Direct electron transfer of PQQ-glucose dehydrogenase at modified carbon nanotubes electrodes

In order to establish efficient enzyme-electrode-contacts for the pyrroloquinoline quinone dependent glucose dehydrogenase (PQQ-GDH) different immobilisation strategies are investigated. Multi-walled carbon nanotubes (MWCNT) on gold electrodes are modified by chemical treatment and by (poly)-aniline derivatives. The electropolymerisation of methoxy-m-anilinesulfonic acid and m-aminobenzoic acid on the MWCNTs allows the covalent coupling of the PQQ-GDH. Such a poly-[ASA-ABA]/MWCNT/Au electrode can achieve current densities of up to 500 μA/cm² at a potential of 100 mV vs. Ag/AgCl. Furthermore investigations with small amounts of free PQQ indicate direct electron transfer between enzyme and electrode.     

Predominating stable adsorption and direct electrochemistry of glucose oxidase on carbon nanotubes by oxygen-containing groups

Stable adsorption and direct electrochemistry of glucose oxidase (GOx) occurred on nitric acid (HNO3)-treated multi-walled carbon nanotubes (MWNTs) instead of as-received MWNTs, demonstrating the critical roles of oxygen-containing groups in stableadsorption and direct electrochemistry of GOx on carbon nanotubes (CNTs).     

Direct electron transfer of glucose oxidase and dual hydrogen peroxide and glucose detection based on water-dispersible carbon nanotubes derivative

A water-dispersible multi-walled carbon nanotubes (MWCNTs) derivative, MWCNTs-1-one-dihydroxypyridine (MWCNTs-Py) was synthesis via Friedel–Crafts chemical acylation. Raman spectra demonstrated the conjugated level of MWCNTs-Py was retained after this chemical modification. MWCNTs-Py showed dual hydrogen peroxide (H₂O₂) and glucose detections without mutual interference by adjusting pH value. It was sensitive to H₂O₂ in acidic solution and displayed the high performances of sensitivity, linear range, response time and stability; meanwhile it did not respond to H₂O₂ in neutral solution. In addition, this positively charged MWCNTs-Py could adsorb glucose oxidase (GOD) by electrostatic attraction. MWCNTs-Py-GOD/GC electrode showed the direct electron transfer (DET) of GOD with a pair of well-defined redox peaks, attesting the bioactivity of GOD was retained due to the non-destroyed immobilization. The high surface coverage of active GOD (3.5 × 10⁻⁹ mol cm⁻²) resulted in exhibiting a good electrocatalytic activity toward glucose. This glucose sensor showed high sensitivity (68.1 μA mM⁻¹ cm⁻²) in a linear range from 3 μM to 7 mM in neutral buffer solution. The proposed sensor could distinguish H₂O₂ and glucose, thus owning high selectivity and reliability.     

Direct electron transfer of glucose oxidase immobilized in an ionic liquid reconstituted cellulose–carbon nanotube matrix

Conductive cellulose-multiwalled carbon nanotube (MWCNT) matrix with a porous structure and good biocompatibility has been prepared using a room temperature ionic liquid (1-ethyl-3-methylimidazolium acetate) as solvent. Glucose oxidase (GOx) was encapsulated in this matrix and thereby immobilized on a glassy carbon surface. The direct electron transfer and electrocatalysis of the encapsulated GOx has been investigated using cyclic voltammetry and chronoamperometry. The GOx exhibited a pair of stable, well defined and nearly symmetric reversible redox peaks. The experimental results also demonstrate that the immobilized GOx retains its biocatalytic activity toward the oxidation of glucose and therefore can be employed in a glucose biosensor. The results show that the bioelectrode modified by the cellulose-MWCNT matrix has potential for use in biosensors and other bioelectronics devices.     

