Bioelectrochemistry (v.89, #C)

Contents (v).

This paper describes the synthesis of 4-amino-6-hydroxy-2-mercaptopyrimidine capped gold nanoparticles (AHMP-AuNPs) in aqueous medium and their immobilization on indium tin oxide (ITO) electrode modified with (3‐mercaptopropyl)trimethoxysilane (MPTS) sol–gel for the determination of tannic acid (TA). The high resolution transmission electron microscopy (HR-TEM) images show that the particles are spherical in shape with a diameter of ~ 6 nm. The heterogeneous electron transfer rate constant (ket) of [Fe(CN)6]3 −/4 − at ITO/MPTS/AHMP-AuNPs electrode was found to be 1.14 × 10− 7  m/s. This value was much higher than the values obtained at ITO/MPTS (4.94 × 10− 9  m/s) and bare ITO (8.79 × 10− 8  m/s) electrodes, indicating that the electron transfer reaction was faster at AuNPs modified electrode. Further, the ITO/MPTS/AHMP-AuNPs electrode shows excellent electrocatalytic activity toward TA oxidation when compared to bare ITO electrode. This was understood from the obtained higher heterogeneous rate constant (ks) value at AuNPs modified electrode (7.35 × 10− 5  m/s) than at bare ITO electrode (5.45 × 10− 6  m/s). Using the amperometry method, detection of 20 nmol/L TA was achieved. The practical application of the present method was demonstrated by determining the concentration of TA in commercial beer samples.► Functionalized pyrimidine capped gold nanoparticles were prepared in water. ► Synthesized AuNPs were immobilized on ITO electrode using MPTS sol–gel as linker. ► AuNPs modified electrode was used for the determination of tannic acid (TA). ► The modified electrode showed a detection limit of 1.26 × 10− 10  M for TA. ► Modified electrode was successfully used for the determination of TA in beer samples.
Keywords: 4-Amino-6‐hydroxyl-2-mercaptopyrimidine capped gold nanoparticles; ITO electrode; Electrical impedance spectroscopy; Tannic acid; Beer samples;

The direct electrochemical behaviour of peptide methionine sulfoxide reductase A (MsrA) adsorbed on glassy carbon and boron doped diamond electrodes surface, was studied over a wide pH range by cyclic and differential pulse voltammetry. MsrA oxidation mechanism occurs in three consecutive, pH dependent steps, corresponding to the oxidation of tyrosine, tryptophan and histidine amino acid residues. At the glassy carbon electrode, the first step corresponds to the oxidation of tyrosine and tryptophan residues and occurs for the same potential. The advantage of boron doped diamond electrode was to enable the separation of tyrosine and tryptophan oxidation peaks. On the second step occurs the histidine oxidation, and on the third, at higher potentials, the second tryptophan oxidation. MsrA adsorbs on the hydrophobic carbon electrode surface preferentially through the three hydrophobic domains, C1, C2 and C3, which contain the tyrosine, tryptophan and histidine residues, and tryptophan exists only in these regions, and undergo electrochemical oxidation.► Direct electrochemical behaviour of peptide methionine sulfoxide reductase A (MsrA). ► pH-dependent process investigated at a glassy carbon electrode. ► The oxidation of tyrosine, tryptophan and histidine amino acid residues.
Keywords: Peptide methionine sulfoxide reductase A; Proteins; Amino acid oxidation; Adsorption; Voltammetry;

Rapid detection of alcohol is important in clinical diagnosis and fermentation industry. An octameric alcohol oxidase (AOx) (Mr 675 kDa) from Pichia pastoris, immobilized on multiwalled carbon nanotubes—Nafion® (MWCNT-Nf) matrix and encapsulated with polyethylenimine (PEI) on gold electrode (AuE), showed a redox peak at 0.21 V (vs. Ag/AgCl electrode at pH 7.5) for oxidation of alcohol. The electron transfer rate constant and surface coverage of the immobilized AOx were 1.69 ± 0.15 s− 1 and 2.43 × 10− 12  mol cm− 2, respectively. Studies on response and kinetics of Au-MWCNT‐Nf‐AOx-PEI bioelectrodes for alcohol showed a linear response in the range of 8 μM–42 μM, response time of 55 s for steady state current, and detection limit of 5 μM. The bioelectrode retains ~ 90% of the original response even after four weeks when stored in potassium phosphate buffer pH 7.5 at 4 °C. The fabricated bioelectrode was found to exclude interference caused by the common electroactive species such as ascorbic acid, uric acid, lactic acid, glucose and urea. The bioelectrode also showed reliable response characteristics in blood serum samples. The findings of the investigation have established the direct electrochemistry of the AOx protein and its potential biosensor application for quantitative detection of alcohol in blood serum.► Direct electrochemistry of alcohol oxidase in carbon nanotube matrix-based bioelectrode was established. ► The bioelectrode showed reliable response characteristics in the sample. ► Nearly 90% of the original response of the bioelectrode retained even after four weeks. ► The bioelectrode excluded interference caused by the common electroactive species of body fluid.
Keywords: Alcohol; Bioelectrode; Alcohol oxidase; Multiwalled carbon nanotubes; Direct electron transfer;

