Electrocatalytic Oxidation Of NADH Research Articles

Electrochemical generation of 1-amino-pyrene-4,5,9,10 tetrol on the MWCNT surface for low potential electrocatalytic NADH oxidation

Electrochemical generation of 1-amino-pyrene-4,5,9,10 tetrol on the MWCNT surface for low potential electrocatalytic NADH oxidation

Electrocatalytic oxidation of NADH at graphene-modified electrodes based on electropolymerized poly(thionine-methylene blue) films from nature deep eutectic solvents

• Electropolymerization of PTH-MB films in ternary nature deep eutectic solvents. • PTH-MB NADES and ERG have a synergistic effect on the oxidation of NADH. • The prepared PTH-MB NADES -ERG electrode has excellent NADH electrocatalytic oxidation performance. • Sensitive detection of NADH in artificial urine samples. In this paper, a sensing platform for the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) was proposed. It was prepared by the electropolymerization of poly(thionine-methylene blue) (PTH-MB) in ternary nature deep eutectic solvent (NADES) on a glassy carbon electrode (GCE) that was modified with electrochemically reduced graphene oxide (ERG). The modified electrode was denoted as PTH-MB NADES -ERG/GCE. Cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), Raman spectroscopy, and Ultra Violet-Visible Spectroscopy (UV–Vis) were used to characterize the preparation processes. The electrochemical performances of the electrode in NADH oxidation were studied via CV and current-time methods. The NADH oxidation overpotential was lower on PTH-MB NADES -ERG/GCE compared to that on GCE, ERG/GCE, and PTH-MB NADES /GCE. The PTH-MB NADES -ERG/GCE showed excellent electrocatalytic activity for NADH oxidation with a linear range of 0.51–3333.33 µM (R 2 = 0.9534) and a detection limit of 0.159 nM. The sensor was further tested for NADH determination in artificial urine samples, showing promising biomedical applications.

Facile fabrication of electrochemically reduced graphene oxide/polythionine-methylene blue and its use as a platform for detection of nicotinamide adenine dinucleotide in the artificial urine sample

Here we report on a facile, rapid, selective, and stable electrochemical sensing platform for nicotinamide adenine dinucleotide (NADH) based on polythionine-methylene blue/electrochemically reduced graphene oxide modified glassy carbon electrode (PTH-MBDES-ERG/GCE). The ERG was directly formed on a glassy carbon electrode (ERG/GCE) through one-step electrochemical reduction of GO in PBS solution (10 mM, pH 7.4). In a PBS electrolyte, respectively, containing 50% (v/v) three different deep eutectic solvents (DES), thionine and methylene blue were polymerized on the surface of ERG/GCE. The electrochemical properties of the polymers polymerized in different electrolytes were investigated. The PTH-MBDES-ERG composite has a higher performance in the electrocatalytic oxidation of NADH than that of PTH-MBDES. The as-prepared PTH-MBDES-ERG/GCE demonstrated excellent direct electrocatalytic oxidation toward NADH, providing a favorable platform for electron transfer from NADH to the electrode. The sensor displayed a wide linear range from 1.52 μM to 3333.33 μM with a limit of detection of 0.51 nM. The interference from the ascorbic acid and uric acid was negligible. The prepared sensor was further tested for the determination of NADH in artificial urine samples, showing the PTH-MBDES-ERG/GCE formed by electropolymerization have promising biomedical applications.

Porous graphene oxide based disposable non-enzymatic electrochemical sensor for the determination of nicotinamide adenine dinucleotide

Electrochemical detection of β-nicotinamide adenine dinucleotide (NADH) has fascinated the scientific community due to its significance in pharmaceuticals, food supplements as well as in various biological reactions and pathways. Herein, a facile and low-cost disposable non-enzymatic electrochemical sensor for the selective and sensitive determination of NADH was developed using porous graphene oxide (PGO) modified screen printed carbon electrode (SPE). PGO has received growing attention owing to its high internal porosity, improved conductivity, large surface area, excellent stability, improved active sites, and hence expected to show excellent electrocatalytic activity than graphene and other derivatives of carbon. Firstly, graphene oxide (GO) sheets were synthesized, after which pores were created on these GO sheets through simple base reduction and acid treatment and the pore formation was confirmed using different characterization techniques. The PGO was directly dropcasted on the surface of SPE to form PGO/SPE and the fabricated electrode demonstrated eminent electrocatalytic activity towards NADH oxidation. Further, the fabricated sensor has shown significant response over a broad-range of concentration from 30 to 1071 μM with a good sensitivity of 21.83 μA mM −1 cm −2 and a low detection limit of 8.6 μM. Moreover, the fabricated PGO/SPE has advantages like cost-effectiveness, robustness, disposability, ease of fabrication, high stability, and excellent reproducibility. • Porous graphene oxide was synthesized via base reduction and acidification. • Fabricated a disposable electrochemical sensor by dropcasting PGO on SPE (PGO/SPE) • PGO/SPE effectively utilized for the electrocatalytic oxidation of NADH. • Compared to GO/SPE and ERGO/SPE, PGO/SPE showed superior analytical performance. • PGO/SPE exhibits good selectivity for NADH with excellent stability and sensitivity.

