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A portable voltammetric sensor for toxicity assessment was developed based on a screen‐printed carbon electrode modified with SiO2‐CuO‐glucose oxidase (GOx) film. The method is based on the detection of the metabolic activity of E. coli towards glucose as an indicator systems in the presence of antiseptic drugs as model toxic compounds. CuO particles exhibited catalytic activity toward hydrogen peroxide produced by the GOx‐induced oxidation of glucose. A well‐defined reduction peak was registered at E=−0.50 V (vs. Ag/AgCl). The metabolism of glucose by E. coli resulted in a decrease in analytical signal of glucose with the increasing bacteria content in the range of 0.8×109–5.0×109 CFU mL−1 with a calculated limit of detection (LOD) of 0.59×109 CFU mL−1. To evaluate the effect of antiseptics the biosensor was tested in E. coli solution with chlorhexidine (CHD) or decamethoxine (DMT). A linear dependence of glucose consumption by E. coli solution on the antiseptic concentration was obtained in the range of 3.0–12.0 μg mL−1 for CHG and 1.0–12.0 μg mL−1 for DMT, respectively. The developed third generation biosensor showed satisfactory stability and reproducibility of the analytical response. A modified electrode can be used for at least two months. [ABSTRACT FROM AUTHOR]

Diabetes is an important public health problem all over the world that affects the quality of life, and its late diagnosis leads to serious complications such as stroke, blindness, limb amputations, and kidney failure. Fabrication of economical and user‐friendly biosensor systems allows the rapid and early detection of prediabetes and type 2 diabetes. Accordingly, a novel, amino‐functionalized, conjugated, alternating polymer was synthesized, characterized, and coated on a glassy carbon electrode (GCE) to be used as an immobilization platform for the glucose oxidase (GOx) enzyme. The decline in oxygen level due to the enzymatic reaction at a potential of −0.7 V vs. silver/silver chloride (Ag/AgCl) is screened as a biosensor response. The proposed biosensor displayed high selectivity and specificity for glucose with a broad linear range, a low detection limit, good reproducibility and repeatability, and a long shelf life. Surface modifications were characterized using cyclic voltammetry (CV) and field emission scanning electron microscopy (FE‐SEM) techniques. The real‐life sample application of the constructed biosensor to determine the glucose amount was performed in human serum. [ABSTRACT FROM AUTHOR]

This research investigated the possibility of using the method of adding an additional enzyme to a monoenzyme oxidase‐based biosensor to improve the biosensor's analytical characteristics. Namely, the catalase (CAT) was used to better saturate the biomembrane with oxygen for the best glucose oxidase (GOx) performance. For this purpose, two different biosensors were created – based on one enzyme (GOx) and two (GOx and CAT). To create a bioselective membrane, the method of covalent binding in vapors of glutaraldehyde was used. The method of coimmobilization of catalase (CAT) and glucose oxidase (GOx) enzymes, as well as the concentration of enzymes in the mixture, was chosen in the work. The stability of the biosensor functioning, i. e. the repeatability during measurements and the reproducibility of the biosensors' preparation, were investigated. Analytical characteristics of the proposed biosensor were studied in comparison with a monoenzyme biosensor based on glucose oxidase only. It was shown that the addition of catalase as an auxiliary enzyme significantly improves the analytical characteristics of the biosensor, in particular, the sensitivity, the repeatability of the measurement results, and the limits of the linear and dynamic ranges of operation. The developed method can be successfully used to optimize conductometric enzyme biosensors based on oxidases. [ABSTRACT FROM AUTHOR]

One‐dimensional Ni/Au/PPy‐COOH nanowires with multiple segments were synthesized in this study. Smooth surfaces and magnetic properties of nanowires were investigated by scanning transmission electron microscopy (SEM), Energy‐dispersive X‐ray spectroscopy (EDX), and Electron Spin Resonance (ESR) techniques. The nanowires were used to modify the screen‐printed electrode surface and as a micro‐environment for Trametes versicolor laccase. The ability of this enzyme biosensor to detect dopamine change in human biological samples was demonstrated by a wide linear range (0.01–50 μM) and a low LOD (2.265 nM). In addition, the biosensor exhibited excellent selectivity allowing the detection of dopamine in the presence of ascorbic acid, uric acid, L‐Cys, serotonin, and glucose, with high sensitivity of reduction currents obtained at −0.2 V (vs. Ag/AgCl). The proposed biosensor allowed the detection of dopamine in commercial serum and artificial urine with recovery values close to 100 %. It also demonstrated reproducibility, reusability, and long‐term storage stability. The sensitivity, Kmapp, and Imax values of the biosensor were determined as 2.05 μM and 1.03 μA, respectively. The LAC‐Ni/Au/PPy‐COOH/NAF/SPE biosensor is a reliable design for detecting dopamine with a wide linear range. [ABSTRACT FROM AUTHOR]

In this research a Hg2+ ion biosensor was developed by combining Prussian blue (PB) with glucose oxidase (GOx) – an enzyme that can be inhibited by Hg2+ ions. An application of PB in the design of Hg2+ ion biosensor enabled detecting changes in hydrogen peroxide reduction current at low operational potential of 0.2 vs Ag|AgCl,KClsat. The described Hg2+ ion biosensor exhibited wide linear range from 27 μM to 247 μM of Hg2+ and higher maximal detectable concentration of Hg2+ than other GOx inhibition‐based biosensors, making it convenient for the analysis of samples with high concentration of Hg2+ ions. [ABSTRACT FROM AUTHOR]

Carbon composite electrodes are frequently used for enzymatic electrodes but suffer from poor electrocatalytic activity and/or are single use. Our group has recently developed thermoplastic electrodes (TPEs) that use a thermopolymer binder. The electrodes can be easily molded without extensive use of organic solvents enabling catalysts and enzymes to be added directly to the electrode material. The TPE material is bulk‐modified with cobalt phthalocyanine and glucose oxidase, resulting in a robust sensor that is stable for over 100 minutes. These sensors can be molded into intricate shapes and sanded for surface renewal, allowing the sensors to be continuously reused. [ABSTRACT FROM AUTHOR]

Advanced glucose biosensors are highly desired for rapid, reliable and cost‐effective sensing of glucose. This work reports on a self‐powered glucose biosensor (SPGB) composed of a Cu anode and a glucose oxidase/Prussian blue/ITO biocathode. The SPGB is available for flow sensing of glucose, with a linear detection range of 0.10 and 1.20 mM, a high sensitivity of 35.62 μA ⋅ cm−2 ⋅ mM−1 and a detection limit of 14.34 μM (S/N=3). The SPGB is reproducible (RSD <5%) and has been successfully employed to determine glucose in juices with satisfactory recoveries (98–100 %). [ABSTRACT FROM AUTHOR]

