The direct electrochemistry and electrocatalysis of heme proteins entrapped in carbon-coated nickel magnetic nanoparticle-chitosan-dimethylformamide (CNN-CS-DMF) composite films were investigated in the hydrophilic ionic liquid [bmim][BF4]. The surface morphologies of a representative set of films were characterised via scanning electron microscopy. The proteins immobilised in the composite films were shown to retain their native secondary structure using UV-vis spectroscopy. The electrochemical performance of the heme proteins-CNN-CS-DMF films was evaluated via cyclic voltammetry and chronoamperometry. A pair of stable and well-defined redox peaks was observed for the heme protein films at formal potentials of -0.151V (HRP), -0.167V (Hb), -0.155V (Mb) and -0.193V (Cyt c) in [bmim][BF4]. Moreover, several electrochemical parameters of the heme proteins were calculated by nonlinear regression analysis of the square-wave voltammetry. The addition of CNN significantly enhanced not only the electron transfer of the heme proteins but also their electrocatalytic activity toward the reduction of H2O2. Low apparent Michaelis-Menten constants were obtained for the heme protein-CNN-CS-DMF films, demonstrating that the biosensors have a high affinity for H2O2. In addition, the resulting electrodes displayed a low detection limit and improved sensitivity for detecting H2O2, which indicates that the biocomposite film can serve as a platform for constructing new non-aqueous biosensors for real detection.

In the present work differential pulse voltammetry coupled with multivariate curve resolution-alternating least squares (MCR-ALS) was applied for simultaneous determination of betaxolol (Bet) and atenolol (Ate) in 0.20M Britton-Robinson (B-R) buffer solution at the surface of a multi-walled carbon nanotube modified carbon paste electrode (MWCNT/CPE). Characterization of the modified electrode was carried out by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). A strategy based on experimental design was followed. Operating conditions were improved with central composite rotatable design (CCRD) and response surface methodology (RSM), involving several chemical and instrumental parameters. Then second order data were built from variable pulse heights of DPV and after correction in potential shift analyzed by MCR-ALS. Analytical parameters such as linearity, repeatability, and stability were also investigated and a detection limit (DL) of 0.19 and 0.29μM for Bet and Ate was achieved, respectively. The proposed method was successfully applied in simultaneous determining the two analytes in human plasma.

The patch clamp technique in the whole cell configuration is potentially a powerful tool to investigate electroporation (electric-field-induced membrane permeabilization). Membrane polarization beyond certain threshold voltages leads to a steep conductance increase either indicating field-induced pore formation or being due to patch clamp artifacts (seal resistance breakdown). Protoplasts derived from tobacco culture cell lines (Bright Yellow-2, BY-2; Virginia bright Italian-0, VBI-0) were stained with the voltage-sensitive dye ANNINE-6. After establishing the whole cell patch clamp configuration 50-ms command voltage (Ucomm) steps ranging from -500mV to +500mV were applied while simultaneously exposing protoplasts to light at 475nm wavelength. Pulse-induced currents and fluorescence intensity (known to be linearly related to the trans-membrane voltage, Um) were recorded. Plotting fluorescence intensity against Ucomm revealed saturation of the curve at values<-300mV and >+300mV and close correlation with theoretical Um values calculated on the basis of membrane pore formation. For BY-2 and VBI-0 protoplasts ANNINE-6 voltage sensitivity was calculated to be -0.0014mV(-1) and -0.0012mV(-1), respectively. Voltage ramp experiments revealed cation-selectivity of field-induced pores. Anions are conducted poorly independent of their size. In conclusion, the patch clamp technique is validated as a useful tool in electroporation research.

Slow accumulation of plasmids from their diluted, pg/mL solutions (pH4.7) on a well defined glassy carbon (GC) electrode surface allowed for the formation of stable electrode layers consisting of two types of plasmid DNAs - pUC19 and pGEX-4T-2, in two forms - supercoiled circular (sc) and linear (lin). In the presence of methylene blue (MB), a typical redox indicator, the oxidation signals of nucleic acid bases are significantly enhanced. The interactions of the plasmids with MB are tested and used to distinguish between various types of plasmids. Instead of an MB reduction signal at ca. -0.2V vs. SCE, typically used to study MB interactions with DNAs, we have used the corresponding oxidation signal at ca. -0.2V, MB(I), as well as another oxidation signal at 1.05V, MB(III). On a bare GC electrode, the MB(III) and MB(I) signals are proportional to each other, while in the presence of the plasmid DNAs the relations between MB(III) and MB(I) depend on the type of plasmid. The plots: MB(III)/MB(I) vs. [MB] and MB(I) potential shift vs. [MB] are used to distinguish between the supercoiled and linear forms of the pUC19 and pGEX-4T-2 plasmids.

