Bioelectrochemistry (v.99, #C)

The proton pump of bacteriorhodopsin in an aqueous solution at varied pH upon pulsed excitation was monitored using a solution-based electrochemical module. The photocurrent action spectrum agreed with the absorption contour at 495–645 nm. Diminishing the photocurrent amplitude by adding a protonophore, carbonyl cyanide m-chlorophenyl hydrazone, revealed that protons were the charge carriers of the photocurrent. The evolution of the conventional proton pump is proposed to occur in three elementary steps consecutively: first, the proton relay from the protonated Schiff base to the purple membrane (PM) surface (k1), then the proton exchange between PM surface and bulk (k2), and finally, the proton uptake (k3). The fitted temporal profiles of the photocurrent agreed with observations in the pH range 5.8–9.5. At pH 7.3, k1, k2, and k3 were 2098 s− 1, 412 s− 1, and 44 s− 1, respectively. The rate coefficients at pH 9.5 were smaller than those at pH 6.3 by a factor of approximately 2, consistent with the differences in the intrinsic mobilities of the charge carriers proton and hydroxide ion. The combination of the electrochemical detection module and the concomitant model provides a promising tool for quantitative and qualitative characterization of the light-driven ion pumps.Display Omitted
Keywords: Bacteriorhodopsin; Proton pump; Electrochemical cell; Kinetics; Action spectrum;

Bioelectrochemical sensing of promethazine with bamboo-type multiwalled carbon nanotubes dispersed in calf-thymus double stranded DNA by Emiliano N. Primo; M. Belén Oviedo; Cristián G. Sánchez; María D. Rubianes; Gustavo A. Rivas (8-16).
We report the quantification of promethazine (PMZ) using glassy carbon electrodes (GCE) modified with bamboo-like multi-walled carbon nanotubes (bCNT) dispersed in double stranded calf-thymus DNA (dsDNA) (GCE/bCNT-dsDNA). Cyclic voltammetry measurements demonstrated that PMZ presents a thin film-confined redox behavior at GCE/bCNT-dsDNA, opposite to the irreversibly-adsorbed behavior obtained at GCE modified with bCNT dispersed in ethanol (GCE/bCNT). Differential pulse voltammetry-adsorptive stripping with medium exchange experiments performed with GCE/bCNT-dsDNA and GCE modified with bCNTs dispersed in single-stranded calf-thymus DNA (ssDNA) confirmed that the interaction between PMZ and bCNT-dsDNA is mainly hydrophobic. These differences are due to the intercalation of PMZ within the dsDNA that supports the bCNTs, as evidenced from the bathochromic displacement of UV–Vis absorption spectra of PMZ and quantum dynamics calculations at DFTB level. The efficient accumulation of PMZ at GCE/bCNT-dsDNA made possible its sensitive quantification at nanomolar levels (sensitivity: (3.50 ± 0.05) × 108  μA·cm− 2·M− 1 and detection limit: 23 nM). The biosensor was successfully used for the determination of PMZ in a pharmaceutical product with excellent correlation.Display Omitted
Keywords: Bamboo carbon nanotube; Dispersion; Double stranded DNA; Intercalation; Promethazine; Electrochemical (bio)sensor;

Idarubicin (IDA), 4-demethoxydaunorubicin, is an anthracycline derivative and widely used treatment of leukemia. The electrochemical behavior of IDA was examined at a glassy carbon electrode (GCE) in different aqueous supporting electrolyte using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The oxidation process of IDA was found to be pH dependent and irreversible proceeding with a transfer of 1 proton and 1 electron under the diffusion controlled mechanism. The electroactive center is the hydroxyl group on the aromatic ring which produces a final quinonic product. The diffusion coefficient of IDA was calculated to be D IDA  = 7.47 × 10− 6  cm2  s− 1 in pH = 4.3 0.1 M acetate buffer.The interaction of IDA and double stranded deoxyribonucleic acid (ds-DNA) was investigated using electrochemical ds-DNA biosensor and incubation solution by means of DPV. The DNA damage was detected following the changes in the oxidation peaks of guanosine and adenosine residues. The results obtained showed that IDA interacts with DNA which causes the change in the DNA morphological structure. In addition to these polynucleotides, PolyG and PolyA, biosensors were also used to confirm the interaction between ds-DNA and IDA. However, no oxidation peaks of the purine base oxidation products, 8-oxoGua and 2,8-oxoAde, were observed.
Keywords: Idarubicin; Electrochemical biosensor; Drug–DNA interaction; Oxidation; Voltammetry;

