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This study investigates the co-catalytic capabilities of MoO 3 nanosheets in enhancing the enzyme-like catalytic activity of a two-dimensional ultrathin Fe(III)-modified covalent triazine framework (Fe-CTF) under neutral pH conditions. The unique physicochemical surface properties and two-dimensional structures of Fe-CTF enable the direct immobilization of native enzymes (glucose oxidase (GOD) and xanthine oxidase (XOD)) through adsorption, eliminating the need for chemical processes. Efficient immobilization of the native enzymes within the Fe-CTF/GOD(XOD) hybrid is achieved through multipoint attachment involving various interactions. The Fe-CTF/MoO 3 co-catalytic system exhibits enzyme-mimicking activity at neutral pH and, when combined with the high catalytic activity of the immobilized native enzymes, enables the development of a colorimetric method for glucose detection. This method demonstrates excellent facilitation, rapidity, sensitivity, and selectivity, with a linear detection range of 50–1000 μM and a limit of detection of 8.8 μM for glucose. Furthermore, a straightforward one-pot colorimetric method is established for screening XOD inhibitors. The inhibitory potential of a crude extract derived from Chinese water chestnut peel on XOD activity is evaluated using this method. The findings of this study pave the way for the utilization of nanozyme/native enzyme hybrids in pH-neutral conditions for one-pot colorimetric sensing. This work contributes to the advancement of enzyme-based sensing technologies and holds promise for various applications in biosensing and biomedical research. [Display omitted] • MoO 3 boost the enzyme-like activity of Fe-CTF under neutral pH conditions. • Fe-CTF achieves direct immobilization of native enzymes by adsorption. • Fe-CTF/MoO 3 is utilized for colorimetric sensing of glucose and screening of inhibitors. [ABSTRACT FROM AUTHOR]

Abstract Glucose oxidase (GOx) based biosensor is an effective method to determine glucose level. However, the biosensors embedded with high electroactive species suffered from high background signal levels, which leading to relative low sensitivity for glucose sensing. In this work, a novel 3D network materials based glucose biosensor with low background signal was constructed, which demonstrated high sensitivity and selectivity towards glucose assay. Here, the combination of ionic liquid modified graphene sheets (GS-IL) and Au nanorods (Au NRs) acted as high electroactive catalyst, and thiol-containing silica sol-gel served as a nonconductive matrix to self-assembly of GS-IL and Au NRs to form the three-dimensional (3D) network materials. Meanwhile, the doping amount of the sol-gel had significant influences on electrochemical performance of the 3D network materials based biosensor. As a result, optimized 3.75% doping 3D network materials were selected to construct the glucose biosensor, which exhibited low background signal and high sensitivity. This biosensor was successfully applied in monitoring the glucose levels of serum and brain microdialysate samples. Highlights • The novel 3D network materials based glucose biosensor exhibiting high sensitivity with low background signal was designed. [ABSTRACT FROM AUTHOR]

As a type of nanomaterials with enzyme-mimetic catalytic properties, nanozymes have attracted wide concern in biological detection. H 2 O 2 was the characteristic product of diverse biological reactions, and the quantitative analysis for H 2 O 2 was an important way to detect disease biomarkers, such as acetylcholine, cholesterol, uric acid and glucose. Therefore, there is of great significance for developing a simple and sensitive nanozyme to detect H 2 O 2 and disease biomarkers by combining with corresponding enzyme. In this work, Fe-TCPP MOFs were successfully prepared by the coordination between iron ions and porphyrin ligands (TCPP). In addition, the peroxidase (POD) activity of Fe-TCPP was proved, in detail, Fe-TCPP could catalyze H 2 O 2 to produce ·OH. Herein, glucose oxidase (GOx) was chosen as the model to build cascade reaction by combining Fe-TCPP to detect glucose. The results indicated glucose could be detected by this cascade system selectively and sensitively, and the limit of detection of glucose was achieved to 0.12 μM. Furthermore, a portable hydrogel (Fe-TCPP@GEL) was further established, which encapsulated Fe-TCPP MOFs, GOx and TMB in one system. This functional hydrogel could be applied for colorimetric detection of glucose by coupling with a smartphone easily. Nanozyme of Fe-TCPP and corresponding hydrogel were constructed, and they were further developed to detect glucose. [Display omitted] • A simple and efficient nanozyme for the detection of glucose is reported. • A universal hydrogel system containing both natural enzymes and nanozymes is developed. • Fe-TCPP@GEL could carry out the quantitative analysis of glucose by coupling with a smartphone easily. [ABSTRACT FROM AUTHOR]

