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• Encapsulation of horseradish peroxidase (HRP), glucose (GOx), lactate (LOx) and cholesterol (ChOx) oxidases within cryogels. • Electrodeposition of luminol forming an ECL-active layer of polyluminol on GCE surface. • Optimization and characterization of oxidases-PEG-cryogels deposited on polyluminol-modified GCE. • ECL detection of glucose and lactic acid in artificial sweat solution, cholesterol in commercial milk samples, and hydrogen peroxide in contact lenses solution. Enzymes-based electrochemical biosensors require the immobilisation of the enzymes on the electrode surfaces as well as their storage in aqueous environments to maintain the enzymatic activity. Herein, we described an enzyme-based electrochemiluminescence biosensor fabricated by incorporating oxidase enzymes (horseradish peroxidase, HRP; glucose, GOx, lactate, LOx, and cholesterol oxidases, ChOx) within poly(ethylene glycol)diacrylate (PEGDA) cryogels, which retain their activity when stored in dry conditions. The redox reactions between the oxidase enzymes and their corresponding substrates produce hydrogen peroxide that can be detected in the presence of a layer of polyluminol deposited on the electrode surface. These oxidases PEG-based cryogels were characterized using cyclic voltammetry and electrochemiluminescence (ECL) to assess the redox reactions between the enzymes and the corresponding substrates. The proposed biosensors were characterised by good stability and repeatability with a calculated limit of detections (LODs) in the micromolar concentration range. The performances of PEG cryogels over the time evidenced the stability of the as-prepared materials up to 30 days in dry conditions, confirming good retention of the encapsulated enzymes. Furthermore, the biosensors were tested in the presence of interferent species showing good selectivity. Finally, these oxidases-PEG cryogels were tested in real samples (commercial contact lenses, artificial sweat and commercial milk) confirming the suitability of such material for the detection of hydrogen peroxide with calculated LoDs as 10.37 ± 0.4 µM for HRP/contact lenses liquid; 3.87 ± 0.3 µM for GOx/artificial sweat; 1.09 ± 0.6 µM for LOx/artificial sweat; and 6.59 ± 0.5 for ChOx/milk. [Display omitted] [ABSTRACT FROM AUTHOR]

• A smartphone-interfaced flow injection sensing system was developed. • An electrode was modified with Pd-PANI/Carbon microspheres@carbon nanotubes. • Sensitive determination of glucose was achieved in real human serum samples. Integrating a flow injection system with an electrochemical sensor controlled by a smartphone enables rapid, precise real-time monitoring and reduces analyte consumption, contamination and costs. An enzyme-free electrochemical sensor is presented for the monitoring of glucose, an important indicator of diabetes. The sensor integrates a smartphone and a flow injection amperometric system. The flow cell is fabricated from acrylic plastic and includes an electrochemical three-electrode cell that comprises a working electrode modified with a catalyst of palladium-polyaniline/carbon microspheres@carbon nanotubes (Pd-PANI/CM@CNTs/E) for the detection of glucose oxidation. In the optimal condition, the proposed system produced good analytical performances. The sensor determined glucose linearly in a range from 0.020 to 100 mM, with a sensitivity of 51.51 μA mM−1 cm−2, and a detection limit (LOD) of 0.0071 mM. The developed system also exhibited good repeatability, reproducibility, operational stability, and anti-interference properties, and accurately determined glucose levels in real human serum samples. This sensing platform provides an alternative tool for the development of a continuous glucose monitor system for clinical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Regular monitoring of blood sugar levels is essential for diabetics, both for adjusting medication or insulin doses and for preventing complications like blindness, nerve damage, heart disease, and kidney failure. This paper presents a novel smartphone-based electrochemical-colorimetric dual-mode detecting system for detecting glucose at low concentrations. This system utilizes a smartphone as a mobile terminal to control the electrochemical circuit board and enable data analysis. The circuit board integrates cyclic voltammetry and differential pulse voltammetry, providing a low-cost and palm-sized solution for glucose detection. Additionally, digital image colorimetry is employed to enable efficient and accurate colorimetric detection. The use of glucose oxidase and horseradish peroxidase (GOx/HRP) in combination with 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ABTS substrates facilitates glucose dual-mode quantitative analysis in a-coreaction system. The electrochemical and colorimetric methods exhibit limits of detection of 0.467 µM and 10 µM, respectively. This system shows a point-of-care testing (POCT) potential for reliable and convenient monitoring of blood glucose levels, particularly for individuals with diabetes. [ABSTRACT FROM AUTHOR]

In this study the development of a biofuel cell for potential application in microfluidics is described. The biocatalysts support is produced through vacuum-filtration of a Vulcan carbon black suspension resulting in flexible, paper-like electrodes. The glucose oxidase bioanode was assembled using an enzyme precipitate coating procedure whereas the biocathode was implemented by attaching bilirubin oxidase enzyme onto the carbon black surface via a pyrene intermediate. The bioelectrodes were first characterized by voltammetry and by chronoamperometry on their sensing ability towards the respective substrates, namely glucose and oxygen. Finally, bioanode and biocathode were integrated in a single-compartment of a heterogeneous poly (methyl methacrylate) - polydimethylsiloxane microfluidic platform and the power density produced was assessed. In 10 mM glucose solution at pH 7.0, the biofuel cell showed an open circuit potential (OCP) of 0.43 V and a maximum power density of about 28 μW cm−2 at 0.24 V. Also we demonstrate here the viability of human propelled fluidics by introducing in the microfluidic device a finger-pressure mechanism. [ABSTRACT FROM AUTHOR]

Electropolymerization of brilliant cresyl blue (BCB) in ethaline deep eutectic solvent (DES) has been carried out. Poly(brilliant cresyl blue) (PBCB) films were formed by electrodeposition on carbon nanotube modified glassy carbon electrodes by potential cycling in ethaline (choline chloride + ethylene glycol) with the addition of different ionic species i.e. NO 3 −, SO 4 2−, Cl−, ClO 4 −. The novel nanocomposite films were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The composition of the polymerization solution had a large influence on the morphology as well as on the electrochemical behaviour of the electrodeposited films. The effect of scan rate on BCB polymerization was also investigated and the PBCB film synthesized at 150 mV s−1 in ethaline + NO 3 − presented a superior electrochemical performance. The PBCB Ethaline -HNO 3 /MWCNT and PBCB aqueous /MWCNT nanocomposite films were used as electrode support for the enzymes glucose oxidase and tyrosinase for the biosensing of glucose and catechol, respectively and were more sensitive than the PBCB based electrodes prepared in aqueous solution. Image 101 • Electropolymerization of brilliant cresyl blue (BCB) in ethaline DES. • Ethaline doped with various acids (HNO 3 , H 2 SO 4 , HCl, HClO 4) for BCB polymerization. • Morphology of PBCB films influenced by polymerization solution composition. • Improved electrochemical performance of PBCB DES compared with PBCB aqueous films. • Application of PBCB DES modified carbon nanotubes as enzyme biosensors. [ABSTRACT FROM AUTHOR]

