Glucose Oxidase Surface Research Articles

Conductive single enzyme nanocomposites prepared by in-situ growth of nanoscale polyaniline for high performance enzymatic bioelectrode

Enzyme-based electrochemical biosensors hold great promise for applications in health/disease monitoring, drug discovery, and environmental monitoring. However, inherently non-conductive nature of proteinaceous enzymes often hampers effective electron transfer at enzyme-electrode interface, limiting biosensor performance of enzyme bioelectrodes. To address this problem, we present an approach to synthesize polyaniline (PAN)-based conductive single enzyme nanocomposites of glucose oxidase (GOx) (denoted as PAN-GOx). To prevent multimerization of enzymes during nanocomposite synthesis and enable single enzyme wrapping, we activate GOx surface with phenylamine groups based on the programmed diffusion of reactants in the reaction solution. Subsequent in-situ polymerization enables the synthesis of nanoscale conductive PAN layer (∼2.7 nm thickness) grafted from individual GOx molecule. PAN-GOx retains 83% and 74% of its specific activity and catalytic efficiency, respectively, compared to free GOx, while demonstrating a ∼500% improved conductivity. Furthermore, PAN-GOx-based glucose biosensors show an approximately 16- and 3-fold higher sensitivity compared to biosensors prepared by using free GOx and a mixture of PAN and GOx, respectively. This study provides a facile method to fabricate conductive single enzyme nanocomposites with enhanced electron transfer, which can potentially be further modified and/or compounded with conductive materials for demonstrating high performance enzymatic bioelectrodes.

Simultaneously enhancing the selectivity and stability of enzymatic probes via bio-imprinting technology

The application of enzymes in sensing has been severely limited due to their low stability. Moreover, some enzymes could catalyze diverse substrates, meaning their out-standing selectivity is still facing challenges in sensing systems containing multiple substrates. Therefore, their catalytic selectivity and stability enhancement is still of great significance for fabrication of biosensors with excellent sensing performance. However, few works for simultaneously enhancing the selectivity and stability of enzymes have been reported yet. Herein, an exquisite molecular coat prepared by molecular imprinting polymers, which could simultaneously enhance the selectivity and conformational stability of enzymes is directly weaved on the surface of glucose oxidase (GOx) immobilized on Ti-NiCo2O4 @Fe3O4-Au nanoarrays. Accordingly, the relative selectivity coefficients K(β-D-glucose/mannose), K(β-D-glucose/xylose) of molecularly imprinted GOx are 803% and 874% higher than that of pristine GOx, respectively. Moreover, the as-prepared biosensors show improved stability and sensitivity (LOD = 20 μM) with a wide detection range of 0.2–8 mM in practical β-D-glucose detection. Impressively, after consecutive glucose detection for five times, only a slight decrease (3.46%) of signal could be observed, indicating that the as-prepared biosensor with superior stability is reusable in practical sensing applications.

The construction of molecularly imprinted electrochemical biosensor for selective glucose sensing based on the synergistic enzyme-enzyme mimic catalytic system.

It is generally accepted that glucose oxidase (GOx) shows unique specificity in β-d-glucose catalysis. However, it has been found that GOx can catalyze diverse monosaccharides. Therefore, the sensing accuracy for glucose biosensors using GOx as probes will be largely compromised by the presence of other monosaccharides. Herein, multifunctional bi-nanospheres (Fe3O4@Au NCs), which show both peroxidase-like and catalase-like catalytic activities in different working conditions, are successfully constructed and served as desirable platform with huge surface area for the immobilization of large amount of GOx probes. In acidic environment, hydroxyl radicals could be generated via the cascaded catalysis of β-d-glucose by Fe3O4@Au-GOx, and then employed to initiate the polymerization of boric acid derivative to prepare molecularly imprinted polymers (MIPs) on the surface of GOx using β-d-glucose as template. Then, the molecularly imprinted GOx are immobilized on the surface of highly oriented pyrolytic graphite (HOPG) electrode and an electrochemical biosensor (Fe3O4@Au-GOx-HOPG) for glucose sensing is successfully obtained. Interestingly, the as-prepared biosensors could selectively detect glucose in the range of 10.0μM - 5.0mM with a LOD=5.0μM with the help of MIPs, which is comparable or better than other glucose sensors reported recently.