This work reports an amperometric enzyme-electrode prepared with glucose oxidase, which have been immobilized by a cross-linking step with glutaraldehyde in a mixture containing albumin and a novel carbon nanotubes-mucin composite (CNT-muc). The obtained hydrogel matrix was trapped between two polycarbonate membranes and then fixed at the surface of a Pt working electrode. The developed biosensor was optimized by evaluating different compositions and the analytical properties of an enzymatic matrix with CNT-muc. Then, the performance of the resulting enzymatic matrix was evaluated for direct glucose quantification in human blood plasma. The novel CNT-muc composite provided a sensitivity of 0.44 ± 0.01 mA M −1 and a response time of 28 ± 2 s. These values were respectively 20% higher and 40% shorter than those obtained with a sandwich-type biosensor prepared without CNT. Additionally, CNT-muc based biosensor exhibited more than 3 orders of magnitude of linear dynamic calibration range and a detection limit of 3 μM. The short-term and long-term stabilities of the biosensors were also examined and excellent results were obtained through successive experiments performed within the first 60 days from their preparation. Finally, the storage stability was remarkable during the first 300 days. [ABSTRACT FROM AUTHOR]

Many industries are striving for the development of more reliable and robust β-galactosidase biosensors that exhibit high response rate, increased detection limit and enriched useful lifetime. In a newfangled technological atmosphere, a trivial advantage or disadvantage of the developed biosensor may escort to the survival and extinction of the industry. Several alternative strategies to immobilize β-galactosidase enzyme for their utilization in biosensors have been developed in recent years in the quest of maximum utility by controlling the defects seen in the previous biosensors. The overwhelming call for on-line measurement of different sample constituents has directed science and industry to search for best practical solutions and biosensors are witnessed as the best prospect. The main objective of this paper is to serve as a narrow footbridge by comparing the literary works on the β-galactosidase biosensors, critically analyze their use in the construction of best biosensor by showing the pros and cons of the predicted methods for the practical use of biosensors. [ABSTRACT FROM AUTHOR]

The study presents a novel electrochemical glucose biosensor based on glucose oxidase (GOx) immobilized on Au@Pd core-shell nanoparticles supported on carboxylated graphene oxide (cGO). The immobilization of GOx was achieved by cross-linking the chitosan biopolymer (CS) including Au@Pd/cGO and glutaraldehyde (GA) on a glassy carbon electrode. The analytical performance of GCE/Au@Pd/cGO-CS/GA/GOx was investigated using amperometry. The biosensor had fast response time (5.2 ± 0.9 s), a satisfactory linear determination range between 2.0 × 10−5 and 4.2 × 10−3 M, and limit of detection of 10.4 μM. The apparent Michaelis-Menten constant (K app) was calculated as 3.04 mM. The fabricated biosensor also exhibited good repeatability, reproducibility, and storage stability. No interfering signals from dopamine, uric acid, ascorbic acid, paracetamol, folic acid, mannose, sucrose, and fructose were observed. The large electroactive surface area of carboxylated graphene oxide is a promising candidate for sensor preparation. [Display omitted] • Au@Pd decorated c-GO was synthesized for fabrication of enzyme-based glucose biosensor. • The constructed biosensor had fast response time, a satisfactory linear determination range, and limit of detection of 10.4 μM. • The biosensor also exhibited good selectivity, repeatability, reproducibility, and storage stability. • Glucose level in serum samples was successfully determined by the proposed method. [ABSTRACT FROM AUTHOR]

Cascade reactions catalyzed by natural uricase and mimic peroxidase (MPOD) have been applied for uric acid (UA) detection. However, the optimal catalytic activity of MPOD is mostly in acidic conditions (pH 2–5), mismatching the optimal catalytic alkaline environment of uricase. In this paper, using CuSO 4 and urea as raw materials, a MPOD with high catalytic activity in alkaline environment was synthesized by hydrothermal method. Then, based on coupling reaction of uricase/UA/MPOD/guaiacol (GA) system, a novel spectrophotometric method was established to detect 5–60 μmol/L UA (limit of detection = 3.14 μmol/L (S/N = 3)) and accurately quantified serum UA (275.6 ± 39.9 μmol/L, n = 5) with 95–105% of standard addition recovery. The results were consistent with commercial UA kit (p > 0.05). The MPOD could replace natural POD to reduce the cost of UA detection due to simple preparation and cheap raw materials, and is expected to achieve the specific detection of some substances, like glucose and cholesterol, combined with glucose oxidase and cholesterol oxidase. [Display omitted] • A copper doped mimic peroxidase with optimal activity at pH 8 was synthesized. • Due to the instability of ascorbic acid at pH 8, the interference was eliminated. • The new method was successfully applied to detect serum uric acid (UA). • The method for UA detection (including pretreatments) avoids pH adjustment steps. [ABSTRACT FROM AUTHOR]