This research is aimed to the study and application of an electrochemical immunosensor for the detection of ovalbumin (OVA) from egg white (or albumen) used as a binder in some works of art, such as some historical photographic prints and tempera paintings. The immunosensor takes advantage of the interesting biodetection capabilities offered by nanoelectrode ensembles (NEEs). The NEEs used to this aim are prepared by template deposition of gold nanoelectrodes within the pores of track-etched polycarbonate (PC) membranes. The affinity of polycarbonate for proteins is exploited to capture OVA from the aqueous extract obtained by incubation in phosphate buffer of a small sample fragment (<1 mg). The captured protein is reacted selectively with anti-OVA antibody, labelled with glucose oxidase (GOx). In the case of positive response, the addition of the GOx substrate (i.e. glucose) and a suitable redox mediator (a ferrocenyl derivative) reflects in the up rise of an electrocatalytic oxidation current, which depends on the OVA amount captured on the NEE, this amount correlating with OVA concentration in the extract. After optimization, the sensor is successfully applied to identify OVA in photographic prints dating back to the late 19th century, as well as in ancient tempera paintings from the 15th and 18th centuries. Image 1 [ABSTRACT FROM AUTHOR]

In this work, an electrochemiluminescence (ECL) biosensor based on interparticle DNA walker as effective signal amplification strategy and N-Ti 3 C 2 QDs as high-efficiency emitters was designed for sensitive assay of mucin 1 (MUC1), which is closely related to the occurrence and development of tumors. First, an interparticle DNA walker which contains walking particles (WPs) and orbit particles (OPs) was fabricated. In the presence of target MUC1 and DNAzyme, the WPs can walk along the surface of OPs, and they can continue to walk along next OPs after completing previous walk. As the moving freedom and area improved, the interparticle DNA walker could effectively improve the conversion efficiency of target. Furthermore, N-Ti 3 C 2 QDs with high ECL luminous efficiency were synthesized by using polyethyleneimine (PEI) as nitrogen source. Due to the nitrogen-rich of PEI, the relative ECL quantum efficiency of the proposed N-Ti 3 C 2 QDs was calculated to be 1.5 times higher than our previous reported N-Ti 3 C 2 QDs that utilizing ethylenediamine as nitrogen source. Therefore, taking the advantage of the improved moving freedom and area of the interparticle DNA walker and high ECL efficiency of the proposed N-Ti 3 C 2 QDs, the fabricated ECL biosensor for MUC1 determination displayed a low detection limit with a wide linear range, which provides a potential feasible method for other protein sensitive assay. [Display omitted] A sensitive electrochemiluminescent (ECL) biosensor was fabricated and achieved ultrasensitive assay of mucin1 by utilizing N-Ti 3 C 2 QDs as high-efficiency ECL emitters and interparticle DNA walker as effective signal amplifier. [ABSTRACT FROM AUTHOR]

A mathematical model is developed for the impedance response of immobilized glucose oxidase electrochemical biosensors. The coupling between the homogeneous reactions and heterogeneous reactions considered in the model included anomerization between α - d -glucose and β - d -glucose and four reversible enzymatic catalytic reactions transforming β - d -glucose and oxygen into gluconic acid and hydrogen peroxide. The electroactive hydrogen peroxide was considered to be reversibly oxidized or reduced at the electrode. The electrochemical system was modeled mathematically as a one-dimensional boundary-value problem and solved by use of Newman's BAND algorithm. The corresponding impedance was calculated for each specified frequency. The resulted limiting current, reaction profiles, and impedance response provide insights into the influence of system parameters such as interstitial glucose concentration and enzymatic rate constants. This model has a potential application in predicting sensor design and diagnosing sensor failure mechanisms. [ABSTRACT FROM AUTHOR]

The electrochemistry, optical properties, wettability and morphology of polydopamine (PDA) thin films were extensively studied on carbon electrodes, in order to evaluate their potential to be used as electrochemical biosensor interfaces. To fulfil this purpose, several PDA films with different thicknesses were allowed to grow spontaneously and their electrochemical stability and coverage of active quinone/hydroquinone groups were assessed by cyclic voltammetry. Ellipsometry was used to evaluate the dielectric properties of PDA, and film thickness increase with the deposition time on glassy carbon electrodes. Atomic Force Microscopy corroborates film thickness and revealed the formation of uniform coatings for all dopamine incubation times. PDA wettability validates the presence of hydrophilic quinone/hydroquinone. Electrochemical and optical characterization of the modified electrodes points to the formation of a poorly conducting polymeric matrix, yet allowing the charge transfer process of electroactive probes, for 3 ± 1 nm thick films, proving their applicability as electrochemical transducers. The catalytic activity of immobilized Glucose Oxidase or Laccase on graphite/PDA electrodes were validated against glucose and 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), respectively. The analytical parameters are particularly promising for Laccase modified electrodes towards ABTS detection, undoubtedly proving the biocompatibility and excellent electrochemical transduction of thin polydopamine films. [ABSTRACT FROM AUTHOR]

Enzyme-based amperometric biosensors measure target analyte concentrations through the transduction of enzymatically generated electrons into a detectable current at an electrode surface. To achieve efficient electron transfer, many such systems rely on the use of diffusive electron mediators or intricate, nanostructured electrode materials, which can limit applicability. Herein, we report on the development and characterization of enzyme-based glucose biosensors operating using a combination of intramolecular electron transfer and electron self-exchange through ferrocene-containing redox mediators covalently coupled directly to glucose oxidase (GOX). To accomplish this, we applied polymer-based protein engineering to grow poly( N -(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide (pFcAc) via atom-transfer radical polymerization from initiator molecules attached to the GOX surface. The use of these GOX-pFcAc conjugates allowed the fabrication of simple, paper-based glucose biosensors through crosslinking with the carrier protein human serum albumin (HSA) within a viscous chitosan solution and drop casting onto carbon paper strips. Chit-GOX-pFcAc-HSA-carbon paper biosensors yielded a glucose sensitivity of 0.33 ± 0.01 μA mM −1 cm −2 and exhibited selectivity when challenged with other sugars. The ease of sensor fabrication further afforded a tailorable response through variation of GOX-pFcAc concentration upon crosslinking and drop casting. The reported approach shows the glucose sensing capabilities of a system that merges the characteristics of bioelectronics fabricated using redox-containing polymer networks with those based on the surface modification of enzymes with electron relays. [ABSTRACT FROM AUTHOR]

A high-sensitivity amperometric glucose biosensor was developed using iron oxide nanoparticles (IONPs), glucose oxidase (GOx) enzyme, and Nafion layer immobilized on screen-printed carbon electrode (SPCE) (Nafion/GOx/IONPs/SPCE). IONPs were synthesized through precipitation and functionalized with citric acid (CA) to provide a hydrophilic surface and functional groups for immobilization of the GOx enzyme. The transmission electron microscopy image showed that size of the obtained IONPs is ∼20 nm. The X-ray diffraction pattern showed the presence of spinel cubic lattice of maghemite (γ-Fe 2 O 3 ). Under the optimal condition, the amperometric responses of the resulting bioelectrode Nafion/GOx/CA-IONPs/SPCE presented high sensitivities of 175 and 5.31 μAmM −1 cm −2 for the detection of 0.02–0.25 and 0.25–8.00 mM glucose, respectively. The biosensor exhibited low limit of detection of 7 μM, good repeatability by maintaining 93% of the initial peak current after 10 cycles of cyclic voltammetry measurement, and sufficient reproducibility of 4.2% (number of sensors n = 7). The fabricated amperometric biosensor features high sensitivity, disposability, low cost, and simple procedure for glucose detection. [ABSTRACT FROM AUTHOR]