Efficient electrocatalytic oxidation of NADH by highly dispersible in situ N‐doped ionic liquid‐functionalized graphene nanosheets

AbstractA suitable β‐nicotinamide adenine dinucleotide (NADH) probe shall be capable of decreasing the oxidation overpotential and improving the electron transfer rate by direct electrocatalytic oxidation of NADH. Taking advantage of the combination of N‐doped graphene and ionic liquid (IL) as an electrocatalyst, a facile and useful approach comprising covalent grafting of imidazolium IL on reduced graphene oxide (ie, rGO‐IL) and in situ insertion of N‐atoms within the graphene framework, using the grafted IL as the N‐source (ie, N‐rGO‐IL), is demonstrated in this study. Additionally, their electrocatalytic efficiency toward NADH oxidation is systematically analyzed. Remarkably low peak potentials at 0.141 and 0.125 V and high current signals are observed for rGO‐IL‐ and N‐rGO‐IL‐modified electrodes, respectively, in presence of 200 μM NADH. Furthermore, the current‐time response is recorded at significantly low working potential of 0.0 V and ‐0.05 V, using rGO‐IL‐ and N‐rGO‐IL‐modified glassy carbon electrode, respectively, on injecting 5 μM NADH in successive steps. The response shows a good linear relationship from 5 to 30 μM of successive addition of NADH, with demonstration of correlation coefficients of 0.98 and 0.99, as well as good sensitivity of 50.0 and 39.0 nA μM−1 cm−2 (S/N = 3), respectively, for N‐rGO‐IL and rGO‐IL.

Porous PtAg nanoshells/reduced graphene oxide based biosensors for low-potential detection of NADH

A superior NADH sensing platform was constructed based on porous PtAg nanoshells supported on reduced graphene oxide (PtAg/rGO) in the absence of any enzymes and redox mediators. The PtAg/rGO composite was prepared via one-step reduction combined with galvanic replacement reaction. The as-made PtAg/rGO assembles multiple structural advantages of coherent conductive matrix, rich electroactive sites, and high specific surface area, accompanied bythe unique alloying effect. The PtAg/rGO possesses adequate active reactionsites and fluent electron transport pathway towards the electrocatalytic NADH oxidation, thus presenting significantly increased oxidation current and negative shift of 330mV in applied potential relative to the bare GCE. By virtues of the outstanding electrocatalytic activity, PtAg/rGO exhibits effective amperometric detection ofNADH at 0.15V within a wide linear concentration rangeof 2-2378μM, a high sensitivity of 92.62μAmM-1cm-2, low detection limit of 0.2μM, and long-term detection over 2500s. Moreover, the as-constructed biosensors can achieve accurate NADH detection in human serum samples, indicating its promising application feasibility in fundamental and clinic research. Graphical Abstract Porous PtAg alloy nanoshells supported on reduced graphene oxide (PtAg/rGO) was prepared via a facile one-step reduction and spontaneous replacement reaction strategy. A sensitive and highly stable electrochemical biosensor based on PtAg/rGO is constructed for the quantitative detection of NADH at low applied potential.