An electrochemical study of the oxidation of 8-hydroxyguanine (8-OH-Gua) at gold nanoparticles attached to single walled carbon nanotube modified edge plane pyrolytic graphite electrode (AuNP-SWCNT/EPPGE) has been carried out to develop a method for the self diagnosis of diabetes. The level of 8-OH-Gua, an important biomarker of oxidative DNA damage, is higher in urine of diabetic patients than control subjects. A detailed comparison has been made between the square wave voltammetric (SWV) response of SWCNT/EPPGE and AuNP-SWCNT/EPPGE towards the oxidation of 8-OH-Gua in respect of several essential analytical parameters viz. sensitivity, detection limit, peak current and peak potential. The AuNP-SWCNT/EPPGE exhibited a well defined anodic peak at potential of ~ 221 mV for the oxidation of 8-OH-Gua as compared to ~ 312 mV using SWCNT/EPPGE at pH = 7.2. Under optimized conditions linear calibration curve for 8-OH-Gua is obtained over a concentration range of 0.01–10.0 nM in phosphate buffer solution (PBS) of pH = 7.2 with detection limit and sensitivity of 5.0 (± 0.1) pM and 4.9 (± 0.1) μA nM− 1, respectively. The oxidation of 8-OH-Gua occurred in a pH dependent process and the electrode reaction followed adsorption controlled pathway. The electrode exhibited an efficient catalytic response with good reproducibility and stability. The method has been found selective and successfully implemented for the determination of 8-OH-Gua in urine samples of diabetic patients.
Keywords: SWCNT; Square wave voltammetry; 8-Hydroxyguanine; Diabetes;

Dynamic effects of point source electroporation on the rat brain tissue by Shirley Sharabi; David Last; David Guez; Dianne Daniels; Mohammad Ibrahim Hjouj; Sharona Salomon; Elad Maor; Yael Mardor (30-39).
In spite of aggressive therapy, existing treatments offer poor prognosis for glioblastoma multiforme due to tumor infiltration into the surrounding brain as well as poor blood–brain barrier penetration of most therapeutic agents.In this paper we present a novel approach for a minimally invasive treatment and a non-invasive response assessment methodology consisting of applying intracranial point-source electroporation and assessing treatment effect volumes using magnetic resonance imaging. Using a unique setup of a single intracranial electrode and an external surface electrode we treated rats' brains with various electroporation protocols and applied magnetic resonance imaging to study the dependence of the physiological effects on electroporation treatment parameters. The extent of blood–brain barrier disruption and later volumes of permanent brain tissue damage were found to correlate significantly with the treatment voltages (r2  = 0.99, p < 0.001) and the number of treatment pulses (r2  = 0.94, p < 0.002). Blood–brain barrier disruption depicted 3.2 ± 0.3 times larger volumes than the final permanent damage volumes (p < 0.0001). These results indicate that it may be beneficial to use more than one modality of electroporation when planning a treatment for brain tumors.
Keywords: Blood brain barrier; Electroporation; Brain; Tumor; MRI;