Enzyme-based biosensors have garnered intense research interest due to the catalytic properties and physiologic applicability of enzymes. However, the use of these biological catalysts also introduced persistent lifetime limiting stability issues that hinder device longevity. We report on the identification and understanding of sources of long-term stability loss within a glucose oxidase (GOX)-based biosensor. Through polymer-based protein engineering (PBPE), we grew poly( N -(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide (pFcAc) directly from initiator sites at the GOX surface via atom-transfer radical polymerization. The resulting GOX-pFcAc conjugates were crosslinked along with human serum albumin (HSA) within chitosan (Chit)-containing solution and drop cast onto carbon paper strips. Chit-GOX-pFcAc-HSA-carbon paper biosensors generated current by intramolecular electron transfer and electron self-exchange through the GOX-pFcAc conjugates as well as through oxygen mediated electron transfer under varied cell potentials and solution conditions. A systematic characterization method identified the leading sources of instability within the enzyme-polymer conjugate system. We found that a physically crosslinked network prevented GOX leaching from the functionalized electrode. Pre-wetting the electrode also increased current outputs. A reduction in ferrocene-mediated current generation resulted from instability of the ferrocenium ion produced during operation. This issue could be solved through the use of freely diffusing ferrocene, which indicated a path toward improvement for enzyme-polymer conjugate systems with carefully engineered redox characteristics. [ABSTRACT FROM AUTHOR]

In the present work, MoS 2 nanosheets were composited with TiO 2 nanorods to obtain a heterostructure with improved photoelectrochemical (PEC) performance. TiO 2 nanorods were initially prepared using a hydrothermal method, and then MoS 2 nanosheets were synthesized using TiO 2 nanorods as the substrates. Various spectroscopic and microscopic methods were used to investigate the morphology and composition of the composite. Electrochemical impedance spectroscopy was also conducted to demonstrate the excellent electrical conductivity of the composite. The bioactivity of glucose oxidase (GOx) to glucose was validated with cyclic voltammetry in air-saturated solution. Finally, a PEC biosensor was fabricated by immobilizing GOx on MoS 2 nanosheet-TiO 2 nanorod composite modified ITO electrode. Owing to the high specific surface area, good conductivity, excellent biocompatibility and small band gap associated with this composite, the PEC glucose biosensor exhibited a dynamic range of 0.1–10.5 mM, sensitivity of 0.81 μA mM −1 , and a detection limit of 0.015 mM within the visible spectrum. [ABSTRACT FROM AUTHOR]

A highly selective and accurate on-off ratiometric electrochemical biosensor to detect glucose was proposed based on gold nanoparticles (AuNPs)-glucose oxidase (GOD) nanocomposites as the catalyst for both the oxidation of glucose and the electrochemical reduction of O 2 and the thionine as the inner reference signal for the first time. The reduction peak of O 2 catalyzed by AuNPs-GOD at −0.45 V decreased in GOD-glucose reaction in which the O 2 was consumed gradually to produce H 2 O 2 . While, the reduction peak of the produced H 2 O 2 catalyzed by thionine at −0.24 V increased gradually. By using the ratiometric peak current as detection signal, a novel on-off ratiometric electrochemical biosensor for glucose detection was developed and exhibited an acceptable detection limit of 11.66 μM and a wide linear range from 35.43 μM to 15 mM. The biosensor also exhibited high accuracy, high selectivity, good reproducibility and high sensitivity. The ratiometric electrochemical approach not only developed a new method for highly selective and accurate detection of glucose but also provided a good idea for accurate and selective analysis of other analytes. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate high current densities per projected surface area for the electroenzymatic oxidation of glucose at low potential using a hierarchically structured electrode based on MgO-templated carbon. The modified electrode was prepared by assembling glucose oxidase (GOx) with an osmium-based redox polymer with a low formal potential (−0.03 V vs. Ag|AgCl), in which Os complexes are tethered to the polymer backbone via a 13-atom alkyl chain and a crosslinker. A glucose oxidation current density of 15 mA cm −2 was measured at 0 V vs. Ag|AgCl at 37 °C and pH 7, with a plateau value of 50 mA cm −2 at 0.3 V. The hydrogel electrodes composed of the same redox polymer and FAD-dependent glucose dehydrogenase delivered only 10% of the current densities obtained with the GOx electrode. [ABSTRACT FROM AUTHOR]

We present for the first time a mathematical model of osmium redox polymer mediated glucose oxidase enzyme electrodes. This model is based on a system of three coupled nonlinear reaction-diffusion equations under steady-state conditions for biochemical reactions occurring in the biofuel cells that describes the oxidized mediator, oxygen and substrate (Glucose) concentration within the biofuel cell. Simple analytical expressions for the concentration of oxidized mediator, oxygen and substrate and the corresponding current-potential response have been derived for all the values of reaction diffusion parameters using the new homotopy perturbation method (NHPM).The current-potential response in osmium redox polymer mediated glucose oxidase enzyme electrodes is discussed. The analytical results for the concentrations are also compared with numerical results and a satisfactory agreement is noted. The influence of diffusion coefficient of mediator, thickens of the film, turnover rate of Gluocose Oxidase and Michaelis-Menten constant on current-potential curve is also analyzed. [ABSTRACT FROM AUTHOR]

Scanning electrochemical microscopy (SECM) is an advanced electrochemical method, which is based on electrochemical scanning of electrochemical system surface by an ultramicroelectrode. Due to very high complexity of such systems the evaluation of data collected by this electrochemical method is a challenging task, which could be partly solved by mathematical modeling of processes that are influencing the signal of SECM. Several attempts to describe these processes mathematically have been performed for both feedback and generation-collection SECM modes. However, mathematical models for the redox competition SECM mode still were not elaborated due to high complexity of this problem. Therefore in this research work we have developed a mathematical model for the evaluation of enzyme − glucose oxidase (GOx) − modified surface by SECM, which was acting at redox competition mode. The rates of (i) GOx catalyzed processes, (ii) electrode reactions and (iii) diffusion were taken into account by proposed mathematical model. Using this model, it is possible to calculate oxygen consumption rate, to evaluate enzymatic reaction kinetics, and to determine diffusion coefficients of oxygen diffusion in the SECM-based systems. [ABSTRACT FROM AUTHOR]

This study presents the synthesis and characterization of a novel glucose electrochemical biosensor based on gold nanoparticles/bovine serum albumin/Fe 3 O 4 (AuNPs/BSA/Fe 3 O 4 ) composite nanoparticles. The prepared magnetic composite nanoparticles consist of a BSA protein shell, providing biocompatible environment for enzyme immobilization. Furthermore, in situ immobilization of gold nanoparticles greatly enhances the performance of electron transfer. Using these composite nanoparticles, the model enzyme, glucose oxidase (GOx) was readily adsorbed to surface so as the GOx/AuNPs/BSA/Fe 3 O 4 electrochemical biosensor was developed. The electrochemical performance of the biosensor was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry. Under the optimal preparation conditions, the resultant biosensor has a short response time of 0.8 s, an excellent sensitivity of 115.3 μA mM −1 cm −2 , and a linear dynamic range from 0.25 to 7.0 mM with a low detection limit of 3.54 μM (S/N = 3). The high sensitivity, good reproducibility and stability of the biosensor presented in this study show that the as-prepared AuNPs/BSA/Fe 3 O 4 composite nanoparticles are a promising material for the development and construction of biosensors. [ABSTRACT FROM AUTHOR]