A novel electrochemiluminescence biosensor was presented for the assay of hepatitis B virus (HBV) DNA. Coralloid poly(aniline‐luminol)‐MWCNTs was prepared on an electrode surface, which was followed by the attachment of capture DNA via amide bond formation. The HBV‐DNA and ferrocene labelled DNA hybridized with capture DNA to form a sandwich structure on electrode surface. Ferrocene can effectively increase the signal output of the ECL sensor due to the catalysis of ferrocene on electrochemiluminescence of luminol. The biosensor rendered a linear dependence over the range from 1.0×10−16 to 1.0×10−7 M with a low detection limit of 2.4×10−17 M. [ABSTRACT FROM AUTHOR]

In this study we report the development of an amperometric cholesterol biosensor based on cholesterol oxidase from Pseudomonas sp. and catalase immobilized in carbon paste electrode (CPE) modified with multiwall carbon nanotubes (MWCNT) and ionic liquid (IL). The working electrode (CPE/MWCNT-IL/Microorganism (MO)-Catalase) was characterized by impedance spectroscopy and cyclic voltammetry at different stages of its construction. This proposed cholesterol biosensor performed linear relationship in the range of 5-600 μM with a low detection limit of 1.52 μM. The biosensor showed good sensitivity and high selectivity and it was successfully applied for the measurement of cholesterol levels in lyophilized serum samples. [ABSTRACT FROM AUTHOR]

Magnetic core‐regular nanostructures composed of magnetite and regular Prussian blue was prepared by self‐sacrificial macro‐oriented method. Magnetic graphene oxide (MGO) was vertically oriented on the surface of home‐made screen‐printing electrode with the help of constant magnetic field (CMF).Then regular nanostructured Prussian blue (RPB) was realized by chemical reaction through an aerosol deposition. Finally, glucose oxidase (GOx) was immobilized by glutaraldehyde cross‐linking to fabricate glucose biosensors. The linear range of CMF‐RPB/MGO sensor towards glucose was 0.03∼1.35 mM, and the detection limit was 13.4 μM. The CMF‐RPB/MGO sensor could apply to analyze glucose in human serum samples. [ABSTRACT FROM AUTHOR]

Many studies have focused on effective ways to exploit enzyme immobilization on an electrode surface to help improve the performance of enzymatic electrochemical biosensors. Herein, a novel glucose sensor was fabricated by immobilizing glucose oxidase (GOx) onruthenium‐based conjugated polymer (CP) and metal‐organic framework (MOF) nanocomposites. This has not only reduced the applied potential to 0.2 V (vs. Ag/AgCl), but also improved the effective surface area for enzyme immobilization.PPG@Ru@UiO‐66‐NH2 was tailored by controlled chemical synthesis from a pre‐synthesized water‐soluble conjugated polymer (poly(N‐phenylglycine)) and metal‐organic framework (UiO‐66‐NH2). The resulting nanocomposites were characterized using Fourier transform infrared spectroscopy, X‐ray fluorescence, scanning electron microscopy, and cyclic voltammetry. The PPG@Ru@UiO‐66‐NH2/GOx coated electrodedisplayed a linear measurementrange for glucose from 1 mM to 10 mM, with a sensitivity of 45.92 μA ⋅ mM−1cm−1 and limit of detection of5 μM(S/N=3). Furthermore, the practical application of the fabricatedglucosesensor was tested in simulative blood samples with satisfactoryaccuracy. This approach alsoopens a new door for applications regarding both enzymatic electrochemical biosensors and enzymatic biofuel cells (EBFCs). [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) is an enzyme frequently used in glucose biosensors. As increased temperatures can enhance the performance of electrochemical sensors, we investigated the impact of temperature pulses on GOx that was drop‐coated on flattened Pt microwires. The wires were heated by an alternating current. The sensitivity towards glucose and the temperature stability of GOx was investigated by amperometry. An up to 22‐fold increase of sensitivity was observed. Spatially resolved enzyme activity changes were investigated via scanning electrochemical microscopy. The application of short (<100 ms) heat pulses was associated with less thermal inactivation of the immobilized GOx than long‐term heating. [ABSTRACT FROM AUTHOR]

A biofuel cell (BFC) was fabricated by combining multiwalled carbon nanotube ‐platinum‐gold (MWCNT−Pt−Au) hybrid nanomaterial, glucose oxidase (GOx) and benzoquinone included carbon felt electrode (CFE) bioanode with apple tissue included CFE biocathode. The working parameters of bioanode were optimized both experimentally and chemometrically. For the biocathode, apple, banana and pear tissues were tried and best power output was obtained with apple tissue. By combining MWCNT−Pt−Au/GOx/CFE bioanode with apple tissue based biocathode, single cell, double cell with membrane and with salt‐bridge BFCs were formed. The best power output with highest current density were obtained with single cell BFC. [ABSTRACT FROM AUTHOR]

A novel enzymatic biosensing platform toward glucose is achieved with nanocomposite of magnetic nanoparticles (Fe3O4−CS−CD) and multi‐walled carbon nanotubes (MWCNTs). The synergistic effect of chitosan, β‐cyclodextrin and MWCNTs can facilitate electron transfer between enzyme and electrode based on the promoting results of the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The new biosensors exhibited direct electron transfer (DET) from enzyme to electrode after glucose oxidase (GOx) was immobilized on the modified electrode with the nanocomposite. Consequently, the enzymatic glucose biosensor displayed a considerably wide linear range (40 μM to 1.04 mM) with a high sensitivity of 23.59 μA mM−1cm−2, low detection limit of 19.30 μM, good selectivity, reproducibility and repeatability for detecting glucose. In addition, the current response still retained at 93.4 % after 25 days. Furthermore, the practical application of glucose biosensor was test in human serum samples with satisfactory accuracy, demonstrating promising and practical potential in biomedical diagnostics. [ABSTRACT FROM AUTHOR]

This paper reports on the electrochemical behavior of an ATP biosensor that utilizes glucose oxidase (GOx) and hexokinase (Hex) immobilized within the electroactive polymer, polyethylenedioxythiophene (PEDOT). This biosensor design detects ATP indirectly at 0.85 V vs. Ag/AgCl based on the oxidation current for enzymatically generated H2O2, and at −0.20 V; a potential at which improved analyte selectivity is achieved. The detection figures of merit at both detection potentials are a response time of 15±1 s, an experimental detection limit of 10.0±0.2 μmol L−1 (S/N=3), and a sensitivity in the range of 100–500 mA M−1cm−2. [ABSTRACT FROM AUTHOR]

