Bioelectrochemistry (v.72, #2)

Contents (iv).

The inhibition of Saccharomyces cerevisiae cells by acetic acid quantified by electrochemistry and fluorescence by Jinsheng Zhao; Zhong Wang; Min Wang; Qingpeng He; He Zhang (117-121).
In this paper, the effect of acetic acid on S. cerevisiae metabolism was studied for the first time with the combinational utilization of the mediated electrochemical method and intrinsic fluorescence method, and the results from both methods were compared with each other. It was confirmed in vivo that not only the glycolysis enzymes but also the NADH dehydrogenase were sensitive to acetic acid. The established technique might also be applicable in studying the toxicity of other environmental pollutants, such as phenol and its derivatives.
Keywords: Electrochemical methods; Menadione; Double mediator system; Intrinsic fluorescence;

Evaluation of the physico-chemical properties of chitosan as a potential carrier for rifampicin, using voltammetric and spectrophotometric techniques by Renê H.T. Santos; Neemias G. Santos; José P.H. Alves; Carlos A.B. Garcia; Luciane C.P. Romão; Maria Lara P.M. Arguelho (122-126).
Rifampicin is an antibiotic which, on a carbon paste electrode, shows an oxidation response of 0.492 V (vs. Ag/AgCl) at pH 7.0, due to the electroactivity of the hydroquinone group. Interaction of rifampicin with chitosan is strongly dependent on pH, species concentrations and contact time between the latter. Compared to the carbon paste electrode, electrodes modified with chitosan showed greater sensitivity, with optimum voltammetric profile obtained at pH 8.0. Spectrophotometric measurements indicate that rifampicin is strongly absorbed by chitosan at pH less than the pKa of the pharmaceutical, such behaviour being favourable for the use of chitosan as a carrier for the controlled release of rifampicin in the intestinal tract.
Keywords: Rifampicin; Chitosan; Controlled release; Voltammetry;

The current theory of enzymes and electric field interaction does not account for all the observed data since we could not observe non-linear behavior of cell suspensions as anticipated by other authors. In our case, we used a pure sinusoidal source, however the experiments that do account for responses used a sum of a central sinusoidal and its harmonics frequencies. As a result, we suggest that the enzyme and electric interaction are favored when the field has a non-strictly sinusoidal waveform, and this behavior is related to the true intermediate transitions of the enzyme during its catalytic cycle. Therefore, we developed an iterative model of the interaction process based on previous models and actual trends. The model well verified all the previous simulations and showed that, for a non-symmetrical enzyme, the energy can harvest its maximal for non sinusoidal fields.
Keywords: Proteins; Harmonic; Non-linear; Simulation; Iterative model;

Direct electron-transfer of native hemoglobin in blood: Kinetics and catalysis by Yanxia Xu; Chengguo Hu; Shengshui Hu (135-140).
A novel approach that uses nature biological tissues, fish blood, for the study of the direct electron-transfer of hemoglobin and its catalytic activity for H2O2 and NO2 is observed. The direct electron-transfer of hemoglobin in red blood cells in fish blood on glassy carbon electrode was observed for the first time. By simply casting fish blood on GC electrode surface and being air-dried, a pair of well-defined redox peaks for HbFe (III)/HbFe (II) appeared at about − 0.36 V (vs SCE) at the fish blood film modified GCE in a pH 7.0 phosphate buffer solution. Ultraviolet visible (UV/VIS) characterization and the enhancement of the redox response of Hb by adding pure Hb in fish blood suggested that Hb preserved the native second structures in the fish blood film. Optical micrographs showed that the RBCs retained its integrity in blood. Hb in blood/GCE maintained its activity and could be used to electrocatalyze the reduction H2O2 and NO2 .
Keywords: Direct electrochemistry; Hemeglobin (Hb); Blood; Electrocatalytic activity; Red blood cells (RBCs);

Gene delivery by electroporation after dielectrophoretic positioning of cells in a non-uniform electric field by Luke A. MacQueen; Michael D. Buschmann; Michael R. Wertheimer (141-148).
We report the use of dielectrophoresis (DEP) to position U-937 monocytes within a non-uniform electric field, prior to electroporation (EP) for gene delivery. DEP positioning and EP pulsing were both accomplished using a common set of inert planar electrodes, micro-fabricated on a glass substrate. A single-shell model of the cell's dielectric properties and finite-element modeling of the electric field distribution permitted us to predict the major features of cell positioning. The extent to which electric pulses increased the permeability of the cell membranes to florescent molecules and to pEGFPLuc DNA plasmids were found to depend on prior positioning. For a given set of pulse parameters, EP was either irreversible (resulting in cytolysis), reversible (leading to gene delivery), or not detectable, depending on where cells were positioned. Our results clearly demonstrate that position-dependent EP of cells in a non-uniform electric field can be controlled by DEP.
Keywords: Electroporation; Electropermeabilization; Dielectrophoresis; Non-uniform electric field; Gene delivery; Transfection; Micro-electrode;