The performance characteristics of two new plastic membrane ion selective electrodes (ISEs) used for the determination of famciclovir (Fcv) based on the ion associate of Fcv with phosphotungstic acid (PTA) or phosphomolybdic acid (PMA) are described. Different experimental conditions as type of plasticizer to be incorporated in the membrane, life span, effect of soaking, pH, temperature, and interferences were studied. Both electrodes showed similar performance under these conditions, exhibiting Nernstian slopes of S (Fcv-PTA) = 58.60 ± 0.84 mV/decade and S (Fcv-PMA) = 58.77 ± 0.68 mV/decade within a usable concentration range of 10− 5–10− 2 [Fcv/M] at 298/K. Famciclovir was assayed potentiometrically in its pure solution, pharmaceutical preparations and biological fluids (urine and plasma) using proposed electrodes under batch and flow injection analysis (FIA) conditions with a recovery % ranging between 96.76% and 102.83% having RSD of 0.66%–1.81%. The electrodes were also successfully applied in the determination of the dissolution profile of Fcv tablets and the results came in agreement with the validated results of the HPLC method obtained from the quality control unit of the company producing the tablets.
Keywords: Flow injection analysis; Dissolution testing; Famciclovir; Ion-selective electrodes;

Electrofusion of B16-F1 and CHO cells: The comparison of the pulse first and contact first protocols by Marko Usaj; Karel Flisar; Damijan Miklavcic; Masa Kanduser (34-41).
High voltage electric pulses induce permeabilisation (i.e. electroporation) of cell membranes. Electric pulses also induce fusion of cells which are in contact. Contacts between cells can be established before electroporation, in so-called contact first or after electroporation in pulse first protocol. The lowest fusion yield was obtained by pulse first protocol (0.8% ± 0.3%) and it was only detected by phase contrast microscopy. Higher fusion yield detected by fluorescence microscopy was obtained by contact first protocol. The highest fusion yield (15%) was obtained by modified adherence method whereas fusion yield obtained by dielectrophoresis was lower (4%). The results are in agreement with current understanding of electrofusion process and with existing electrochemical models. Our data indicate that probability of stalk formation leading to fusion pores and cytoplasmic mixing is higher in contact first protocol where cells in contact are exposed to electric pulses. Another contribution of present study is the comparison of two detection methods. Although fusion yield can be more precisely determined with fluorescence microscopy we should note that by using this detection method single coloured fused cells cannot be detected. Therefore low fusion yields are more reliably detected by phase contrast microscopy.► Phase contrast and fluorescence microscopy for pulse first and contact first electrofusion yield evaluation. ► The systematical comparison of the pulse first and contact first electrofusion protocols. ► The comparison of different methods for achieving cell contacts and its effect on fusion yield. ► The final fusion yield depends on the method used for a cell contact achievement.
Keywords: Electrofusion protocols; Phase contrast microscopy; Fluorescence microscopy; Electroporation; Cell contact;

A novel cysteic acid modified carbon paste electrode (cysteic acid/CPE) based on electrochemical oxidation of l-cysteine was developed to simultaneously determine ofloxacin and gatifloxacin in the presence of sodium dodecyl benzene sulfonate (SDBS). Fourier transform infrared spectra (FTIR) indicated that l-cysteine was oxidated to cysteic acid. Electrochemical impedance spectroscopy (EIS) and cyclic voltammograms (CV) indicated that cysteic acid was successfully modified on electrode. The large peak separation (116 mV) between ofloxacin and gatifloxacin was obtained on cysteic acid/CPE while only one oxidation peak was found on bare electrode. And the peak currents increased 5 times compared to bare electrode. Moreover, the current could be further enhanced in the presence of an anionic surfactant, sodium dodecyl benzene sulfonate. The differential pulse voltammograms (DPV) exhibited that the oxidation peak currents were linearly proportional to their concentrations in the range of 0.06–10 μM for ofloxacin and 0.02–200 μM for gatifloxacin, and the detection limits of ofloxacin and gatifloxacin were 0.02 μM and 0.01 μM (S/N = 3), respectively. This proposed method was successfully applied to determine ofloxacin and gatifloxacin in pharmaceutical formulations and human serum samples.► Cysteic acid modified electrode based on electrochemical oxidation of l-cysteine ► Simultaneous detection of ofloxacin and gatifloxacin ► Obviously catalytic performance to the electrochemical response ► Determination in pharmaceutical formulations and human serum samples ► It showed high stability, repeatability, reproducibility, good sensitivity.
Keywords: Ofloxacin; Gatifloxacin; l-Cysteine; Simultaneous determination; Differential pulse voltammetry;

Triazole–acridine conjugates: Redox mechanisms and in situ electrochemical evaluation of interaction with double-stranded DNA by A. Dora R. Pontinha; Silvia Sparapani; Stephen Neidle; Ana Maria Oliveira-Brett (50-56).
Redox mechanisms and in situ electrochemical interaction with double-stranded DNA were investigated using a DNA-electrochemical biosensor for two disubstituted triazole-linked acridine compounds (GL15 and GL7), previously reporting as quadruplex DNA-binding molecules. The redox properties of GL15 and GL7 involve a complex, pH-dependent, adsorption-controlled irreversible process and were investigated using cyclic, differential pulse, and square wave voltammetry at a glassy carbon electrode. The interaction between duplex DNA and GL15 or GL7 was investigated in incubated solutions using dsDNA-, poly[G]-, and poly[A]-electrochemical biosensors. It was demonstrated that the interaction is time-dependent, both GL15 and GL7 interacting with dsDNA, causing condensation of dsDNA morphological structure but not oxidative damage.► Clarify the redox mechanism of two disubstituted triazole-linked acridine compounds ► pH-dependent process investigated at a glassy carbon electrode ► In situ evaluation of DNA-disubstituted triazole-linked acridine compounds
Keywords: Disubstituted triazole-linked acridines; GL15; GL7; Electrochemistry; DNA;