Bioelectrochemistry (v.81, #1)

Editorial by Eberhard Neumann (1).

Anisotropy and nonlinear properties of electrochemical circuits in leaves of Aloe vera L. by Alexander G. Volkov; Justin C. Foster; Emil Jovanov; Vladislav S. Markin (4-9).
Plant tissue has biologically closed electrical circuits and electric fields that regulate its physiology. The biologically closed electrochemical circuits in the leaves of Aloe vera were analyzed using the charge stimulation method with Ag/AgCl electrodes inserted along a leaf at 1–2 cm distance. The electrostimulation was provided with different timing and different voltages. Strong electrical anisotropy of the leaves was found. In the direction across the leaf the electrical circuits remained passive and linear, while along the leaf the response remained linear only at small voltages not exceeding 1 V. At higher potentials the circuits became strongly non-linear pointing to the opening of voltage gated ion channels in the plant tissues. Changing the polarity of electrodes located along conductive bundles led to a strong rectification effect and to different kinetics of capacitor discharge. Equivalent electrical circuit models of the leaf were proposed to explain the experimental data.
Keywords: Aloe vera; Plant electrophysiology; Electrostimulation; Electrical signaling; Charge stimulation method;

Current technology has limited applicability for electroporation based treatment of deep-seated tumors, and is in general, not optimized in terms of compliance with clinically relevant parameters. Here we present a novel electrode device developed for electrotransfer of antineoplastic drugs and genes to intracranial tumors in humans, and demonstrate a method to optimize the design (i.e. geometry) of the electrode device prototype to improve both clinical performance and geometrical tolerance (robustness). We have employed a semiempirical objective function based on constraints similar to those used in radiation oncology. The results show that small geometrical changes may yield a significant improvement. For example, a 2 mm displacement of 6 electrodes yields 14% better compliance with the clinical parameters, compared to the prototype, and additionally makes the electrode device less sensitive to random geometrical deviations. The method is readily applicable to other electrode configurations.Display Omitted► Novel electrode device for intracranial electroporation introduced. ► Volume definitions from radiation therapy employed in electroporation based treatment. ► Improved clinical performance of electrode device by semiempirical optimization. ► Geometrical robustness of electrode device assessed and improved.
Keywords: Electroporation; Electrode device; Optimization; Geometrical robustness; Brain tumor; Treatment planning;

All the intermediates of the bacteriorhodopsin photocycle are excitable with light of suitable wavelength. This property might regulate the activity in the cells when they are exposed in the nature to high light intensity. On the other hand this property is involved in many applications. In this study the ground state and M intermediate of dried oriented samples of wild-type bacteriorhodopsin and its mutant D96N were excited with 406 nm laser flashes. Substantial M populations were generated with quasi-continuous illumination. The decay of the absorption of M intermediate had three components: their lifetimes were very different for laser flash and quasi-continuous illuminations in cases of both bacteriorhodopsin species. The optical answer for the excitation of M intermediate had a lifetime of 2.2 ms. Electric signals for M excitation had large fast negative components and small positive components in the 100 μs time domain. The results are expected to have important implications for bioelectronic applications of bacteriorhodopsin.► Double-flash-induced absorption and electric signals of bacteriorhodopsin. ► Rate-limiting steps of the photoreaction cycle. ► Implications for Bioelectronic applications.
Keywords: Bacteriorhodopsin mutants; Quasi-continuous illumination; M intermediate; Blue excitation; Lifetimes;

