Electrocatalytic Oxidation Of NADH Research Articles

Layer-by-Layer Assembly of Carbon Nanotubes Modified with Invertase/Glucose Dehydrogenase Cascade for Sucrose/O2 Biofuel Cell

A layer-by-layer (LbL) assembly technique was employed to modify glassy carbon electrodes (GCEs) and screen printed electrodes (SPEs) utilizing multiwalled carbon nanotubes (MWCNTs)/polyelectrolyte binary composites and an enzyme cascade to facilitate efficient electron transfer in sucrose/O2 biofuel cell. In this study, MWCNTs immobilized invertase (INV) and glucose dehydrogenase (GDH) were alternatively assembled upon polyethyleneimine (PEI) and DNA nanocomposites to construct a bioanode. [Ni(phendion)(phen)]Cl2 complex and methylene green (MG) were investigated as redox mediators for electrocatalytic oxidation of NADH at reduced overpotentials. The LbL architecture showed advantages for sequential enzymatic reaction that favored the efficient penetration of substrate and products in a cascade system while MWCNTs facilitated the efficient electron transfer from sucrose oxidation and enhancement of the current density. With a GCE bioanode modified with a MG or Ni complex, the biofuel cell produced a higher power density (μW/cm2) with 145.8% and 130.11% enhancement comparing to a SPE bioanode, respectively. Moreover, the Ni complex modified GCEs and SPEs produced power densities (μW/cm2) 93.7% and 107.0% higher compared to MG modified bioanodes, respectively. The maximum current density of 1400 ± 46 μA/cm2 was obtained with the Ni complex on GCE at an OCP of 604 ± 17 mV with a maximum power density of 405 ± 6 μW/cm2. The LbL assembly showed great feasibility as a simple and efficient way to construct controlled MWCNT-multi-enzyme modified electrodes for biofuel cell applications.

Mediator-Less Electrocatalytic Oxidation of NADH at Oxygen Plasma Treated Screen Printed Carbon Electrodes

Mediator-Less Electrocatalytic Oxidation of NADH at Oxygen Plasma Treated Screen Printed Carbon Electrodes

Facile and stable immobilization of adenine on screen printed carbon electrode assisted by electrogenerated chlorine for electrocatalytic oxidation of NADH

Abstract This work presents a facile method to electrochemically immobilize adenine, which represents an amine-containing model molecule, on screen printed carbon electrode. Various chloride-containing supporting electrolytes can be employed to electrogenerate chlorine for activating the amine functionality to result in a strong covalent bonding on the “preanodized” screen printed carbon electrode. As confirmed by both cyclic voltammetry and X-ray photoelectron spectroscopy, the as-immobilized 2,8-dihydroxyadenine is highly stable and cannot be removed even under ultrasonication. Good electrocatalytic activity towards β-nicotinamide adenine dinucleotide (NADH) oxidation is further demonstrated for its applicability.

Layer-by-Layer Assembled Enzyme Cascade Bioanode for Catalyzing Oxidation of Sucrose

We report here a novel layer-by-layer (LbL) assembled enzyme cascade bioanode incorporated with CNT-invertase and CNT-glucose dehydrogenase for sucrose oxidation in a biofuel cell. Methylene green (MG) was used as redox mediator for electrocatalytic oxidation of NADH at reduced overpotentials on screen printed electrode (SPE). The LbL architecture showed advantages for sequential enzymatic reaction that favored the efficient penetration of substrate and products in a cascade system. The maximum current density and power density achieved were 412 ± 36 μA/cm2 and 85±6μW/cm2.The high current density/power density obtained showed LbL assembly is of great advantage and can be employed as a simple and efficient way to construct enzyme cascade bioanode for biofuel cell applications.

Layer-By-Layer Assembled Carbon Nanotube Immobilized Enzyme Cascade for Sucrose/O2 Biofuel Cell Utilization