A sensitive voltammetric method was developed to determine maltose in beverage products using a carbon nanostructured screen‐printed electrode modified with CuO/glucose oxidase/maltase/SiO2 biocomposite film. Adding CuO particles was done to possess catalytic activity toward hydrogen peroxide. Electrode modified by glucose oxidase and maltase shows a good response to maltose. A well‐defined reduction peak was registered at the potential of −0.55 V (vs. Ag/AgCl) which intensity increases linearly with the concentration of maltose ranging from 0.01 to 0.1 mmol L−1. The calculated limit of detection was 0.005 mmol L−1. Tested on the beer samples, the developed CuO/glucose oxidase/maltase/SiO2 biocomposite film covered carbon nanostructured screen‐printed electrode is showed to be a prospective sensitive element of the third generation biosensor for maltose. [ABSTRACT FROM AUTHOR]

Considerably stable enzymatic fuel‐cells (single cell and 5‐cells stack) were prepared by using chitosan based membranes along with glucose oxidase attached bioanode. Continuous operation of fuel‐cells were monitored under short circuit conditions reaching half‐life over a week. Detailed analysis for the effects of pH, temperature, buffer types and concentration on different type of in‐house produced chitosan membranes were performed by electrochemical impedance spectroscopy (EIS). EIS was utilized to observe, total electrolyte resistance, charge transfer properties, mass transfer and double layer effects on integrated fuel cells (single cell and 5‐cells stack). Performance of the fuel cells was also analyzed by the polarization experiments. Current density of the fuel cell increased at higher operation temperatures not only due to better enzyme kinetics, but also due to increase in electrolyte (membrane+buffer solution) conductivity. Buffer concentration in the fuel (glucose) solution was found as an important parameter. Under optimum fuel cell operation conditions (i. e. 30–40 °C, pH 5 0.3 M buffer solution), maximum current densities of 3.0–3.2 mA cm−2 were reached. Low‐power devices (i. e. a calculator, step motor) were powered with 5‐cell stack producing 3 mW at 1.3 V. [ABSTRACT FROM AUTHOR]

A disposable electrochemical paper‐based analytical device was constructed based on use of sequential analysis with multiplexed working electrodes and applied for the determination of glucose, creatinine, and uric acid. The device was constructed with 16 microfluidic channels, with 16 working electrodes arranged in four set with four components surrounding the sample injection hole. In addition, a commercial multiplexing module was used, which allowed for multiplexing of the 16 working electrodes. This design allowed for radial and homogeneous sample elution to each sensing spot for high throughput analysis. In the multiplexed determinations, distinct electrochemical procedures were employed for each analyte. Furthermore, each working electrode spot was modified to increase the respective analytical signals. For glucose detection, the sensor was based on electron mediation by ferrocenecarboxylic acid over the modified surface with glucose oxidase. The principle for creatinine detection was based on electrochemical reduction of non‐complexed Fe3+ in excess after complex formation between Fe3+ and creatinine in the chemical step. The anodic peak current responses for uric acid detection increased due to working electrode surface modification with carbon black nanoparticles. In the multiplexed analysis, the device provided limits of detection of 0.120 mmol L−1, 0.084 mmol L−1, and 0.012 mmol L−1 for glucose, creatinine, and uric acid, respectively. The developed device was successfully applied in the analyses of real urine samples. [ABSTRACT FROM AUTHOR]

Monomeric sarcosine oxidase (mSOx) fusion with the silaffin peptide, R5, designed previously for easy protein production in low resource areas, was used in a biosilification process to form an enzyme layer electrode biosensor. mSOx is a low activity enzyme (10–20 U/mg) requiring high amounts of enzyme to obtain an amperometric biosensor signal, in the clinically useful range <1 mM sarcosine, especially since the Km is >10 mM. An amperometric biosensor model was fitted to experimental data to investigate dynamic range. mSOx constructs were designed with 6H (6×histidine) and R5 (silaffin) peptide tags and compared with native mSOx. Glutaraldehyde (GA) cross‐linked proteins retained ∼5 % activity for mSOx and mSOx‐6H and only 0.5 % for mSOx‐R5. In contrast R5 catalysed biosilification on (3‐mercaptopropyl) trimethoxysilane (MPTMS) and tetramethyl orthosilicate (TMOS) particles created a 'self‐immobilisation' matrix retaining 40 % and 76 % activity respectively. The TMOS matrix produced a thick layer (>500 μm) on a glassy carbon electrode with a mediated current due to sarcosine in the clinical range for sarcosinemia (0–1 mM). The mSOx‐R5 fusion protein was also used to catalyse biosilification in the presence of creatinase and creatininase, entrapping all three enzymes. A mediated GC enzyme linked current was obtained with dynamic range available for creatinine determination of 0.1–2 mM for an enzyme layer ∼800 nm. [ABSTRACT FROM AUTHOR]

In this study, a new glucose biosensor was fabricated by immobilizing glucose oxidase (GOx) on platinum nanoparticles (Pt NPs) decorated reduced graphene oxide (rGO)/Zn‐MOF‐74 hybrid nanomaterial. Herein, the biosensor fused the advantages of rGO with those of porous Zn‐MOF and conductive Pt NPs. This has not only enlarged the surface area and porosity for the efficient GOx immobilization and faster mass transport, but also provided favorable electrochemical features such as high current density, remarkable electron mobility through metal nanoparticles, and improved electron transfer between the components. The GOx‐rGO/Pt NPs@Zn‐MOF‐74 coated electrode displayed a linear measurement range for glucose from 0.006 to 6 mM, with a detection limit of 1.8 μM (S/N: 3) and sensitivity of 64.51 μA mM−1 cm−2. The amperometric response of the enzyme biosensor demonstrated the typical behavior of Michaelis‐Menten kinetics. The obtained satisfying sensitivity and measurement range enabled fast and accurate glucose measurement in cherry juice using the fabricated biosensor. The water‐stable Zn‐MOF‐74 demonstrated higher enzyme loading capacity and can be potent supporting material for biosensor construction. [ABSTRACT FROM AUTHOR]

