to be highly important for the assessment of the freshness of fish. The present work reports for the first time nanocellulose as an immobilization matrix for xanthine oxidase (XO) to detect xanthine and to construct an electrochemical biosensor for fish spoilage monitoring. Nanocellulose was prepared from raw cotton using acid hydrolysis. Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) studies depicted the nanosized crystalline structure of the prepared nanocellulose, confirming its high surface area. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) studies confirm the proper immobilization of XO onto nanocellulose surface. Electrochemical impedance spectroscopy predicts (EIS) high enzyme (XO) loading on nanocellulose immobilized glassy carbon electrode. pH studies confirm the active pH of the biosensor to be 7.5. Differential pulse voltammetry (DPV) showed the linear range of detection of xanthine by the developed biosensor was 3–50 µM with a detection limit of 47.96 nM, and a sensitivity of 5281 µA mM−1 cm−2. The relatively low Michaelis–Menten constant (Km) value of 12.2 μM shows the high affinity of the enzyme (XO) for xanthine. The proposed sensor exhibits a very good performance concerning the detection limit, preparation method, cost, sample preparation, stability (one month with 97% activity), and selectivity. This sensor was successfully applied for the detection of xanthine in fish samples stored for 30 days, which were in good agreement with the commercial spectrophotometric method. [ABSTRACT FROM AUTHOR]

Membranekess enzymatic biofuel cells (EBFCs) have the potential to be used in biocompatible devices, such as implantable or wearable devices. However, they face challenges due to low reaction surface area and high resistance attributed to large particle size and protein composition of enzyme catalysts used. In this study, to improve the performance of membraneless EBFCs, three-dimensional graphite felt (3D-GF) electrode was utilized. The 3D-GF electrode has high electrical conductivity and large surface area, allowing the large loading of catalytic components and increasing the reactivity of redox reaction required for EBFC operation. Membraneless EBFC using the 3D-GF electrode is prepared with anodic catalyst including glucose oxidase (GOx) and tetrathiafulvalene mediator, and cathodic catalyst of horseradish peroxidase and GOx. The outermost layer of 3D-GF electrode is coated with gelatin crosslinked by glutar-aldehyde to prevent leaching of components of catalysts. According to evaluations, both anodic and cathodic catalysts are evenly distributed on 3D-GF electrode, and anodic and cathodic currents of 103.5 and 68.7 µA at 0.3 V vs. Ag/AgCl are measured. Additionally, EBFCs using the optimized electrodes demonstrate high power output of 82 µW in a small cell kit size of 1.5×1.5×1.5 cm3, with excellent design flexibility. [ABSTRACT FROM AUTHOR]

Chemodynamic therapy (CDT) based on cascade catalytic nanomedicine has emerged as a promising cancer treatment strategy. However, most of the reported cascade catalytic systems are designed based on symmetric- or co-assembly of multiple catalytic active sites, in which their functions are difficult to perform independently and may interfere with each other. Especially in cascade catalytic system that involves fragile natural-enzymes, the strong oxidation of free-radicals toward natural-enzymes should be carefully considered, and the spatial distribution of the multiple catalytic active sites should be carefully organized to avoid the degradation of the enzyme catalytic activity. Herein, a spatially-asymmetric cascade nanocatalyst is developed for enhanced CDT, which is composed by a Fe3O4 head and a closely connected mesoporous silica nanorod immobilized with glucose oxidase (mSiO2-GOx). The mSiO2-GOx subunit could effectively deplete glucose in tumor cells, and meanwhile produce a considerable amount of H2O2 for subsequent Fenton reaction under the catalysis of Fe3O4 subunit in the tumor microenvironment. Taking the advantage of the spatial isolation of mSiO2-GOx and Fe3O4 subunits, the catalysis of GOx and free-radicals generation occur at different domains of the asymmetric nanocomposite, minimizing the strong oxidation of free-radicals toward the activity of GOx at the other side. In addition, direct exposure of Fe3O4 subunit without any shelter could further enhance the strong oxidation of free-radicals toward objectives. So, compared with traditional core@shell structure, the long-term stability and efficiency of the asymmetric cascade catalytic for CDT is greatly increased by 138%, thus realizing improved cancer cell killing and tumor restrain efficiency. [ABSTRACT FROM AUTHOR]

