Bioelectrochemistry (v.80, #2)

Microbial electricity generation of diversified carbonaceous electrodes under variable mediators by Park In Ho; G. Gnana Kumar; A.R. Kim; Pil Kim; Kee Suk Nahm (99-104).
To evaluate a suitable electrode material for the efficient green energy generation of a bio-fuel cell, carbonaceous based carbon cloth, carbon paper, and carbon felt electrodes were investigated under different mediators. The larger surface area, low resistance, and open network of interwoven fibers of the carbon felt electrode facilitated higher electron transfer from the microbial organisms to the electrode surface than that of other carbonaceous electrodes. Carbon paper electrode exhibited lower fuel cell performances due to its lower roughness and high tortuous nature. The green power generation experiments were also carried out under different mediators such as 2-hydroxy-l,4-naphthoquinone and thionin. The electrons mitigation and power generation was augmented by 2-hydroxy-l,4-naphthoquinone than thionin due to its high solubility, stability, and minimal adsorption characteristic to the electrodes. By the combined efforts of extended electrons generation and transportation, bio-fuel cell performances were extended and endorsed its doable applications in bio-fuel cells.
Keywords: Conduction; Electrode; Electron transfer; Green power; Membrane;

The oxidation of ascorbate at copolymeric sulfonated poly(aniline) coated on glassy carbon electrodes by C. Sanchis; M.A. Ghanem; H.J. Salavagione; E. Morallón; P.N. Bartlett (105-113).
Self-doped poly(aniline)s as electrode coatings to catalyze ascorbate oxidation are revisited in this article. Sulfonated poly(aniline) (SPAN) was deposited on glassy carbon electrodes as a copolymer of aniline and its sulfonated derivative, 2-aminobenzenesulfonic acid (2-ABSA). The resulting deposits are reproducible and show good stability and electroactivity at pH > 7, enabling studies at typical physiological pH values. Calibration curves were obtained using a rotating disc electrode at a sampling potential of 0.2 V, displaying linear dependence in the region 0–20 mM ascorbate. A kinetic model based on the Michaelis–Menten reaction mechanism, previously validated for poly(aniline) composites, was used to analyse the form of the calibration curve leading to values of the effective reaction constants K ME and k′ ME. New calibration curves constructed for different sampling potentials were used to elucidate the rate limiting step at saturated kinetics. Rotating disc voltammetry performed at increasing pH (from pH 2 to 9) showed a dramatic decrease in the limiting current, without any evidence for a change in the reaction mechanism.
Keywords: Sulfonated poly(aniline); Ascorbate; Electrocatalysis; Kinetics;

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 (ΔEp) 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.
Keywords: Direct electrochemistry; Glucose oxidase; Gelatin; Multiwalled carbon nanotubes; Electrocatalysis;

Determination of formal potential of NADH/NAD+ redox couple and catalytic oxidation of NADH using poly(phenosafranin)-modified carbon electrodes by Farhana S. Saleh; Mohammad R. Rahman; Takeyoshi Okajima; Lanqun Mao; Takeo Ohsaka (121-127).
The electrochemical regeneration of NADH/NAD+ redox couple has been studied using poly(phenosafranin) (PPS)-modified carbon electrodes to evaluate the formal potential and catalytic rate constant for the oxidation of NADH. The PPS-modified electrodes were prepared by electropolymerization of phenosafranin onto different carbon substrates (glassy carbon (GC) and basal-plane pyrolytic graphite (BPPG)) in different electrolytic solutions. The formal potential was estimated to be − 0.365 ± 0.002 V vs. SHE at pH 7.0. As for the bare carbon electrodes, the oxidation of NADH at the BPPG electrode was found to be enhanced compared with the GC electrode. For the PPS-modified electrodes, it was found that the electrocatalysis of PPS-modified electrodes for the oxidation of NADH largely depends on the carbon substrate and electrolyte solution employed for their preparation, i.e., the PPS-modified BPPG electrode prepared in 0.2 M NaClO4/acetonitrile solution exhibits an excellent and persistent electrocatalytic property toward NADH oxidation in phosphate buffer solution (pH 7.0) with a diminution of the overpotential of about 740 and 670 mV compared with those at the bare GC electrode and the PPS-modified GC electrode prepared in 0.2 M H2SO4 solution, respectively. A quantitative analysis of the electrocatalytic reaction based on rotating disk voltammetry gave the electrocatalytic reaction rate constants of the order of 103–104  M 1  s− 1 depending on the preparation conditions of the PPS-modified electrodes.
Keywords: NADH/NAD+ regeneration; Formal potential; Poly(phenosafranin); Carbon electrodes;

6-Vinyl coenzyme Q0 serves as a convenient starting material for the formation of electropolymerized coenzyme Q0 on glassy carbon electrodes and the modified electrodes displays electrocatalytic activity toward NADH (β-nicotinamide adenine dinucleotide) oxidation. The detection of NADH was measured by differential pulse voltammetry, which reveals that the peak current is linear to the concentration of NADH within the range of 10–100 μM. This would be helpful for the understanding of the interaction between coenzyme Q0 and NADH in the biological process.
Keywords: 6-Vinyl coenzyme Q0; Electropolymerization; Electrocatalytic oxidation; NADH;

