An approach of the preparation of catalysts based on copper oxide-polypyrrole (PPy) composites formed via electrooxidation of CuI–PPy layers on the surface of inert glassy carbon electrode was proposed. The pure CuI without polypyrrole matrix was used for comparison. The formation of CuO and the presence of CuO phase in electrooxidized samples was confirmed by EDX and XRD analysis correspondingly. Electrochemical properties of electrooxidized CuI–PPy composite (EOCP) were studied in formaldehyde and methanol oxidation reactions and compared with electrochemical properties of electrooxidized CuI (EOC) sample. Tests in methanol and in formaldehyde solutions confirmed the highest sensitivity of studied samples to formaldehyde. The linear detection range (LDR) of formaldehyde detection in alkaline solution for EOC system was 0–10 mM, the sensitivity was 125 ± 4 nA µg–1 mM–1, the detection limit was 15.9 ± 0.6 µM, while EOCP system demonstrated the extended LDR of 0–60 mM, the slightly lower sensitivity of 103 ± 0.5 nA µg–1 mM–1 but the lower detection limit of 7.3 ± 0.3 µM.

Herein, the electrochemical responses of Saccharomyces cerevisiae cultivated in YPD medium were tested in amperometric mode using microanalytical screen-printed electrodes modified with potassium ferricyanide and 1,10-phenanthroline-5,6-dione as mediators. The electrochemical signals obtained correlated well with the yeast growth curve. Electrochemical analysis of the cell-free supernatants (CFSs), obtained after removing S. cerevisiae cells, indicated that the mediator response, whether using potassium ferricyanide or phenanthroline-5,6-dione, depends more on the composition of the CFSs than on the intrinsic electroactivity of the cells. FT-IR and GC-MS investigations confirmed the formation of several electroactive compounds in the CFSs, such as hydroquinones and organohydrazines. Model electrochemical tests using ferricyanide as redox mediator indicated that quinones and organohydrazines are the most electroactive components formed during microbial activity. These results suggest that the electrochemical response in mediated bioanodes containing living cells is primarily driven by interactions between the mediator and electroactive metabolic products, rather than by direct interactions between the mediator and the cells.

Chronoamperometry and steady-state voltammetry data for a specially designed working electrode composed of a Pt disk covered mechanically with various perfluorinated cation-exchange membranes in contact with an external 2 M sulfuric acid solution with addition of various NaBr concentrations have been employed to estimate crossover parameters of bromide ions in relation to redox-flow battery applications. This technically simple but efficient approach has allowed us to determine the values of the diffusion coefficient of the electroactive Br-co-ion inside each membrane and of its equilibrium distribution coefficient between the membrane and the outer solution via an express experimental procedure and subsequent simple calculations. These crossover parameters of bromide co-ions have been found for Nafion NR211, Nafion XL, Nafion NR212, Nafion N115, Nafion N117 as well as GP-IEM-103, GP-IEM-105 membranes. Correlation of the steady-state diffusion-limited current due to the bromide oxidation both with its concentration in the outer solution and with the membrane thickness has been analyzed. It has been established that the transport characteristics of the bromide anion are close to each other for all homogeneous membranes under study in contact with a mixed X M NaBr +2 M H2SO4 solution (the value of X varies between 0.125 and 0.75): their values belong to the range from 2.6 10-6 cm2 s-1 to 3.4 10-6 cm2 s-1 for its diffusion coefficient inside membrane and to the range from 0.13 to 0.18 for its distribution coefficient at the membrane/solution boundary. Compared to the homogeneous membranes, the Br-anion diffusion inside the heterogenous (Nafion XL) membrane is slower and there is a tendency to its accumulation to a larger amount. Comparison of these results for Nafion NR212 in contact with the NaBr+H2SO4 solution with those previously obtained for the same membrane in contact with the HBr + H2SO4 solution has allowed us to conclude that the applied approximate treatment of experimental data based on the theory of molecular-diffusion transport of this co-ion inside the membrane (without taking into account the migration contribution to the bromide flux owing to the suppression of the electric field by highly mobile H+ cations) remains applicable for systems where the NaBr concentration inside the external solution does not exceed 0. 75 M.

The development is proposed of a specific non-enzymatic amperometric sensor based on electrodeposited copper nanoparticles (Cu-NPs) for the determination of uric acid (UA) in fermentation samples. Through optimization of the Cu-NPs-containing sensing layer, it was demonstrated that copper(II)-induced oxidation (catalytic effect) in the presence of molecular oxygen is more effective for determining UA than the adsorption of UA on Cu and Cu-oxide surfaces. More importantly, simply changing the sensing layer’s surface chemistry by increasing the defect CuxOy on the surface of Cu-NPs after heating at 70 °C for only 20 min significantly improved the specificity of UA determination in both model and real fermentation samples (viz. supernatants of S. cerevisiae and E. coli). This study can be used as a guideline for the future assembly of functional electrodeposited sensing layers for the specific determination of target electroactive bioanalyte(s).