In this work, Au nanoparticles were synthesized using eco-friendly protocol and then supported on reduced graphene oxide (rGO) nanosheets through in-situ polymerization of indole (In), focusing on their electrochemical efficiency against glucose oxidation in glucose-based biofuel cells (glucose/O2). The bioanode was fabricated by applying ferritin (Frt) and glucose oxidase (GOx) on the glassy carbon electrode (GCE) followed by deposition of Au@rGO/PIn nanocomposite. The physical characterizations such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM), have revealed the successful synthesis of Au@rGO/PIn nanocomposite. In addition, the electrochemical behavior of different modified bioanodes were analyzed using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The modified bioanode Au@rGO/PIn/Frt/GOx attained a maximum current output of 7.2 mA cm−2 at the optimum glucose concentration of 50 mM in phosphate buffer solution (PBS) as an electrolyte. However, the obtained result is not the highest current density as reported in the literature but the materials are cost effective and method is easier and ecofriendly. This suggests that 3D fabricated bioanode could be used in enzymatic biofuel cell (EBFC) applications and allied fields, such as biosensors and bioreactors. [ABSTRACT FROM AUTHOR]

Bioinspired multi-compartment architectures are desired in synthetic biology and metabolic engineering, as credited by their cell-like structures and intrinsic ability of assembling catalytic species for spatiotemporal control over cascade reactions like in living systems. Herein, we describe a general Pickering double emulsion-directed interfacial synthesis method for the fabrication of multicompartmental MOF microreactors. This approach employs multiple liquid–liquid interfaces as a controllable platform for the self-completing growth of dense MOF layers, enabling the microreactor with tailor-made inner architectures and selective permeability. Importantly, simultaneous encapsulation of incompatible functionalities, including hydrophilic enzyme and hydrophobic molecular catalyst, can be realized in a single MOF microreactor for operating chemo-enzymatic cascade reactions. As exemplified by the Grubb' catalyst/CALB lipase driven olefin metathesis/ transesterification cascade reaction and glucose oxidase (GOx)/Fe-porphyrin catalyzed oxidation reaction, the multicompartmental microreactor exhibits 2.24–5.81 folds enhancement in cascade reaction efficiency in comparison to the homogeneous counterparts or physical mixture of individual analogues, due to the restrained mutual inactivation and substrate channelling effects. Our study prompts further design of multicompartment systems and the development of artificial cells capable of complex cellular transformations. The cell-like structures and the ability of assembling catalytic species are interesting features of bioinspired multicompartment architectures but it remains a challenge to build them. Here, the authors describe a Pickering double emulsion-directed interfacial synthesis to fabricate multi-compartmented metal-organic framework microreactors. The cell-like structures and the ability of assembling catalytic species are interesting features of bioinspired multicompartment architectures but it remains a challenge to build them. Here, the authors describe a Pickering double emulsion-directed interfacial synthesis to fabricate multi-compartmented metal-organic framework microreactors. [ABSTRACT FROM AUTHOR]

Spotted pod borer, Maruca vitrata (F.), is one of the severe threats to grain legumes in the tropics and subtropics owing to its destructiveness and broad host range. It is imperative to look for safer alternatives for its management, such as the utilization of host plant resistance which can be induced upon the exogenous application of jasmonic acid (JA) and salicylic acid (SA). We studied the changes induced in the digestive and detoxifying enzymes of M. vitrata upon its feeding on JA and SA-treated pigeonpea plants in comparison with the untreated plants. Both JA and SA induced a defense response in pigeonpea plants against M. vitrata, which in turn affected the pest's development and physiology. The effect on the digestive enzymes (amylase, total proteases, elastase, lactate dehydrogenase) and developmental parameters (larval duration, larval weight, pupal weight, pupal percent, adult emergence and adult longevity) of M. vitrata was more pronounced and significant in the plants pre-treated with JA and then infested with M. vitrata after 12 h of JA application, compared to other treatments and untreated plants. The resistant genotype, AL 1747 responded better to the exogenous application of elicitors and M. vitrata infestation than the susceptible genotype MN 1. As a counter-response to induced plant defenses, an increase in the activity of glutathione-S-transferases (GST) and glucose oxidase (GOX) enzymes was observed in M. vitrata. Despite elevating its GOX activity upon elicitor application, the pod borer was unable to overcome the induced pigeonpea defences consequent of elicitor application as was indicated by its reduced larval weight and other biological parameters. SA also altered the activities of digestive and defense-related enzymes in M. vitrata; however, the effect was not as pronounced as JA. Both JA and SA seem to be involved in triggering the pigeonpea defenses and their exogenous application can be utilized to develop sustainable pest management strategies against M. vitrata. [ABSTRACT FROM AUTHOR]