Oxygen self-supplied enzyme nanogels for tumor targeting with amplified synergistic starvation and photodynamic therapy

Tumor tissues need vast supply of nutrients and energy to sustain the rapid proliferation of cancer cells. Cutting off the glucose supply represents a promising cancer therapy approach. Herein, a tumor tissue-targeted enzyme nanogel (rGCP nanogel) with self-supply oxygen capability was developed. The enzyme nanogel synergistically enhanced starvation therapy and photodynamic therapy (PDT) to mitigate the rapid proliferation of cancer cells. The rGCP nanogel was fabricated by copolymerizing two monomers, porphyrin and cancer cells-targeted, Arg-Gly-Asp (RGD), onto the glucose oxidase (GOX) and catalase (CAT) surfaces. The cascade reaction within the rGCP nanogel could efficiently consume intracellular glucose catalyzed by GOX. Concurrently, CAT safely decomposed the produced H2O2 with systemic toxicity to promote oxygen generation and achieved low toxicity starvation therapy. The produced oxygen subsequently facilitated the glucose oxidation reaction and significantly enhanced the generation of cytotoxic singlet oxygen (1O2) in the presence of 660 nm light irradiation. Combining starvation therapy and PDT, the designed enzyme nanogel system presented an amplified synergic cancer therapy effect. This approach potentially paved a new way to fabricate a combinatorial therapy approach by employing cascaded catalytic nanomedicines with good tumor selectivity and efficient anti-cancer effect. Statement of significanceThe performance of starvation and photodynamic therapy (PDT) is usually suppressed by intrinsic tumorous hypoxia. Herein, an oxygen self-supplied and tumor tissue-targeted enzyme nanogel was created by copolymerization of two monomers, porphyrin and cancer cell-targeted Arg-Gly-Asp (RGD), onto the surface of glucose oxidase (GOX) and catalase (CAT), which synergistically enhanced starvation therapy and PDT. Moreover, the enzyme nanogels possessed high stability and could be synthesized straightforwardly. This anti-cancer system provides an approach for constructing a combinatorial therapy approach by employing cascaded catalytic nanomedicine with good tumor selectivity and therapeutic efficacy.

Scanning electrochemical microscopy and electrochemical impedance spectroscopy-based characterization of perforated polycarbonate membrane modified by carbon-nanomaterials and glucose oxidase

In this research, scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS) were applied for the evaluation of surface characteristics of electrochemical (amperometric) biosensor based on two composite structures consisting of perforated polycarbonate membrane modified by carbon-nanomaterials and glucose oxidase. The first structure consisted of the polycarbonate filter membrane, punctured by 400 nm holes (PCM) consequently modified with single walled carbon nanotubes (SWCNT) and graphene oxide (GO) layer (PCM/SWCNT/GO); and the other structure consisted of the same PCM, consequently modified with SWCNT and reduced graphene oxide (rGO) layer (PCM/SWCNT/rGO). These two composite structures were developed and applied in biosensor design. In order to form a biosensing surfaces the PCM/SWCNT/GO and PCM/SWCNT/rGO composite structures were modified by immobilized glucose oxidase (GOx). The surface of GOx modified PCM/SWCNT/GO composite structure (PCM/SWCNT/GO/GOx) was evaluated by SECM redox-competition mode at different glucose concentrations. It was determined that PCM/SWCNT/GO/GOx composite structure is suitable for the design of amperometric glucose biosensors, because SWCNT/GO layer facilitates electron transfer from GOx via the oxidation of formed catalyzed reaction product H 2 O 2 . Therefore, the PCM/SWCNT/GO/GOx structure is a promising material for the design of amperometric glucose biosensors and biofuel cells, which are useful for a wide variety of environmental purposes and green energy production using food-industry waste. • Punctured polycarbonate membrane (PCM) was modified by single walled carbon nanotubes (SWCNT). • PCM/SWCNT-based structure was modified by graphene oxide (GO) or reduced graphene oxide (rGO). • On the surface of PCM/SWCNT/GO and PCM/SWCNT/rGO structures glucose oxidase (GOx) was immobilized. • Scanning electrochemical microscopy (SECM) and impedance spectroscopy (EIS) were applied. • It was determined that PCM/SWCNT/GO/GOx structure is suitable for the design of glucose biosensor.