Interaction of uranyl ion (UO2(2+)) with immobilized double strand calf thymus DNA (ds-ct-DNA) on zirconium attached gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) is monitored by electrochemical techniques. The results show that after 15min proximity of the immobilized DNA with UO2(2+), the peak currents of the square wave voltammograms are decreased (about 80%), and the equivalent circuit model of electrochemical impedance spectroscopy (EIS) data, requires two constant phase elements (CPE) instead of only one. By using the surface concentration of DNA (≈2.3×10(-13)mol/cm(2)) and the number of the anthraquinonedisulfonic acid (AQDS) adsorbed on DNA (1.34×10(-10)mol/cm(2)) the ration of AQDS per DNA base pairs is obtained ≈1/30 before proximity to UO2(2+). Based on EIS technique, we find that the double strand structure of immobilized DNA on the electrode surface has been changed (damaged) by UO2(2+). This modified electrode has potential of becoming a screening tool for the rapid assessment of the interaction and genotoxicity of existing and new chemicals.

A cathode is a critical factor that limits the practical application of microbial fuel cells (MFCs) in terms of cost and power generation. To develop a cost-effective cathode, we investigate a cathode preparation technique using nickel foam as a current collector, activated carbon as a catalyst and PTFE as a binder. The effects of the type and loading of conductive carbon, the type and loading of activated carbon, and PTFE loading on cathode performance are systematically studied by linear sweep voltammetry (LSV). The nickel foam cathode MFC produces a power density of 1190±50mWm(-2), comparable with 1320mWm(-2) from a typical carbon cloth Pt cathode MFC. However, the cost of a nickel foam activated carbon cathode is 1/30 of that of carbon cloth Pt cathode. The results indicate that a nickel foam cathode could be used in scaling up the MFC system.

Horse erythrocytes, murine lymphoblasts (L5178Y) and lipid vesicles that were treated with dipicrylamine (DPA) as a lipophilic ion were studied by dielectric spectroscopy over a frequency range of 10Hz to 10MHz. The DPA-treated cells and lipid vesicles showed low-frequency (LF) dielectric dispersion around 1-10kHz in addition to β-dispersion due to the Maxwell-Wagner effect. The LF dispersion corresponds to that found in previous electrorotation (ROT) studies on DPA-treated cells, being due to the translocation of mobile ions in the plasma membranes. Analysis of the LF dispersion based on the mobile charge model provided the area-specific concentration Nt of DPA ions adsorbed at the membrane interfaces and their translocation rate constant ki between the interfaces. The values of Nt and ki were respectively 13-21nmol/m(2) and 0.7-1.6×10(4)s(-1) for both horse erythrocytes and L5178Y cells at 10μM DPA, being consistent with those determined by ROT for human erythrocytes and cultured cells.

The oxygen reduction due to microaerophilic biofilms grown on graphite cathodes (biocathodes) in Single Chamber Microbial Fuel Cells (SCMFCs) is proved and analysed in this paper. Pt-free cathode performances are compared with those of different platinum-loaded cathodes, before and after the biofilm growth. Membraneless SCMFCs were operating in batch-mode, filled with wastewater. A substrate (fuel) of sodium acetate (0.03M) was periodically added and the experiment lasted more than six months. A maximum of power densities, up to 0.5Wm(-2), were reached when biofilms developed on the electrodes and the cathodic potential decreased (open circuit potential of 50-200mV vs. SHE). The power output was almost constant with an acetate concentration of 0.01-0.05M and it fell down when the pH of the media exceeded 9.5, independently of the Pt-free/Pt-loading at the cathodes. Current densities varied in the range of 1-5Am(-2) (cathode area of 5cm(2)). Quasi-stationary polarization curves performed with a three-electrode configuration on cathodic and anodic electrodes showed that the anodic overpotential, more than the cathodic one, may limit the current density in the SCMFCs for a long-term operation.

Scanning electrochemical microscopy (SECM) is useful for analyzing various cellular responses. We have combined a micropipette (MP) with SECM to perform quantitative solution delivery to single cells. In this system, since the concentrations of electrochemical mediators are changed by the volume of solution delivered from the MP, we constructed a feedback control system to regulate MP delivery by SECM-detected signals. Cellular responses induced by MP delivery could be monitored by the SECM, and cell apoptosis was successfully detected by adding a kinase inhibitor of two orders of magnitude less than what is required in the conventional method. The SECM-based MP can activate a target cell, requiring a minimal amount of agent, and can continually examine target cell responses. This system improves the accuracy of delivery from the MP and is useful for single-cell analysis.