The overshoot phenomenon as a function of internal resistance in microbial fuel cells by Jonathan Winfield; Ioannis Ieropoulos; John Greenman; Julian Dennis (22-27).
A method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1 mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30 s produced 23% higher maximum power than at 3 min. MFCs with an immature anodic biofilm (5 days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5 weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1 mM acetate) feedstock with low conductivity (< 100 μS) but not when fed with a higher concentration (20 mM acetate) feedstock with high conductivity (>1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24 h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot suggesting that this is an anodic phenomenon.► This study examines the causes of power overshoot in microbial fuel cells (MFC). ► Insufficient sample rate exaggerated overshoot and overestimated maximum power. ► An adequate inoculation period eliminated the presence of overshoot. ► Weak and/or toxic feedstock produced overshoot in healthy MFC. ► Overshoot not induced when cathode subjected to sub-optimal conditions.
Keywords: Microbial fuel cell; Overshoot; Polarisation; Conductivity; Power curve;

Most of biological cells have microvilli on their surfaces, which significantly influence their dielectric properties. The complex permittivity of a cubical system containing a spherical cell model with cylindrical projections was calculated over a frequency range of 10 kHz to 100 MHz using the three-dimensional finite-element method. The spectra of the complex permittivity consisted of low- and high-frequency relaxation processes which were respectively attributed to the polarization of the membranes covering the projections and the spherical body. Conventional analysis based on the spherical shell model was applied to the simulated spectra to discuss the effects of cell surface morphology on the electric parameters estimated for the plasma membrane and the cytoplasm.► Dielectric relaxation of microvillous cells is simulated by 3D-FEM. ► Cells are modeled as a sphere with cylindrical projections. ► Surface morphology of cells seriously influences dielectric properties of cells.
Keywords: Interfacial polarization; Dielectric spectroscopy; Biological cell; Microvillus; Simulation;

This work demonstrates that liquid phase deposition (LPD) technique provides a novel approach to the immobilization of hemoglobin (Hb) in TiO2 film for studying the direct electron transfer of Hb. Using the LPD process, a hybrid film composed of Hb, TiO2 and sodium dodecylsulfonate (SDS) is successfully prepared on the electrode surface. The surface morphology of as-deposited Hb/SDS/TiO2 film shows a flower-like structure. The cyclic voltammetric measurement indicates that the LPD hybrid film facilitates the electron transfer of Hb, which yields a pair of redox peaks prior to the characteristic voltammetric peaks of TiO2. Due to the electrocatalytic activity of Hb towards H2O2, the Hb/SDS/TiO2 hybrid LPD film can be utilized as an H2O2 sensor, showing a sensitive response linearly proportional to the concentration of H2O2 in the range of 5.0 × 10− 7–4.0 × 10− 5  mol/L. At the same time, the Hb/SDS/TiO2 hybrid film preserves the photoelectrochemical activity of TiO2. The photovoltaic effect on the electrochemical behavior of Hb/SDS/TiO2 film is observed after long-time UV irradiation on the film, which could improve the calibration sensitivity for H2O2.► Hb/SDS/TiO2 hybrid film is prepared on electrode surface by LPD technique. ► Electron transfer between Hb and electrode is facilitated in the hybrid LPD film. ► The LPD Hb/SDS/TiO2 film preserves the photoelectrochemical activity of TiO2. ► The sensitivity for H2O2 is improved based on the photovoltaic effect of TiO2.
Keywords: Hemoglobin; Direct electrochemistry; TiO2; Liquid phase deposition; Photovoltaic effect;