Self-adaptability is highly envisioned for artificial devices such as robots with chemical noses. For this goal, seeking catalysts with multiple and modulable reaction pathways is promising but generally hampered by inconsistent reaction conditions and negative internal interferences. Herein, we report an adaptable graphitic C6N6-based copper single-atom catalyst. It drives the basic oxidation of peroxidase substrates by a bound copper-oxo pathway, and undertakes a second gain reaction triggered by light via a free hydroxyl radical pathway. Such multiformity of reactive oxygen-related intermediates for the same oxidation reaction makes the reaction conditions capable to be the same. Moreover, the unique topological structure of CuSAC6N6 along with the specialized donor-π-acceptor linker promotes intramolecular charge separation and migration, thus inhibiting negative interferences of the above two reaction pathways. As a result, a sound basic activity and a superb gain of up to 3.6 times under household lights are observed, superior to that of the controls, including peroxidase-like catalysts, photocatalysts, or their mixtures. CuSAC6N6 is further applied to a glucose biosensor, which can intelligently switch sensitivity and linear detection range in vitro. Catalysts with multiple and modulable reaction pathways are promising but generally hampered by inconsistent reaction conditions and negative internal interferences. Herein, the authors report an adaptable graphitic C6N6-based copper singleatom catalyst [ABSTRACT FROM AUTHOR]

The hydrogen peroxide (H2O2) measurement is considered highly important in industrial wastewater quality assessment, environmental protection, and disease detection. Here, a simple high-performance paper-based sensor is proposed for rapid and in situ detection of H2O2. To this end, 3,3′,5,5′-tetramethylbenzidine is embedded in the sensor to act as a color indicator, whose reaction with hydrogen peroxide is catalyzed by a silver nanozyme modified by sericin. The result of the reaction clarified by the appearance of blue color in the sensor detection zone is received by a portable scanner, while also calculating its intensity by image analysis software. This method is sensitive to hydrogen peroxide in the concentration range of 0.5‒240 mg/dL, providing a detection limit of 0.15 mg/dL. The ability of the sensor to determine glucose is also evaluated by adding a layer containing glucose oxidase enzyme to the sensor structure. A desirable response is obtained in the range of 1.0‒160 mg/dL, together with a detection limit of 0.37 mg/dL. Accordingly, the proposed sensor shows satisfactory results compared to clinical methods for monitoring the amount of glucose in biological samples such as serum and saliva. [ABSTRACT FROM AUTHOR]

Brown algae contain a β-glucan called laminaran that exhibits various biological activities, such as immune-enhancing, anti-cancer, and antioxidant properties. The laminaran content in brown algae varies depending on species, habitat, and season. When developing a laminaran-containing functional food using brown algae or its extract, accurate quantitative methods to determine laminaran content in a variety of brown algae and foodstuffs are required. In this study, we examined the applicability of the existing sodium hypochlorite extracting and enzymatic digesting (SEED) assay for the determination of the laminaran content of the brown alga Eisenia bicyclis. The laminaran content of E. bicyclis could be determined using the SEED assay. Furthermore, we developed a rapid and concise acid extraction enzymatic method. This method can specifically extract total water-soluble β-glucan (laminaran) and selectively convert it to glucose. The generated glucose content was determined using the glucose oxidase/peroxidase method. The validation test using brown algae E. bicyclis and Sargassum horneri revealed that the acid extraction-enzymatic method is accurate, precise, and applicable to the determination of the laminaran content in these brown algae. Furthermore, developed method was also applicable to laminaran-added processed foods. [ABSTRACT FROM AUTHOR]