Enhanced Electrochemical Characteristics of the Glucose Oxidase Bioelectrode Constructed by Carboxyl-Functionalized Mesoporous Carbon.

This research revealed the effect of carboxyl-functionalization on the mesoporous carbon (MC)-fixed glucose oxidase (GOx) for promoting the properties of bioelectrodes. It showed that the oxidation time, temperature and concentration, can significantly affect MC carboxylation. The condition of 2 M ammonium persulfate, 50 °C and 24 h was applied in the study for the successful addition of carboxyl groups to MC, analyzed by FTIR. The nitrogen adsorption isotherms, and X-ray diffraction analysis showed that the carboxylation process slightly changed the physical properties of MC and that the specific surface area and pore size were all well-maintained in MC-COOH. Electrochemical characteristics analysis showed that Nafion/GOx/MC-COOH presented better electrocatalytic activity with greater peak current intensity (1.13-fold of oxidation peak current and 4.98-fold of reduction peak current) compared to Nafion/GOx/MC. Anodic charge-transfer coefficients (α) of GOx/MC-COOH increased to 0.77, implying the favored anodic reaction. Furthermore, the GOx immobilization and enzyme activity in MC-COOH increased 140.72% and 252.74%, leading to the enhanced electroactive GOx surface coverage of Nafion/GOx/MC-COOH electrode (22.92% higher, 1.29 × 10−8 mol cm−2) than the control electrode. Results showed that carboxyl functionalization could increase the amount and activity of immobilized GOx, thereby improving the electrode properties.

Fabrication of Activity-Reporting Glucose Oxidase Nanocapsules with Oxygen-Independent Fluorescence Variation.

Glucose oxidase (GOx) has seen large-scale technological applications, and the determinations of its activity that is directly related to the enzymatic functions are extremely important. However, conventional methods to analyze the enzymatic activity involving high oxygen dependency and indirect redox reactions are usually tedious and restricted in complicated environments. For analyzing enzymatic activity by direct detection of the electron signals from the active centers, mediators are often used for facilitating the electron transfer. Differing from common methods of preparing electron mediators-contained GOx composites, a strategy aiming at remolding of the enzyme itself has been proposed in this work. Cofactor-like molecule 2'-diallyamino-ethyl flavin (DAA-flavin) derived from riboflavin is synthesized and incorporated as cross-linker into the polyacrylamide (PAAm) network around GOx surface by in situ polymerization to obtain enzyme nanocapsules termed as GOx@Fla-c-PAAm. The peripheral polymer shell confines the orientation of GOx and prevents it from denaturing, whereas incorporated DAA-flavin can replace the oxygen as an alternative electron acceptor to interact with the active centers of GOx in the presence of the substrate, thus giving the nanocapsules oxygen-independent characteristics. The introduced unlimited cofactor-like molecules endow the nanocapsules redox-related fluorescence, and the intensity variation is closely correlated with the enzymatic activity. There is a high goodness of fitting ( R2 ∼ 0.990) between the slope of linear fluorescence-time plots and enzymatic activity, thereby making the nanocapsules a reliable activity-reporting enzymatic nanosystem with oxygen-independent fluorescence variation for further extended potential application in biofuel cells and biosensors.

Intramolecular Electron Transfer through Poly-Ferrocenyl Glucose Oxidase Conjugates to Carbon Electrodes: 1. Sensor Sensitivity, Selectivity and Longevity

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

Intramolecular Electron Transfer through Poly-Ferrocenyl Glucose Oxidase Conjugates to Carbon Electrodes: 2. Mechanistic Understanding of Long-Term Stability

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

Polymer-based protein engineering grown ferrocene-containing redox polymers improve current generation in an enzymatic biofuel cell