In the present study, the phthalocyanine (Pc) integrated mercaptopropionic acid capped quantum dot (mpa@QD) biosensor has been developed for the quantitative determination of G-quadruplex and double-stranded DNA. The working principle of the developed biosensor platform is based on the quenching of the emission signal of the mpa@QD in the presence of Pc (closed position) and the recovery of the fluorescence signal in the presence of DNA (open position). The parameters affecting biosensor performance, such as Pc type and concentration, were optimized. Since the developed biosensor aimed to determine G-quadruplex and double-stranded DNA in biological samples, the effect of common ions (such as Na+, Mg2+) and serum albumin found in many biological matrices on the biosensor performance were examined. The effect of common ions on biosensor signal was negligible, except Zn2+. The analytical properties of the biosensor, such as linear range, calibration sensitivity, relative standard deviation %, the limit of detection, and quantification, were determined. The limit of detection and quantification values were found 0.055 μM and 0.18 μM for AS1411 , 0.061 μM and 0.20 μM for Tel21 , 0.038 μM and 0.13 μM for Tel45 and 0.091 μM and 0.30 μM for ctDNA. Several different synthetic samples were prepared. The spiked synthetic samples such as mammalian cell medium were used to evaluate the analytical performance of Pc-mpa@QD. All synthetic samples were prepared with polyethylene glycol, which resembles biological samples' crowded environment. The phthalocyanine (Pc) integrated mercaptopropionic acid capped quantum dot (mpa@QD) biosensor (Pc-mpa@QD) has been developed for quantitative determination of G-quadruplex and double-stranded DNA in biological matrices. [Display omitted] • A novel biosensor has been developed for quantitative determination of G-quadruplex and double-stranded DNA. • The effect of common ions on biosensor signal was found to be negligible, except Zn2+. • The biosensor may have the potential for the determination of G-quadruplex and double helix DNA species in vivo. [ABSTRACT FROM AUTHOR]

A novel continuous spectrophotometric assay to measure the activity of the debranching enzyme and α-amylase has been developed. The assay mixture comprises the debranching enzyme (GlgX from Escherichia coli ) or α-amylase (PPA from porcine pancreas), a reducing end-specific α-glucosidase (MalZ), maltodextrin-branched β-cyclodextrin (Glc n -β-CD) as the substrate, and the glucose oxidase/peroxidase system (GOPOD). Due to its high reducing end specificity, the branch chains of the substrates are not hydrolyzed by MalZ. After hydrolysis by GlgX or PPA, the released maltodextrins are immediately hydrolyzed into glucose from the reducing end by MalZ, whose concentration is continuously measured by GOPOD at 510 nm in a thermostat spectrophotometer. The kinetic constants determined for GlgX ( K m = 0.66 ± 0.02 mM and k cat = 76.7 ± 1.5 s −1 ) are within a reasonable range compared with those measured using high-performance anion-exchange chromatography (HPAEC). The assay procedure is convenient and sensitive, and it requires lower concentrations of enzymes and substrate compared with dinitrosalicylic acid (DNS) and HPAEC analysis. [ABSTRACT FROM AUTHOR]

The interfacial electron transfer of glucose oxidase (GOx) on a poly(glutamic acid)-modified glassy carbon electrode (PGA/GCE) was investigated. The redox peaks measured for GOx and flavin adenine dinucleotide (FAD) are similar, and the anodic peak of GOx does not increase in the presence of glucose in a mediator-free solution. These indicate that the electroactivity of GOx is not the direct electron transfer (DET) between GOx and PGA/GCE and that the observed electroactivity of GOx is ascribed to free FAD that is released from GOx. However, efficient electron transfer occurred if an appropriate mediator was placed in solution, suggesting that GOx is active. The PGA/GCE-based biosensor showed wide linear response in the range of 0.5–5.5 mM with a low detection limit of 0.12 mM and high sensitivity and selectivity for measuring glucose. [ABSTRACT FROM AUTHOR]

The existing zymography method for the detection of diamine oxidase (DAO) activity has been improved by a new staining procedure with the aim to ameliorate its sensitivity. Both procedures used SDS-PAGE gels containing uniformly distributed entrapped peroxidase (that wouldn't migrate during electrophoresis). The new approach with 3,5-dichloro-2-hydroxybenzenesulfonate (DCHBS) as peroxidase substrate and with 4-amino-antipyrine as color stabilizer allows a more sensitive detection of DAO when compared to the previously reported o -phenylenediamine (o -PDA) as peroxidase substrate. The newly improved method appears faster, simple and environmentally friendly. It can be used for most of oxidases releasing hydrogen peroxide as reaction product. [Display omitted] • Diamine oxidase (DAO) catalyses the oxidative deamination of biogenic amines with the release of H 2 O 2. • Zymography with entrapped peroxidase in PAA gel allows DAO detection in presence of interfering enzymes. • The Zymography method with DCHBS-AAP is more sensitive compared than that with o -PDA for DAO detection. • The method allows determination of various oxidases, even in the presence of interfering catalase. • The chromogen DCHBS-AAP is safer and less toxic than o -PDA. [ABSTRACT FROM AUTHOR]