Electrocatalytic NADH Sensing using Electrodes Modified with 2‐[2‐(4‐Nitrophenoxy)ethoxy]ethylthio‐Substituted Porphyrazine/Single‐Walled Carbon Nanotube Hybrids

AbstractThe electrochemical properties of a modified electrode covered with 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine/single‐walled carbon nanotube hybrids were investigated. The electrochemical study revealed that the electrode mechanism is more complex in acidic conditions in comparison to neutral buffer. According to our study, the nitro groups constituting the part of porphyrazine substituents can be electrochemically reduced to the corresponding hydroxylamine moieties; surprisingly, however, the latter can be additionally transformed to o‐aminophenol/o‐iminoquinone groups, but only in acidic conditions. The electrode covered with hybrid material was used in the electrocatalytic oxidation of NADH. According to these results, it seems that after the electrochemical activation of the electrode material, 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine reveals strong electrocatalytic behavior towards NADH oxidation, owing to the appearance of reversible surface‐anchored o‐aminophenol/o‐iminoquinone intermediate redox couples. In the amperometric determination, the limit of detection (LOD) and limit of quantification (LOQ) of NADH were calculated and found to be LOD=0.16 and LOQ=0.48 μM. Moreover, the relative standard deviation of the response was 3.32 %, indicating excellent reproducibility. Thus, the novel electrode based on 2‐[2‐(4‐nitrophenoxy)ethoxy]ethylthio‐substituted porphyrazine and single‐walled carbon nanotubes present an interesting opportunity in the fields of electroanalytical and biosensing applications, and can be considered for amperometric NADH determination.

Dopamine-functionalized graphene oxide as a high-performance material for biosensing

We describe a nanocomposite material for the electrochemical detection of β-nicotinamide adenine dinucleotide (NADH), a coenzyme involved in redox reactions of all living cells and in the detection of many organic species by electrochemical biosensors. The composite is made of nanosheets of electrochemically exfoliated graphene oxide (EGO) covalently functionalized with dopamine (DP) molecules. The EGODP material finally obtained is rich of 1,2-dihydroxyphenyl moieties and is able to detect NADH at a particular low potential value with higher sensitivity with respect to pristine EGO.To study the effectiveness of 1,2-dihydroxyphenyl moieties in inducing electrocatalytic oxidation of NADH, we combined standard voltammetric techniques with UV–Vis absorption spectroelectrochemistry, which allowed us to measure the variations in composition occurring at the electrode|solution interface, i.e. to measure the consumption rate of NADH.Spectroelectrochemical tests performed by polarising the electrode at a fixed potential value were finally used to compare the performance of EGODP with both EGO and EGO-DP blend (MIX) for the detection of NADH. The covalently functionalized EGO (EGODP) shows sensitivity to NADH up to 300 M−1, around 180 % and 140 % better than either pristine EGO or MIX, respectively.

Electrocatalytic oxidation of NADH in a new nanostructured interface with an entrapped butylpyrene nitroaromatic derivative

In a previous study, we revealed a new way to modify multi-walled carbon nanotubes (MWCNTs) with 3,5-dinitrobenzoic acid (35DNB). Furthermore, we proved that a 35DNB-MWCNTGC electrode efficiently catalysed the oxidation of NADH. In this paper, with the aim of obtaining a stronger bond of the electrocatalytic mediator 35DNB with the MWCNTs, we have synthesized a modified compound of 35DNB. The modification consisted of adding a 4-(piren-1-yl)butyl terminal to 35DNB to form 4-(pyren-1-yl)butyl 3,5-dinitrobenzoate (35DNBpy). The synthesis of 35DNBpy was obtained with a yield of 78.3% (mp=202–204°C). With this change, we improved the electrocatalytic activity by several oxidation cycles, conferring electrocatalytic stability.The preparation and modification of electrodes with carbon nanotubes and 35DNBpy is fast and simple. The electrochemical study was performed by cyclic voltammetry in 3mM NADH solutions. Oxidation of NADH occurs at 0.1 (V vs Ag/AgCl) in aqueous media at pH7 and the same electrode can be used for up to 50min.In this work, the electrocatalytic activity of new modified electrodes with MWCNTs and 35DNBpy is reported. The electrocatalytic activity was evaluated by cyclic voltammetry. The electrocatalytic capacity of the electrode and the heterogeneous electron transfer rate constant were calculated.Sensitivity of the modified electrode 35DNBpy/MWCNT/GCE is measured by voltammetric method which showed linear variation with NADH concentration with limit of detection (LOD) and sensitivity of 0.885μM (3S/N) and 0.33μA/μM, respectively.