A simple, organic solvent free ultrasonic exfoliation method was developed to produce exfoliated SnS 2 nanoplates of an average size of 24 nm and thickness of 8 nm. These SnS 2 nanoplates were decorated onto the surfaces of multi-walled carbon nanotubes (MWCNT) to serve as the sensing electrode for glucose oxidase (GOx) based direct electron transfer sensing of glucose. The decoration of exfoliated SnS 2 nanoplates significantly improved hydrophilicity of the electrode and the electron transfer micro-environment between the redox-active site of GOx and the electrode surface, both beneficial to the direct electron transfer sensing of glucose. A high sensitivity of 28.9 μA/mM cm 2 was achieved, 1.77 times that of the SnS 2 -free case and among the highest reported for CNT and GOx based direct electrochemical glucose sensing. [ABSTRACT FROM AUTHOR]

Cu 2 O/Ppy composites coated linen texture (LT) papers possess enzyme activities of glucose oxidase (GOx) and horseradish peroxidase (HRP) in alkaline solution (0.5 M NaOH). At the potential of 0 V vs. Ag/AgCl reference electrode, H 2 O 2 was produced through oxidation of glucose on the functional LT paper electrode in the presence of O 2 . The as-produced H 2 O 2 was reduced on the electrode at the potential of −0.57 V vs. Ag/AgCl reference electrode. Cyclic voltammograms (CVs) reveal that Cu(I)/Cu(II), Cu(II)/Cu(I), and Cu(I)/Cu transitions occur at ca. 0, −0.57, and −0.85 V respectively. The electrode allows detections of glucose and H 2 O 2 down to 0.16 and 0.41 mM, respectively. The high catalytic activity of the Cu 2 O/Ppy composites is attributed to the stable coatings of Ppy and the high-index facets of Cu 2 O octahedra and microflowers. Having advantages of a low onset potential ( ca. −0.02 V), high sensitivity (28 μA mM −1 cm −2 ), and selectivity, the stable and durable LT paper electrode has been validated for the quantitation of glucose in blood samples, showing its great potential for monitoring blood glucose levels. [ABSTRACT FROM AUTHOR]

Miniaturized chemical sensors are desirable for field analysis and screening trials aiming at point-of-care diagnostics. For this purpose, nanostructured materials, including those of the 2D family, are highly promising once they can add to sensing devices improved properties regarding sensitivity, the limit of detection, and portability. Here we report the synthesis, characterization, and application of 2D-carbonylated graphitic carbon nitride (c-g- C 3 N 4) in the modification of screen-printed electrodes for photoelectrochemical analysis. Morphological and structural features of the material were studied through atomic force microscopy, scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction, Fourier transformed-infrared spectrophotometry, and X-ray photoelectron spectroscopy. The optical bandgap of the semiconductor was estimated using diffuse reflectance spectrophotometry. Glucose determination was performed as proof of concept using c-g- C 3 N 4 as support for the immobilization of glucose oxidase and application of the photoelectrochemical sensor. The device presented a linear range from 0 to 5.00 mmol L−1 and a limit of detection of 0.43 mmol L−1. Our results indicate the suitability of employing c-g- C 3 N 4 for designing photoelectrochemical sensors for detecting analytes of biological and medical interest. [Display omitted] [ABSTRACT FROM AUTHOR]

• Bioanode of fuel cell was successfully designed using S. platensis -based lysates. • S. platensis lysates reduce the open circuit potential (OCP) drop. • Algae's lysates facilitate the immobilization of GOx and serve as a redox mediator. • The power density of biofuel cell comprised with S. platensis -based lysate bioanode was 21.8 times higher. • OCP value of -259 mV vs Ag/AgCl was achieved in the presence of 12.5 mM glucose. In this study, the GC/PEI/CNT/S.p./GOx bioanode was successfully designed using the chemical oxidized multi-walled carbon nanotubes (CNT) and Spirulina platensis -based lysates that facilitate the electron transfer and reduce the open circuit potential (OCP) drop along the electron transfer pathway. Composition, morphology and chemical modification efficiency of CNT was examined using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and simultaneous thermal analysis (STA) coupled with mass spectrometric (MS) analysis of evolving gaseous species (TG/DTA–MS). The power density generated by GC/PEI/CNT/S.p./GOx bioelectrode was 21.8 times higher if S. platensis -based lysates were applied in bioanode design (than GC/PEI/CNT/GOx bioelectrode). The magnitude of maximal power density evaluated by linear sweep voltammetry (LSV) measurements was estimated to be 3.2 µW cm−2 at 213 mV voltage, whereas the bioelectrode act as a bioanode and bare glassy carbon as a cathode in a single-compartment biofuel cell design. Furthermore, the GC/PEI/CNT/S.p./GOx bioanode shows high long-term stability, while the magnitude of power density after seven days achieved approximately 89.6 % (2.87 µW cm−2) of its initial value. The initial OCP value of bioanode with S. platensis -based lysates was found to be -156 mV, which was reduced after the addition of 12.5 mM glucose. The equilibrated average value of OCP (-259 mV vs Ag/AgCl (3 M KCl)) indicates that glucose oxidase (GOx) immobilized on CNT functionalized with S. platensis -based lysates possess superior electron transfer and reduce the OCP drop along the electron transfer pathway. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, combining poly (methylene green)/glucose dehydrogenase (PMG/GDH) bioanode with Prussian blue/glucose oxidase (PB/GOD) biocathode, we developed a hybrid bioelectrochemical device based on glucose/O 2 enzymatic biofuel cell (EBFC) to achieve energy conversion and storage. Depending on the reversible redox behaviors, PMG and PB play roles of dual-functional nanomaterials, not only as mediators to accelerate electrons transport between enzymes and electrodes surface, but also as pseudocapacitive materials to achieve energy storage. As a result, this hybrid device exhibited superior performance towards energy storage with a specific capacitance of 158.5 mF cm−2 at the current density of 1 mA cm−2. Meanwhile, a maximum output power density of 783.5 μW cm−2 in the pulse mode could be obtained, which had a prominent increment than that of the prototypical EBFC (87.5 μW cm−2) in the steady state. Furthermore, this hybrid device also exhibited better operational stability in long-term charge/discharge cycles test, at the current pulse of 1 mA cm−2. Through the combination of bioelectrocatalysis and capacitive energy storage, this developed hybrid device achieves effective energy conversion and storage, and provides a high output power to address the insufficient power supply of traditional EBFCs, which may enlarge the practical application of EBFCs in self-powered implantable and wearable devices. [ABSTRACT FROM AUTHOR]