This present study reports a novel laboratory protocol, the glucose oxidase peroxidase (GOPOD)-coupled continuous assay (GcCA) which is based on the general principle that all cellulases generate β- d -glucose as one of their hydrolytic products. Resultantly, the β- d -glucose generated serves as a substrate to an auxiliary enzyme, GOPOD, coupled to the cellulase hydrolytic process, in a simultaneous secondary reaction which continuously quantifies the concentration of glucose generated as a measure of incremental cellulase activity in the laboratory. The protocol is initial hydrolytic rate-driven. Thus, making it very suitable for kinetic studies of pure cellulase samples in the laboratory. GcCA protocol is simple, rapid, specific, highly sensitive and accurate, non-laborious and saves cost in terms of time and materials. It is robust and dynamic and could be modified or adapted to suit either standard, 1000 μ L cuvette or 96-well microtiter plate formats. Its optimized total assay reaction mixture of 500 μ L constitutes a substrate, enzyme, buffer, distilled water and coupled GOPOD components. The GcCA protocol was validated for linearity, applicability, sensitivity, precision and compared with a standard and widely used assay method for optimized enzyme activity. It was further compared with the most widely used routine assay procedure for determination of reducing sugars, the DNS method. The GcCA protocol is a high throughput technique which enables the assay of over 120 samples in one day. [Display omitted] • A new GcCA protocol for the determination of cellulase activity was developed. • The protocol is novel, simple, rapid, sensitive and reproducible. • It enables continuous reading of incremental absorbance up to a plateau. • The protocol is robust and dynamic and could be adapted to suit different formats. • The assay protocol is a high throughput technique suitable for kinetic assay. [ABSTRACT FROM AUTHOR]

A novel self-assembled glucose biosensor based on graphene oxide (GO) was constructed by using 1-pyrenebutyric acid-N-hydroxysuccinimide ester (PANHS) as linking molecular. The stepwise self-assembly process was performed for PANHS anchoring in N,N-dimethylformamide (DMF) solvent and the further glucose oxidase (GOD) binding in aqueous solution, respectively. The molecular interactions and the morphologic properties were characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electronic microscopy (FESEM), and atomic force microscopy (AFM). In addition, the quantitative loadings of anchored PANHS and GOD were well elucidated by surface plasmon resonance (SPR) measurements. The obtained novel glucose sensor exhibited satisfactory analytical performance to glucose: wide linear range (4.0 x 10-6 to 4.4 x 10-3M), fast response (10s), high sensitivity (40.5±0.4mAM-1cm-2), and low detection limit (2µM, S/N=3). Furthermore, the biosensor exhibited excellent long-term stability and satisfactory reproducibility. [ABSTRACT FROM AUTHOR]

Abstract: A highly sensitive electrochemical glucose sensor has been developed by the co-immobilization of glucose oxidase (GOx) and horseradish peroxidase (HRP) onto a gold electrode modified with biocompatible cyclic bisureas–gold nanoparticle conjugate (CBU–AuNP). A self-assembled monolayer of mercaptopropionic acid (MPA) and CBU–AuNP was formed on the gold electrode through a layer-by-layer assembly. This modified electrode was used for immobilization of the enzymes GOx and HRP. Both the HRP and GOx retained their catalytic activity for an extended time, as indicated by the low value of Michaelis–Menten constant. Analytical performance of the sensor was examined in terms of sensitivity, selectivity, reproducibility, lower detection limit, and stability. The developed sensor surface exhibited a limit of detection of 100nM with a linear range of 100nM to 1mM. A high sensitivity of 217.5μAmM−1 cm−2 at a low potential of −0.3V was obtained in this sensor design. Various kinetic parameters were calculated. The sensor was examined for its practical clinical application by estimating glucose in human blood sample. [Copyright &y& Elsevier]

Abstract: A novel glucose oxidase/chitosan/α-zirconium phosphate (GOD/chitosan/α-ZrP) ternary biocomposite was prepared by co-intercalating glucose oxidase (GOD) and chitosan into the interlayers of α-zirconium phosphate (α-ZrP) via a delamination–reassembly procedure. The results of X-ray diffraction, infrared spectroscopy, circular dichroism, and ultraviolet spectrum characterizations indicated not only the layered and hybrid structure of the GOD/chitosan/α-ZrP ternary biocomposite but also the recovered activity of the intercalated GOD improved by the co-intercalated chitosan. By depositing the GOD/chitosan/α-ZrP biocomposite film onto a glassy carbon electrode, the direct electrochemistry of the intercalated GOD was achieved with a fast electron transfer rate constant, k s, of 7.48 ± 3.52s−1. Moreover, this GOD/chitosan/α-ZrP biocomposite modified electrode exhibited a sensitive response to glucose in the linear range of 0.25–8.0mM (R =0.9994, n =14), with a determination limit of 0.076mM. [Copyright &y& Elsevier]