A Glucose-Responsive Enzymatic Electrode on Carbon Nanodots for Glucose Biosensor and Glucose/Air Biofuel Cell

In this study, an enzymatic electrode for glucose biosensing and bioanode of glucose/air biofuel cell has been fabricated by immobilizing poly (methylene green) (polyMG) for electrocatalytic NADH oxidation and NAD+-dependent glucose dehydrogenase (GDH) for oxidizing glucose on carbon nanodots (CNDs). The polyMG-CNDscomposites obtained by electro-polymerization of dye MG molecules adsorbed on CNDs display excellent electrocatalytic activity toward NADH electro-oxidation at a low overpotential of ca. -0.10 V (vs. Ag/AgCl) and the integrated enzymatic electrode shows fast response to glucose electrooxidation. Using the fabricated GDH-based enzymatic electrode, a glucose biosensor was constructed and exhibits a wide linear dynamic range from 0 to 8 mM, a low detection limit of 0.02 μM (S/N = 3), and fast response time (ca. 4 s) under the optimized conditions. The developed glucose biosensor was used to detect glucose content in human blood with satisfactory results. The fabricated GDH-based enzymatic electrode was also employed as bioanode to assembly a glucose/air biofuel cell with the laccase-CNDs/GC as the biocathode. The maximum power density delivered by the assembled glucose/air biofuel cell reaches 3.1 μW·cm-2 at a cell voltage of 0.22 V in real sample fruit juice. The present study demonstrates that potential applications of GDH-based CNDs electrode in analytical and biomedical measurements.

Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules.

Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.

Selective and low potential electrocatalytic oxidation of NADH using a 2,2-diphenyl-1-picrylhydrazyl immobilized graphene oxide-modified glassy carbon electrode

DPPH (2,2-diphenyl-1-picrylhydrazil), a free radical-containing organic compound, is used widely to evaluate the antioxidant properties of plant constituents. Here, we report an efficient electroactive DPPH molecular system with excellent electrocatalytic sensor properties, which is clearly distinct from the traditional free radical-based quenching mechanism. This unusual molecular status was achieved by the electrochemical immobilization of graphene oxide (GO)-stabilized DPPH on a glassy carbon electrode (GCE). Potential cycling of the DPPH adsorbed-GCE/GO between − 1 and 1 V (Ag/AgCl) in a pH 7 solution revealed a stable and well-defined pair of redox peaks with a standard electrode potential, E0′ = 0 ± 0.01 V (Ag/AgCl). Several electrochemical characterization studies as well as surface analysis of the GCE/GO@DPPH-modified electrode by transmission electron microscopy, Raman, and infrared spectroscopy collectively identified the imine/amine groups as the redox centers of the electroactive DPPH on GO. The use of different carbon-supports showed that only oxygen-functionalized GO and MWCNTs could provide major electroactivity for DPPH. This highlights the importance of a strong hydrogen-bonded network structure assisted by the concomitant π-π interactions between the organic moiety and oxygen function groups of carbon for the high electroactivity and stability of the GCE/GO@DPPH-NH/NH2-modified electrode. The developed electrode exhibited remarkable performance towards the electrocatalytic oxidation of NADH at 0 V (Ag/AgCl). The amperometric i-t sensing of NADH showed high sensitivity (488 nA μM−1 cm−2) and an extended linear range (50 to 450 μM) with complete freedom from several common biochemical/chemical interferents, such as ascorbic acid, hydrazine, glucose, cysteine, citric acid, nitrate, and uric acid.

A low-cost, fast, disposable and sensitive biosensor study: flow injection analysis of glucose at poly-methylene blue-modified pencil graphite electrode

In this work, firstly methylene blue (MB) was electropolymerized onto pencil graphite electrode (PGE) surface for the electrocatalytic oxidation of NADH. Cyclic voltammograms show that oxidation potential of NADH at Poly-MB/PGE shifted to negative direction about 300 mV compared with bare PGE. These results indicate that Poly-MB/PGE exhibits a good electrocatalytic activity toward NADH oxidation. Then, a glucose biosensor study was performed based on the determination of enzymatically generated NADH by glucose dehydrogenase (GDH) which immobilized onto Poly-MB/PGE using glutaraldehyde cross-linking procedure. The biosensing of glucose in flow injection analysis (FIA) system was performed at GDH/Poly-MB/PGE for the first time. The electrocatalytic oxidation currents of enzymatically produced NADH obtained from FI amperometric current–time curves recorded at + 200 mV and in phosphate buffer solution at pH 7.0 containing 1.0 M KCl were linearly related to the concentration of glucose. Linear calibration plots are obtained in the concentration range from 0.01 to 1.0 mM. The limit of detection (LOD) was found to be 4.0 µM. A fast, sensitive, low-cost and disposable glucose biosensor was constructed in FIA system using GDH/Poly-MB/PGE; therefore, it might provide a new perspective for the fabrication of biosensor of other compounds such as glutamate, lactate and alcohol.