We describe the consistent effect of salts in the electrolyte solution on glucose oxidation current production in the redox hydrogel-modified electrode containing glucose oxidase as an electrocatalyst and Os complex mediator. The ions affect not only on the electron transfer between the enzyme and the Os complex, but also on the hydrogel structure. This study found that the degree of the effect can be characterized by Hofmeister series. The relative decrease in oxidization current is the lowest in the middle of the Hofmeister series, and increases monotonically on either side. An increase of ionic strength inhibits the electron transfer from the active site of glucose oxidase to Os complex. In addition to this, the kosmotropic anions, which are strongly hydrated, caused hydrogel deswelling (shrinking). The more chaotropic an ion is, the more it adsorbs to uncharged parts of polymer/enzyme with dispersion force, and the swelling of the hydrogel decreases the catalytic current. This study impacts the design of hydrogel electrode and selection of electrolyte ions for bioelectronic applications. [ABSTRACT FROM AUTHOR]

Comparative electrochemical behavior of three types of proteins; cytochrome c (Cyt c), Agaricus Bisporus laccase (LacAB) and glucose oxidase (GOx) immobilized on gold mercaptopropionic acid self-assembled monolayer via three different methods, including (a) covalent attachment by using EDC/NHS organic activators, (b) electrostatic interactions, and (c) covalent-coordinate binding by using Zr(IV) ion glue is investigated. Immobilization steps and electrochemical behavior of the immobilized proteins are traced by means of cyclic and differential pulse voltammetry (CV and DPV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results indicate that characteristics of the immobilized systems including; surface coverage, electrocatalytic activity and stability of the proteins are considerably affected by type of the bond formed between electrode and protein (the immobilization method), and nature of the protein. Immobilization via Zr(IV) ion resulted in higher activities for metalloproteins, i.e. Cytc with Heme active center and LacAB with T copper active center, while EDC/NHS method was more efficient for GOx having FAD cofactor. The experimental data will be presented and discussed from which the efficient immobilizing method for each case is introduced. [ABSTRACT FROM AUTHOR]

This work reports the successful application of bamboo-like multiwalled carbon nanotubes (bCNT) non-covalently functionalized with calf-thymus double stranded DNA (dsDNA) as a robust platform (bCNT-dsDNA) to build electrochemical biosensors. The “model system” proposed here as a proof of concept was an enzymatic biosensor devoted to glucose quantification obtained by layer-by-layer self-assemby of polydiallyldimethylammonium (PDDA) and glucose oxidase (GOx) at glassy carbon electrodes (GCE) modified with bCNT-dsDNA (GCE/bCNT-dsDNA/(PDDA/GOx) n ). The influence of GOx and PDDA assembling conditions and the effect of the number of PDDA/GOx bilayers (n) on the performance of the resulting biosensor is critically discussed. The supramolecular architecture was characterized by electrochemical impedance spectroscopy from the charge transfer resistance of quinone/hydroquinone and potassium ferrocyanide/potassium ferricyanide; by cyclic voltammetry from the surface concentration of GOx using ferrocene methanol as enzyme regenerator; by amperometry from the response of the enzymatically generated hydrogen peroxide; and by surface plasmon resonance from the changes in the plasmon resonance angle. The analytical parameters obtained with GCE/bCNT-dsDNA/(PDDA/GOx) 3 for the amperometric quantification of glucose at 0.700 V were: sensitivity of (265 ± 7) μA mM −1 cm −2 , linear range between 0.25 and 2.50 × 10 −3 M, detection limit of 50 μM, repeatability of 3.6% (n = 10), and negligible interference from maltose, galactose, fructose and manose. The biosensor was successfully used for the sensitive quantification of glucose in beverages and a medicine sample. [ABSTRACT FROM AUTHOR]

Glucose was selectively oxidized to gluconic acid in a membraneless, flow-through electroenzymatic reactor operated in the mode of co-generating chemicals and electrical energy. At the anode the enzyme glucose oxidase (GOx) in combination with the redox mediator tetrathiafulvalene (TTF) was used as catalyst, while the cathode was equipped with an enzyme cascade consisting of GOx and horseradish peroxidase (HRP). The influence of the electrode preparation procedure, the structural and the operating parameters on the reactor performance was investigated in detail. Under optimized conditions, an open circuit potential of 0.75 V, a current density of 0.6 mA cm −2 and a power density of 100 μA cm −2 were measured. The space time yield of gluconic acid achieved at a glucose conversion of 47% was 18.2 g h −1 cm −2 . [ABSTRACT FROM AUTHOR]

We report on a small and simple graphene-based potentiometric sensor for the measurement of intracellular glucose concentration. A fine borosilicate glass capillary coated with graphene and subsequently immobilized with glucose oxidase (GOD) enzyme is inserted into the intracellular environment of a single human cell. The functional groups on the edge plane of graphene assist the attachment with the free amine terminals of GOD enzyme, resulting in a better immobilization. The sensor exhibits a glucose-dependent electrochemical potential against an Ag/AgCl reference microelectrode which is linear across the whole concentration range of interest (10 – 1000 μM). Glucose concentration in human fat cell measured by our graphene-based sensor is in good agreement with nuclear magnetic resonance (NMR) spectroscopy. [ABSTRACT FROM AUTHOR]

The amperometric glucose biosensors based on adsorbed electron transfer mediator (ETM) tetrathiafulvalene (TTF) or 1,10-phenanthroline-5,6-dione (PD) and glucose oxidase (GOx) from Aspergillus niger (GOx A.niger ), Penicillium adametzii (GOx P.adametzii ) or Penicillium funiculosum (GOx P.funiculosum ) cross-linked with glutaraldehyde were investigated. ETM and enzyme were immobilized layer by layer on bare graphite rod electrode (GR) premodified with gold nanoparticles (AuNP) of (i) 3.5 nm (GOx/ETM/AuNP 3.5 /GR), (ii) 6.0 nm (GOx/ETM/AuNP 6.0 /GR) and (iii) 13.0 nm (GOx/ETM/AuNP 13.0 /GR) size. The amperometric signals for all the developed biosensors were higher using PD in comparison with TTF. The biosensor based on GOx P.funiculosum showed higher analytical signal to glucose in a comparison to biosensors based on GOx A.niger and GOx P.adametzii . The registered current to glucose using GOx P.funiculosum /PD/AuNP 3.5 /GR electrode was linear in the glucose range from 0.1 to 10.0 mmol L −1 and the limit of detection was 0.024 mmol L −1 . Enzymatical synthesis of polypyrrole (Ppy) layer on the electrode was applied in order to expand the linear glucose detection range. After 22 h of polymerization the amperometric signal was linear in the glucose concentration range from 0.1 to 25.0 mmol L −1 , while after 69 h this rage was increased up to 50.0 mmol L −1 . Additionally Ppy layer on the electrode surface reduced the influence of interfering species on the amperometric signal. The performance of developed biosensor was investigated in human serum samples. [ABSTRACT FROM AUTHOR]