Powerful connection of laccase and carbon nanotubes: Material for mediator-free electron transport on the enzymatic cathode of the biobattery

We describe the preparation of laccase/single-walled carbon nanotube bioconjugates, their application for the modification of electrodes and application of the electrodes as cathodes for the catalytic reduction of oxygen in a hybrid biofuel cell with Zn anode. Carbon nanotubes functionalized with aminoethyl residues, activated and reacted with laccase show high bioelectrocatalytic activity and are promising for the biofuel cell applications. The power density of the cell was 1 mW cm^− 2 at working voltage of 0.8 V. The open circuit voltage of this hybrid cell was as high as 1.5 V.     

Decorating anode with bamboo-like nitrogen-doped carbon nanotubes for microbial fuel cells

Anode electrodes play a key role in generating electricity from microbial fuel cells (MFCs) because they directly affect microbial activities. This communication reports the preparation of nitrogen-doped carbon nanotubes with a bamboo-like nanostructure (Bamboo-NCNTs) by catalytic pyrolysis of ethylene diamine and application of the Bamboo-NCNTs as anode-modifying materials in MFCs. The Bamboo-NCNTs significantly improved performance of an MFC in current production and power output, and reduced internal resistance of the anode compared with conventional CNTs-modified and unmodified anodes. The improved performance could be attributed to the increased active sites induced by multiple joint structures and enhanced biocompatibility originated from nitrogen dopant.     

Direct electrochemistry of glucose oxidase based on its direct immobilization on carbon ionic liquid electrode and glucose sensing

Direct electrochemistry of glucose oxidase (GOx) has been achieved by its direct immobilization on carbon ionic liquid electrode (CILE) with a conductive hydrophobic ionic liquid, 1-butyl pyridinium hexafluophosphate ([BuPy][PF₆]) as binder for the first time. A pair of reversible peaks is exhibited on GOx/CILE by cyclic voltammetry. The peak-to-peak potential separation (ΔE_P) of immobilized GOx is 0.056 V in 0.067 M phosphate buffer solution (pH 6.98) with scan rate of 0.1 V/s. The average surface coverage and the apparent Michaelis–Menten constant are 6.69 × 10⁻¹¹ mol·cm⁻² and 2.47 μM. GOx/CILE shows excellent electrocatalytic activity towards glucose determination in the range of 0.1–800 μM with detection limit of 0.03 μM (S/N = 3). The biosensor has been successfully applied to the determination of glucose in human plasma with the average recoveries between 95.0% and 102.5% for three times determination. The direct electrochemistry of GOx on CILE is achieved without the help of any supporting film or any electron mediator. GOx/CILE is inexpensive, stable, repeatable and easy to be fabricated.     

Biocomposites of covalently linked glucose oxidase on carbon nanotubes for glucose biosensor

The formation of covalently linked composites of multi–walled carbon nanotubes (MWCNT) and glucose oxidase (GOD) with high-function density for use as a biosensing interface is described. The reaction intermediates and the final product were characterized by using FT–IR spectroscopy, and the MWCNT-coated GOD nanocomposites were examined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Interestingly, it was found that the GOD–MWCNT composites are highly water soluble. Electrochemical characterization of the GOD–MWCNT composites that were modified on a glassy carbon electrode shows that the covalently linked GOD retains its bioactivity and can specifically catalyze the oxidation of glucose. The oxidation current shows a linear dependence on the glucose concentration in the solution in the range of 0.5–40 mM with a detection limit of 30 μM and a detection sensitivity of 11.3 μA/mMcm². The present method may provide a way to synthesize MWCNT related composites with other biomolecules and for the construction of enzymatic reaction-based biofuel cells and biosensors. Supported by grants from the National Natural Science Foundation of China (NSFC, No. 20125515; 90206037; 20375016) and the Natural Science Foundation of Jiangsu Province (Grant No. BK 2004210)     

Polymerized ionic liquid-wrapped carbon nanotubes: The promising composites for direct electrochemistry and biosensing of redox protein