Chitosan based reasonably stable membranes were prepared as polymeric electrolyte and separator for enzymatic fuel cell applications. Glucose oxidase (GOx) bioanode centered biofuel cell with the developed chitosan membranes performed much better in stability with high current densities than that of the biofuel cell utilizing a 125 μ‐thick perfluorosulfonic acid‐type membrane (i. e. Nafion® 115). Proposed chitosan membrane structural stability was enhanced by employing cellulosic support materials and chemical crosslinking. The effects of pH, buffer type, buffer concentration, temperature on the manufactured chitosan membranes along with the biofuel cell system were investigated. The biofuel cell operation parameters were optimized for the current density and stability aspects and more than 3 mA cm−2 current density was acquired from the cell at optimum conditions. Operational half‐life of the chitosan membrane was found as higher than the half‐life of the GOx immobilized bioanode. Therefore, this result indicates that chitosan membrane structural stability was not a limiting issue for the biofuel cell lifespan. [ABSTRACT FROM AUTHOR]

In a tannic acid assisted synthesis of mesoporous TiO2, tannic acid was used as a cost effective and non‐toxic template for pore formation. Meanwhile, a gold nanoparticles (Au NPs) deposited TiO2 nanocomposite was coated on an indium tin oxide electrode for the fabrication of a photoelectrochemical (PEC) biosensing system. Upon the formation of anatase structure, the electrode was coated with MoS2 for effective visible light absorption. The mesoporous structure led to an enhanced surface area by improving Au NPs and glucose oxidase adsorption. Incorporation of Au NPs led to an enhanced photonic efficiency due to the generation of Schottky barriers. The obtained nanocomposite was used for the light‐driven, real‐time, and selective PEC glucose sensing. Under visible light irradiation, the enzyme immobilized electrodes yielded significant photocurrent improvement owing to the releasing electron donor H2O2. The obtained PEC biosensor demonstrated acceptable reproducibility and stability with a sensitivity of 4.42 μA mM−1 cm−2 and a low detection limit of 1.2 μM glucose. Also, the linear measurement range was found to be 0.004–1.75 mM glucose. The results indicated that the proposed production method of mesoporous TiO2 will pave the way for a green chemistry based porous material production, along with the extension of the implementation of semiconductors in PEC biosensing systems. [ABSTRACT FROM AUTHOR]

Textile dyes appear as an important class of compounds that has become a matter of public concern and a serious challenge for scientists and environmentalists due to their large‐scale production and extensive application. In this work, a non‐conventional competitive‐type amperometric immunosensor was successfully developed for detection of the textile dye Disperse Orange 1 (DO1). The DO1 was magnetically captured and separated from the sample solution using magnetic particles (MP) functionalized with the antibody anti‐DO1 and with HRP and gold electrodes were modified with the conjugate DO1‐BSA. Molecules of DO1 immobilized on the electrode surface and DO1 captured by MP compete for antibody binding sites. As a result, the amperometric signal decreases with increasing target DO1 concentration at the capture step, because this decreases, the attachment between the HRP coated MP and the electrode. This strategy allowed us to determine DO1 at the low detection limit of 0.87 ng mL−1 with great specificity. Also, there were good recoveries for detection of the textile dye in river water samples without the need of sample pre‐treatment. The competitive amperometric immunosensor shows applicability for the determination of small molecules that cannot be determined by conventional competitive or sandwich immunosensors. [ABSTRACT FROM AUTHOR]

In a tannic acid assisted synthesis of mesoporous TiO2, tannic acid was used as a cost effective and non‐toxic template for pore formation. Meanwhile, a gold nanoparticles (Au NPs) deposited TiO2 nanocomposite was coated on an indium tin oxide electrode for the fabrication of a photoelectrochemical (PEC) biosensing system. Upon the formation of anatase structure, the electrode was coated with MoS2 for effective visible light absorption. The mesoporous structure led to an enhanced surface area by improving Au NPs and glucose oxidase adsorption. Incorporation of Au NPs led to an enhanced photonic efficiency due to the generation of Schottky barriers. The obtained nanocomposite was used for the light‐driven, real‐time, and selective PEC glucose sensing. Under visible light irradiation, the enzyme immobilized electrodes yielded significant photocurrent improvement owing to the releasing electron donor H2O2. The obtained PEC biosensor demonstrated acceptable reproducibility and stability with a sensitivity of 4.42 μA mM−1 cm−2 and a low detection limit of 1.2 μM glucose. Also, the linear measurement range was found to be 0.004–1.75 mM glucose. The results indicated that the proposed production method of mesoporous TiO2 will pave the way for a green chemistry based porous material production, along with the extension of the implementation of semiconductors in PEC biosensing systems. [ABSTRACT FROM AUTHOR]

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL−1 MWCNTs in a solution of 2.00 mg mL−1 GOx+1.00 mg mL−1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at −0.100 V in the presence of 5.0×10−4 M hydroquinone, was (4.8±0.3) μA mM−1 (r2=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk. [ABSTRACT FROM AUTHOR]

A high power enzymatic fuel‐cell was anticipated by using a recently developed glucose oxidase (GOx) immobilized bio‐anode, a conventional platinum−carbon based cathode and a popular high performance 125 μ‐thick perfluorosulfonic acid‐type proton exchange membrane (i. e. Nafion® 115). Unexpected current density decay from 2.13 mA cm−2 to 0.28 mA cm−2 was observed within 2 hours. Polarization measurements and AC impedance analysis indicated that loss of performance was linked to the membrane behavior. Ion exchange between buffer solution and membrane was perceived as the main cause for the fast performance loss. Saturation of the membrane with the cation in the buffer solution diminished proton transfer needed for cathode reaction. Charge transfer resistances, obtained from AC impedance data, increased with time substantially due to cation exchange within membrane. Replacement of membrane with the same enzyme electrode and cathode has resulted 100 % current density recovery on the fuel cell performance. It was concluded that a membrane, not affected by the buffer cations, was required for successful enzymatic fuel cell applications. [ABSTRACT FROM AUTHOR]

One of the major problems in amperometric biosensors based on detection of H2O2 produced by enzymatic reaction between oxidase enzymes and substrate is the interference of redox active compounds such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). To minimize these interferences, sodium bismuthate was used for the first time as an insoluble pre‐oxidant in the flow injection (FI) amperometric glucose biosensor at a Glucose oxidase (GOx) immobilized Pt/Pd bimetallic modified pre‐anodized pencil graphite electrode (p.PGE). In this context, these interfering compounds were injected into a flow injection analysis (FIA) system using an injector which was filled with NaBiO3. Thus, these interferents were converted into their redox inactive oxidized forms before reaching the electrode in the flow cell. While glucose was not influenced by the pre‐oxidant in the injector, the huge oxidation peak currents of the interferents decreased significantly in the biosensor. FI amperometric current time curves showed that the AA, DA and UA were minimized by 96 %, 86 %, and 98 % respectively, in the presence of an equivalent concentration of interferences in a 1.0 mM glucose solution. The proposed FI amperometric glucose biosensor exhibits a wide linear range (0.01–10 mM, R2=0.9994) with a detection limit of 2.4×10−3 mM. Glucose levels in the artificial serum and two real samples were successfully determined using the fabricated FI amperometric biosensor. [ABSTRACT FROM AUTHOR]

