Direct Electrochemistry of Glucose Oxidase on Nail‐like Carbon and Its Biosensing for Glucose

Nail‐like carbon (NLC) was synthesized by a simple hydrothermal method. It was the first time that a novel electrochemical biosensing of glucose was explored based on the glucose oxidase (GOx)‐NLC‐chitosan (CHIT) glassy carbon electrode. Morphology and structure of NLC were characterized by scanning electron microscope; meanwhile the chemical composition was determined by X‐ray diffraction and energy dispersive X‐ray spectroscopy. The cyclic voltammetry of immobilized GOx showed a pair of quasireversible redox peaks with the formal potential (E°′) of ?0.458 V and the peak‐to‐peak potential separation was 47 mV at a scan rate of 100 mV s^?1. The present biosensor has a linear range of glucose from 0.02 to 1.84 mM (correlation coefficient of 0.9991) and detection limit of 0.01 mM (S/N=3). Compared with the previous reports based on the carbon material biosensor, it has a high sensitivity of 165.5 μA mM^?1 cm^?2 and low apparent Michaelis–Menten constant of 0.506 mM. Thus, the NLC may have potential applications in the field of bioelectrochemistry, bioelectronics and biofuels.     

Fabrication of a Highly Sensitive Glucose Biosensor Based on Immobilization of Osmium Complex and Glucose Oxidase onto Carbon Nanotubes Modified Electrode

In this research a novel osmium complex was used as electrocatalyst for electroreduction of oxygen and H₂O₂ in physiological pH solutions. Electroless deposition at a short period of time (60 s), was used for strong and irreversible adsorption of 1,4,8,12‐tetraazacyclotetradecane osmium(III) chloride (Os(III)LCl₂) ClO₄ onto single‐walled carbon nanotubes (SWCNTs) modified GC electrode. The modified electrode shows a pair of well defined and reversible redox couple, Os(IV)/Os(III) at wide pH range (1–8). The glucose biosensor was fabricated by covering a thin film of glucose oxidase onto CNTs/Os‐complex modified electrode. The biosensor can be used successfully for selective detection of glucose based on the decreasing of cathodic peak current of oxygen. The fabricated biosensor shows high sensitivity, 826.3 nA μM^?1cm^?2, low detection limit, 56 nM, fast response time <3 s and wide calibration range 1.0 μM–1.0 mM. The biosensor has been successfully applied to determination of glucose in human plasma. Because of relative low applied potential, the interference from electroactive existing species was minimized, which improved the selectivity of the biosensor. The apparent Michaelis‐Menten constant of GOx on the nanocomposite, 0.91 mM, exhibits excellent bioelectrocatalytic activity of immobilized enzyme toward glucose oxidation. Excellent electrochemical reversibility, high stability, technically simple and possibility of preparation at short period of time are of great advantages of this glucose biosensor.     

Minimally‐invasive Microneedle‐based Biosensor Array for Simultaneous Lactate and Glucose Monitoring in Artificial Interstitial Fluid

Here we report the first mediated pain free microneedle‐based biosensor array for the continuous and simultaneous monitoring of lactate and glucose in artificial interstitial fluid (ISF). The gold surface of the microneedles has been modified by electrodeposition of Au‐multiwalled carbon nanotubes (MWCNTs) and successively by electropolymerization of the redox mediator, methylene blue (MB). Functionalization of the Au‐MWCNTs/polyMB platform with the lactate oxidase (LOX) enzyme (working electrode 1) and with the FAD‐Glucose dehydrogenase (FADGDH) enzyme (working electrode 2) enabled the continuous monitoring of lactate and glucose in the artificial ISF. The lactate biosensor exhibited a high sensitivity (797.4±38.1 μA cm^?2 mM^?1), a good linear range (10–100 μM) with a detection limit of 3 μM. The performance of the glucose biosensor were also good with a sensitivity of 405.2±24.1 μA cm^?2 mM^?1, a linear range between 0.05 and 5 mM and a detection limit of 7 μM. The biosensor array was tested to detect the amount of lactate generated after 100 minutes of cycling exercise (12 mM) and of glucose after a normal meal for a healthy patient (10 mM). The results reveal that the new microneedles‐based biosensor array seems to be a promising tool for the development of real‐time wearable devices with a variety of sport medicine and clinical care applications.     

Direct Electrochemistry of Glucose Oxidase at Reduced Graphene Oxide and β‐Cyclodextrin Composite Modified Electrode and Application for Glucose Biosensing

A simple glucose biosensor has been developed based on direct electrochemistry of glucose oxidase (GOx) immobilized on the reduced graphene oxide (RGO) and β‐cyclodextrin (CD) composite. A well‐defined redox couple of GOx appears with a formal potential of ～?0.459 V at RGO/CD composite. A heterogeneous electron transfer rate constant (K_s) has been calculated for GOx at RGO/CD as 3.8 s^?1. The fabricated biosensor displays a wide response to glucose in the linear concentrations range from 50 µM to 3.0 mM. The sensitivity and limit of detection of the biosensor is estimated as 59.74 µA mM^?1 cm^?2 and 12 µM, respectively.     