Polymerized ionic liquid-wrapped carbon nanotubes (PIL-CNTs) were firstly designed for direct electrochemistry and biosensing of redox proteins. The CNTs were coated successfully with polymerized ionic liquid (PIL) layer, as verified by transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The PIL-CNTs were dispersed better in water and showed superior electrocatalysis toward O₂ and H₂O₂ comparing to pristine CNTs and the mixture of IL monomer and CNTs. With glucose oxidase (GOD) as a protein model, the direct electrochemistry of the redox protein was investigated on the PIL-CNTs modified glassy carbon (GC) electrode and excellent direct electrochemical performance of GOD molecules was observed. The proposed biosensor (GOD/PIL-CNTs/GC electrode) displayed good analytical performance for glucose with linear response up to 6 mM, response sensitivity of 0.853 μA mM⁻¹, good stability and selectivity.     

Direct electron transfer reaction of glucose oxidase at bare silver electrodes and its application in analysis

The direct electron transfer reaction of glucose oxidase (GOx) at a bare silver electrode is verified. The electron transfer number n = 2, electron transfer coefficient α = 0.45 and rate constant of the electrochemical reaction K_s = 0.1 s⁻¹ are obtained. This communication presents a multimolecular adsorption model to explain the properties of the direct electron reaction between GOx and bare silver electrodes. The residual valence force may be an important factor to ensure a direct electron transfer reaction on the bare electrode. On the basis of the experimental fact that only biologically active GOx exhibits electrochemical activity in solution, a facile analytical method for analyzing the active GOx concentration is developed. The results determined correspond very well to that of a spectrometric method.     

Amperometric glucose sensor based on glucose oxidase immobilized on gelatin-multiwalled carbon nanotube modified glassy carbon electrode

We investigated the direct electrochemistry of glucose oxidase (GOx) at gelatin-multiwalled carbon nanotube (GCNT) modified glassy carbon electrode (GCE). GOx was covalently immobilized onto GCNT modified GCE through the well known glutaraldehyde (GAD) chemistry. The immobilized GOx showed a pair of well-defined reversible redox peaks with a formal potential (E⁰′) of ? 0.40 V and a peak to peak separation (ΔE_p) of 47 mV. The surface coverage concentration (Г) of GOx in GCNT/GOx/GAD composite film modified GCE was 3.88 × 10^? 9 mol cm^? 2 which indicates the high enzyme loading. The electron transfer rate constant (k_s) of GOx immobilized onto GCNT was 1.08 s^? 1 which validates a rapid electron transfer processes. The composite film shows linear response towards 6.30 to 20.09 mM glucose. We observed a good sensitivity of 2.47 μA mM^?1 cm^? 2 for glucose at the composite film. The fabricated biosensor displayed two weeks stability. Moreover, it shows no response to 0.5 mM of ascorbic acid (AA), uric acid (UA), acetaminophen (AP), pyruvate (PA) and lactate (LA) which shows its potential application in the determination of glucose from human serum samples. The composite film exhibits excellent recovery for glucose in human serum at physiological pH with good practical applicability.     

Electrochemical Characteristics of Glucose Oxidase Adsorbed at Carbon Nanotubes Modified Electrode with Ionic Liquid as Binder

Multiwall carbon nanotubes (CNTs)‐modified electrode has been prepared by using ionic liquid (IL) as the binder. The as‐prepared CNTs‐IL composite modified electrode has good biocompatibility and is a suitable matrix to immobilize biomolecules. Glucose oxidase (GOx), containing flavin adenine dinucleotide as active site, stably adsorbed on modified electrode surface has resulted in the direct electron transfer. The electron transfer rate of 9.08 s^?1 obtained is much higher than that of GOx adsorbed on the CNTs papers (1.7 s^?1), and the process is more reversible with small redox peak separation of 23 mV. This may be due to the synergetic promotion of CNTs and IL to electron transfer of the protein, especially the IL as the binder, showing better electrochemical properties than that of chitosan and Nafion. Furthermore, GOx adsorbed at the modified electrode exhibits good stability and keeps good electrocatalytic activity to glucose with broad linear range up to 20 mM. Besides, the simple preparation procedure and easy renewability make the system a basis to investigate the electron transfer kinetics and biocatalytic performance of GOx and provide a promising platform for the development of biosensors.     