One of the major problems in amperometric biosensors based on detection of H2O2 produced by enzymatic reaction between oxidase enzymes and substrate is the interference of redox active compounds such as ascorbic acid (AA), dopamine (DA) and uric acid (UA). To minimize these interferences, sodium bismuthate was used for the first time as an insoluble pre‐oxidant in the flow injection (FI) amperometric glucose biosensor at a Glucose oxidase (GOx) immobilized Pt/Pd bimetallic modified pre‐anodized pencil graphite electrode (p.PGE). In this context, these interfering compounds were injected into a flow injection analysis (FIA) system using an injector which was filled with NaBiO3. Thus, these interferents were converted into their redox inactive oxidized forms before reaching the electrode in the flow cell. While glucose was not influenced by the pre‐oxidant in the injector, the huge oxidation peak currents of the interferents decreased significantly in the biosensor. FI amperometric current time curves showed that the AA, DA and UA were minimized by 96 %, 86 %, and 98 % respectively, in the presence of an equivalent concentration of interferences in a 1.0 mM glucose solution. The proposed FI amperometric glucose biosensor exhibits a wide linear range (0.01–10 mM, R2=0.9994) with a detection limit of 2.4×10−3 mM. Glucose levels in the artificial serum and two real samples were successfully determined using the fabricated FI amperometric biosensor. [ABSTRACT FROM AUTHOR]

The development of a simple directly wearable approach for the rapid, specific and sensitive determination of biomarkers is of great importance to a variety of biomedical applications. Dental floss can provide a unique device platform for sensing of oral biomarkers. We show here for the first time the development of a smart dental floss for biosensing of glucose. The sensor was made by painting carbon graphite ink and Ag/AgCl ink on dental floss. Via the immobilization of glucose oxidase, we show the detection of glucose with a detection range of 0.048 mM to 19.5 mM and a response time of about 2 min. It is expected that our results could provide new exciting opportunities for the development of various flexible smart sensing devices in oral health applications. [ABSTRACT FROM AUTHOR]

Electron transfer (ET) reactions in bioelectrocatalysis of enzymes at electrode surfaces require not only the efficient immobilization, but also highly conductive nanostructured platform, which allows for retaining its bioactivity and structural conformation. The novel architecture of spatially separated electrochemically reduced graphene oxide (ERGO) by multi‐walled carbon nanotubes functionalized with 4‐(pyrrole‐1‐yl) benzoic acid (MWCNT/PyBA) with the accurate porous structure could be an alternative for earlier approaches to the construction of bioelectrocatalytic systems with rapid diffusion of reagents from the solution to the enzyme molecule. The formation of ERGO/MWCNT/PyBA system was confirmed by electrochemical, spectroscopic and microscopic methods. The cyclic voltammetry experiments revealed that the presence of ERGO in the conductive material affects the electronic communication between the enzyme molecule and modified electrode surface greatly improving its ET properties resulting in a double increase of the heterogeneous ET rate constant value (ks=6.5 s−1). The fabricated glucose oxidase based biosensor sensitively detects glucose, therefore, ERGO/MWCNT/PyBA architecture could provide a novel and efficient platform for immobilization of redox enzymes. [ABSTRACT FROM AUTHOR]

This work presents a single analytical system able to perform high‐throughput determinations of different pharmaceutical molecules on screen‐printed electrodes (SPEs) assembled on a batch‐injection analysis (BIA) cell. Two types of SPEs, both containing a carbon conductive ink as working electrode, were selected for the determination of levamisole (LVM) in aqueous and sodium levothyroxine (NaLVT) in hydroethanolic media. The main analytical characteristics of the proposed system for both examples are high precision (RSD <3.8 %, n=10), low detection limits (submicromolar range), and high sample‐throughput (>150 h−1) using a single SPE, demonstrating the extended lifetime of such sensors, which are adequate for routine pharmaceutical analysis. The proposed analytical system requires battery‐powered portable devices, including potentiostat and reader, electronic micropipette, BIA cell and SPEs, and can be applied for a wide range of pharmaceutical molecules. In case of analyte adsorption on electrode surface, fast electrode cleaning can be supplied by external stirring easily adapted to the cell, which is demonstrated in this work for NaLVT determination. [ABSTRACT FROM AUTHOR]

In this work, three types of electrodes suitable for amperometric glucose biosensors were designed. One type of electrode was based on bio‐selective layer of polypyrrole/(glucose oxidase)/(Prussian Blue) (Ppy/GOx/PB) and it was used as a control electrode regarding to which electrochemical properties of two other types of electrodes were compared. During the formation of Prussian blue layers graphite electrodes were additionally modified by Ni‐hexacyanoferrate (NiHCF) and by Co‐hexacyanoferrate (CoHCF) in order to design Ppy/GOx/PB‐NiHCF and Ppy/GOx/PB‐CoHCF electrodes, respectively. Some physicochemical characteristics of all three types of electrodes were evaluated and compared. The Ppy/GOx/PB‐NiHCF electrode showed wider linear range of the calibration curve than Ppy/GOx/PB and Ppy/GOx/PB‐CoHCF electrodes. The effect of temperature on analytical performance of the Ppy/GOx/PB‐NiHCF based biosensor has been evaluated and activation energy of enzyme catalysed reaction has been calculated within the temperature range of 15 °C to 30 °C. [ABSTRACT FROM AUTHOR]

Thermosensitive microgel particles based on the polymeric network synthesized from N‐isopropylacrylamide, sodium acrylate and N,N′‐bisacryloylcystine have been functionalized with aminoferrocene, a mediatior, and a model enzyme‐glucose oxidase (GOx). The product was very stable. A thin coating of that material has been successfully attached to the glassy carbon electrode surface to form a sensing layer. A temperature increase to a value higher than the volume phase transition temperature led to a substantial increase in the amperometric signal. That behavior was well switchable. The amperometric signal was linearly dependent on glucose concentration in the physiological concentration range. It appeared that the synthesized and functionalized microgel was a kind of microreactor and might be very useful for the construction of the platforms that can enhance the activity of enzymes in biosensors. [ABSTRACT FROM AUTHOR]