Biosensor Based on Self‐Assembling Glucose Oxidase and Dendrimer‐Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

A novel amperometric glucose biosensor based on layer‐by‐layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer‐encapsulated Pt nanoparticles (Pt‐DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt‐DENs layer and an anionic GOx layer. Transmission electron microscopy images and ζ‐potentials proved the formation of layer‐by‐layer nanostructures on carboxyl‐functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt‐DENs toward H₂O₂ and special three‐dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5 μM, a wide linear range of 5 μM–0.65 mM, a short response time (within 5 s), and high sensitivity (30.64 μA mM^?1 cm^?2) and stability (80% remains after 30 days).     

Development of a Glucose Biosensor Using Advanced Electrode Modified by Nanohybrid Composing Chemically Modified Graphene and Ionic Liquid

Nanohybrids of chemically modified graphene (CMG) and ionic liquid (IL) were prepared by sonication to modify the electrode. The modified CMG‐IL electrodes showed a higher current and smaller peak‐to‐peak potential separation than a bare electrode due to the promoted electron transfer rate. Furthermore, the glucose oxidase (GOx) immobilized on the modified electrode displayed direct electron transfer rate and symmetrical redox potentials with a linear relationship at different scan rates. The fabricated GOx/CMG‐IL electrodes were developed selective glucose biosensor with respect to a sensitivity of 0.64 μA mM^?1, detection limit of 0.376 mM, and response time of <5 s.     

Electrochemical Behaviors of Glucose Oxidase Based on Biocatalytic Deposition of Gold Nanoparticles

Coupling nanotechnology with biocatalysis, a highly sensitive glucose biosensor for the study of electrochemical behaviors of glucose oxidase (GOx) was proposed by using monkshoodvine root–bark like carbon (MLC) as the platform for the biocatalytic deposition of AuNPs. The biosensor showed a linear range from 0.25 to 130 μM with a detection limit of 0.1 μM (S/N = 3) towards glucose and sensitivity of 3010 μA/mM. K value was calculated to be 67.4 μM. Furthermore, the proposed AuNPs/GOx–MLC modified pyrolytic graphite electrode (AuNPs/GOx–MLC/PGE) achieved direct electron transfer of GOx. Γ* was calculated to be 2.79 × 10^?11 mol/cm² and k_s was 1.79 s^?1. It also showed a remarkable electrocatalysis towards glucose.     

Preparation of GOD/Sol‐Gel Silica Film on Prussian Blue Modified Electrode for Glucose Biosensor Application

A novel amperometric glucose biosensor was fabricated by in situ incorporating glucose oxidase (GOD) within the sol‐gel silica film on a Prussian blue (PB) modified electrode. The method is simple and controllable, which combined the merits of in situ immobilizing biomolecules in sol‐gel silica film by electrochemical method and the synergic catalysis effects of PB and GOD molecules. Scanning electron microscopy (SEM) showed that the GOD/sol‐gel silica film was homogeneous with a large number of three‐dimensional nanopores, which not only enhanced mass transport, but also maintained the active configuration of the enzyme molecule and prevented the leakage of enzyme, therefore improved the stability and sensitivity of the biosensor. The fabricated biosensor showed fast response time (10 s), high sensitivity (26.6 mA cm^?2 M^?1), long‐term stability, good suppression of interference, and linear range of 0.01 mM–5.8 mM with a low detection limit of 0.94 μM for the detection of glucose. In addition, the biosensor was successfully applied to determine glucose in human serum samples.     

Direct Electrochemistry of Glucose Oxidase Immobilized at a Novel Composite Material β‐Cyclodextrin/poly(4‐aminothiophenol)/Au Nanoparticle Modified Electrode

A novel complex material was fabricated by three steps. In the first step, gold nanoparticle (Au_nano) was prepared with the method of chemistry and dialysis. In the second step, 4‐aminothiophenol (AT) was encapsulated in the cavity of β‐cyclodextrin and formed inclusion complex, cyclodextrin/4‐aminothiophenol (CD/AT). And then inclusion complex was adsorbed to the surface of Au_nano based on the bond of Au‐S interaction. In the last step, a complex material, cyclodextrin/poly(4‐aminothiophenol)‐Au nanoparticles (CD/PAT‐Au_nano) was obtained by the polymerizing in the acid solution initiated by chlorauric acid. The CD/PAT‐Au_nano has spherical nanostructure with the average diameter of 55 nm. Glucose oxidase (GOx) was anchored with this complex material and direct electrochemistry of GOx was achieved. A couple of stable and well‐defined redox peaks were observed with the formal potential (E^0′) of ‐0.488 V (vs. SCE) in a pH 6.98 buffer solution. The GOx modified electrode also exhibited an excellent electrocatalytic activity to the reduction of glucose, a linearity range for determination of glucose is from 0.25 mM to 16.0 mM with a detection limit of 0.09 mM (S/N = 3). This protocol had potential application to fabricate the third‐generation biosensor.     