A layer by layer (LbL) assemble technique for the first time was employed to modify glassy carbon electrode (GCE) and screen printed electrode (SPE) utilizing multiwalled carbon nanotube (MWCNTs) based polyelectrolytes and enzyme cascade to facilitate efficient electron transfer in Sucrose/O2 biofuel cell. Previously, our group demonstrated layer-by-layer (LbL) assembly in fabrication of carbon nanotube (CNT) immobilized multi-enzyme biosensors for discriminative detection of multiple analytes. In this study, electrostatically interacted CNT-Invertase (INV), CNT-glucose dehydrogenase (GDH, NAD+-dependent) with cushioning bilayers CNT-polyethyleneimine (PEI) and CNT-DNA were alternatively assembled in LbL fashion on SPE (0.2 cm2) and GCE (0.07065 cm2). [Ni(phendion)(phen)]Cl2 complex and methylene green (MG) were investigated as redox mediator for electrocatalytic oxidation of NADH at reduced overpotentials. The LbL architecture showed advantages for sequential enzymatic reaction that favored the efficient penetration of substrate and products in a cascade system while MWCNT facilitated the direct electron transfer from sucrose oxidation and enhancement of the current density. With GCE as modified bioanode using MG and Ni complex, the biofuel cell produced a higher power density (μW/cm2) with 134.4% and 34.3% enhancement comparing with SPE bioanode, respectively. With Ni complex compared modified on GCE and SPE, the biofuel cell produced a higher power density (μW/cm2) with 16.6% and 101.9 % higher comparing with MG modified on GCE and SPE, respectively. The LbL assembly showed great feasibility as a simple and efficient way to construct controlled CNT-multi-enzyme modified electrodes for biofuel cell applications.

Electrocatalytic oxidation of NADH at low overpotential using nanoporous poly(3,4)-ethylenedioxythiophene modified glassy carbon electrode

Nanoporous-poly(3,4)ethylenedioxythiophene (PEDOT) modified glassy carbon electrode (GCE) significantly lowers the overpotential and shows high resistance against fouling while oxidizing β-nicotinamide adenine dinucleotide (NADH). The electrocatalytic behaviour of nanoporous-PEDOT modified GCE was studied using cyclic voltammetry in 0.1M phosphate buffer solution (pH 7.0) containing 5mM NADH. Studies revealed that nanoporous-PEDOT/GCE exhibited strong electrocatalytic activity on the oxidation of NADH with a decreased overpotential of about 0.318V as compared to a bare GCE. In addition, chronoamperometric measurements were studied to understand the electron transfer kinetics of nanoporous-PEDOT/GCE which revealed an average diffusion co-efficient (D) and apparent rate constant (k) of 1.56×10−6cm2s−1 and 1.09×102M−1s−1, respectively. Sensitivity of nanoporous-PEDOT/GCE is measured by amperometric method which showed linear variation in the concentration range between 5 and 45μM at an applied overpotential of 0.5V. Limit of detection (LOD) and sensitivity are found to be 3.8μM and 0.026μA/μM, respectively. While quantifying the sensitivity of the electrode, it is found that the electrode surface fouling towards NADH oxidation decreased to an extent of 85%. Interference study is examined in the presence of ascorbic acid (AA) where a peak separation of more than 0.370V is observed between AA and NADH. Thus, nanoporous-PEDOT/GCE provides a simple platform for the oxidation of NADH at low overpotential with high resistance against fouling and without AA interference.

Enhanced Electrochemical Oxidation of NADH at Carbon Nanotube Electrodes Using Methylene Green: Is Polymerization Necessary?

Carbon nanotubes (CNTs) have been established as an electrocatalytic material for the oxidation of dihydronicotinamide adenine dinucleotide (NADH). Heteroatom doped CNTs, either boron or nitrogen, have been shown to enhance the electrocatalytic oxidation. Methylene green (MG), a well-established redox mediator for NADH oxidation, is shown here to further enhance the electrocatalytic oxidation of NADH at CNTs and nitrogen-doped CNTs (N-CNTs), but the standard technique of electropolymerizing MG on the surface of the electrode attenuates the natural reactivity of the nanotube/MG couple as formed through spontaneous adsorption. Additionally, MG coupled CNT/N-CNTs produces a leveling effect on N-CNTs, eliminating their electrocatalytic enhancement due to nitrogen doping. Nondoped CNTs display a slightly more efficient oxidation of NADH after adsorption of MG, due to an increased hydrophobic character which causes the adsorbed MG to reside slightly closer to the nanotube surface, and thus, facilitates more facile electron transfer between the nanotube/MG redox couple. Investigation of the influence of potential on MG adsorbed onto CNT/N-CNT electrodes allows the detection of MG polymerization, which is initiated at 0.05 V (vs. Hg/Hg2SO4) as an anodic stripping peak, along with the appearance of a reversible surface wave with E1/2 at −1.0 V (0.1 M sodium phosphate buffer pH 7.0).