Sensor and biosensor application of a new redox mediator: Rosmarinic acid modified screen-printed carbon electrode for electrochemical determination of NADH and ethanol

The effects of rosmarinic acid (RA) immobilized onto a screen printed carbon electrode (SPCE) were investigated for the development of an NADH sensor and an ethanol biosensor. RA was electrodeposited on SPCE by cyclic voltammetry. Scan rate and number of cycles were optimized for electrodeposition. RA modified SPCE (SPCE/RA) was found to facilitate the electrocatalytic oxidation of NADH by the action of RA as a natural antioxidant mediator. pH and working potential were optimized for the determination of NADH with the developed SPCE/RA sensor. They were found as 7.25 and 0.25 V, respectively. Alcohol dehydrogenase (ADH) enzyme was immobilized onto this sensor to prepare a disposable amperometric ethanol biosensor. NAD+ was used as a cofactor for ADH. pH, working potential, amounts of ADH and NAD+ were optimized for the developed biosensor. The optimum values were found as 7.75, 0.20 V, 250 unit and 7 mM, respectively. Analytical characterization parameters for ethanol analysis were determined. The sensitivity, linear range, limits of detection and quantification were 1.36 μA mM−1, 23.71 μM–1000 μM, 7.1 μM and 23.7 μM, respectively. The repeatability, operational stability and storage life studies were performed. RA is found to enhance the operational stability of the biosensor. The developed biosensor has been tested on a few commercial alcoholic drinks for the analysis of their ethanol contents.

Electropolymerization of ferulic acid on multi-walled carbon nanotubes modified glassy carbon electrode as a versatile platform for NADH, dopamine and epinephrine separate detection

The polymerization of ferulic acid (poly-FA) on multi-walled carbon nanotubes (MWCNT) modified glassy carbon electrode was performed and the modified platform applied for the determination of NADH, epinephrine (EP) and dopamine (DA), one at a time. Cyclic voltammetry and chronoamperometry were employed to investigate the electrocatalytic oxidation of NADH, EP and DA on the modified electrode, in aqueous solutions. The obtained analytical curves for NADH, EP, and DA showed linear ranges between 59–1560, 73–1406, and 5–120μmolL−1, respectively. The detection limits were 17.7, 22.2 and 2.2μmolL−1 for NADH, EP and DA, respectively. The catalytic constant for the oxidation of NADH, EP and DA on the modified electrode were 5.56×103, 6.99×103 and 1.15×104Lmol−1s−1, respectively. The obtained versatile electrode was applied to the successful determination of EP, in epinephrine hydrochloride injection and DA in pharmaceutical samples.

A Biofuel Cell Based on Biocatalytic Reactions of Lactate on Both Anode and Cathode Electrodes – Extracting Electrical Power from Human Sweat

AbstractElectrodes composed of carbon fibers were modified with graphene nano‐sheets in order to increase their surface area and facilitate electrochemical reactions. Electrocatalytic species, such as Meldola's blue (MB) and hemin were immobilized on the graphene surface due to their π‐π stacking and then used for electrocatalytic oxidation of NADH and reduction of H2O2, respectively. Further modification of these electrodes with enzymes producing NADH and H2O2 in situ (lactate dehydrogenase, LDH, and lactate oxidase, LOx, respectively), allowed assembling of a biofuel cell operating in the presence of lactate, oxygen and NAD+. The cathode of the biofuel cell required lactate and O2 for its operation, while the anode operated in the presence of lactate and NAD+. Notably, both bioelectrocatalytic electrodes operated in the presence of lactate, one producing H2O2 in the reaction catalyzed by LOx in the presence of O2, second producing NADH in the reaction catalyzed by LDH in the presence of NAD+. Both reactions were performed in the biofuel cell without separation of the cathodic and anodic solutions and with no need of a membrane. The biofuel cell was tested in solutions mimicking human sweat and then in real human sweat samples, demonstrating substantial power release being able to activate electronic devices.