Abstract: Four types of nanozeolite (NZ) particles (Silicalite S-1, BEA, Silicalite S-1–DT, and BEA–DT) with different physicochemical properties have been used for preparation of the new glucose oxidase (GOD) biosensor. Cyclic voltammetric studies were carried out with four different Pt/NZ electrodes, and it was found that the electrode prepared with BEA–DT NZ showed the highest electroactivity. These cyclic voltammograms (CVs) were compared with the CVs of four Pt/NZ–GOD electrodes. The presence of the oxidoreductase (GOD) on the electrode surface was the reason for the shifting of the potential peaks and corresponding currents. The magnitudes of the cathodic peak of Pt/NZ–S-1–GOD and Pt/NZ–S-1–DT–GOD electrodes had the highest values. The surface concentration (I ∗) of the adsorbed electroactive species (NZ–GOD) on the electrode was estimated according to the Brown–Anson model. The pH effect on the cathodic peak potential of Pt/NZ–GOD electrodes was investigated. The influence of different nanozeolites on sensitivity of GOD biosensors was studied. The most sensitive biosensor was obtained with NZ–S-1–DT, which had a porous surface, a higher degree of hydrophobicity, and a relatively high negative charge. The sensitivity of this electrode was 1.8044μALmmol−1, the concentration limit was 0.8mmolL−1 glucose, and the linear correlation was from 2 to 18mmolL−1 glucose. [Copyright &y& Elsevier]

Abstract: An online immobilized glucose oxidase (GOx) capillary microreactor was developed based on an enzymatic redox reaction with 1,4-benzoquinone as an acceptor of electrons, replacing the molecular oxygen typically used in a GOx reaction to achieve direct ultraviolet detection without derivation. A high efficiency of enzymolysis was obtained at 1mgml−1 1,4-benzoquinone for 5min of incubation at 25°C, and baseline separation of the substrate and product could be achieved with a resolution of 3.85 by employing 20mM phosphate buffer (pH8.0) containing 40mgml−1 sulfated β-cyclodextrin as an additive, a constant voltage of 15kV, and a detection wavelength of 220nm. In addition, an online enzyme inhibition study was performed on the immobilized GOx microreactor with metal ions Ag+ and Cu2+ used as model inhibitors. The results indicate that Ag+ (IC50 =69.16μM) has a markedly higher inhibitory effect than Cu2+ (IC50 =1.33mM). The protocol described can be applied in high-throughput screening of enzyme reactions and inhibitors. [Copyright &y& Elsevier]

Abstract: Signaling and insulin secretion in β cells have been reported to demonstrate oscillatory modes, with abnormal oscillations associated with type 2 diabetes. We investigated cellular glucose influx in β cells with a self-referencing (SR) microbiosensor based on nanomaterials with enhanced performance. Dose–response analyses with glucose and metabolic inhibition studies were used to study oscillatory patterns and transporter kinetics. For the first time, we report a stable and regular oscillatory uptake of glucose (averaged period 2.9±0.6min), which corresponds well with an oscillator model. This oscillatory behavior is part of the feedback control pathway involving oxygen, cytosolic Ca2+/ATP, and insulin secretion (periodicity approximately 3min). Glucose stimulation experiments show that the net Michaelis–Menten constant (6.1±1.5mM) is in between GLUT2 and GLUT9. Phloretin inhibition experiments show an EC50 value of 28±1.6μM phloretin for class I GLUT proteins and a concentration of 40±0.6μM phloretin caused maximum inhibition with residual nonoscillating flux, suggesting that the transporters not inhibited by phloretin are likely responsible for the remaining nonoscillatory uptake, and that impaired uptake via GLUT2 may be the cause of the oscillation loss in type 2 diabetes. Transporter studies using the SR microbiosensor will contribute to diabetes research and therapy development by exploring the nature of oscillatory transport mechanisms. [Copyright &y& Elsevier]

Abstract: A sensitive, selective, and rapid enzymatic method is proposed for the quantification of hydrogen peroxide (H2O2) using 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and 10,11-dihydro-5H-benz(b,f)azepine (DBZ) as chromogenic cosubstrates catalyzed by horseradish peroxidase (HRP) enzyme. MBTH traps free radical released during oxidation of H2O2 by HRP and gets oxidized to electrophilic cation, which couples with DBZ to give an intense blue-colored product with maximum absorbance at 620nm. The linear response for H2O2 is found between 5×10−6 and 45×10−6 molL−1 at pH 4.0 and a temperature of 25°C. Catalytic efficiency and catalytic power of the commercial peroxidase were found to be 0.415×106 M−1 min−1 and 9.81×10−4 min−1, respectively. The catalytic constant (k cat) and specificity constant (k cat/K m) at saturated concentration of the cosubstrates were 163.2min−1 and 4.156×106 Lmol−1 min−1, respectively. This method can be incorporated into biochemical analysis where H2O2 undergoes catalytic oxidation by oxidase. Its applicability in the biological samples was tested for glucose quantification in human serum. [Copyright &y& Elsevier]