Optimizing the Electrocatalytic Oxidation of NADH At Nitrogen-Doped Carbon Nanotubes

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Reduced Graphene Oxide and Single-Walled Carbon Nanotubes Composite Material for Electrocatalytic Oxidation of NADH

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Functionalized carbon nanotubes for bioelectrochemical applications: Critical influence of the linker

A series of covalently bonded ferrocene derivatives to carbon nanotubes via either alkyl or poly(ethylene glycol) (PEG) spacers has been prepared and deposited onto glassy carbon electrodes using chitosan as a binder. Evaluation of the effect of spacer arms revealed that the hydrophilic and flexible PEG chain greatly facilitates electron transfer reactions. When adding diaphorase in the composite, effective electrocatalytic oxidation of NADH was achieved. The PEG spacer also permitted an efficient dispersion of the functionalized carbon nanotubes, without additives. In this way, they can be easily incorporated in water-based sol–gel matrices, as illustrated for bioelectrochemical applications with co-immobilized glucose dehydrogenase, diaphorase and NAD+ cofactor.

Amperometric biosensor for NADH and ethanol based on electroreduced graphene oxide–polythionine nanocomposite film

A nanocomposite film is prepared by cyclic voltammetric deposition of electroreduced graphene oxide (ERGO) and polythionine (PTH) on a glassy carbon (GC) electrode. The electrodeposition of ERGO–PTH film is also investigated via the electrochemical quartz crystal microbalance (EQCM) method for more in-depth understanding of the process. The ERGO–PTH nanocomposite film is applied as transducer for facilitated electrocatalytic oxidation of NADH and for the construction of dehydrogenase-based amperometric biosensor. Under optimum conditions, the amperometric detection of NADH provides a wide linear detection range (0.01–3.9mM), a high sensitivity (143μAmM−1cm−2) and a low limit of detection (LOD=0.1μM, S/N=3). With alcohol dehydrogenase (ADH) as a model, we obtain a linear amperometric response of the ADH-modified ERGO–PTH/GC electrode to ethanol concentration from 0.05 to 1.0mM, a sensitivity of 2.8μAmM−1cm−2, and a LOD of 0.3μM (S/N=3).

Electrocatalytic oxidation of NADH using a pencil graphite electrode modified with quercetin

In the present study, the electrocatalytic oxidation of reduced β nicotinamide adenine dinucleotide (NADH) was investigated using a pencil graphite electrode modified with quercetin (PGE/QH2). The PGE/QH2 was prepared through two steps: (i) the pre-treatment of PGE at 1.40V vs. Ag|AgCl|KCl(sat.) in pH 7.0 phosphate buffer containing 0.1M KCl for 60s and (ii) adsorption of QH2 on the PGE via immersion of PGE into a 1.0mM QH2 solution (in ethanol) for 60s. Cyclic voltammetric studies show that the peak potential of NADH oxidation shifts from +500mV at bare PGE to +300mV at PGE/QH2. The electrocatalytic currents obtained from amperometric measurements at +300mV vs. Ag|AgCl|KCl(sat.) and in phosphate buffer solution at pH 7.0 containing 0.1M KCl were linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 0.5μM to 100μM. The limit of detection was found to be 0.15μM.

Electrocatalytic Oxidation of NADH Using a Pencil Graphite Electrode Modified with Hematoxylin

Electrocatalytic Oxidation of NADH Using a Pencil Graphite Electrode Modified with Hematoxylin

Graphene-carbon nanotubes modified graphite electrode for the determination of nicotinamide adenine dinucleotide and fabrication of alcohol biosensor

Through layer-by-layer adsorption (LBL) technique, the positively charged multiwalled carbon nanotubes (MWCNTs) and negatively charged graphene multilayer film were formed on graphite-poly(diallyldimethylammoniumchloride)-polystyrenesulphonate (Gr/PDDA/PSS) modified electrode. Due to large surface area and remarkable electrocatalytic properties of MWCNTs and graphene, the Gr/(PDDA/PSS-[MWCNTs-NH3+-graphene-COO−]5) electrode exhibits potent electrocatalytic activity towards the electro-oxidation of nicotinamide adenine dinucleotide (NADH). A substantial decrease in the overpotential was observed at modified electrode, and the electrode showed high sensitivity to the electrocatalytic oxidation of NADH. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The diffusion coefficient was calculated by chronocoulometry. Chronoamperometric studies showed the linear relationship between oxidation peak current and the concentration of NADH in the range 25–250 μM (R = 0.999) with the detection limit of 0.1 μM (S/N = 3). Further, dopamine, uric acid, acetaminophen and hydrogen peroxide do not interfere in the detection of NADH. The ability of MWCNTs and graphene to promote the electron transfer between NADH and the electrode exhibits a promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. Alcohol dehydrogenase (ADH) was casted on Gr/(PDDA/PSS-[MWCNTs-NH3+-graphene-COO−]5) electrode; the resulting biosensor showed rapid and high sensitive amperometric response to ethanol with the detection limit of 10 μM (S/N = 3).