• Mathematical model for biosensor acting in trigger mode is discussed. • Nonlinear differential equations are solved and validated with simulation results. • Transient current, sensitivity, resistance and gain expressions are derived. • The influence of various system parameters on biosensor response has been examined. The transient response of amperometric enzyme-based biosensors working in trigger mode is discussed. Nonlinear time-dependent partial differential equations for Michaelis–Menten reaction kinetics are solved analytically using a new approach of homotopy perturbation technique. The simple and closed-form analytical expression for concentration profiles are provided. Subsequently, the biosensor's current, sensitivity, resistance, and amplification are derived from the concentration profiles. The current response is predicted under steady-state conditions when T → ∞ , proving the validity of the mathematical analyses. The limiting situations of catalytic sites (unsaturation and saturation) are considered. The compatibility of analytical results with simulation and limiting case results can be observed from the graphs and tables presented. The existence of the moving boundary between the two categories of catalytic sites is also discussed. [ABSTRACT FROM AUTHOR]

Aminophenylboronic acid moieties were covalently grafted onto mercaptobenzoic acid moieties, and glucose oxidase was then immobilized through boronic acid-diol specific recognition to form a pH-sensitive electrosensor switching between pH 5.8 and pH 8.0 base solution. Using potassium ferricyanide as electroactive probe, the response was intensified in acidic condition while hindered in alkaline condition. The sharp and stable contrast in current was performed alternately upon the change of pH like a “pH switch”. In the presence of glucose, the response to glucose was further amplified catalytically by glucose oxidase on “ON” state, while electron transfer was inhibited on “OFF” state. Furthermore, when our sensor was on “ON” state, it showed a good linearity ranging from 0 to 30 μmol L −1 of glucose, with a detection limit of 348 nmol L −1 (S/B = 3) and a dynamic range extending to 50 μmol L −1 . Glucose-responsive, pH-switchable and catalytically-amplified, our biosensor provided a new method for the detection of glucose in the form of pH switch in human serum sample, and was promising to more complicated environment. [ABSTRACT FROM AUTHOR]

Tetramethylferrocene-modified linear(polyethylenimine) (FcMe 4 -C 3 -LPEI) was cross-linked with ethylene glycol diglycidyl ether (EGDGE) in the presence of glucose oxidase (GOx) to form enzymatic glucose bioanodes capable of generating 1.034 ± 0.039 mA/cm 2 with 3 mm glassy carbon electrodes and 15.1 ± 0.8 mA/cm 2 with 0.5 × 0.5 cm carbon felt electrodes at 25 °C. FcMe 4 -C 3 -LPEI/GOx films were characterized by varying the amount of EGDGE, pH, and electrode material. The electrochemical potential was shown to vary with the amount of EGDGE used to cross-link the film, from 0.068 ± 0.016 V to 0.122 ± 0.003 V vs SCE using 4 mol% to 32 mol% EGDGE respectively. A similar trend occurred upon varying pH from 0.073 ± 0.004 V vs SCE at pH 4.0 to 0.118 ± 0.003 at pH 8.0. The optimized materials described herein have direct practical use as enzymatic bioanodes and as glucose biosensors. [ABSTRACT FROM AUTHOR]

LiNbO 3 nanotubes are prepared by biotemplate-assisted synthetic route. The mesoporous LiNbO 3 nanotubes can be an ideal platform to immobilize glucose oxidase (GOx) for glucose biosensing. As the GOx-biocatalyzed oxidation of glucose yield H 2 O 2 , and LiNbO 3 can direct catalyze the generated H 2 O 2 . What's more, one dimensional channels will facilitate the diffusion of reactants and ensure adequate contact between glucose and enzymes. Thus the as-prepared biosensor exhibit high sensitivity (52.4 μA·mM −1 ·cm −2 ), fast response (<2 s) and excellent selectivity to glucose. The results suggest the potential implementation of LiNbO 3 as a sensing platform for electrochemical detection of biology reagents. [ABSTRACT FROM AUTHOR]

1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite electrodes were analysed in buffer/glucose media by the electrochemical impedance spectroscopy (EIS) method. The EIS analysis was carried out under potentiostatic conditions. The gathered impedimetric data was evaluated applying estimated equivalent circuits. It was determined that equivalent circuit R Ω ( R F2 C 2 )( C [ R F W ]) most optimally describes this electrochemical system. The study revealed redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on graphite electrodes. [ABSTRACT FROM AUTHOR]

Enzymatic biological fuel cells (E-BFCs) were prepared using glucose oxidase (GOx) or FAD-dependent glucose dehydrogenase (FAD-GDH) as the anodic enzyme, coupled with direct electrocatalytic bilirubin oxidase (BOd) biocathodes obtained via incorporation of anthracene-modified multi-walled carbon nanotubes (Ac-MWCNTs). For GOx/BOd E-BFCs operating at pH 6.5 (200 mM glucose), open-circuit potentials, maximum current densities and maximum power densities of 0.47 ± 0.02 V, 332.7 ± 19.6 μA cm −2 , and 46.5 ± 2.8 μW cm −2 were observed. For FAD-GDH/BOd E-BFCs operating in the same conditions, open-circuit potentials, maximum current densities and maximum power densities of 0.40 ± 0.01 V, 226.6 ± 8.0 μA cm −2 , and 35.9 ± 1.3 μW cm −2 were observed. The effect of H 2 O 2 (as produced by the enzymatic side-reaction of GOx) on BOd bioelectrocatalytic cathodes in E-BFCs was also investigated. Short-term testing (steady state) revealed that GOx did not produce significant quantities of H 2 O 2 to affect BOd biocathodes. However, long-term testing (steady state, 24 hours) revealed that the quantity of H 2 O 2 produced by GOx is large enough to have detrimental effects on the performance of the E-BFCs. [ABSTRACT FROM AUTHOR]

The successful implementation of redox-enzyme electrodes in biosensors and enzymatic biofuel cells has been the subject of extensive research.For high sensitivity and high energy-conversion efficiency, the effective electron transfer at the protein-electrode interface has a key role. This is difficult to achieve in the case of glucose oxidase, due to the fact that for this enzyme the redox centre is buried inside the structure, far from any feasible electrode binding sites.This study reports, a simple and rapid methodology for the direct immobilisation of glucose oxidase into highly porous gold electrodes. When the resulting electrode was tested as glucose sensor, a Michaelis-Menten kinetic trend was observed, with a detection limit of 25μM. The bioelectrode sensitivity, calculated against the superficial surface area of the bioelectrode, was of 22.7±0.1μAmM-1cm-2.This glucose oxidase electrode was also tested as an anode in a glucose/O2 enzymatic biofuel cell, leading to a peak power density of 6μWcm-2 at a potential of 0.2V. [ABSTRACT FROM AUTHOR]

We fabricated bioanodes based on PAMAM (polyamidoamine) dendrimers to immobilize glucose oxidase (GOx), using ferrocenium hexafluorophosphate (Fc) entrapped in electropolymerized polypyrrole films (Fc-polypyrrole) as mediator. We conducted a comparative study of the GOx kinetic parameters as a function of the enzyme environment; i.e., in solution and immobilized onto carbon platforms. Kinetic studies revealed that the Michaelis-Menten constants (KM) of the anchored and soluble GOx were quite similar, KM=21.2 (± 0.6) mmol L−1 in solution, and 21.5 (± 0.8) mmol L−1 when immobilized, demonstrating that enzyme immobilization did not affect the enzyme-substrate affinity. However, the maximum reaction rate (Vmax) obtained for the immobilized GOx (Vmax=0.72 (± 0.03) μmol min−1mg−1) was lower than the reaction rate achieved for the free enzyme in solution (Vmax=64 (± 2) μmol min−1mg−1), due to diffusional effects. Cyclic voltammetry assays confirmed the incorporation of entrapped Fc species into the polypyrrole net films. The performance of the prepared bioelectrodes in a glucose/O2 semi-cell revealed a maximum power density around 130 (± 15) μW cm−2 at pH 5.0, in 100mmolL−1 glucose. Considering all the electrochemical data and biofuel cell tests, we can infer that the bioanode based on Fc and polypyrrole presented here, is easy to prepare, and the electrocatalyst film efficiently transfers electrons between GOx and the electrode surface. Therefore, it has potential application in glucose/O2 biofuel cells. [ABSTRACT FROM AUTHOR]