A new non‐enzymatic glucose sensor based gold nanoparticle (AuNp)‐chitosan (Ch/AuNp) was developed in this study. Gold nanoparticles were synthesized by using the green synthesis method, in which chitosan is used as both reducing and stabilizing agent. Gold nanoparticle surfaces were modified with different molecular agents (4‐mercaptophenyl boronic acid,MPB, and 1‐decanethiol,DT) being sensitive to glucose. Modified gold nanoparticles were immobilized to electrode surfaces and used for the glucose measurements by the potentiometric method. The best working conditions were determined for the glucose measurements. It was found that linear working range is 0.5–30 mM, while limit of detection is 0.3 mM for the glucose measurement of the prepared non‐enzymatic sensor. It was stated that the prepared sensor could be used at least 6 times and glucose response decreased approximately 10.97 % when it is waited for 30 days. Interference effect of some molecules for glucose measurement was investigated and usability of developed sensor was tested in human blood serum. [ABSTRACT FROM AUTHOR]

Nanoparticles and their composites are considered to play a significant role in the development of electrochemical biosensors. In the present work, we have synthesized titanium dioxide (TiO2) nanoparticles comprising poly (3‐hexylthiophene) (PHT) nanohybrid for the fabrication of glucose biosensor. The thin film of hybrid PHT/TiO2 nano‐composite was deposited onto indium‐tin‐oxide (ITO) glass substrate followed by immobilization of glucose oxidase (GOx). The developed sensor was characterized using X‐Ray Diffraction, Fourier Transform Infrared Spectroscopy, UV‐visible spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. The electrochemical response of the nanocomposite coated electrode was studied which shows a quasi‐reversible electrochemical behavior. The experimental conditions for glucose detection were optimized in terms of GOx immobilization time, GOx concentrations, temperature, and pH, in order to obtain maximum sensitivity. Under the optimized experimental conditions, the ITO/TiO2/PHT/GOx sensor probe displays excellent catalytic activity towards glucose with the response time of <10.0 sec, showing its robustness for direct clinical analysis. Chronoamperometry was performed for the quantitative detection of glucose which displays the linear dynamic range between 1–310 mg/dL with the detection limit of 0.62±0.02 mg/dL. The developed biosensor was successfully applied to detect glucose in human saliva samples without any pre‐treatment step. Importantly, the detection range of the designed biosensor was in range of normal and clinical salivary glucose levels. Interferences due to nontarget biochemicals was investigated and long term stability of the sensor probe was evaluated. [ABSTRACT FROM AUTHOR]

Abstract: Acid functionalized multi‐walled carbon nanotubes (f‐MWCNTs) were decorated with Au and Fe2O3 nanoparticles (FeONPs) and deposited on glassy carbon electrode (GCE). The resulting hybrid Au/Fe2O3/f‐MWCNTs/GCE electrode and the one further modified by glucose oxidase were compared for detection of glucose. FeONPs and Au were deposited on the f‐MWCNTs by sonication‐assisted precipitation and deposition‐precipitation methods, respectively. The morphology and structure of the samples were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction and Raman spectroscopy. A uniform distribution of FeONPs with an average size of 5 nm increased the surface area of functionalized nanotubes from 39 to 50 m2/g. The electrocatalytic glucose detection on the modified electrodes was evaluated using cyclic voltammetry and chronoamperometry in 0.1 M phosphate buffer solution at pH 7.0. The non‐enzymatic and enzymatic electrodes show sensitivity of 512.4 and 921.4 mA/mM.cm2 and detection limit of 1.7 and 0.9 mM, respectively. The enzymatic and enzymeless electrodes retained more than 70 % and 80 % of their cathodic faradic current after 70 days, respectively. The sensing mechanism of the non‐enzymatic biosensor is described through the reaction of glucose with iron (III) ions, while in the case of enzymatic electrode, glucose is oxidized by glucose oxidase. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a simple, convenient approach to the fabrication of microband electrodes and microband biosensors based on screen printing technology. These devices were printed in a three‐electrode configuration on one strip; a silver/silver chloride electrode and carbon counter electrode served as reference and counter electrodes respectively. The working electrodes were fabricated by screen‐printing a water‐based carbon ink containing cobalt phthalocyanine for hydrogen peroxide detection. These were converted into a glucose microband biosensor by the addition of glucose oxidase into the carbon ink. In this paper, we discuss the fabrication and application of glucose microband electrodes for the determination of glucose in cell media. The dimensions (100–400 microns) of the microband electrodes result in radial diffusion, which results in steady state responses in the absence of stirring. The microband biosensors were investigated in cell media containing different concentrations of glucose using chronoamperometry. The device shows linearity for glucose determination in the range 0.5 mM to 2.5 mM in cell media. The screen‐printed microband biosensor design holds promise as a generic platform for future applications in cell toxicity studies. [ABSTRACT FROM AUTHOR]

Abstract: A newly developed amperometric glucose biosensor based on graphite rod (GR) working electrode modified with biocomposite consisting of poly (pyrrole‐2‐carboxylic acid) (PCPy) particles and enzyme glucose oxidase (GOx) was investigated. The PCPy particles were synthesized by chemical oxidative polymerization technique using H2O2 as initiator of polymerization reaction and modified covalently with the GOx (PCPy‐GOx) after activation of carboxyl groups located on the particles surface with a mixture of N‐(3‐dimethylaminopropyl)‐N′‐ethylcarbodiimide hydrochloride (EDC) and N‐hydroxysuccinimide (NHS). Then the PCPy‐GOx biocomposite was dispersed in a buffer solution containing a certain amount of bovine serum albumin (BSA). The resulting biocomposite suspension was adsorbed the on GR electrode surface with subsequent solvent airing and chemical cross‐linking of the proteins with glutaraldehyde vapour (GR/PCPy‐GOx). It was determined that the current response of the GR/PCPy‐GOx electrodes to glucose measured at +300 mV vs Cl reference electrode was influenced by the duration of the PCPy particles synthesis, pH of the GOx solution used for the PCPy particles modification and the amount of immobilized PCPy‐GOx biocomposite. An optimal pH of buffer solution for operation of the biosensor was found to be 8.0. Detection limit was determined as 0.039 mmol L−1 according signal to noise ratio (S/N: 3). The proposed glucose biosensor was tested in human serum samples. [ABSTRACT FROM AUTHOR]