Enzymatic biofuel cells (EBFCs) are capable of generating electricity from physiologically present fuels making them promising power sources for the future of implantable devices. The potential application of such systems is limited, however, by inefficient current generation. Polymer-based protein engineering (PBPE) offers a unique method to tailor enzyme function through tunable modification of the enzyme surface with functional polymers. In this study, we report on the modification of glucose oxidase (GOX) with ferrocene-containing redox polymers to increase current generation efficiency in an enzyme-modified anode. Poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide) (pFcAc) was grown from covalently attached, water-soluble initiator molecules on the surface of GOX in a “grafting-from” approach using atom transfer radical polymerization (ATRP). The covalently-coupled ferrocene-containing polymers on the enzyme surface promoted the effective “wiring” of the GOX active site to an external electrode. The resulting GOX-pFcAc conjugates generated over an order of magnitude increase in current generation efficiency and a 4-fold increase in maximum EBFC power density (≈1.7µWcm−2) with similar open circuit voltage (0.27V) compared to native GOX when physically adsorbed onto paddle-shaped electrodes made up of electrospun polyacrylonitrile fibers coated with gold nanoparticles and multi-wall carbon nanotubes. The formation of electroactive enzyme-redox polymer conjugates using PBPE represents a powerful new tool for the improvement of mediated enzyme-based bioelectronics without the need for free redox mediators or anode/cathode compartmentalization.

Rational surface silane modification for immobilizing glucose oxidase

Glucose oxidase (GOx) has many significant applications in biosensor and biocatalysis. In this study, we firstly quantitatively analyzed the binding efficiency of (3-aminopropyl) trimethoxysilane (APTES) modified onto the surface of GOx. It was found that the contents of the grafted silane did not significantly influence the relative activities and tertiary structures of all surface modified GOxs. Immobilization ratio and relative activity of all instances of APTES modified GOx increased, compared with those of native enzyme. However, good stability of immobilized GOx at extreme pH and high temperature could only be obtained when modified protein with low binding silane content. At pH 2.0, the immobilized GOx with low binding content showed a more than 600% activity, compared to the free enzyme. Therefore, rational surface modification would be beneficial to improving the activity and stability of immobilized enzyme as well as increasing loading amount.

Chitosan coated on the layers’ glucose oxidase immobilized on cysteamine/Au electrode for use as glucose biosensor

A glucose biosensor was developed via direct immobilization of glucose oxidase (GOD) by self-assembled cysteamine monolayer on Au electrode surface followed by coating chitosan on the surface of electrode. In this work, chitosan film was coated on the surface of GOD as a protection film to ensure the stability and biocompatibility of the constructed glucose biosensor. The different application ranges of sensors were fabricated by immobilizing varied layers of GOD. The modified surface film was characterized by a scanning electron microscope (SEM) and the fabrication process of the biosensor was confirmed through electrochemical impedance spectroscopy (EIS) of ferrocyanide. The performance of cyclic voltammetry (CV) in the absence and presence of 25mM glucose and ferrocenemethanol showed a diffusion-controlled electrode process and reflected the different maximum currents between the different GOD layers. With the developed glucose biosensor, the detection limits of the two linear responses are 49.96μM and 316.8μM with the sensitivities of 8.91μAmM−1cm−2 and 2.93μAmM−1cm−2, respectively. In addition, good stability (up to 30 days) of the developed biosensor was observed. The advantages of this new method for sensors construction was convenient and different width ranges of detection can be obtained by modified varied layers of GOD. The sensor with two layers of enzyme displayed two current linear responses of glucose. The present work provided a simplicity and novelty method for producing biosensors, which may help design enzyme reactors and biosensors in the future.

Preparation of biodegradable and thermoresponsive enzyme–polymer conjugates with controllable bioactivity via RAFT polymerization