• Surface-clean AuNPs/N-GQDs anchored on the P-MOF surface. • Enhanced electrochemical sensing and electrocatalytic abilities of H 2 O 2. • "Cascade nanoreactor" amplification for glucose detection. • Amperometric biosensor shows excellent anti-interference ability and sensitivity. • Glucose detection in serum samples under a low overpotential. Robust and efficient multimodal catalysis platforms that possess high catalytic activity and enhanced electrical conductivity are preferred for enhancing the electrical analysis performance under a low overpotential. This report describes a function-switchable amperometric sensor for electrochemical monitoring hydrogen peroxide and glucose under relatively low overpotential based on PEI-functionalized metal–organic framework (P-MOF) supported gold nanoparticles/nitrogen-doped graphene quantum dots (AuNPs/N-GQDs) and glucose oxidase. AuNPs/N-GQDs with high peroxidase mimicking activity was anchored on the P-MOF modified electrode surface as H 2 O 2 sensors, exhibiting a high sensitivity of 134.26 μA mM−1 cm−2 and a detection limit of 3.38 μM. Subsequently, AuNPs/N-GQDs-P-MOF used as a nanocarrier for glucose oxidase (GOx) to achieve "cascade nanoreactor" amplification for glucose detection. The amplified amperometric glucose biosensor showed excellent anti-interference ability, reproducibility, and a limit of detection as low as 0.7 μM (S/N = 3) with high sensitivity of 1512.4 μA mM−1 cm−2. In addition, the feasibility of the electrochemical biosensor for accurate and quantitative detection of glucose in human serum samples was confirmed with a recovery ranging from 93.2 to 99.3%. The strategy of combining AuNPs/N-GQDs-P-MOF and glucose oxidase for cascade catalysis in this work provides a simple yet efficient approach to prepare nanomaterial-based enzyme-mimics and enzymes hybrids with high performance, which holds great potential in biological and chemical applications of electrochemical devices and biosensing. [Display omitted] [ABSTRACT FROM AUTHOR]

• Electrodeposition of nanoplatelets like structure of samarium oxides. • High charge transfer rate constant and roughness factor. • Hydrogen peroxide reduction from −0.10 V (vs. Ag/AgCl). • Physical adsorption of glucose oxidase. • Glucose determination in serum samples. A nanostructured samarium oxide electrode was constructed by electrodeposition onto the surface of a gold electrode on SiO 2 /Si wafer. The samarium oxides electrode's surface morphology was investigated by scanning electron microcopy showing a quasi-monodispersed nanoplatelets like structure. X-rays diffraction analysis demonstrated a mixture of monoclinic and hexagonal phases while the X-rays photoelectron spectroscopy indicated the co-existence of both Sm2+ and Sm3+ species in a 1:3 proportion. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the charge transfer processes at the surface of the samarium oxide electrode in the absence and in the presence of redox probes. A roughness factor of 2.5 was determined from the samarium oxide electrode while the charge transfer constant was almost double when compared to the planar gold electrode. Then, the samarium oxide electrode was used for the H 2 O 2 detection by fixed potential amperometry at -0.20 V (vs. Ag/AgCl) with a linear region between 0.01 and 1.00 mM, a sensitivity of 153 µA cm−2 mM−1 and a LoD = 2.70 µM. Glucose oxidase was used as a model enzyme in order to test the capacity of the samarium oxides electrode for biosensing. The enzyme was immobilized by physical adsorption and the optimum conditions for glucose analysis investigated. The biosensor showed a linear range for glucose detection between 0.10 and 1.20 mM with a sensitivity of 8.40 µA cm−2 mM−1 and a LoD = 8.00 µM. Selectivity was tested toward common interfering species, and the results revealed the lack of biosensor response. The glucose biosensor on samarium oxides was tested for glucose detection in serum samples with a recovery factor of 90%, and the result validated with a commercial glucometer. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Nanoporous gold (NPG) is composed of three-dimensional (3D) bicontinuous nanostructures with large surface area. Nano-channels inside NPG provide an ideal local environment for immobilization of enzyme molecules with expected stabilization of the protein molecules. In this work, glucose oxidase (GOx) has been brought to assemble on NPG via surface chemical reactions to form enzyme modified NPG nanomaterial with promising sensitivity for glucose detection. Cyclic voltammetry and single-potential step chronoamperometry (SPSC) are employed to study the electrochemical behavior of both bare and enzyme-modified NPG. Two redox mediators, p-benzoquinone (BQ) and ferrocenecarboxylic acid (FCA) are used to shuttle electrons between the enzyme redox center inside of GOx and the NPG electrode. Diffusion patterns at the functionalized NPG electrode are found significantly different from those on planar gold electrodes. This is mainly caused by internal 3D single crystal-like structures of NPG. Electrostatically neutral BQ mediator gives much higher voltammetric sensitivity than negatively charged FCA for GOx modified NPG electrodes.This study provides insight into the understanding of the intrinsic properties of NPG materials aiming at evolving enzymatic biosensors with high performance. [Copyright &y& Elsevier]

Abstract: Glucose oxidase (GOx) is an important industrial enzyme and is recognized as the gold standard for monitoring blood glucose. However, due to its inherent oxidase property, the presence of oxygen affects electrochemical measurements of venous blood glucose employing artificial electron mediators. We therefore attempted to engineer Penicillium amagasakiense-derived GOx into a dehydrogenase by focusing on the amino acid residues predicted to interact with oxygen. Our rational amino acid substitution approach resulted in the construction of the Ser114Ala/Phe355Leu mutant, which has an 11-fold decrease in oxidase activity and 2.8-fold increase in dehydrogenase activity compared with wild-type GOx. As a result, the dehydrogenase/oxidase activity ratio of the engineered enzyme was 32-fold greater than that of the wild-type enzyme. The enzyme sensor constructed with Ser114Ala/Phe355Leu was considerably less affected by oxygen than the wild-type GOx-based sensor at lower glucose concentrations. [Copyright &y& Elsevier]

Highlights: [•] A new biosensor was fabricated for bioelectrochemical determination of glucose. [•] Biosensor has excellent anti-interference ability due to permselectivity of PoPD. [•] Electrocatalytic effect of PtNPs on signal of biosensor was studied in detail. [•] Applicability to blood sample of biosensor analysis was evaluated. [Copyright &y& Elsevier]