Abstract: A kind of nanocomposite with good dispersion in water was prepared through covalent adsorption of ferrocenecarboxaldehyde on multiwalled carbon nanotubes (MWNTs) for electrical communication between glucose oxidase (GOD) and electrode. The ferrocene-modified multiwalled carbon nanotube nanocomposites (MWNTs-Fc) could be conveniently cast on electrode surfaces. With the aid of chitosan, GOD was then immobilized on the nanostructure film to form a reagentless amperometric sensor for glucose determination. FTIR spectra and cyclic voltammetry were used to characterize the nanocomposites. The presence of both ferrocene as mediator of electron transfer and MWNTs as conductor enhanced greatly the enzymatic response to the oxidation of glucose. The novel biosensor exhibited a fast response toward glucose with a detection limit of 3.0×10−6 mol/L and the linear range extended up to 3.8×10−3 mol/L. [Copyright &y& Elsevier]

Traditional methods for regulating oxygen concentration ([O 2 ]) in in vitro experiments over the range found in normal and tumor tissues require the use of expensive equipment to generate controlled gas atmospheres or the purchase of a range of gas cylinders with certified O 2 percentages. Here we describe a simple and inexpensive enzymatic method for generating low, precise steady-state [O 2 ] levels that are stable for several hours. This method is particularly applicable to the in vitro study of some classes of hypoxia-targeted antitumor prodrugs and bioreductively activated agents. [ABSTRACT FROM AUTHOR]

Herein, to improve the current density and sensitivity for biofuel cell and glucose sensing application, a bioanode based on redox polymer (PEI-Fc) binding polydopamine (PDA) coated MWCNTs (PEI-Fc/PDA/MWCNTs) nanocomposite and glucose oxidase (GOD) was fabricated. PDA/MWCNTs nanocomposite was prepared by spontaneous self–polymerization of dopamine on MWCNTs surface and the PEI-Fc/PDA/MWCNTs nanocomposite was prepared by a simple self-assembly method. The PEI-Fc/PDA/MWCNTs nanocomposite and the resulting bioanode were fully characterized. A maximum current density of 0.73 mA cm−2 at the resulting bioanode was obtained by linear sweep voltammetry (LSV) at the scan rate of 50 mV s−1 with 20 mM glucose concentration. Moreover, a linear range up to 4 mM, a high sensitivity of 57.2 μA mM−1 cm−2, a fast response time reaching 95% of the steady current (2 s) and a low limit of detection (0.024 mM) were achieved. The amperometric method demonstrated both the sensitivity and the stability of the bioanode for glucose–sensing was improved by the employed PDA layer. Finally, the biosensor was used for glucose detection in human serum samples showing good recoveries. This study proposed an excellent functional material prepared by a facile self-assembled method for applying in biofuel cells and second-generation biosensors. [Display omitted] • PEI-Fc/PDA/MWCNTs nanocomposite was prepared by a simple self-assembly method. • PEI-Fc/PDA/MWCNTs nanocomposite based bioanode exhibited a maximum current density of 0.73 mA cm−2. • A high sensitivity of 57.2 μA mM−1 cm−2 for glucose – sensing was realized, both sensitivity and stability were improved by PDA layer. [ABSTRACT FROM AUTHOR]

Abstract: The communication demonstrates feasibility of an enzyme microassay for glucose oxidase with 1,4-benzoquinone as an acceptor of electrons. The protocol uses the plug–plug mode of electrophoretically mediated microanalysis, with nanolitre injected volumes of enzyme and reactant solutions. The reactant and product, 1,4-benzoquinone and hydroquinone, are separated during the assay by differential binding to sulfated-β-cyclodextrin used as additive to the phosphate buffer (pH 7) and monitored at selected wavelengths in their UV spectra. The assay covers glucose oxidase concentration from 0.01 to 0.1mgml−1. Due to the strong UV absorbance of the both reactant and product, there is no need for use of a second enzyme (peroxidase) in the present assay. [Copyright &y& Elsevier]