Fe–N-doped carbon nanomaterials (Fe–N/CMs) were designed as a novel biomimetic enzyme with excellent peroxidase-like activity to achieve high-efficient enzyme cascade catalytic amplification with the aid of glucose oxidase (GOx), which was further combined with target-induced DNA walker amplification to develop a sensitive electrochemical biosensor for thrombin detection. Impressively, massive output DNA was transformed from small amounts of target thrombin by highly effective DNA walker amplification as protein-converting strategy, which could then induce the immobilization of functionalized nanozyme on the electrode surface to achieve the high-efficient electrochemical biomimetic enzyme cascade amplification. As a result, an amplified enzyme cascade catalytic signal was measured for thrombin detection ranging from 0.01 pM to 1 nM with a low detection limit of 3 fM. Importantly, the new biomimetic enzyme cascade reaction coupled the advantages of natural enzyme and nanozyme, which paved an avenue to construct varied artificial multienzymes amplification systems for biosensing, bioanalysis, and disease diagnosis applications. [ABSTRACT FROM AUTHOR]

An accurate and sensitive competitive enzyme-linked immunosorbent assay (ELISA) based on persistent luminescence nanoparticles Zn2GeO4:Mn2+, Eu3+ (ZGME) was developed for detecting ochratoxin A (OTA), a powerfully toxic mycotoxin usually found in grains. As a signal output element of autofluorescence-free biosensors, ZGME can be integrated into ELISA with glucose oxidase (GOx)-binding OTA molecules due to its excellent pH-responsive persistent luminescence. In the absence of OTA, the OTA-GOx conjugate was captured by the anti-OTA monoclonal antibody (anti-OTA mAb) pre-coated on the 96-well plate. The results indicate a decrease in the pH value of the solution, which triggered the quenching of ZGME luminescence due to GOx-dependent gluconic acid production. The presence of OTA inhibited the binding of OTA-GOx on the plate, thus decreasing the production of gluconic acid and increasing the persistent luminous intensity of ZGME. Under the optimized concentrations of anti-OTA mAb and OTA-GOx, quantitative determination of OTA was achieved by plotting the increase or decrease in persistent luminescence intensity of ZGME at 535 nm. In this study, the linear range was from 0.1 μg L−1 to 63 μg L−1, and the limit of detection (LOD) was as low as 0.045 μg L−1. In five food samples (corn grit, brown rice, soybean, rice, and wheat), the results exhibited good stability and repeatability, with a recovery range from 81.3% to 94.4% and a relative standard deviation (RSD) of less than 4.2%. Hence, the established method provides a sensitive, accurate, and autofluorescence-free approach for the determination of OTA in different grain samples. [ABSTRACT FROM AUTHOR]

Coculture and whole-cell immobilization have myriad industrial applications for enhancing enzyme production. Using pretreated wheat straw as the sole carbon source, improving glucose isomerase production and cell growth by synthetic bacterial consortia was investigated. Thirteen cocultures were constructed based on the performance and antagonistic activities of monocultures from six cellulolytic soil bacteria. The performance of monocultures immobilized with calcium alginate was also tested. Only five cocultures (A, B, C, G and J) exhibited cell growth and enzyme production synergies. The highest level of synergism (15.17 U/mL) was found in coculture J composed of Mycobacterium sp. MKAL3 (4.06 U/mL) and Stenotrophomonas sp. MKAL4 (3.37 U/mL) with a synergism degree of 2.04. The synergism was unique to growth on wheat straw as it was completely absent in xylose-grown cocultures. The wheat straw degradation synergism could rely on specific compounds released by the MKAL3 strain that promote the activity of the MKAL4 strain and vice versa. However, immobilized strains MKAL1, MKAL2, MKAL3, MKAL4 and MKAL5 improved glucose isomerase production in the wheat straw fermentation process at different sodium alginate concentrations. Immobilization studies of purified glucose isomerases for hydrolysis and saccharification of wheat straw are now being conducted. [ABSTRACT FROM AUTHOR]