In situ evaluation of gemcitabine–DNA interaction using a DNA-electrochemical biosensor by Rafael M. Buoro; Ilanna C. Lopes; Victor C. Diculescu; Silvia H.P. Serrano; Liseta Lemos; Ana Maria Oliveira-Brett (40-45).
The electrochemical behaviour of the cytosine nucleoside analogue and anti-cancer drug gemcitabine (GEM) was investigated at glassy carbon electrode, using cyclic, differential pulse and square wave voltammetry, in different pH supporting electrolytes, and no electrochemical redox process was observed. The evaluation of the interaction between GEM and DNA in incubated solutions and using the DNA-electrochemical biosensor was studied. The DNA structural modifications and damage were electrochemically detected following the changes in the oxidation peaks of guanosine and adenosine residues and the occurrence of the free guanine residues electrochemical signal. The DNA–GEM interaction mechanism occurred in two sequential steps. The initial process was independent of the DNA sequence and led to the condensation/aggregation of the DNA strands, producing rigid structures, which favoured a second step, in which the guanine hydrogen atoms, participating in the C–G base pair, interacted with the GEM ribose moiety fluorine atoms.
Keywords: Gemcitabine; DNA; Guanine; Electrochemical DNA-biosensor; Interaction mechanism;

A new self-assembled layer-by-layer glucose biosensor based on chitosan biopolymer entrapped enzyme with nitrogen doped graphene by Madalina M. Barsan; Melinda David; Monica Florescu; Laura Ţugulea; Christopher M.A. Brett (46-52).
The layer-by-layer (LbL) technique has been used for the construction of a new enzyme biosensor. Multilayer films containing glucose oxidase, GOx, and nitrogen-doped graphene (NG) dispersed in the biocompatible positively-charged polymer chitosan (chit+(NG + GOx)), together with the negatively charged polymer poly(styrene sulfonate), PSS, were assembled by alternately immersing a gold electrode substrate in chit+(NG + GOx) and PSS solutions. Gravimetric monitoring during LbL assembly by an electrochemical quartz microbalance enabled investigation of the adsorption mechanism and deposited mass for each monolayer. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the LbL modified electrodes, in order to establish the contribution of each monolayer to the overall electrochemical properties of the biosensor. The importance of NG in the biosensor architecture was evaluated by undertaking a comparative study without NG in the chit layer. The GOx biosensor's analytical properties were evaluated by fixed potential chronoamperometry and compared with similar reported biosensors. The biosensor operates at a low potential of − 0.2 V vs., Ag/AgCl, exhibiting a high sensitivity of 10.5 μA cm− 2  mM− 1, and a detection limit of 64 μM. This study shows a simple approach in developing new biosensor architectures, combining the advantages of nitrogen-doped graphene with the LbL technique for enzyme immobilization.Display Omitted
Keywords: Layer-by layer; Quartz crystal microbalance; Nitrogen doped graphene; Enzyme; Chitosan;

A simple method for determination of d-penicillamine on the carbon paste electrode using cupric ions by Ali Ghaffarinejad; Fatemeh Hashemi; Zahra Nodehi; Razieh Salahandish (53-56).
The interaction of d-penicillamine (PA) with copper at the carbon paste electrode (CPE) in the presence of cupric ions (Cu2 +) was used for the determination of PA at very low potential (0.1 V vs. Ag/AgCl) without applying of any modifier. The electrochemical response of copper is changed considerably in the presence of negligible amount of PA. In this report some important parameters, such as pH effect, Cu2 + concentration and scan rate are studied, which the selected conditions were acetate buffer (pH = 6) and 1 mM Cu2 +. The linear range for PA was from 1.0 × 10− 6 to 1.0 × 10− 4  M with an experimental detection limit of 1.0 × 10− 7  M. The relative standard deviation for 6 measurements was 3.8%. The interfering effects of some important inorganic ions were investigated, which there was no significant effect on the PA measurements. Also three organic interferences including ascorbic acid (AA), uric acid (UA) and l-cysteine (Cys) were examined, which the effect of AA was not notable, the interference of UA was moderate and for Cys was significant, but moderate at the levels which fined in the urine samples. This method was applied successfully for the determination of PA in urine sample.
Keywords: d-penicillamine; Carbon paste electrode; Cupric ion; Urine sample;