Abstract: The rational design of electrocatalysts with abundant active sites and high conductivity is the key to the development of glucose sensors. Herein, we report the preparation of a Cu2+‐doped C3N4 supported on multi‐walled carbon nanotube (MWCNT) network (Cu2+‐C3N4/MWCNT) as a highly efficient non‐enzymatic glucose sensing system. The morphologic and structural investigations using TEM, AFM, XRD, XPS, EPR, and i‐V response indicate the successful insertion of Cu2+ into the C3N4 inter‐layers via an out‐of‐plane on‐top configuration and the consequent exfoliation of C3N4 layers without forming CuO or Cu(OH)2. Such material can act as an electrocatalyst for glucose electrooxidation, and MWCNT can greatly reduce the charge transfer resistance and enhances activity. An optimised Cu2+ doping level (12 wt%) in Cu2+‐C3N4/MWCNT was established to realise high sensitivity towards glucose sensing (929 mA/M cm2), large linear range (0.5 μM∼12 mM), low detection limit (0.35 μM), and short response time (<3 s). Excellent selectivity against the interferents, such as dopamine, ascorbic acid, sucrose, and lactose, is also observed. In the blood serum tests, as‐prepared glucose sensor reports comparable and reproducible results, demonstrating its practical potentials. [ABSTRACT FROM AUTHOR]

Abstract: The development of O2 tolerant glucose sensors based on the highly active and robust enzyme glucose oxidase is still a major challenge because of the competition between the natural electron acceptor O2 and free‐diffusing or polymer‐bound artificial electron acceptors. We report the fabrication of a glucose oxidase based bioanode that operates under ambient conditions. Combination of this bioanode with a bilirubin oxidase based biocathode enabled the fabrication of a glucose/O2 powered biofuel cell as integrated power source for a self‐powered device. Glucose oxidase at the anode was electrically wired via a low‐potential redox polymer, i. e. a Toluidine Blue‐modified poly(methacrylate) based polymer, that ensures a high open‐circuit voltage of the biofuel cell but also catalytically reduces O2 and hence requires a protection shield for measurements under ambient conditions. The sensing layer was deposited by means of potential pulse‐assisted co‐deposition of glucose oxidase within the redox polymer and was protected from O2 by a newly proposed lactate oxidase/catalase based O2 removal layer that was immobilized within a hydrophilic redox‐silent polymer on top of the sensing layer. The protection layer was powered by lactate, a natural component in human blood. The biofuel cell exhibited an OCV of ca. 650 mV and the power output was dependent on the glucose concentration without any interference from oxygen providing that lactate was available in the analyte solution. [ABSTRACT FROM AUTHOR]

Abstract: Graphite electrodes are modified with a redox polymer, [Os(4,4′‐dimethoxy‐2,2′‐bipyridine)2(polyvinylimidazole)10Cl]+ (E°′=−0.02 V vs Ag/AgCl (3 M KCl), crosslinked with a flavin adenine dinucleotide glucose dehydrogenase and multi‐walled carbon nanotubes for electrocatalytic oxidation of glucose. The enzyme electrodes provide 52 % higher current density, 1.22±0.10 mA cm−2 in 50 mM phosphate‐buffered saline at 37 °C containing 5 mM glucose, when component amounts are optimised using a design of experiments approach compared to one‐factor‐at‐a‐time. Current densities of 0.84±0.15 mA cm−2 were achieved in the presence of oxygen for these enzyme electrodes. Further analysis of the model allowed for altering of the electrode components while maintaining similar current densities, 0.78±0.11 mA cm−2 with 34 % less enzyme. Application of the cost‐effective anodes in membrane‐less enzymatic fuel cells is demonstrated by connection to cathodes prepared by co‐immobilisation of [Os(2,2′‐bipyridine)2(polyvinylimidazole)10Cl+] redox polymer, Myrothecium verrucaria bilirubin oxidase and multi‐walled carbon nanotubes on graphite electrodes. Power densities of up to 285 μW cm−2, 146 μW cm−2 and 60 μW cm−2 are achieved in pseudo‐physiological buffer, artificial plasma and human plasma respectively, showing promise for in vivo or ex vivo power generation under these conditions. [ABSTRACT FROM AUTHOR]

Abstract: Paper‐based analytical devices, which are suited to point‐of‐care diagnostics and on‐site detection because of cheap price and portability, have attracted increasing attention for improving global health and in other applications. Here, we constructed one carbon nanotube paper‐based electrode (CNTPE) for the detection of neurochemicals in brain microdialysate. CNTPE was directly fabricated through filter depositing CNT dispersion onto the surface of filter paper. The fabricated CNTPE have good electrochemical performance with advantage of CNT, which not only facilitate ascorbic acid (AA) oxidation, also could as a good platform to functionalize. As a proof, we demonstrate that the CNTPE act as electrode to detect AA directly and detect glucose with further modified CNTPE through electrodeposited Prussian blue (PB). The results show that the easily prepared CNTPE can be used for the selective measurement of AA without interference from dopamine and other electrochemical active substances; what's more, PB and glucose oxidase (GOx) modified CNTPE has good performance towards the specific detection of glucose. Therefore, we believe that CNTPE would have great potential application in detection of chemicals to understand the function of brain. [ABSTRACT FROM AUTHOR]

A novel glucose biosensor was constructed through the immobilization of glucose oxidase (GOx) on gold nanoparticles (Au NPs) deposited, and chemically reduced graphene oxide (rGO) nanocomposite. In the synthesis, tannic acid (TA) was used for the reduction of both graphene oxide, and Au3+ to rGO, and Au NPs, respectively. Also, by harnessing the π-π interaction between graphene oxide and TA, and protein-TA interaction, a novel nanocomposite for the fabrication of a third generation biosensor was successfully constructed. Upon the oxidation of TA to quinone, which is easily reducible at the negative potential range, enhanced electron transfer was obtained. The cyclic voltammetry (CV) results demonstrated a pair of well-defined and quasi-reversible redox peaks of active site molecule of GOx. The biosensor exhibited a linear response to glucose concentrations varying from 2 to 10 mM with a sensitivity of 18.73 mA mM−1 cm−2. The fabricated biosensor was used for the determination of glucose in beverages. [ABSTRACT FROM AUTHOR]

In this study, we have carried out electrodeposition of tantalum (Ta) nanostructures on pencil lead electrode in non-aqueous media at room temperature by applying a constant potential. The deposited Ta on pencil lead was examined for the catalytic effect regarding hydrogen peroxide (H2O2) reduction with voltammetry and amperometry. Ta/pencil lead electrode exhibited amperometric sensitivity of 0.317 μA mM−1 cm−2 and fast response time of 0.75 s, where selective detection of H2O2 was fulfilled without interruption from common electroactive biomaterials such as O2, uric acid, ascorbic acid, dopamine, acetamidophenol, and glucose. For practical applications, the dynamic concentration changes of H2O2 during catalase and glucose oxidase-involved reactions, either eliminating or producing H2O2, were successfully traced in real time with as-prepared electrode. From the kinetics study for catalase and glucose oxidase, we evaluated Michaelis constants ( Kmapp) as 7.8 mM for catalase and 37 mM for glucose oxidase, respectively. [ABSTRACT FROM AUTHOR]