The impact of composition, concentration, and pH of buffer solution on the activity and viability of Escherichia coli BB cells has been studied. Potassium/sodium phosphates with different composition and pH and TRIS buffer solutions used for microbiological and biotechnological applications as well as in microbial bioanodes were compared. The optimal buffer solution to achieve the highest dehydrogenase activity was 50 м\M potassium phosphate buffer solution, KH2PO4, isotonized by sodium chloride either with pH 7.4 for freshly obtained E. coli cells or with pH 7.8 to maintain the activity and viability of the microorganisms while storing. The cells concentration in solution was important to achieve the highest dehydrogenase activity, viz. 0.6-0.8 mg of cells (in terms of the dry weight) per mL of buffer solution with 0.2 M dextrose (substrate) was optimal. The good correlation between dehydrogenase activity and electrochemical current responses of bioanodes with E. coli and methyl orange as a redox mediator was shown.

Herein, we present a novel approach for the characterization of Escherichia coli cell-free supernatant (CFS), based on sample preparation with microfluidic superheating technology and electrodetection of total amount of low molecular weight compounds. CFS pretreatment through an innovative microfluidic superheating enabled removal of extracellular vesicles primary masking the oxidation of electroactive metabolites at screen-printed electrodes. After vesicles removal, the electrooxidation of low molecular weight compounds formed in CFSs as a result of bacterial activity became possible. Our protocol showed low intra-day deviation for CFSs after superheating and high run-to-run electric signal reproducibility and can provide quantitative information on the total content of electroactive compounds. This study represents a significant advance in our comprehension of E. coli CFSs as a source of electroactive low molecular weight compounds and their in vitro profiling by means of electrochemical techniques.

Glycerol is a widely used signaling bioanalyte in biotechnology. Glycerol can serve as a substrate or product of many metabolic processes in cells. Therefore, quantification of glycerol in fermentation samples with inexpensive, reliable, and rapid sensing systems is of great importance. In this work, an amperometric assay based on one-step designed electroplated functional Pd layers with controlled design was proposed for a rapid and selective measurement of glycerol in yeast fermentation medium. A novel assay utilizing electroplated Pd-sensing layers allows the quantification of glycerol in yeast fermentation medium in the presence of interfering species with RSD below 3

Herein, a study dealing with a progress on palladium (Pd) electrocatalysts for an efficient glycerol electrooxidation in model aqueous and real fermentation solutions with special focus on some physicochemical parameters (e.g., the impact of adsorption stage of multiple species, presence of oxygen, influence of anodic limits and Pd-size) was conducted. During the course of investigations by tandem of an optical oxygen minisensor and cyclic voltammetry a significant impact of oxygen on the efficiency of glycerol electrooxidation on Pd electrocatalysts at alkali pH in model aqueous and yeast fermentation media was revealed.The obtained knowledge was used for the optimization of an assay utilizing Pd-sensing layers for glycerol determination and quantification in yeast fermentation medium. Received results showed a satisfactory agreement with a control measurement carried out by gas chromatography mass-spectrometry.

In this study, fundamental aspects that have impact on the electroanalytical detection of hydrazine in phosphate, acetate and yeast fermentation medium in an analytically significant concentration range by several types of palladium (Pd)-modified electrodes, namely, Pd-ink, Pd-sputtered films and palladium nanoparticles (Pd-NPs) were systematically studied. The efficiency of hydrazine electrooxidation is not affected by the composition of multicomponent medium (i), presence of oxygen (ii), morphology or electroactive area (iii), but more likely depends on the purity degree of the electrode surface from residual palladium oxides (iv). In addition, using advanced methods of nanoanalytics and quantum chemistry, the crucial role of hydrazine surface adsorption (v) on oxide-free and oxide-based Pd-electrodes is highlighted. The obtained knowledge will provide future development strategies of electrodes based on nanoparticles of noble metals for tuned and efficient hydrazine electrooxidation in complex fermentation media.

Catalytic oxidation of methanol (MeOH) in the absence of noble metals and noble metal oxides as catalysts, and the use of metal-free materials are inexpensive and attractive process for practical use in electrocatalysis, sensors, and in direct methanol fuel cells. In previous works, it was found that the use of single-walled (SWCNT) or multi-walled (MWCNT) carbon nanotube paper electrodes instead of GC increases the catalytic efficiency of organic compounds oxidation in the presence of aromatic di-N-oxides by several times. In this work, the effect of non-covalent interactions on the catalytic efficiency of MeOH oxidation in the presence of 2,5-di-Me-pyrazine-di-N-oxide (Pyr(1)) in 0.1 M Bu4NClO4 solution in acetonitrile at SWCNT and MWCNT paper electrodes was studied by the methods of quantum chemical modeling, Raman spectroscopy, and using electrochemical data. New factors determined the features of mechanism of MeOH oxidation on CNT electrodes and lead to an increase in the catalytic efficiency of the electrode process in comparison with the GC electrode were established.