A Biofuel Cell Based on Biocatalytic Reactions of Glucose on Both Anode and Cathode Electrodes

AbstractBiofuel cells based on electrocatalytic oxidation of NADH and reduction of H2O2 have been prepared using carbon fiber electrodes functionalized with graphene nano‐flakes. The electrochemical oxidation of NADH was catalyzed by Meldola's blue (MB), while the reduction of H2O2 was catalyzed by hemin, both catalysts were adsorbed on the graphene flakes due to their π‐π staking. In the next set of experiments, the MB‐ and hemin‐electrodes were additionally modified with glucose dehydrogenase (GDH) and glucose oxidase (GOx), respectively. The enzyme catalyzed reactions in the presence of glucose, NAD+ and O2 resulted in the production of NADH and H2O2 in situ. The produced NADH and H2O2 were oxidized and reduced, respectively, at the bioelectrocatalytic electrodes, thus producing voltage and current generated by the biofuel cell. The enzyme‐based biofuel cells operated in a human serum solution modelling an implantable device powered from the natural biofluid. Finally, two enzyme‐based biofuel cell connected in series and operating in the serum solution produced electrical power sufficient for activation of an electronic watch used as an example device.

Enzymatic versus Electrocatalytic Oxidation of NADH at Carbon‐Nanotube Electrodes Modified with Glucose Dehydrogenases: Application in a Bucky‐Paper‐Based Glucose Enzymatic Fuel Cell

AbstractIn this work, we have designed and compared functionalized carbon‐nanotube‐based electrodes for the electrocatalytic oxidation of NADH. We show that oxidation of NADH at neutral pH values can be performed by pristine multi‐walled carbon nanotubes (MWCNT) and directly wired diaphorase or ruthenium phenanthrolinequinone molecular catalysts. Glucose dehydrogenase was immobilized on these MWCNT electrodes by an activated‐ester‐modified pyrene linker. Glucose‐oxidizing bioelectrodes were compared and integrated into a bucky‐paper‐based glucose/O2 biofuel cell, using a bilirubin‐oxidase‐modified bucky‐paper cathode. The best configuration was obtained using a NADH‐oxidizing molecular catalyst at the anode. The biofuel cell exhibits an open‐circuit voltage of 0.62 V and delivers a power output of 0.47 mW cm−2.

Electrocatalysis of NADH on 3,5-Dinitrobenzoic Acid Encapsulated on Multiwalled Carbon Nanotube-Modified Electrode

We report that glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNTs) can encapsulate or entrap 3,5-dinitrobenzoic acid (35DNB) generating a 35DNB-MWCNTGC electrode. After electrochemical reduction in situ of only one nitro group of 35DNB, it turns into the hydroxylamine derivative (R-NHOH), which can be further oxidized to the nitroso derivative (R-NO). Then, R-NO/R-NHOH redox couple was electrogenerated in situ by cycling the potential between 0.20 and −0.20 V vs Ag/AgCl. The very well-defined and persistent redox couple was characterized with a formal potential, E o ’ = −28 mV vs Ag/AgCl at a scan rate of 20 mV s−1. Using the Laviron’s plot, a transfer coefficient, α = 0.45, and an electron transfer rate constant, k s = 10.5 s−1, for the electron transfer of the couple R-NO/R-NHOH, were calculated. This redox reaction results to be a very efficient mediator for electrocatalytic NADH oxidation. The 35DNB-MWCNTGC electrode efficiently catalyzes the oxidation of NADH with a decrease of more than 0.60 V vs Ag/AgCl in the overpotential compared to the bare GCE and a difference of 0.25 V vs Ag/AgCl with respect to the situation without mediator. The preparation of the electrode is very easy and not time-consuming.

Synergistic effect of pyrroloquinoline quinone and graphene nano-interface for facile fabrication of sensitive NADH biosensor

A self-assembly composite of graphene-pyrroloquinoline quinone (PQQ) was fabricated and modified on glassy carbon electrode (GCE) for sensitive detection of nicotinamide adenine dinucleotide (NADH). Chitosan (CTS) was applied to disperse graphene to form a stable robust film on GCE. A synergistic effect between PQQ and graphene was observed during the electrocatalytic oxidation of NADH, with about 260mV reduction in the oxidation potential and 2.5-fold increase in the oxidation current compared with those on the bare GCE. The electrochemical sensors based on the modified electrodes allowed the detection of NADH with a good linear dependence from 0.32 to 220µM with a high sensitivity of 0.421µAµM−1cm−2 and a low detection limit of 0.16µM (S/N=3). It could also eliminate the interference of electroactive substances like ascorbic acid (AA), uric acid, and dopamine and its derivatives. The outstanding performances of graphene-PQQ/CTS composite capable of improving the electrical conductivity and accelerating the electron transport suggested its promising applications for design of different graphene based composites used in electrochemical sensing and energy fields.