Abstract: In this study, we investigated the influence of nature of the electropolymerized monomer on the resulting power output and stability of a glucose/O2 powered biofuel cells (BFCs). The bioanode was prepared from a mixture of glucose oxidase-polymeric monomer-ferrocenium hexafluorophosphate-pyrroloquinoline quinone (abbreviated as, GOx-monomer-FHFP-PQQ) and the biocathode from laccase enzyme-polymeric monomer-4,4-sulfonyldiphenol-Bis-(bipyridine)-(5-aminophenanthroline) ruthenium bis (hexafluorophosphate) (abbreviated as, LAc-monomer-SDP-RuPy) electrodeposited from low conductivity solutions using pulsed square wave potentials (10 s at 4V, then 3 s at 0.5V) for 180 cycles. Three different monomers were investigated: aniline, phenol and pyridine. The power output of the aniline based BFCs reached 5.97μW.mm−2 which is higher than the pyrrole based BFCs reported previously (3.17μW.mm−2). With phenol monomer, the estimated maximum power density was only 0.276μW.mm−2. The pyridine based BFCs showed the lowest power density (0.046μW.mm−2) of all, even lower than the monomer-free BFC (0.124μW.mm−2). The evaluation of the BFCs in buffer solution pH 7.4 under air at 37°C for 3 days of continuous operation showed that pyrrole and aniline based BFCs are the most stable followed by phenol based BFCs. Pyridine and monomer-free BFCs undergo significant deterioration with up to 75% loss in power density. [Copyright &y& Elsevier]

Abstract: The development of nanostructured electrodes for electrochemical biosensors is of significant interest for modern detection, portable devices, and enhanced performance. However, development of such sensors still remains challenging due to the time-consuming, detriment-to-nature, and costly modifications of both electrodes and enzymes. In this work, we report a simple one-step approach to fabricating high-performance, direct electron transfer (DET) based nanoporous enzyme-embedded electrodes by electrodeposition coupled with recent progress in potential-controlled interfacial surfactant assemblies. In contrast to those previously electrodeposited mesoporous materials that are not bioactive, we imparted the biofunctionality to electrodeposited mesoporous thin films by means of the amphiphilic phospholipid templates strongly interacting with enzymes. Thus, phospholipid-templated mesoporous ZnO films covalently inlaid with the pristine enzymes were prepared by simple one-step electrodeposition. We further demonstrate two examples of such hybrid film electrodes embedded with alcohol dehydrogenase (ADH) and glucose oxidase (GOx), which are effectively employed as electrochemical biosensors for amperometric sensing of ethanol and glucose without using any electron relays. The favorable mass transport and large contact surface area provided by nanopores play an important role in improving the performance of these two biosensors, such as excellent sensitivities, low detection limits, and fast response. The matrix mesoporous films acting as effective electronic bridges are responsible for DET between enzyme molecules and metal electrode. [Copyright &y& Elsevier]

Highlights: [•] Graphene/nano-Au composite was synthesized by electrochemical co-reduction method in one step. [•] Glucose oxidase achieves direct electrochemistry on the graphene/nano-Au composite film. [•] The glucose biosensor shows a high sensitivity of 56.93μAmM−1 cm−2 toward glucose. [•] Glucose was detected with a wide linear range and low detection limit. [ABSTRACT FROM AUTHOR]

Abstract: This study reports a novel, simple and fast approach for construction of a highly stable glucose biosensor based on the immobilization of glucose oxidase (GOx) onto a glassy carbon electrode (GCE) electrografted with 4-aminophenyl (AP) by diazonium chemistry. Aminophenyl was used as cross-linker for covalent attachment of glucose oxidase to the electrode surface. Cyclic voltammograms of the GOx-modified GCE in phosphate buffer solution exhibited a pair of well-defined redox peaks, attesting the direct electron transfer (DET) of GOx with the underlying electrode. The proposed biosensor could be used to detect glucose based on the consumption of O2 with the oxidation of glucose catalyzed by GOx and exhibited a wide linear range of glucose from 0.05mM to 4.5mM and low detection limit of 10μM. The surface coverage of active GOx, heterogeneous electron transfer rate constant (k s ) and Michaelis–Menten constant (K M ) of immobilized GOx were 1.23×10−12 molcm−2, 4.25s−1 and 2.95mM, respectively. The great stability of this biosensor, technically simple and possibility of preparation at short period of time make this method suitable for fabrication of low-cost glucose biosensors. [Copyright &y& Elsevier]

Highlights: [•] We investigate the effect of O2 reduction on the calibration curves of wired GOx and PQQ-GDH glucose biosensors. [•] Experiments are performed under 1atm O2 and forced convection to maximize the O2 effect. [•] The effect of O2 drastically decreases when the concentration of glucose increases. [•] For GOx biosensor, it is due to O2 depletion in the hydrogel at high glucose concentration. [•] For PQQ-GDH biosensors, it may be due to a decrease in the average distance the electrons need to cover. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic single-enzyme nanoparticles (MSENs) encapsulated within a composite Fe3O4/poly(pyrrole-N-propylsulfonic acid) network were successfully fabricated via the surface modification and in situ aqueous polymerization of separate enzyme molecules. The resulting MSENs with magnetism and conductivity exhibited high activity and stability. An amperometric glucose biosensor has been developed based on the modification of MSENs onto magnetic glassy carbon electrode (MGCE) through magnetism immobilization. The performance of the developed glucose biosensor was evaluated and the results indicated that a sensitive glucose biosensor could be fabricated. The obtained glucose biosensor presents high-selectivity monitoring of glucose, satisfactory stability, fast response time (4s), wide linear range (0.0005–3.5mM) and low detection limit (0.2μM). The analytical application of the glucose biosensor confirms the feasibility of glucose detection in serum sample. [Copyright &y& Elsevier]

Highlights: [•] A multilayered glucose biosensor with enhanced sensitivity was fabricated. [•] Combination of Ni2+/Ni3+ redox couple and glucose oxidase has been exploited for the first time. [•] Exhibits a lower detection limit of 100nM with a high sensitivity of 16,840μAmM−1 cm−2. [•] The surface shows a low Michaelis–Menten constant value of 2.4μM. [•] Detailed mechanism of sensing was proposed and justified. [ABSTRACT FROM AUTHOR]

Abstract: Au core/Ag shell nanorods (Au@Ag NRs) were synthesized through the seed-mediated growth procedure using Au nanorods (Au NRs) as templates and characterized by UV–vis and TEM methods. The as-prepared Au@Ag NRs were used as a new electrode material for construction of sensor by surface casting of Au@Ag NRs aqueous solution on a glassy carbon electrode (GCE). The fabricated sensor exhibits excellent catalytic performance toward H2O2 reduction with a fast amperometric response time of less than 2s, a wide linear response ranging from 0.02 to 7.02mM (R =0.99), and a lower detection limit of 0.67μM estimated on a signal-to-noise ratio of 3. A glucose biosensor was further fabricated by immobilization of glucose oxidase (GOD) onto the core/shell Au@Ag NRs-modified GCE. The resultant biosensor exhibits high sensitivity, selectivity and stability for glucose detection in phosphate buffer solution. Even in human blood serum, the biosensor also exhibits good performance for glucose detection with an enhanced sensitivity of 33.67μAmM−1 cm−2. [Copyright &y& Elsevier]