Electrocatalytic Oxidation of NADH Using Alizarin Immobilized Carbon Nanotube Modified Electrode

Electrocatalytic oxidation of NADH has been demonstrated using an electrochemically immobilized Alizarin (AZ) on multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/AZ@MWCNT) in pH 7 phosphate buffer solution. The GCE/AZ@MWCNT shows three surface-confined redox peaks centered (E1/2) at -0.067, -0.351 and -0.620 V vs Ag/AgCl, due to the 1,2 dihydroxy and anthraquinone (at two different energetic MWCNT) redox sites of the AZ. Calculated respective surface excess values are 59.13, 8.12 and 9.73'10-10 mol.cm-2 . Amongst the three, the E1/2 = -0.067 redox peak shows specific NADH electrocatalytic oxidation behavior in a concentration range = 0−7 mM by cyclic voltammetry. Transmission electron microscope characterization reveals immobilization of the AZ both on inner and outer walls of the MWCNT. Investigation on different CNTs viz., impure, purified, functionalized MWCNT, and single-walled carbon nanotube systems, the impure MWCNT shows the highest AZ immobilization and electrocatalytic behavior towards NADH oxidation.

In situ regeneration of NADH via lipoamide dehydrogenase-catalyzed electron transfer reaction evidenced by spectroelectrochemistry

NAD/NADH is a coenzyme found in all living cells, carrying electrons from one reaction to another. We report on characterizations of in situ regeneration of NADH via lipoamide dehydrogenase (LD)-catalyzed electron transfer reaction to regenerate NADH using UV–vis spectroelectrochemistry. The Michaelis–Menten constant (Km) and maximum velocity (Vmax) of NADH regeneration were measured as 0.80±0.15mM and 1.91±0.09μMs−1 in a 1-mm thin-layer spectroelectrochemical cell using gold gauze as the working electrode at the applied potential −0.75V (vs. Ag/AgCl). The electrocatalytic reduction of the NAD system was further coupled with the enzymatic conversion of pyruvate to lactate by lactate dehydrogenase to examine the coenzymatic activity of the regenerated NADH. Although the reproducible electrocatalytic reduction of NAD into NADH is known to be difficult compared to the electrocatalytic oxidation of NADH, our spectroelectrochemical results indicate that the in situ regeneration of NADH via LD-catalyzed electron transfer reaction is fast and sustainable and can be potentially applied to many NAD/NADH-dependent enzyme systems.

In vivo electrochemical recording of continuous change of magnesium in medial vestibular nucleus following vertigo induced by ice water vestibular stimulation

Vertigo is one of the most common clinical symptoms. However, the chemical processes involved in the pathological mechanism of vertigo remain to be fully understood. In this study, we investigate the dynamic changes in the magnesium (Mg2+) concentration in medial vestibular nucleus (MVN) of guinea pigs following vertigo induced by vestibular ice water stimulation with an electrochemical detection method consisting of in vivo microdialysis and on-line selective electrochemical detection. Electrochemical detection of Mg2+ was accomplished based on the current enhancement of Mg2+ towards the electrocatalytic oxidation of NADH at the electrodes modified with the polymerized film of toluidine blue O (TBO). Selectivity for the on-line electrochemical detection against Ca2+ was achieved by using ethyleneglcol-bis(2-aminoethylether) tetraacetic acid (EGTA) as the selective masking agent for Ca2+. The basal level of the extracellular Mg2+ in the MVN of guinea pigs was determined to be 759.7 ± 176.2 μM(n = 16). Upon ice water irrigation of the left external ear canal, the concentration of Mg2+ in the MVN decreases significantly, reaches 72 ± 6% (n = 8) of the basal level, and maintains for at least 1000 s. Control experiments reveal that neither warm water irrigation of the external ear canal nor ice water irrigation of the auricle induces the decrease in the concentration of Mg2+ in the MVN. These results demonstrate that the extracellular Mg2+ in the MVN decreases significantly following vertigo induced by vestibular ice water stimulation. This demonstration suggests that Mg2+ might play an important role in the pathological mechanism of vertigo.