The preparation of biodegradable and thermoresponsive enzyme–polymer bioconjugates with controllable enzymatic activity via reversible addition−fragmentation chain transfer (RAFT) polymerization and amidation conjugation reaction is presented. A new 2-mercaptothiazoline ester functionalized RAFT agent with intra-disulfide linkage was synthesized and used as chain transfer agent (CTA) to generate a biocompatible homopolymer, poly(ethyleneglycol) acrylate (polyPEG-A) and a thermoresponsive copolymer of poly(ethyleneglycol) acrylate with di(ethyleneglycol)ethyl ether acrylate [poly(PEG-A-co-DEG-A)]. These biodegradable and thermoresponsive polymers were then conjugated to the surface of glucose oxidase (GOx) under mild condition to afford the biodegradable and thermoresponsive enzyme–polymer conjugates. Cleavage of the polymer chains from the GOx surface obviously recovered the enzymatic activity. The thermoresponsive test of GOx-poly(PEG-A-co-DEG-A) revealed that the bioconjugate exhibited regular enzymatic activity fluctuation upon the temperature change below or above the lower critical solution temperature (LCST). The as-prepared enzyme–polymer conjugates were also characterized using 1H NMR, UV–vis spectroscopy, polyacrylamide gel electrophoresis (PAGE) and biocatalytic activity tests. These smart enzyme–polymer conjugates would envision promising applications in biotechnology and biomedicine.

Towards a reliable and high sensitivity O2-independent glucose sensor based on Ir oxidenanoparticles

The primary goal of this work is the development of a rapidly responding, sensitive, and biocompatible Ir oxide (IrOx)-based glucose sensor that regenerates solely via IrOx-mediation in both O2-free and aerobic environments. An important discovery is that, for films composed of IrOx nanoparticles, Nafion® and glucose oxidase (GOx), a Michaelis–Menten constant (K′m) of 20–30mM is obtained in the case of dual-regeneration (O2 and IrOx), while K′m values are much smaller (3–5mM) when re-oxidation of GOx occurs only through IrOx-mediation. These smaller K′m values indicate that the regeneration of GOx via direct electron transfer to the IrOx nanoparticles is more rapid than to O2. Small K′m values, which are obtained more commonly when Nafion® is not present in the films, are also important for the accurate measurement of low glucose concentrations under hypoglycemic conditions. In this work, the sensing film was also optimized for miniaturization. Depending on the IrOx and GOx surface loadings and the use of sonication before film deposition, the imax values ranged from 5to 225μAcm−2, showing very good sensitivity down to 0.4mM glucose.

Direct electrochemical sensing of glucose using glucose oxidase immobilized on functionalized carbon nanotubes via a novel metal chelate-based affinity method

We report on a novel amperometric glassy carbon biosensing electrode for glucose. It is based on the immobilization of a highly sensitive glucose oxidase (GOx) by affinity interaction on carbon nanotubes (CNTs) functionalized with iminodiacetic acid and metal chelates. The new technique for immobilization is exploiting the affinity of Co(II) ions to the histidine and cysteine moieties on the surface of GOx. The direct electrochemistry of immobilized GOx revealed that the functionalized CNTs greatly improve the direct electron transfer between GOx and the surface of the electrode to give a pair of well-defined and almost reversible redox peaks and undergoes fast heterogeneous electron transfer with a rate constant (k s) of 0.59 s−1. The GOx immobilized in this way fully retained its activity for the oxidation of glucose. The resulting biosensor is capable of detecting glucose at levels as low as 0.01 mM, and has excellent operational stability (with no decrease in the activity of enzyme over a 10 days period). The method of immobilizing GOx is easy and also provides a model technique for potential use with other redox enzymes and proteins.

Comparison of Catalytic Electrochemistry of Glucose Oxidase between Covalently Modified and Freely Diffusing Phenothiazine-Labeled Poly(ethylene oxide) Mediator Systems

The enzyme catalytic reaction is electrochemically compared under a substrate-saturated and diffusion-limited condition between native glucose oxidase (GOx) mixed with phenothiazine-labeled poly(ethylene oxide) (PT-PEO) and GOx-(PT-PEO) hybrid with PT-PEO covalently bonded to lysine residues on the enzyme surface. Although the catalytic current (icat) increases with the ratio of [PT-PEO]/[GOx] in both systems, the dependence of the icat on the molecular weight of PT-PEO is totally different. In the mixed systems, the icat decreases with increasing the molecular weight of PT-PEO, which reflects the decreases in the diffusion coefficient (D) of PT-PEO and the intermolecular electron transfer (ET) rate from FADH2/FADH to PT+-PEO. In the hybrids, on the other hand, the icat reveals a maximum at the molecular weight of 3000 (PT-PEO3000), which originates from the dependence of the intramolecular ET rate from FADH2/FADH to PT+ on the molecular weight of PT-PEO. The greater ET rate is enough to make up for the smaller D of PT groups attached on GOx in the hybrid with PT-PEO3000, yielding to the slightly larger icat than that of the corresponding mixed system. The active local motion of the long and hydrophilic PEO chain, the higher local concentration of PT groups due to their immobilization on the GOx surface, and the simultaneous oxidation of multiple attached PT groups at the electrode are possible reasons for the large ET rate constant of the hybrid systems.