The use of electrochemical impedance spectroscopy (EIS) in the evaluation of the electrochemical properties of a microbial fuel cell by Aswin K. Manohar; Orianna Bretschger; Kenneth H. Nealson; Florian Mansfeld (149-154).
Electrochemical impedance spectroscopy (EIS) has been used to determine several electrochemical properties of the anode and cathode of a mediator-less microbial fuel cell (MFC) under different operational conditions. These operational conditions included a system with and without the bacterial catalyst and EIS measurements at the open-circuit potential of the anode and the cathode or at an applied cell voltage. In all cases the impedance spectra followed a simple one-time-constant model (OTCM) in which the solution resistance is in series with a parallel combination of the polarization resistance and the electrode capacitance. Analysis of the impedance spectra showed that addition of Shewanella oneidensis MR-1 to a solution of buffer and lactate greatly increased the rate of the lactate oxidation at the anode under open-circuit conditions. The large decrease of open-circuit potential of the anode increased the cell voltage of the MFC and its power output. Measurements of impedance spectra for the MFC at different cell voltages resulted in determining the internal resistance (R int) of the MFC and it was found that R int is a function of cell voltage. Additionally, R int was equal to R ext at the cell voltage corresponding to maximum power, where R ext is the external resistance that must be applied across the circuit to obtain the maximum power output.
Keywords: Microbial fuel cell; Electrochemical impedance spectroscopy; Internal resistance of a microbial fuel cell;

Electrocatalysis of emodin at multi-wall nanotubes by Zhao-Hui Yin; Qiao Xu; Yi Tu; Qiu-Ju Zou; Jiu-Hong Yu; Yuan-Di Zhao (155-160).
In this article, the electrochemical behavior of emodin at multi-wall carbon nanotube modified glassy carbon electrodes (MWNTs/GCE) was studied. The result showed that MWNTs/GCE had high electrocatalytic activity for emodin. And the electrocatalytic redox process was a two-charge-two-proton process. Diffusion coefficient (D R ) of 8.403 × 10− 5 cm2 s1 of emodin was obtained. Further experiments demonstrated that the oxidative peaks increased linearly with emodin concentrations in the range of 1.0 × 106 to 1.0 × 104 M with a limit of detection of 3.0 × 107 M. This electrochemical method was accurate and reliable, therefore, it might provide a novel way for emodin detection.
Keywords: Carbon nanotube; Modified electrode; Emodin; Determination;

This paper presents a novel method to measure the dynamic process of membrane permeability during electroporation (EP) on microchips for human cancer cells. Micro EP chips with three-dimensional gold electrodes accommodating a single cell in between were fabricated with a modified electroplating process. Electrochemical impedance spectroscopy (EIS) was carried out with an electrochemistry analyzer on micro EP chips and a nonlinear equivalent circuit model was proposed to describe the dynamic response of the whole system. Using such a method, micro EP current was isolated from undesired leakage current to study the corresponding electroporation dynamics under different input voltages. In addition, cell membrane recovery dynamics after electroporation was also studied and the resealing time constants were determined for different pulse treatments.
Keywords: Electroporation; Electric current response; MEMS; HeLa cell; Equivalent circuit;

The electron transfer reactivity of kaempferol and its interaction with amino acid residues by Guifang Chen; Xiang Ma; Fanben Meng; Genxi Li (169-173).
In this work, the electron transfer reactivity of kaempferol was studied and the interaction in vivo between kaempferol and protein was simulated. Dimethylsulfoxide (DMSO) as an aprotic solvent was employed to simulate the specific environment. Various residues of amino acids were used to study the effect of the amino acids in the active site of protein on the electron transfer reactivity of kaempferol. Experimental results revealed that the redox activity of kaempferol was different in aprotic medium DMSO from that in water, and a new redox process was further found. Of all the residues tested, nitrogenous nucleophile, for example, imidazole, was observed to be able to facilitate the electron transfer of kaempferol, and the mechanism was also proposed. This work might provide a simple model to study the electron transfer reactivity of some small active organic molecules, especially medicines, in specific environment, which might approach a more accurate understanding of the activity of some medicines in vivo.
Keywords: Kaempferol; Imidazole; Amino acid residues; Simulation; Electron transfer;

Scanning electrochemical microscopy study of laccase within a sol–gel processed silicate film by Wojciech Nogala; Malte Burchardt; Marcin Opallo; Jerzy Rogalski; Gunther Wittstock (174-182).
The enzyme p-diphenol:dioxygen oxidoreductase (laccase, EC 1.10.3.2) was isolated from Cerrena unicolor fungus and embedded in a sol–gel film obtained by acidic condensation of TMOS. The gel was cast to thin films on glass. The laccase-containing silicate films were inspected by confocal laser scanning microscopy (CLSM), scanning force microscopy (SFM) and scanning electrochemical microscopy (SECM). CLSM images in the reflection mode showed aggregates within the silicate films. SECM images in the substrate-generation/tip-collection mode using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) as electron donor for laccase showed that the position of aggregates coincides with increased enzymatic activity within the silicate film. The flux from individual aggregates was detected. SECM images in the redox competition mode confirmed the assignment and could exclude that topographic features observed by CLSM and SFM could be the reason for the image contrast. SFM images showed that the aggregates partially dissolve during prolonged exposure to aqueous buffer. The experimental setup allowed following one individual aggregate over time with all three microscopic techniques which enabled the collection of complementing information on morphology and catalytic activity as well as their development over time.
Keywords: Laccase; Sol–gel; Dioxygen reduction; Scanning electrochemical microscopy (SECM); Scanning force microscopy (SFM); Confocal laser scanning microscopy (CLSM);