Abstract: This paper describes the optimisation of a screen-printing water-based carbon ink containing cobalt phthalocyanine (CoPC) and glucose oxidase (GOD) for the fabrication of a glucose biosensor. To optimise the performance of the biosensor, the loadings of the electrocatalyst (CoPC) and enzyme (GOD) were varied. It was found that the maximum linear range was achieved with a CoPC loading of 20% (m/m, relative to the mass of carbon) and a GOD loading of 628U per gram of carbon. In our studies we chose to employ chronoamperometry, as this technique is commonly used for commercial devices. The optimum operating applied potential was found to be +0.5V, following an incubation period of 60s. The optimum supporting electrolyte was found to be 0.05M phosphate buffer at pH 8.0, which resulted in a linear range of 0.2–5mM, the former represents the detection limit. The sensitivity was 1.12μAmM−1. The effect of temperature was also investigated, and it was found that 40°C gave optimal performance. The resulting amperometric biosensors were evaluated by measuring the glucose concentrations for 10 different human plasma samples containing endogenous glucose and also added glucose. The same samples were analysed by a standard spectrophotometric method, and the results obtained by the two different methods were compared. A good correlation coefficient (R 2 =0.95) and slope (0.98) were calculated from the experimental data, indicating that the new devices hold promise for biomedical studies. [Copyright &y& Elsevier]

Abstract: A method for optical imaging of the activity of glucose oxidase (GOx) using a fluorescent europium(III) tetracycline probe for hydrogen peroxide is presented. A decay time in the microsecond range and the large Stokes shift of 210nm of the probe facilitate intensity-based, time-resolved, and decay-time-based imaging of glucose oxidase. Four methods for imaging the activity of GOx were compared, and rapid lifetime determination imaging was found to be the best in giving a linear range from 0.32 to 2.7mUnit/mL. The detection limit is 0.32mUnit/mL (1.7ngmL−1) which is similar to that of the time-resolved (gated) imaging using a microtiterplate reader. Fluorescent imaging of the activity of GOx is considered to be a useful tool for GOx-based immunoassays with potential for high-throughput screening, immobilization studies, and biosensor array technologies. [Copyright &y& Elsevier]

A new glucose biosensor has been fabricated by immobilizing glucose oxidase into a sol-gel composite at the surface of a basal plane pyrolytic graphite (bppg) electrode modified with multiwall carbon nanotube. First, the bppg electrode is subjected to abrasive immobilization of carbon nanotubes by gently rubbing the electrode surface on a filter paper supporting the carbon nanotubes. Second, the electrode surface is covered with a thin film of a sol-gel composite containing encapsulated glucose oxidase. The carbon nanotubes offer excellent electrocatalytic activity toward reduction and oxidation of hydrogen peroxide liberated in the enzymatic reaction between glucose oxidase and glucose, enabling sensitive determination of glucose. The amperometric detection of glucose is carried out at 0.3V (vs saturated calomel electrode) in 0.05M phosphate buffer solution (pH 7.4) with linear response range of 0.2–20mM glucose, sensitivity of 196nA/mM, and detection limit of 50μM (S/N=3). The response time of the electrode is < 5s when it is stored dried at 4°C, the sensor showed almost no change in the analytical performance after operation for 3 weeks. The present carbon nanotube sol-gel biocomposite glucose oxidase sensor showed excellent properties for the sensitive determination of glucose with good reproducibility, remarkable stability, and rapid response and in comparison to bulk modified composite biosensors the amounts of enzyme and carbon nanotube needed for electrode fabrication are dramatically decreased. [Copyright &y& Elsevier]

A stable suspension of carbon nanotubes (CNT) was obtained by dispersing the CNT in a solution of surfactant, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant). CNT (dispersed in the solution of 0.1% CTAB) has promotion effects on the direct electron transfer of glucose oxidase (GOx), which was immobilized onto the surface of CNT. The direct electron transfer rate of GOx was greatly enhanced after it was immobilized onto the surface of CNT. Cyclic voltammetric results showed a pair of well-defined redox peaks, which corresponded to the direct electron transfer of GOx, with a midpoint potential of about -0.466 V (vs SCE (saturated calomel electrode)) in the phosphate buffer solution (PBS, pH 6.9). The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (ks) and the value of midpoint potential (E1/2) were estimated. The dependence of E1/2 on solution pH indicated that the direct electron transfer reaction of GOx is a two-electron-transfer coupled with a two-proton-transfer reaction process. The experimental results also demonstrated that the immobilized GOx retained its bioelectrocatalytic activity for the oxidation of glucose, suggesting that the electrode may find use in biosensors (for example, it may be used as a bioanode in biofuel cells). The method presented here can be easily extended to immobilize and obtain the direct electrochemistry of other redox enzymes or proteins. [Copyright &y& Elsevier]