Glucose oxidase (GOx) is an enzyme, which is used for the development of enzymatic biofuel cells. Therefore in this research redox competition mode of scanning electrochemical microscopy (RC-SECM) was applied for the investigation of glucose oxidase (GOx) catalyzed reaction kinetics. The GOx was immobilized by glutaraldehyde on substrates of different electrical conductivity: (i) gold covered glass was used as conducting substrate and (ii) plastic poly(methyl methacrylate) was used as non-conducting substrate. Current vs distance dependencies were registered by SECM at different concentrations of glucose in the absence of redox mediator. The potential of −750 mV vs Ag/AgCl(3 M KCl) was applied to the microelectrode (ME), which was used as a probe in SECM, in order to register oxygen reduction current. Consumption of oxygen by the GOx based layer was evaluated according to principles determined by Michaelis-Menten kinetics. Apparent Michaelis constants K M(app.) were calculated from the dependencies of current vs glucose concentration. In both these cases the K M(app.) value increased when the distance between ME and enzyme modified surface was increasing from 10 to 30 μm, while the K M(app.) value decreased by increasing the distance from 30 to 60 μm. [ABSTRACT FROM AUTHOR]

In this work, a photoamperometric glucose biosensor based on glucose oxidase (GODx) was developed in flow injection analysis (FIA) system using ZnS-CdS quantum dot (QD) modified multiwalled carbon nanotube/glassy carbon electrode (ZnS-CdS/MWCNT/GCE). Cyclic voltammograms of the proposed electrode (GODx/ZnS-CdS/MWCNT/GCE) showed a pair of well-defined reversible redox peak attributing that direct electron transfer between the protein and electrode. The current of the reduction peak became more cathodic in the presence of O2 due to the electrocatalytic activity of the electrode towards the reduction of dissolved O2, but reduction current shifted to a less negative value upon addition of glucose in the solution. The obtained CV currents were affected by the irradiation of the electrode surface. Thus, the photoelectrochemical biosensing of glucose in the FIA system was studied by monitoring of the changes in the electrocatalyzed reduction peak current of dissolved O2 at the proposed electrode dependent on glucose concentration. The proposed photoelectrochemical FIA method has a linear response to glucose ranging from of 0.01 to 1.0 mM with detection limit of 3.0 μM under optimized conditions. Photoelectrochemical biosensor was successfully fabricated in FIA system for selective, sensitive and repeatable detection of glucose and has been satisfactorily applied to determination of glucose in real sample. [ABSTRACT FROM AUTHOR]

Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy-layer formation and the linear interval was extended up to 19.9 mmol L−1 after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM−1 cm−2, the limit of detection - 0.20 mmol L−1. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples. [ABSTRACT FROM AUTHOR]

A new fast, cheap and efficient epoxy-amine immobilized enzyme reactor (IMER) is demonstrated. Polyethyleneimine (PEI) was used as the curing agent of an epoxy resin (bisphenol-A diglycidyl ether (BADGE)) in order to introduce a high number of reactive -NH2 groups at the substrate. A ratio mixture of 3:2 PEI:BADGE (w/w) was shown to be the most suitable for curing, taking into account the number of immobilization sites and the resistance of the material towards channeling. Electrochemical measurements made by a three electrode system, adapted at the IMER, showed that the Km value for immobilized glucose oxidase (GOx) was half the value commonly reported for GOx immobilized at PEI derived substrates. The IMER response decreased by around 41 % after one week of intense usage. Even so, the remaining activity was sufficient for quantifications of approximately 0.1 mmol L−1, merely requiring a new calibration of the reactor before its utilization. The developed system was applied to D-glucose quantification of beverage samples, requiring an injection volume of only 10 μL and a flow rate of 150 μL min−1 (almost 60 samples per hour). Low detection and quantification limits (1.94 and 5.89 μmol L−1, respectively) and a wide linear range (from 8 μmol L−1 to 2 mmol L−1) were also found, which are useful characteristics for quality control analysis. [ABSTRACT FROM AUTHOR]

Herein, a uniform porous highly oriented pyrolytic graphite (HOPG) electrode was prepared via diazonium salt assisted electrochemical etching method and firstly utilized to immobilize enzymes for the construction of a high-performance glucose biosensor. The formation mechanism and morphology structure of the porous HOPG electrode were investigated using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations. The glucose oxidase (GOx) was functionalized with pyrene groups and then immobilized on the porous HOPG substrate through π-π stacking interactions and hydrogen bonding. As a result, eight times higher oxidation current density can be obtained for a given glucose concentration for the porous HOPG electrode than the pristine one. Detection limit of 5 μM for glucose was achieved for the as-fabricated biosensor. It was obtained that 78 % biocatalytical activity of GOx can be retained after the pyrene functionalization and 65.7 % one can even be maintained after four weeks, which confirmed the high efficiency and good stability of the as-prepared biosensor. What's more, it can be anticipated that various other enzymes can be loaded into this porous HOPG platform using the same enzyme modification methodology for the construction of efficient biosensors. [ABSTRACT FROM AUTHOR]

Biofuel cells based on electrocatalytic oxidation of NADH and reduction of H2O2 have been prepared using carbon fiber electrodes functionalized with graphene nano-flakes. The electrochemical oxidation of NADH was catalyzed by Meldola's blue (MB), while the reduction of H2O2 was catalyzed by hemin, both catalysts were adsorbed on the graphene flakes due to their π-π staking. In the next set of experiments, the MB- and hemin-electrodes were additionally modified with glucose dehydrogenase (GDH) and glucose oxidase (GOx), respectively. The enzyme catalyzed reactions in the presence of glucose, NAD+ and O2 resulted in the production of NADH and H2O2 in situ. The produced NADH and H2O2 were oxidized and reduced, respectively, at the bioelectrocatalytic electrodes, thus producing voltage and current generated by the biofuel cell. The enzyme-based biofuel cells operated in a human serum solution modelling an implantable device powered from the natural biofluid. Finally, two enzyme-based biofuel cell connected in series and operating in the serum solution produced electrical power sufficient for activation of an electronic watch used as an example device. [ABSTRACT FROM AUTHOR]