Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO₂ nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM^?1 cm^?2, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication.

Chitosan matrices modified with carbon nanotubes for use in mediated microbial biosensing

We describe a microbial sensor based on Pseudomonas fluorescens cells that was prepared by modifying graphite electrodes with chitosan and carbon nanotubes. Chronoamperometry was performed at +0.3 V in the presence of hexacyanoferrate as a mediator and revealed a good response to glucose which is linear in the 1.0 to 5.0 mM concentration range. Linearity was defined by the equation of y?=?102.120x?13.279 (R ²?=?0.998) (y shows current density as nA.cm^?2 and x shows glucose concentration in mM). The effect of the CNTs on the response was compared to that of electrodes made without CNTs.

Arsenic-Centered Molybdenum–Vanadium Polyoxometalate Supporting Three Copper Complexes

A novel compound [HMo ₈ ^VI V ₆ ^V As^VO₄₂][Cu(2,2′-bpy)₂]₂[Cu(2,2′-bpy)]·2H₂O (2,2′-bpy = 2,2′-bipyridine) 1 has been hydrothermally synthesized and structurally characterized by elemental analyses, infrared spectroscopy, ultraviolet spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and single crystal X-ray diffraction. Crystal structure analysis reveals that compound 1 is a bi-capped As/Mo/V Keggin polyoxometalate tri-supported copper complexes, and exhibits an extended three-dimensional supramolecular network via hydrogen-bonding and π–π stacking interactions. The electrochemical and magnetic properties of compound 1 have been studied.     

Glucose biosensor based on a platinum electrode modified with rhodium nanoparticles and with glucose oxidase immobilized on gold nanoparticles

We have developed an enzymatic glucose biosensor that is based on a flat platinum electrode which was covered with electrophoretically deposited rhodium (Rh) nanoparticles and then sintered to form a large surface area. The biosensor was obtained by depositing glucose oxidase (GOx), Nafion, and gold nanoparticles (AuNPs) on the Rh electrode. The electrical potential and the fractions of Nafion and GOx were optimized. The resulting biosensor has a very high sensitivity (68.1 μA mM^?1 cm^?2) and good linearity in the range from 0.05 to 15 mM (r?=?0.989). The limit of detection is as low as 0.03 mM (at an SNR of 3). The glucose biosensor also is quite selective and is not interfered by electroactive substances including ascorbic acid, uric acid and acetaminophen. The lifespan is up to 90 days. It was applied to the determination of glucose in blood serum, and the results compare very well with those obtained with a clinical analyzer.

An enzymatic glucose biosensor based on a glassy carbon electrode modified with manganese dioxide nanowires

A glassy carbon electrode was modified with β-manganese dioxide (β-MnO₂), and glucose oxidase (GOx) was immobilized on its surface. The β-MnO₂ nanowires were prepared by a hydrothermal method and characterized by scanning electron microscopy and powder X-ray diffraction. They were then dispersed in Nafion solution and cast on the glassy carbon electrode (GCE) to form an electrode modified with β-MnO₂ nanowires that exhibits improved sensitivity toward hydrogen peroxide. If GOx is immobilized in the surface, the β-MnO₂ acts as a mediator, and Nafion as a polymer backbone. The fabrication process was characterized by electrochemical impedance spectroscopy, and the sensor and its materials were characterized by cyclic voltammetry and amperometry. The biosensor enables amperometric detection of glucose with a sensitivity of 38.2 μA?·?mM^?1?·?cm^?2, and a response time of?<?5 s. This study also demonstrates the feasibility of realizing inexpensive, reliable, and high-performance biosensors using MnO₂ nanowires.

Direct electrodeposition of a biocomposite consisting of reduced graphene oxide, chitosan and glucose oxidase on a glassy carbon electrode for direct sensing of glucose

We have electrodeposited a composite film consisting of graphene oxide, chitosan and glucose oxidase directly on a glassy carbon electrode (GCE) through electrochemical reduction of a solution of the 3 components under controlled direct electrical potential. The procedure takes only several minutes, and the thickness of the resulting film is uniform and controllable. The GOx has uncompromised bioactivity and exhibits reversible 2-proton and 2-electron transfer in presence of glucose. It therefore can be used amperometric sensing of glucose. The biosensor has a fast response (<3 s), a detection limit of 0.4 μM (which is 50-fold lower compared to the biosensor prepared by drop-casting solutions of the same materials onto an GCE), and a linear response in the 0.4 μM to 2 mM concentration range (which again is much better than that of the biosensor prepared by the drop-casting method). Other features include high reproducibility, long-time storage stability, and satisfactory selectivity. We presume that the direct single-step electrodeposition of this nanocomposite offers a promising approach towards novel types of highly sensitive and stable electrochemical biosensors.