A new amperometric biosensor, based on adsorption of glucose oxidase (GOD) at the platinum nanoparticle-modified carbon nanotube (CNT) electrode, is presented in this article. CNTs were grown directly on the graphite substrate. The resulting GOD/Pt/CNT electrode was covered by a thin layer of Nafion to avoid the loss of GOD in determination and to improve the anti-interferent ability. The morphologies and electrochemical performance of the CNT, Pt/CNT, and Nafion/GOD/Pt/CNT electrodes have been investigated by scanning electron microscopy, cyclic voltammetry, and amperometric methods. The excellent electrocatalytic activity and special three-dimensional structure of the enzyme electrode result in good characteristics such as a large determination range (0.1–13.5 mM), a short response time (within 5 s), a large current density (1.176 mA cm-2), and high sensitivity (91 mA M-1 cm-2) and stability (73.5% remains after 22 days). In addition, effects of pH value, applied potential, electrode construction, and electroactive interferents on the amperometric response of the sensor were investigated and discussed. The reproducibility and applicability to whole blood analysis of the enzyme electrode were also evaluated. [Copyright &y& Elsevier]

Glucose oxidase was embedded in organic films through a layer-by-layer approach, where the enzyme demonstrated significantly enhanced electron-transfer reactivity and finely tuned enzymatic activity. An unmediated, reagentless glucose biosensor was accordingly prepared with two polyethylenimine/glucose oxidase bilayers-modified pyrolytic graphite electrode. A calibration linear range of glucose was 0.5–8.9 mM with a detection limit of 50 μM and sensitivity of 0.76 μA mM-1. [Copyright &y& Elsevier]

Prussian blue (PB), as a good catalyst for the reduction of hydrogen peroxide, has been combined with nonconducting poly(o-aminophenol) (POAP) film to assemble glucose biosensor. Compared with PB-modified enzymatic biosensor, the biosensor based on glucose oxidase immobilized in POAP film at PB-modified electrode shows much improved stability (78% remains after 30 days) in neutral medium. Additionally, the biosensor, at an applied potential of 0.0 V, exhibits other good characteristics, such as relative low detection limit (0.01 mM), short response time (within 5 s), large current density (0.28 mA/cm2), high sensitivity (24 mA M−1 cm−2), and good antiinterferent ability. The apparent activation energy of enzyme-catalyzed reaction and apparent Michaelis–Menten constant are 34.2 KJ mol−1 and 10.5 mM, respectively. In addition, effects of temperature, applied potential used in the determination, pH value of the detection solution, and electroactive interferents on the amperometric response of the sensor were investigated and are discussed. [Copyright &y& Elsevier]

Polypropylene and polyethylene surfaces are activated by introducing an active functional group through 1-fluoro-2 nitro-4-azidobenzene by UV irradiation. Horseradish peroxidase and glucose oxidase are immobilized onto the activated surfaces, simply by incubating the enzymes at 37°C. When untreated surfaces are used, insignificant immobilization of the enzymes is observed. [Copyright &y& Elsevier]

An enzyme-based sensor array has been developed to detect multiple disaccharides in aqueous solutions. Porous agarose beads, derivatized with enzymes for assaying disaccharides, are localized within wells etched into a silicon chip in a regular 5 × 7 array. Each well is individually addressable and acts as a microanalysis chamber where sample solution passes through the agarose matrix and is exposed to the enzymes. Detection is achieved by observing the increase in absorbance of a quinoneimine dye produced during the reaction. This technique is used to quantify the disaccharides lactose, sucrose, and maltose and the monosaccharide glucose. Preexisting glucose in the sample complicates multicomponent sensing but can be accounted for by including a glucose sensor in the array. This detection strategy is applied to the simultaneous analysis of these sugars in several beverages. [Copyright &y& Elsevier]

This work depicts the novel chromogenic system for the assay of glucose in blood samples connected with the chelate formation of sulfosalicylic acid (SSA) with iron (Fe(III)) using glucose oxidase (GOD) presented. The purple-colored Fe-SSA chelate compound formed, maintain a strong absorption at 500 nm in the acidic buffer of pH 3.8. The Beer's law limit for the assay of glucose by rate, and a one-time method is in the range of 46–1295 μmol/L and 9–1110 μmol/L sequentially. Inter and Intraday precision fluctuated amid 0.98–1.4% (n = 10), and 1.33–2.89% (n = 15) sequentially. The recovery of glucose varied from 96.6 to 102%, registering trifling interference by common interferants in blood samples. The accuracy of the outcome, LOD, and LOQ of glucose were within 90–102%, 2.376, and 7.923 μmol/L individually. The introduced method has a coefficient of correlation 0.999 with the standard kit system, and easy to ascertain serum glucose with excellent recovery and insignificant interruption. Nevertheless, the system can be recognized for selection by the biochemical laboratories. Image 1 • The enzymatic pathway is projected for quantification of the clinically significant biomarker. • The proposed method demands the use of a single enzyme for the assay of glucose. • Sulfosalicylic acid is used as a chromogenic probe. • The colored product formed has a high molar extinction coefficient and gives reliable and highly précised results. • The effectiveness of the method has been proved by evaluating kinetic parameters. [ABSTRACT FROM AUTHOR]