Mediator-free amperometric determination of glucose based on direct electron transfer between glucose oxidase and an oxidized boron-doped diamond electrode

A mediator-free glucose biosensor, termed a “third-generation biosensor,” was fabricated by immobilizing glucose oxidase (GOD) directly onto an oxidized boron-doped diamond (BDD) electrode. The surface of the oxidized BDD electrode possesses carboxyl groups (as shown by Raman spectra) which covalently cross-link with GOD through glutaraldehyde. Glucose was determined in the absence of a mediator used to transfer electrons between the electrode and enzyme. O₂ has no effect on the electron transfer. The effects of experimental variables (applied potential, pH and cross-link time) were investigated in order to optimize the analytical performance of the amperometric detection method. The resulting biosensor exhibited fast amperometric response (less than 5 s) to glucose. The biosensor provided a linear response to glucose over the range 6.67×10⁻⁵ to 2×10⁻³ mol/L, with a detection limit of 2.31×10⁻⁵ mol/L. The lifetime, reproducibility and measurement repeatability were evaluated and satisfactory results were obtained.     

葡萄糖氧化酶在炭黑上的固定及直接电化学

经红外光谱和电化学测量证明, 用简单的吸附法能将葡萄糖氧化酶(GOx)固定在炭黑(CB)表面. 电化学测量表明, 固定在CB上的GOx能进行准可逆的直接电化学反应, 其式量电位(E0’)为-0.436 V, 在40-150 mV·s-1范围内, 不随扫描速率而变化. 电化学反应速率常数(ks)为0.800 s-1, 比文献报道的大30多倍. 而且, 固定在CB上的GOx能保持其对葡萄糖氧化的生物电催化活性. 即使在保存两周后, 其电催化活性仅下降了5%, 表明固定在CB上的GOx有良好的稳定性.     

Catalysis of the electrochemical oxidation of glucose by glucose oxidase and a single electron cosubstrate: kinetics in viscous solutions

Catalysis of the electrochemical oxidation of glucose by glucose oxidase with a single electron mediator (cosubstrate) may be used to transform mixtures of concentrated industrial sugars. How the high viscosity of such media may affect the enzymatic reaction and the transport of the mediator can be mimicked by addition of large concentrations of sucrose to glucose solutions. Cyclic voltammetry then provides a simple means of investigating the effect of an increased viscosity on the kinetics of the enzymatic reaction and the diffusion of the mediator. The diffusion coefficient of the mediator is decreased 10 times by addition of 1.6 M sucrose. At pH 8, in the presence of the same concentration of sucrose, the catalytic activity of the enzyme towards its substrate is only slightly affected. A 35% decrease of the glucose Michaelis constant is observed. The reaction of the reduced enzyme with the cosubstrate is six times slower and the mediator Michaelis constant undergoes a three-fold increase. It follows that glucose oxidase remains an efficient catalyst in such viscous media.     

Biosensors for determination of glucose with glucose oxidase immobilized on an eggshell membrane

A glucose biosensor using an enzyme-immobilized eggshell membrane and oxygen electrode for glucose determination has been fabricated. Glucose oxidase was covalently immobilized on an eggshell membrane with glutaraldehyde as a cross-linking agent. The glucose biosensor was fabricated by positioning the enzyme-immobilized eggshell membrane on the surface of a dissolved oxygen sensor. The detection scheme was based on the depletion of dissolved oxygen content upon exposure to glucose solution and the decrease in the oxygen level was monitored and related to the glucose concentration. The effect of glutaraldehyde concentration, pH, phosphate buffer concentration and temperature on the response of the glucose biosensor has been studied in detail. Common matrix interferents such as ethanol, d-fructose, citric acid, sodium benzoate, sucrose and l-ascorbic acid did not give significant interference. The resulting sensor exhibited a fast response (100 s), high sensitivity (8.3409 mg L⁻¹ oxygen depletion/mmol L⁻¹ glucose) and good storage stability (85.2% of its initial sensitivity after 4 months). The linear response is 1.0×10⁻⁵ to 1.3×10⁻³ mol L⁻¹ glucose. The glucose content in real samples such as commercial glucose injection preparations and wines was determined, and the results were comparable to the values obtained from a commercial glucose assay kit based on a spectrophotometric method.     