Novel glucose biosensor based on a glassy carbon electrode modified with hollow gold nanoparticles and glucose oxidase

A novel glucose biosensor is presented as that based on a glassy carbon electrode modified with hollow gold nanoparticles (HGNs) and glucose oxidase. The sensor exhibits a better differential pulse voltammetric response towards glucose than the one based on conventional gold nanoparticles of the same size. This is attributed to the good biological conductivity and biocompatibility of HGNs. Under the optimal conditions, the sensor displays a linear range from 2.0?×?10^?6 to 4.6?×?10^?5?M of glucose, with a detection limit of 1.6?×?10^?6?M (S/N?=?3). Good reproducibility, stability and no interference make this biosensor applicable to the determination of glucose in samples such as sports drinks.

Mediated electron transfer of cellobiose dehydrogenase and glucose oxidase at osmium polymer-modified nanoporous gold electrodes

Nanoporous and planar gold electrodes were utilised as supports for the redox enzymes Aspergillus niger glucose oxidase (GOx) and Corynascus thermophilus cellobiose dehydrogenase (CtCDH). Electrodes modified with hydrogels containing enzyme, Os-redox polymers and the cross-linking agent poly(ethylene glycol)diglycidyl ether were used as biosensors for the determination of glucose and lactose. Limits of detection of 6.0 (±0.4), 16.0 (±0.1) and 2.0 (±0.1) μM were obtained for CtCDH-modified lactose and glucose biosensors and GOx-modified glucose biosensors, respectively, at nanoporous gold electrodes. Biofuel cells composed of GOx- and CtCDH-modified gold electrodes were utilised as anodes, together with Myrothecium verrucaria bilirubin oxidase (MvBOD) or Melanocarpus albomyces laccase as cathodes, in biofuel cells. A maximum power density of 41 μW/cm² was obtained for a CtCDH/MvBOD biofuel cell in 5 mM lactose and O₂-saturated buffer (pH 7.4, 0.1 M phosphate, 150 mM NaCl).     

Mediatorless amperometric bienzyme glucose biosensor based on horseradish peroxidase and glucose oxidase cross-linked to multiwall carbon nanotubes

We report on a bienzyme-channeling sensor for sensing glucose without the aid of mediator. It was fabricated by cross-linking horseradish peroxidase (HRP) and glucose oxidase (GOx) on a glassy carbon electrode modified with multiwalled carbon nanotubes (MWNTs). The bienzyme was cross-linked with the MWNTs by glutaraldehyde and bovine serum albumin. The MWNTs were employed to accelerate the electron transfer between immobilized HRP and electrode. Glucose was sensed by amperometric reduction of enzymatically generated H₂O₂ at an applied voltage of ?50 mV (vs. Ag/AgCl). Factors influencing the preparation and performance of the bienzyme electrode were investigated in detail. The biosensor exhibited a fast and linear response to glucose in the concentration range from 0.4 to 15 mM, with a detection limit of 0.4 mM. The sensor exhibited good selectivity and durability, with a long-term relative standard deviation of <5 %. Analysis of glucose-spiked human serum samples yielded recoveries between 96 and 101 %.

Direct electrochemistry of glucose oxidase and sensing glucose using a screen-printed carbon electrode modified with graphite nanosheets and zinc oxide nanoparticles

We have studied the direct electrochemistry of glucose oxidase (GOx) immobilized on electrochemically fabricated graphite nanosheets (GNs) and zinc oxide nanoparticles (ZnO) that were deposited on a screen printed carbon electrode (SPCE). The GNs/ZnO composite was characterized by using scanning electron microscopy and elemental analysis. The GOx immobilized on the modified electrode shows a well-defined redox couple at a formal potential of ?0.4 V. The enhanced direct electrochemistry of GOx (compared to electrodes without ZnO or without GNs) indicates a fast electron transfer at this kind of electrode, with a heterogeneous electron transfer rate constant (K_s) of 3.75 s^?1. The fast electron transfer is attributed to the high conductivity and large edge plane defects of GNs and good conductivity of ZnO-NPs. The modified electrode displays a linear response to glucose in concentrations from 0.3 to 4.5 mM, and the sensitivity is 30.07 μA mM^?1 cm^?2. The sensor exhibits a high selectivity, good repeatability and reproducibility, and long term stability. Figure

Graphical representation for the fabrication of GNs/ZnO composite modified SPCE and the immobilization of GOx     

Layered-double-hydroxide-modified electrodes: electroanalytical applications

Two-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example.