Circadian variations in biologically closed electrochemical circuits in Aloe vera and Mimosa pudica by Alexander G. Volkov; Kara Baker; Justin C. Foster; Jacqueline Clemmons; Emil Jovanov; Vladislav S. Markin (39-45).
The circadian clock regulates a wide range of electrophysiological and developmental processes in plants. This paper presents, for the first time, the direct influence of a circadian clock on biologically closed electrochemical circuits in vivo. Here we show circadian variation of the plant responses to electrical stimulation. The biologically closed electrochemical circuits in the leaves of Aloe vera and Mimosa pudica, which regulate their physiology, were analyzed using the charge stimulation method. The electrostimulation was provided with different timing and different voltages. Resistance between Ag/AgCl electrodes in the leaf of Aloe vera was higher during the day than at night. Discharge of the capacitor in Aloe vera at night was faster than during the day. Discharge of the capacitor in a pulvinus of Mimosa pudica was faster during the day. The biologically closed electrical circuits with voltage gated ion channels in Mimosa pudica are also activated the next day, even in the darkness. These results show that the circadian clock can be maintained endogenously and has electrochemical oscillators, which can activate ion channels in biologically closed electrochemical circuits. We present the equivalent electrical circuits in both plants and their circadian variation to explain the experimental data.► We show circadian variation of the plant responses to electrical stimulation. ► The circadian clock has electrochemical oscillators, which can activate ion channels. ► We present the equivalent electrical circuits in plants and their circadian variation. ►We found the direct influence of a circadian clock on electrical circuits in plants.
Keywords: Mimosa pudica; Aloe vera; Circadian clock; Electrostimulation; Charge stimulation method;

The electrochemical oxidation behaviour at boron doped diamond and glassy carbon electrodes of the sulphur-containing amino acids cysteine and methionine, using cyclic and differential pulse voltammetry over a wide pH range, was compared. The oxidation reactions of these amino acids are irreversible, diffusion-controlled pH dependent processes, and occur in a complex cascade mechanism. The amino acid cysteine undergoes similar three consecutive oxidation reactions at both electrodes. The first step involves the oxidation of the sulfhydryl group with radical formation, that undergoes nucleophilic attack by water to give an intermediate species that is oxidized in the second step to cysteic acid. The oxidation of the sulfhydryl group leads to a disulfide bridge between two similar cysteine moieties forming cysteine. The subsequent oxidation of cystine occurs at a higher potential, due to the strong disulfide bridge covalent bond. The electro-oxidation of methionine at a glassy carbon electrode occurs in two steps, corresponding to the formation of sulfoxide and sulfone, involving the adsorption and protonation/deprotonation of the thiol group, followed by electrochemical oxidation. Methionine undergoes a one-step oxidation reaction at boron doped diamond electrodes due to the negligible adsorption, and the oxidation also leads to the formation of methionine sulfone.► Redox reactions and oxidation mechanisms of the amino acids cysteine and methionine. ► First comparative study of the electrochemical mechanism of cysteine and methionine using GCE and BDDE. ► Model for the electron exchange between cysteine- and methionine-containing proteins or enzymes and solid surfaces.
Keywords: Cysteine; Methionine; Oxidation; Boron doped diamond; Glassy carbon;

In this work, an amine-terminated poly (amidoamine) dendrimer containing Pt nanoparticles (PAMAM/Pt) nanocomposite was synthesized and a novel amperometric H2O2 biosensor based on PAMAM/Pt and MWCNTs was developed. The resulting film of MWCNTs/PAMAM/Pt was characterized by transmission electron microscopy (TEM), linear sweep voltammetry (LSV) and amperometric it curve. It demonstrates excellent electrocatalytic responses toward the reduction of H2O2 at − 200 mV (vs.SCE) without HRP participation. Immobilized with glutamate oxidase (GlutaOx), an effective glutamate biosensor, was fabricated, and the in vivo detection for glutamate was realized combining with the on-line microdialysis system. The glutamate biosensor showed good linear range from 1.0 μM to 50.0 μM with the detection limit of 0.5 μM (S/N = 3). The basal level of glutamate in the striatum of rat was detected continuously with this on-line system and was calculated to be 5.80 ± 0.12 μM (n  = 3). This method was proved to be sensitive and selective and may be feasible in the further application of physiology and pathology.► We synthesize a PAMAM/Pt nanocomposite. ► MWCNTs/PAMAM/Pt is used as the catalyst for glutamate detection. ► On-line detection for glutamate is realized through microdialysis system. ► The level of glutamate in the striatum of rats is determined in vivo.
Keywords: On-line microdialysis system; PAMAM/Pt nanocomposites; H2O2; Glutamate biosensor;