Minimization of Interferences in Flow Injection Amperometric Glucose Biosensor Based on Oxidation of Enzymatically‐produced H2O2

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.     

Amperometric Glucose Biosensor Based on Rhodium Dioxide‐Modified Carbon Ink

An amperometric method for the determination of glucose using a screen printed carbon electrode is reported. The electrode material was bulk modified with rhodium dioxide and the enzyme glucose oxidase immobilized in a Nafion‐film on the electrode surface and investigated for its ability to serve as a detector of glucose in flow injection analysis. The sensor exhibited a linear increase of the amperometric signal with the concentration of glucose in the range of 1–250 mg L^?1 with a detection limit (evaluated as 3σ) of 0.2 mg L^?1 under optimized flow rate of 0.4 mL min^?1 in 0.1 M phosphate buffer (pH 7.5) carrier. At the potential applied (?0.2 V vs. Ag/AgCl), interferences from redox species present in the sample matrix were negligible. The biosensor reported here retained its activity for more than 40 injections or 4 months of storage at 6 °C. The RSD was determined as 1.8% for a glucose concentration of 25 mg L^?1 (n=5) with a typical response time of about 28 s.     

Magnetite NPs@C with Highly‐Efficient Peroxidase‐Like Catalytic Activity as an Improved Biosensing Strategy for Selective Glucose Detection

This work reports the novel application of carbon‐coated magnetite nanoparticles (mNPs@C) as catalytic nanomaterial included in a composite electrode material (mNPs@C/CPE) taking advantages of their intrinsic peroxidase‐like activity. The nanostructured electrochemical transducer reveals an enhancement of the charge transfer for redox processes involving hydrogen peroxide. Likewise, mNPs@C/CPE demonstrated to be highly selective even at elevated concentrations of ascorbic acid and uric acid, the usual interferents of blood glucose analysis. Upon these remarkable results, the composite matrix was further modified by the addition of glucose oxidase as biocatalyst, in order to obtain a biosensing strategy (GOx/mNPs@C/CPE) with enhanced properties for the electrochemical detection of glucose. GOx/mNPs@C/CPE exhibit a linear range up to 7.5×10^?3 mol L^?1 glucose, comprising the entirely physiological range and incipient pathological values. The average sensitivity obtained at ?0.100 V was (1.62±0.05)×10⁵ nA L mol^?1 (R²=0.9992), the detection limit was 2.0×10^?6 M while the quantification limit was 6.1×10^?6 mol L^?1. The nanostructured biosensor demonstrated to have an excellent performance for glucose detection in human blood serum even for pathological values.     

Electrocatalytic Oxidation of Glucose by the Glucose Oxidase Immobilized in Graphene‐Au‐Nafion Biocomposite

Graphene was successfully prepared and well separated to individual sheets by introducing  SO₃⁻. XRD and TEM were employed to characterize the graphene. UV‐visible absorption spectra indicated that glucose oxidase (GOx) could keep bioactivity well in the graphene‐Au biocomposite. To construct a novel glucose biosensor, graphene, Au and GOx were co‐immobilized in Nafion to further modify a glassy carbon electrode (GCE). Electrochemical measurements were carried out to investigate the catalytic performance of the proposed biosensor. Cyclic voltammograms (CV) showed the biosensor had a typical catalytic oxidation response to glucose. At the applied potential +0.4 V, the biosensor responded rapidly upon the addition of glucose and reached the steady state current in 5 s, with the present of hydroquinone. The linear range is from 15 μM to 5.8 mM, with a detection limit 5 μM (based on the S/N=3). The Michaelis‐Menten constant was calculated to be 4.4 mM according to Lineweaver–Burk equation. In addition, the biosensor exhibits good reproducibility and long‐term stability. Such impressive properties could be ascribed to the synergistic effect of graphene‐Au integration and good biocompatibility of the hybrid material.     

Reduced Graphene Oxide/Pt Nanoparticles/Zn‐MOF‐74 Nanomaterial for a Glucose Biosensor Construction

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.     