Highlights: Screen-printable functional nanocomposite inks are engineered for flexible, single-enzyme-based energy-harvesting, and self-powered biosensing devices. A BFC powered by the same biosubstrate (glucose) is developed to harvest energy in a biofluid model and act as a self-powered electrochemical glucose. Customized inks are advantageous in terms of integrating with flexible materials, which can be integrated with a wide range of wearables and soft bioelectronics. Developing flexible bioelectronics is essential to the realization of artificial intelligence devices and biomedical applications, such as wearables, but their potential is limited by sustainable energy supply. An enzymatic biofuel cell (BFC) is promising for power supply, but its use is limited by the challenges of incorporating multiple enzymes and rigid platforms. This paper shows the first example of screen-printable nanocomposite inks engineered for a single-enzyme-based energy-harvesting device and a self-powered biosensor driven by glucose on bioanode and biocathode. The anode ink is modified with naphthoquinone and multiwalled carbon nanotubes (MWCNTs), whereas the cathode ink is modified with Prussian blue/MWCNT hybrid before immobilizing with glucose oxidase. The flexible bioanode and the biocathode consume glucose. This BFC yields an open circuit voltage of 0.45 V and a maximum power density of 266 μW cm−2. The wearable device coupled with a wireless portable system can convert chemical energy into electric energy and detect glucose in artificial sweat. The self-powered sensor can detect glucose concentrations up to 10 mM. Common interfering substances, including lactate, uric acid, ascorbic acid, and creatinine, have no effect on this self-powered biosensor. Additionally, the device can endure multiple mechanical deformations. New advances in ink development and flexible platforms enable a wide range of applications, including on-body electronics, self-sustainable applications, and smart fabrics. [ABSTRACT FROM AUTHOR]

This research is aimed towards a facile one-step preparation of magnetic poly(styrene-glycidyl methacrylate)-Fe3O4 nanocomposite particles named as P(S-GMA)-Fe3O4. The nanocomposite particles are prepared by a simultaneous free-radical copolymerization and co-precipitation of Fe2+ and Fe3+ salts. Two variable w/w ratios of styrene to GMA (98/2 and 96/4) are used. But, the overall copolymer to iron oxide ratio is kept identical. The structural analyses and morphology revealed the uniform distribution of Fe3O4 nanoparticles and the nanocomposites showed paramagnetic property. The potentiality of nanocomposite particles as glucose bisenosors via adsorption of glucose oxidase (GOD) is investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A comparative analysis of the glucose concentration dependent current response suggested that the modified electrode fabricated from P(S-GMA)-Fe3O4(2) (w/w ratio, 98/2) possessed superior response to other electrodes made from PS, P(S-GMA), PS-Fe3O4 and P(S-GMA)-Fe3O4(4) (w/w ratio, 96/4), respectively. The P(S-GMA)-Fe3O4(2)/GOD/Pt biosensor could measure glucose in the range of 2.2 × 10− 4 to 6.0 × 10− 3 M with a sensitivity of 14.47 µA mM− 1 and exhibited a detection limit of 5.07 µM at a signal to noise ratio of 3. The value of Michaelis-Menten constant (Km) is calculated as 0.019 mM. Overall results indicate that P(S-GMA)-Fe3O4(2) nanocomposite prepared in one-step is suitable for use in glucose biosensors. [ABSTRACT FROM AUTHOR]

A flexible photoelectrochemical (PEC) biosensor is proposed for the sensitive detection of ochratoxin A (OTA) based on glucose oxidase (GOx)-encapsulated target-responsive hydrogel, using Fenton reaction-mediated in situ formation of polyaniline (PANI) as signal amplified strategy. The target-responsive DNA hydrogels with high loading capacity can carry a large amount of GOx, which not only avoids laborious labeling process but also enhances the analytical performance. Upon introduction of target molecules, the hydrogel can be opened, and multiple GOx was released, thus producing lots of H2O2 via catalytic reduction of glucose. As a component of the Fenton reagent, H2O2 can react with the Fe2+ on the graphene oxidase-PAMAM-Fe2+ (GO-PAMAM-Fe2+) to generate Fe3+ and ·OH. This in turn can oxidize aniline and generate polyaniline (PANI), resulting in the enhancement of the photocurrent signal of GO-MoS2-CdS photoelectrode. The GO-PAMAM-Fe2+ as the neighborhood component of GO-MoS2-CdS-based photoactive material not only can increase the loading amount of Fe2+, but also can inhibit the decrease of photocurrent of GO-MoS2-CdS by direct modification of Fe2+ on the photoactive material. Moreover, the high loading capacity of DNA hydrogel can efficiently promote the performance of the PEC biosensor. The PEC biosensor exhibited satisfactory analytical performance for OTA with a linear range of 0.0001–0.1 ng/mL and a low detection limit of 0.05 pg/mL. It presents recommendable specificity, stability, and practical applications. Importantly, the PEC biosensor provides a new concept for construction of PEC biosensing platform. [ABSTRACT FROM AUTHOR]