Amperometric nonenzymatic glucose sensor based on a glassy carbon electrode modified with a nanocomposite made from nickel(II) hydroxide nanoplates and carbon nanofibers

We report on a highly sensitive and selective nonenzymatic glucose sensor based on a glassy carbon electrode modified with a composite prepared from nickel(II) hydroxide nanoplates and carbon nanofibers. The nanocomposite was characterized by scanning electron microscopy and powder X-ray diffraction. Electrodes modified with pure Ni(OH)₂ and with the nanocomposite were characterized by electrochemical impedance spectroscopy. Cyclic voltammetric and amperometric methods were used to investigate the catalytic properties of the modified electrodes for glucose electrooxidation in strongly alkaline solution. The sensor exhibits a wide linear range (from 0.001 to 1.2 mM), a low detection limit (0.76 μM), fast response time (< 5 s), high sensitivity (1038.6 μA?·?mM^?1?·?cm^?2), good reproducibility, and long operational stability. Application of the nonenzymatic sensor for monitoring glucose in real samples was also demonstrated.

Disposable amperometric biosensor for the determination of tyramine using plasma amino oxidase

We have developed screen–printed carbon electrodes for the determination of tyramine (Tyr) via plasma amine oxidase. The enzyme was immobilized on the carbon working electrode by cross–linking it with bovine serum albumin using glutaraldehyde. The employment of the mediator hydroxymethylferrocene lowers the working potential to +260 mV (vs. a screen–printed Ag/AgCl reference electrode). The effects of pH, potential and mediator concentration were optimized and resulted in reproducibility and repeatability values of 8.6 % and 8.7 %, respectively. Response is linear in the range from 2 to 164 μM, and the limit of detection is 2.0?±?0.18 μM. The effects of potentially interfering biogenic amines such as putrescine, cadaverine, histamine, spermine, spermidine and tryptamine were also evaluated. The biosensor was successfully applied to the determination of Tyr in cheese.

Carbon fiber microelectrodes modified with carbon nanotubes as a new support for immobilization of glucose oxidase

Carboxylated carbon nanotubes were coated onto carbon microfiber electrodes to create a micron-scale bioelectrode. This material has a high surface area and can serve as a support for immobilization of enzymes such as glucose oxidase. A typical carbon nanotube loading of 13???g?cm^?1 yields a coating thickness of 17???m and a 2000-fold increase in surface capacitance. The modified electrode was further coated with a biocatalytic hydrogel composed of a conductive redox polymer, glucose oxidase, and a crosslinker to create a glucose bioelectrode. The current density on oxidation of glucose is 16.6?mA?cm^?2 at 0.5?V (vs. Ag/AgCl) in oxygen-free glucose solution. We consider this approach to be useful for designing and characterizing surface treatments for carbon mats and papers by mimicking their local microenvironment.

Reagentless amperometric glucose biosensor based on the immobilization of glucose oxidase on a ferrocene@NaY zeolite composite

Ferrocene (Fc) was encapsulated in the cavities of a NaY zeolite by vapor diffusion via sublimation at below 100?°C. The resulting Fc@NaY zeolite composite was investigated by power X-ray diffraction, diffuse reflectance UV?Cvis and FT-IR spectroscopy, and by cyclic voltammetry. The results indicated that Fc was encapsulated into the zeolite whose microporous structure had remained intact. The Fc in the silica matrix had retained its electroactivity and did not leach out. A glucose biosensor was obtained by immobilization of the modified zeolite and glucose oxidase on a carbon paste electrode. It displays a linear response to glucose (from 0.8???M to 4.0?mM), a detection limit of 0.2???M, and a response time of 4?s. The good performance of the biosensor is ascribed to the biocompatibility of the zeolite and presence of Fc which facilitates the electron transfer from the enzyme to the surface of the electrode.