A Novel Enzymatic Glucose Biosensor and Nonenzymatic Hydrogen Peroxide Sensor Based on (3‐Aminopropyl) Triethoxysilane Functionalized Reduced Graphene Oxide

In the present study, a novel enzymatic glucose biosensor using glucose oxidase (GOx) immobilized into (3‐aminopropyl) triethoxysilane (APTES) functionalized reduced graphene oxide (rGO‐APTES) and hydrogen peroxide sensor based on rGO‐APTES modified glassy carbon (GC) electrode were fabricated. Nafion (Nf) was used as a protective membrane. For the characterization of the composites, Fourier transform infrared spectroscopy (FTIR), X‐ray powder diffractometer (XRD), and transmission electron microscopy (TEM) were used. The electrochemical properties of the modified electrodes were investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The resulting Nf/rGO‐APTES/GOx/GC and Nf/rGO‐APTES/GC composites showed good electrocatalytical activity toward glucose and H₂O₂, respectively. The Nf/rGO‐APTES/GC electrode exhibited a linear range of H₂O₂ concentration from 0.05 to 15.25 mM with a detection limit (LOD) of 0.017 mM and sensitivity of 124.87 μA mM⁻¹ cm⁻². The Nf/rGO‐APTES/GOx/GC electrode showed a linear range of glucose from 0.02 to 4.340 mM with a LOD of 9 μM and sensitivity of 75.26 μA mM⁻¹ cm⁻². Also, the sensor and biosensor had notable selectivity, repeatability, reproducibility, and storage stability.     

Prussian Blue Modified Carbon Ionic Liquid Electrode: Electrochemical Characterization and Its Application for Hydrogen Peroxide and Glucose Measurements

Prussian blue modified carbon ionic liquid electrodes (PB‐CILEs) were fabricated using chemical and electrochemical procedures. Chemically fabricated PB‐CILE exhibited an excellent sensitivity (0.0866 μA μM^?1), low detection limit (0.01 μM) and two linear ranges (0.01–1 and 1–600 μM) toward hydrogen peroxide. Then, glucose oxidase (GOx) was immobilized on the surface of PB‐CILE to fabricate glucose biosensor using three different procedures involving cross linking with glutaraldehyde (GLU) and bovine serum albumin (BSA), entrapment into the Nafion matrix and covering with a sol‐gel layer. Glucose biosensor fabricated using cross linking procedure showed the best sensitivity (0.0019 μA μM^?1) and operational stability for glucose.     

A Novel Amperometric Glucose Biosensor Based on Fe3O4-Chitosan-β-Cyclodextrin/MWCNTs Nanobiocomposite

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.     

Plasma‐functionalized Highly Aligned CNT‐based Biosensor for Point of Care Determination of Glucose in Human Blood Plasma

In this study, a new method for modification of vertically aligned carbon nanotube arrays (VACNTs) for selective detection of glucose was developed. VACNTs were grown by chemical vapor deposition method on a silicon substrate deposited with alumina as a buffer layer and iron as a catalyst using radio frequency (RF) sputtering and electron beam evaporation, respectively. The surface of the electrode was modified with electrodeposition of polyaniline (PANI) followed by covalent attachment of glucose oxidase (GOx). The electrode was characterized using field emission scanning electron microscopy (FESEM), micro‐Raman spectroscopy, and attenuated total reflectance Fourier transform infrared spectrometer (ATR‐FTIR) techniques. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behavior of the electrode. The fabricated electrode was successfully employed as a point‐of‐care (POC) biosensor for the detection of glucose in human blood plasma. The detection limit was 1.1 μM, and the sensitivity was 620 μA mM^?1 cm^?2 at the linear range of 2–426 μM.     

Glucose biosensor based on new carbon nanotube-gold-titania nano-composites modified glassy carbon electrode

In this paper, a novel biosensor was prepared by immobilizing glucose oxidase （GOx） on carbon nanotube-gold-titania nanocomposites （CNT/Au/TiO2） modified glassy carbon electrode （GCE）. SEM was initially used to investigate the surface morphology of CNT/Au/TiO2 nanocomposites modified GCE, indicating the formation of the nano-porous structure which could readily facilitate the attachment of GOx on the electrode surface. Cyclic voltammogram （CV） and electrochemical impedance spectrum （EIS） were further utilized to explore relevant electrochemical activity on CNT]Au/TiO2 nanocomposites modified GCE. The observations demonstrated that the immobilized GOx could efficiently execute its bioelectrocatalytic activity for the oxidation of glucose. The biosensor exhibited a wider linearity range from 0.1 mmol L-1 to 8 mmol L^-1 glucose with a detection limit of 0.077 mmol L^- 1.     

Avidin and Glucose Oxidase‐non‐covalently Functionalized Multi‐walled Carbon Nanotubes: A New Analytical Tool for Building a Bienzymatic Glucose Biosensor

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.