A novel biosensor using poly(3,4-ethylene dioxythiophene) (PEDOT) modified Pt electrode was developed for selective determination of dopamine (DA) in presence of high concentrations of ascorbic acid (AA) and uric acid (UA) with a maximum molar ratio of 1/1000, and 1/100 in the presence of sodium dodecyl sulfate (SDS). SDS forms a monolayer on PEDOT surface with a high density of negatively charged end directed outside the electrode. The electrochemical response of dopamine was improved by SDS due to the enhanced accumulation of protonated dopamine via electrostatic interactions. The common overlapped oxidation peaks of AA, UA and DA can be resolved by using SDS as the DA current signal increases while the corresponding signals for AA and UA are quenched. The use of SDS in the electrochemical determination of dopamine using linear sweep voltammetry at modified electrode PEDOT/Pt resulted in detecting dopamine at relatively lower concentrations. The DA concentration could be measured in the linear range of 0.5 to 25 μmol L− 1 and 30 μmol L− 1 to 0.1 mmol L− 1 with correlation coefficients of 0.998 and 0.993 and detection limits 61 nmol L− 1 and 86 nmol L− 1, respectively. The validity of using this method in the determination of dopamine in human urine was also demonstrated.
Keywords: Dopamine; PEDOT; SDS; EIS; SEM;

Gene expression and deletion analysis of mechanisms for electron transfer from electrodes to Geobacter sulfurreducens by Sarah M. Strycharz; Richard H. Glaven; Maddalena V. Coppi; Sarah M. Gannon; Lorrie A. Perpetua; Anna Liu; Kelly P. Nevin; Derek R. Lovley (142-150).
Geobacter sulfurreducens is one of the few microorganisms available in pure culture known to directly accept electrons from a negatively poised electrode. Microarray analysis was used to compare gene transcript abundance in biofilms of G. sulfurreducens using a graphite electrode as the sole electron donor for fumarate reduction compared with transcript abundance in biofilms growing on the same material, but not consuming current. Surprisingly, genes for putative cell-electrode connections, such as outer-surface cytochromes and pili, which are highly expressed in current-producing biofilms, were not highly expressed in current-consuming biofilms. Microarray analysis of G. sulfurreducens gene transcript abundance in current-consuming biofilms versus current-producing biofilms gave similar results. In both comparative studies current-consuming biofilms had greater transcript abundance for a gene (GSU3274) encoding a putative monoheme, c-type cytochrome. Deletion of genes for outer-surface proteins previously shown to be essential for optimal electron transfer to electrodes had no impact on electron transfer from electrodes. Deletion of GSU3274 completely inhibited electron transfer from electrodes, but had no impact on electron transfer to electrodes. These differences in gene expression patterns and the impact of gene deletions suggest that the mechanisms for electron transfer from electrodes to G. sulfurreducens differ significantly from the mechanisms for electron transfer to electrodes.
Keywords: Microbial fuel cell; Geobacter sulfurreducens; Cathode; Electron donor; Microarray;

A sensitive bacteria biosensor was prepared for the detection of trace lactate. The sensitive bioelement, Lactobacillus bulgaricus and Streptococcus thermophilus mixed cultrue, and palygorskite, a perfect matrix for bacteria, was co-immobilized on the surface of oxygen electrode. The biosensor possesses fine selective specificity, good sensitivity and longer operational life time, which were due to the mutual help relationship of symbiotic bacteria and 240 days acclimation with lactate as the carbon source. Hydrodynamic amperometry, an advanced electrochemical method, is suitable for on-line monitoring the concentration change of dissolved oxygen that is closely accompanied with the metabolism of lactate. Electrochemical data show that the current is very sensitive to the changes of the concentration of lactate. The response current was linear with lactic acid concentration in the range from 0 to 300 μmol L− 1, where the response time is no more than 240 s (R = 0.9952), and the sensitivity was 1.87 mA mol− 1  L. Experiments show the biosensor is also very useful for long time on-line monitoring of lactate, such as fermentation progress.
Keywords: Lactobacillus; Oxygen electrode; Lactate; Acclimation; Palygorskite;