Direct electron transfer of glucose oxidase promoted by carbon nanotubes is without value in certain mediator-free applications

We have investigated the direct electron transfer (DET) promoted by carbon nanotubes (CNTs) on an electrode containing immobilized glucose oxidase (GOx) with the aim to develop a third-generation glucose biosensor and a mediator-free glucose biofuel cell anode. GOx was immobilized via chitosan (CS) on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWCNTs). Cyclic voltammetric revealed that the GOx on the surface of such an electrode is unable to simultaneously demonstrate DET with the electrode and to retain its catalytic activity towards glucose, although the MWCNTs alone can promote electron transfer between GOx and electrode. This is interpreted in terms of two types of GOx on the surface, the distribution and properties of which are quite different. The first type exhibits DET capability that results from the collaboration of MWCNTs and metal impurities, but is unable to catalyze the oxidation of glucose. The second type maintains its glucose-specific catalytic capability in the presence of a mediator, which can be enhanced by MWCNTs, but cannot undergo DET with the electrode. As a result, the MWCNTs are capable of promoting the electron transfer, but this is without value in some mediator-free applications such as in third-generation glucose biosensors and in mediator-free anodes for glucose biofuel cells.

Highly sensitive uric acid biosensor based on individual zinc oxide micro/nanowires

We describe the use of individual zinc oxide (ZnO) micro/nanowires in an electrochemical biosensor for uric acid. The wires were synthesized by chemical vapor deposition and possess uniform morphology and high crystallinity as revealed by scanning electron microscopy, X-ray diffraction, and photoluminescence studies. The enzyme uricase was then immobilized on the surface of the ZnO micro/nanowires by physical adsorption, and this was proven by Raman spectroscopy and fluorescence microscopy. The resulting uric acid biosensor undergoes fast electron transfer between the active site of the enzyme and the surface of the electrode. It displays high sensitivity (89.74 μA cm^?2 mM^?1) and a wide linear analytical range (between 0.1 mM and 0.59 mM concentrations of uric acid). This study also demonstrates the potential of the use of individual ZnO micro/nanowires for the construction of highly sensitive nano-sized biosensors.

Amperometric determination of sulfite using screen-printed electrodes modified with metallic nanoparticles

We report on the amperometric determination of sulfite using screen-printed carbon electrodes (SPCEs) modified with gold and silver nanoparticles that were deposited on the electrode to improve the capabilities of detection. The electrode is fairly selective and responds to sulfite with an oxidation current (at 300 mV and pH 6) in the 9.80 to 83.33 μM concentration range. The precision in terms of repeatability and reproducibility is 14.4 % and 10.7 % in the case of SPCEs modified by gold nanoparticles. The method was applied to the determination of sulfite in drinking water, pickle juice and vinegar. Recoveries ranged from 96 % to 104 %.

Optical determination of glucose and hydrogen peroxide using a nanocomposite prepared from glucose oxidase and magnetite nanoparticles immobilized on graphene oxide

Fe₃O₄ nanoparticles were deposited on sheets of graphene oxide (GO) by a precipitation method, and glucose oxidase (GOx) was then immobilized on this material to produce a GOx/Fe₃O₄/GO magnetic nanocomposite containing crosslinked enzyme clusters. The 3-component composite functions as a binary enzyme that was employed in a photometric method for the determination of glucose and hydrogen peroxide where the GOx/Fe₃O₄/GO nanoparticles cause the generation of H₂O₂ which, in turn, oxidize the substrate N,N-diethyl-p-phenylenediamine to form a purple product with an absorption maximum at 550 nm. The absorbance at 550 nm can be correlated to the concentration of glucose and/or hydrogen peroxide. Under optimized conditions, the calibration plot is linear in the 0.5 to 600 μM glucose concentration range, and the detection limit is 0.2 μM. The respective plot for H₂O₂ ranges from 0.1 to 10 μM, and the detection limit is 0.04 μM. The method was successfully applied to the determination of glucose in human serum samples. The GOx/Fe₃O₄/GO nanoparticles are reusable.

A screen-printed disposable biosensor for selective determination of putrescine

We have developed screen-printed carbon electrodes for the determination of putrescine (Put) via the enzyme monoamine oxidase that was immobilized on the surface of the electrode by cross-linking it with bovine serum albumin using glutaraldehyde. A mixture of 5 % of tetrathiofulvalene (TTF) and carbon ink was used for the fabrication of the screen-printed working electrode. Put was amperometrically detected by measurement of the current due to the oxidation of the mediator TTF. The use of TTF lowers the working potential to +250 mV (vs. a screen-printed Ag/AgCl reference electrode). Response is linear in the range from 16 to 101 μM, and the detection limit is 17.2?±?4.6 μM, with a reproducibility of 9.6 % (n?=?4) in terms of relative standard deviation. The effects of potentially interfering biogenic amines such as cadaverine, histamine, spermine, spermidine and tryptamine were also evaluated. The biosensor was successfully applied to the determination of Put in zucchini and anchovies.