NADH oxidation using modified electrodes based on lactate and glucose dehydrogenase entrapped between an electrocatalyst film and redox catalyst-modified polymers

Electrocatalytic NADH oxidation was investigated at an electrode architecture involving an electropolymerized layer of poly(methylene blue) (pMB) or poly(methylene green) (pMG) in combination with specifically designed toluidine blue or nile blue modified methacrylate-based electrodeposition polymers. Either NAD+-dependent lactate dehydrogenase or NAD+-dependent glucose dehydrogenase were entrapped between the primary electropolymerized layer of pMB or pMG and the methacrylate-based redox polymer. The composition of the polymer backbone and the polymer-bound redox dye was evaluated and it could be demonstrated that the combination of the electropolymerized pMB or pMG layer together with the dye modified methacrylate-based redox polymer shows superior properties as compared with either of the components alone. NADH was oxidized at an applied potential of 0 mV vs Ag/AgCl/KCl 3 M and current densities of 17 μA·cm−2 and 28 μA·cm−2 were obtained for modified electrodes based on lactate dehydrogenase and glucose dehydrogenase, respectively, at substrate saturation.

Rational Design of Surface/Interface Chemistry for Quantitative in Vivo Monitoring of Brain Chemistry

To understand the molecular basis of brain functions, researchers would like to be able to quantitatively monitor the levels of neurochemicals in the extracellular fluid in vivo. However, the chemical and physiological complexity of the central nervous system (CNS) presents challenges for the development of these analytical methods. This Account describes the rational design and careful construction of electrodes and nanoparticles with specific surface/interface chemistry for quantitative in vivo monitoring of brain chemistry. We used the redox nature of neurochemicals at the electrode/electrolyte interface to establish a basis for monitoring specific neurochemicals. Carbon nanotubes provide an electrode/electrolyte interface for the selective oxidation of ascorbate, and we have developed both in vivo voltammetry and an online electrochemical detecting system for continuously monitoring this molecule in the CNS. Although Ca(2+) and Mg(2+) are involved in a number of neurochemical signaling processes, they are still difficult to detect in the CNS. These divalent cations can enhance electrocatalytic oxidation of NADH at an electrode modified with toluidine blue O. We used this property to develop online electrochemical detection systems for simultaneous measurements of Ca(2+) and Mg(2+) and for continuous selective monitoring of Mg(2+) in the CNS. We have also harnessed biological schemes for neurosensing in the brain to design other monitoring systems. By taking advantage of the distinct reaction properties of dopamine (DA), we have developed a nonoxidative mechanism for DA sensing and a system that can potentially be used for continuously sensing of DA release. Using "artificial peroxidase" (Prussian blue) to replace a natural peroxidase (horseradish peroxidase, HRP), our online system can simultaneously detect basal levels of glucose and lactate. By substituting oxidases with dehydrogenases, we have used enzyme-based biosensing schemes to develop a physiologically relevant system for detecting glucose and lactate in rat brain. Because of their unique optical properties and modifiable surfaces, gold nanoparticles (Au-NPs) have provided a platform of colorimetric assay for in vivo cerebral glucose quantification. We designed and modified the surfaces of Au-NPs and then used a sequence of reactions to produce hydroxyl radicals from glucose.

Electrocatalytic oxidation of NADH at electrogenerated NAD+ oxidation product immobilized onto multiwalled carbon nanotubes/ionic liquid nanocomposite: Application to ethanol biosensing

The multiwalled carbon nanotubes/N-butyl-N-methyl-pyrolydinium-bis(trifluoromethylsulfonyl)imide [C4mpyr][NTf2] ionic liquid (MWCNTs/IL) modified glassy carbon (GC) electrode has been utilized as a platform to immobilize electrogenerated NAD+ oxidation products (Ox-P(NAD+)). During potential cycling, the adenine moiety of NAD+ molecule is oxidized and gives rise to generation of a redox active system that shows great electrocatalytic activity toward NADH oxidation. The cyclic voltammetric results indicated the ability of MWCNTs/IL/Ox-P(NAD+) modified GC electrode to catalyze the oxidation of NADH at a very low potential (0.05V vs. Ag/AgCl) and subsequently, a substantial decrease in the overpotential by about 600mV compared with the bare GC electrode. This modified electrode thus allowed highly sensitive amperometric detection of NADH with a very low limit of detection (2×10−8molL−1), low applied potential (+0.05V) at concentration range up to 4.2×10−5molL−1 and minimum of surface fouling. High ability of MWCNTs/IL/Ox-P(NAD+) to promote electron transfer between NADH and the electrode suggested a new promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model enzyme, ethanol sensing ability of the proposed system was examined. The amperometric response of the biosensor increased linearly with increasing ethanol concentration in two concentration ranges, 5×10−6–6×10−5 and 6×10−5–9×10−4molL−1 with detection limit of 5×10−7molL−1 and rapid response of 10s. Furthermore, the interference effects of redox active species, such as ascorbic acid, uric acid, glucose and acetaminophen for the proposed biosensor are negligible. Finally, the ability of the proposed biosensor for detection of ethanol in real complex samples was successfully demonstrated.