Tris(4,4′-dimethoxy-2,2′-bipyridine)osmium(II), amperometric properties and crystal structure

The complex cation [Os(DMO-bpy) 3] 2+ (DMO-bpy = 4,4′-dimethoxy-2,2′-bipyridine) was prepared as Cl − and PF 6 − salts. Using cyclic voltammetry, the system (glucose oxidase + [Os(DMO-bpy) 3]Cl 2 on graphie electrode), closely approaching the biosensor, was examined. The crystal structure of [Os(DMO-bpy) 3](PF 6) 2, solvate with dimethylformamide, was determined at 293 K. The crystals are triclinic, a = 11.634(4), b = 13.375(6), c = 15.113(7) A ̊ , α = 76.95(4)°, β = 84.29(3)°, γ = 79.67(3)°, space group Pl, Z = 2, R = 0.086 for 3628 reflections. The average OsN distance of 2.052 Å agrees with the value observed in other bpy complexes of Os(II). The N(metal)N bond angles and dihedral angles between the bpy ligands are less distorted as in the crystal of the isostructural Fe(II)_complex with smaller FeN separations of 1.967 Å. The terminal C atoms of CH 3O-substituents are coplanar with the planes of corresponding bpy ligands but the orientation of the vectors of the CO bonds are different. The slight increase in intermolecular contacts and metal…metal separations whe going from the Fe(II) to the Os(II) structure may be explained also by exchange of the N-methyl-2-pyrrolidone solvate molecule in the Fe(II) structure for dimethylformamide in the Os(II) structure. The relation between the molecular geometry of the complex and possible types of interaction of the complex with the glucose oxidase surface is discussed.

Sol-gel derived, ferrocenyl-modified silicate-graphite composite electrode: Wiring of glucose oxidase

A new type of porous, hybrid organic-inorganic material is synthesized and used for direct wiring of active enzymes. The material witnesses a dispersion of graphite powder and redox enzyme incorporated in a multi-functional, ferrocene-, amine- and methyl-modified silicate backbone. Each species in this integrated construction accomplishes a specialized task: 1. (a) the graphite provides conductivity by percolation; 2. (b) the silicate provides the highly crosslinked, rigid backbone which is used to cage the redox enzyme; 3. (c) ferrocene functional groups are responsible for the signal transduction from the active center of the enzyme to the electron conductive surface; 4. (d) amine groups are incorporated for their high affinity for excess negative charges on the surface of glucose oxidase. Also, the combination of methyl and amine groups is advantageous to maintain control over the wetted electroactive section of the electrode. Amperometric sensing of glucose demonstrates the application of this new material.

Wiring of Glucose Oxidase to Carbon Matrices VIA Sol-Gel Derived Redox Modified Silicate

Abstract A new type of porous, composite material is synthesized and used for direct wiring of active enzymes. The material is comprised of a dispersion of graphite powder and redox enzymes incorporated in hybrid, pendant ferrocenyl-, alkylamine- and methyl- modified silicate backbone. Each species in this integrated construction accomplishes a specialized task; the percolating graphite powder provides conductivity, the silicate provides highly crosslinked, rigid backbone, which is used to cage the redox enzymes; ferrocene functional groups are responsible for the signal transduction from the active center of the enzyme to the percolating graphite; amine groups were incorporated for their high affinity to excess negative charges on the surface of glucose oxidase; and finally, the combination of methyl- and amine- groups is advantageous to maintain a control over the thickness of the wetted electroactive section of the electrode. Amperometric sensing of glucose demonstrates the application of this new mate...