Multi-wall carbon nanotubes supported ruthenium for glucose hydrogenation to sorbitol

Multi-wall carbon nanotubes (MWNTs) supported ruthenium prepared with an impregnation method was used as catalyst in glucose hydrogenation to sorbitol. The effects of ruthenium loading, reaction time, temperature and initial hydrogen pressure on glucose hydrogenation were investigated. Compared with Raney Ni and ruthenium supported on Al₂O₃, SiO₂, Ru/MWNTs showed higher catalytic activity.     

Direct electrochemistry of glucose oxidase entrapped in nano gold particles-ionic liquid-N,N-dimethylformamide composite film on glassy carbon electrode and glucose sensing

The direct electrochemistry of glucose oxidase (GOD) entrapped in nano gold particles (NAs)-N,N-dimethylformamide (DMF)-1-butyl-3-methylimidazolium hexafluophosphate (BMIMPF₆) composite film on a glassy carbon electrode (NAs-DMF-GOD (BMIMPF₆)/GC) has been investigated for first time. The immobilized GOD exhibits a pair of well-defined reversible peaks in 0.050 M pH 5 phosphate solutions (PS), resulting from the redox of flavin adenine dinucleotide (FAD) in GOD. The peak currents are three times as large as those of GOD-NAs-DMF film coated GC electrode (i.e. NAs-DMF-GOD (water)/GC). In addition, the NAs-DMF-GOD (BMIMPF₆) composite material has higher thermal stability than NAs-DMF-GOD (water). Results show that ionic liquid BMIMPF₆, DMF and NAs are requisite for GOD to exhibit a pair of stable and reversible peaks. Without any of them, the peaks of GOD become small and unstable. Upon the addition of glucose, the peak currents of GOD decrease and a new cathodic peak occurs at −0.8 V (versus SCE), which corresponds to the reduction of hydrogen peroxide (H₂O₂) generated by the catalytic oxidation of glucose. The peak current of the new cathodic peak and the glucose concentration show a linear relationship in the ranges of 1.0 × 10⁻⁷ to 1.0 × 10⁻⁶ M and 2.0 × 10⁻⁶ to 2.0 × 10⁻⁵ M. The kinetic parameter I_max of H₂O₂ is estimated to be 1.19 × 10⁻⁶ A and the apparent K_m (Michaelis-Menten constant) for the enzymatic reaction is 3.49 μM. This method has been successfully applied to the determination of glucose in human plasma and beer samples, and the average recoveries are 97.2% and 99%, respectively.     

Study of the nonenzymatic glucose sensor based on highly dispersed Pt nanoparticles supported on carbon nanotubes

An amperometric biosensor for sensitive and selective detection of glucose has been constructed by using highly dispersed Pt nanoparticles supported on carbon nanotubes (Pt-MWCNTs) as sensing interface. The Pt-MWCNTs were synthesized by using the two-step pyrolysis method. This composite shows good electrocatalytic activity towards the oxidation of glucose in alkaline and thus can be used to selectively detect glucose. We found that detection potential and Nafion amount covered on the Pt-MWCNTs modified glassy carbon electrode had considerable influence on the selectivity for amperometric detection of glucose. Under optimal detection conditions (detection potential of 0.0 V versus SCE and 10 μL 1.5% Nafion), selective detection of glucose in the glucose concentration range of 1.0-26.5 mM (correlation coefficient, >0.999) can be performed. The results demonstrate that the Pt-MWCNTs composite is promising for the fabrication of nonenzymatic glucose sensors.