Impedance spectroscopy and conductometric biosensing for probing catalase reaction with cyanide as ligand and inhibitor by Naima Bouyahia; Mohamed Larbi Hamlaoui; Mouna Hnaien; Florence Lagarde; Nicole Jaffrezic-Renault (155-161).
In this work, a new biosensor was prepared through immobilization of bovine liver catalase in a photoreticulated poly (vinyl alcohol) membrane at the surface of a conductometric transducer. This biosensor was used to study the kinetics of catalase–H202 reaction and its inhibition by cyanide. Immobilized catalase exhibited a Michaelis–Menten behaviour at low H202 concentrations (< 100 mM) with apparent constant KM app  = 84 ± 3 mM and maximal initial velocity VM app  = 13.4 μS min− 1. Inhibition by cyanide was found to be non-competitive and inhibition binding constant Ki was 13.9 ± 0.3 μM. The decrease of the biosensor response by increasing cyanide concentration was linear up to 50 μM, with a cyanide detection limit of 6 μM. In parallel, electrochemical characteristics of the catalase/PVA biomembrane and its interaction with cyanide were studied by cyclic voltammetry and impedance spectroscopy. Addition of the biomembrane onto the gold electrodes induced a significant increase of the interfacial polarization resistance RP. On the contrary, cyanide binding resulted in a decrease of Rp proportional to KCN concentration in the 4 to 50 μM range. Inhibition coefficient I50 calculated by this powerful label-free and substrate-free technique (24.3 μM) was in good agreement with that determined from the substrate-dependent conductometric biosensor (24.9 μM).
Keywords: Cyanide; Catalase; Inhibition; Conductometric biosensor; Impedimetric biosensor; I50;

Nitroxoline has been reduced at the mercury electrode in buffered solutions (pH 2−11) in two irreversible cathodic steps. The first step was attributed to reduction of –NO2 group to the hydroxylamine stage and the second one to reduction-saturation of the C=N double bond. DC-polarographic and various adsorptive stripping voltammetric methods were developed for determination of nitroxoline in bulk form. Limits of quantitation of 1.02 × 10−6, 3.05 × 10−8, 9.01 × 10−9, and 9.12 × 10−10  M nitroxoline were achieved by means of the developed DC-polarography, differential-pulse-, linear-sweep-, and square-wave-adsorptive cathodic stripping voltammetric methods, respectively. All these electroanalytical methods were successfully applied for determination of nitroxoline in its Nibiol® tablets. While only the developed adsorptive stripping voltammetry methods were successfully applied for determination of the drug in spiked human serum and for pharmacokinetic studies in real human plasma. The analysis was carried out without interference from common excipients and without the necessity for prior extraction or interaction with any reagent during the analysis.
Keywords: Nitroxoline; Quantification; Voltammetry; Pharmacokinetics;

A protein-based electrochemical sensor for hydrogen peroxide (H2O2) was developed by an easy and effective film fabrication method where spinach ferredoxin (Fdx) containing [2Fe–2S] metal center was cross linked with 11-mercaptoundecanoic acid (MUA) on a gold (Au) surface. The surface morphology of Fdx molecules on Au electrodes was investigated by atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed to study the electrochemical behavior of adsorbed Fdx on Au. The interfacial properties of the modified electrode were evaluated in the presence of Fe(CN)6 3−/4− redox couple as a probe. From CV, a pair of well-defined and quasi-reversible redox peaks of Fdx was obtained in 10 mM, pH 7.0 Tris–HCl buffer solution at −170 and −120 mV respectively. One electron reduction of the [2Fe-2S]2+ cluster occurs at one of the iron atoms to give the reduced [2Fe-2S]+. The formal reduction potential of Fdx ca. −150 mV (vs. Ag/AgCl electrode) at pH 7.0. The electron-transfer rate constant, k s, for electron transfer between the Au electrode and Fdx was estimated to be 0.12 s−1. From the electrochemical experiments, it is observed that Fdx/MUA/Au promoted direct electron transfer between Fdx and electrode and it catalyzes the reduction of H2O2. The Fdx/MUA/Au electrode displays a linear increase in amperometric current for increasing concentration of H2O2.The sensor calibration plot was linear with r 2  = 0.998 with sensitivity approximately 68.24 μAm M−1  cm−2. Further, the effect of nitrite on the developed sensor was examined which does not interfere with the detection of H2O2. Finally, the addition of H2O2 on MUA/Au electrode was observed which has no effect on amperometric current.
Keywords: Ferredoxin; Cyclic voltammetry; Biosensor; Nanobiochip; Hydrogen peroxide detection;

Anodic behavior of clioquinol at a glassy carbon electrode by Masoumeh Ghalkhani; Isabel P.G. Fernandes; Severino Carlos B. Oliveira; Saeed Shahrokhian; Ana Maria Oliveira–Brett (175-181).
Clioquinol is an antifungal, antiprotozoal and an Alzheimer's disease drug with cytotoxic activity toward human cancer cells. The electrochemical behavior of clioquinol and its oxidation product was studied using cyclic, differential pulse and square-wave voltammetry over a wide pH range on a glassy carbon electrode. The results revealed that the oxidation of clioquinol is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism and results in the formation of a main oxidation product, which adsorbs very strongly on the glassy carbon surface. The charge transfer coefficient was calculated as 0.64. The adsorbed oxidation product presented reversible redox behavior, with two electron and two proton transfer. The electrochemical oxidation of clioquinol as a phenolic compound involves the formation of a phenoxy radical which reacts in at least two ways: in one pathway the radical initiates polymerization, the products remaining at the electrode surface, and in the other the radical is oxidized to a quinone-like structure. A mechanism for the oxidation of clioquinol is proposed.
Keywords: Clioquinol; Oxidation mechanism; Adsorption process; Phenoxy radical; Voltammetry; Glassy carbon;