“Crude” extracts are a new perspective type of bioelectrocatalysts for biofuel cells. The method of obtaining a “crude” extract by disintegrating bacterial cell membranes (for example, by ultrasound) is simpler and more economical in comparison with pure enzymes. From a scientific point of view, the study of the biocatalytic properties of “crude” extracts is very interesting, since the disintegrated biomass contains a cascade of enzymes involved in the metabolism of microorganisms and coenzymes necessary for oxidative/reductive transformation. This set of bioactive substances makes it possible to simulate the processes occurring during the operation of a “natural” fuel cell in an artificial environment. The effect of the pH and composition of the LB nutrient medium used in the cultivation of E.coli on the dehydrogenase activity of protein extracts obtained from this culture was studied. It is shown that by selecting the pH and modifying the composition of the LB nutrient medium, it is possible to increase the value of the specific dehydrogenase activity of extracts by almost 9 times (from 0.25 to 2.2 mg/mg).

Quantum chemical approach has been applied for modeling the change in the conformation of the polypyrrole (PPy) chain both in its neutral and positively charged (doped) states due to its interaction with incorporated counterions. Polymer has been modeled by oligopyrrole molecule of 9-15 monomer units. It is shown that it is energetically favorable to reorient the pyrrole rings closest to the anion from trans to cis position. This reorientation leads to the formation of meanders which include 3-5 pyrrole rings per loop. Reduction in the loop size decreases the energy of interaction with the ion while an increase in the loop size reduces the number of attached ionic species accompanied by a slight change in their interaction energy with the PPy chain. The observed effect of polymer chain structuring in the presence of anions is proposed as a possible reason explaining the experimentally recorded broadening of the electroactivity potential region and the conductive state of the polypyrrole film on the electrode surface as a result of multiple repetitions of charge/discharge cycles of the polymer chain. Vibrational spectra of oligopyrrole complexes have been calculated, and prospects for experimental detection of predicted conformational states by IR spectroscopy are assessed.

Herein an assay toward a rapid and reliable profiling of extracellular matrix of Escherichia coli (E. coli) utilizing a tandem of GC-MS as a tool for definition of the exact chemical nature of low molecular weight compounds and cyclic voltammetry for their high throughput detection is presented.Briefly, during a set of investigations the formation of glycerol in the extracellular matrix (ECM) of E. coli at physiological relevant conditions of cells was revealed. Based on the obtained knowledge, the electrochemical protocol allowing both qualitative and quantitative analyses of glycerol in E. coli ECMs at palladium ink-modified screen printed electrodes with precision values (RSD) <10 % and recovery rates ranged from 98 % to 102 % was proposed.The provided protocol for a rapid electrochemical profiling of the bacterial ECMs can readily be used as a guideline for the controlled electroanalysis of target electroactive signaling analytes in complex biological samples.

Herein, a rapid electrochemical screening of yeasts (Saccharomyces cerevisiae) in vitro mode depending on their optical density, cultivation time and growth medium used was conducted in 3 min by palladium nanoparticles (Pd-NPs)-modified electrodes. Pd-NPs-modified electrodes operated in cyclic voltammetry mode at low scan rates, i.e. 5–20 mV/s supported a low oxidative process in the yeast extracellular matrix. The electrochemical screening relied on an efficient electrooxidation of secondary metabolites, i.e. organohydrazines formed in the extracellular medium as a result of microbial activity of yeast cells.More importantly, during the study the impact of fundamental parameters, viz. type of the matrix and pH on electroanalytical response of Pd-NPs-based electrodes in real fermentation medium was investigated in detail. The efficiency of the proposed in vitro electrochemical screening of yeast extracellular matrix was not affected by pH of the samples or composition of the multicomponent medium, but more likely exclusively depended on the presence of organohydrazines. The potential of this electroanalytical approach towards profiling of the extracellular matrix of Saccharomyces cerevisiae was compared with results obtained by gas chromatography mass-spectrometry (GC–MS) and genetically encoded biosensor (ro-GFP2) assays.

The synthesis of novel Pt-containing catalysts to achieve the high electrocatalytic activity in methanol oxidation reaction is the one of important directions in modern direct methanol fuel cells research and design. However, the comparison of results of electrochemical experiments shown in various works for different compositions of catalyst is practically impossible due to various conditions of experiments used by different authors’ groups. Hence, the importance of the methodology in study of electrochemical properties of Pt-containing catalysts discussed in the current work becomes evident. The Pt/C and PtRu/C commercial catalysts and also model systems with Pd, Rh, Ru, PtRu particles electrodeposited on glassy carbon electrode surface were used to specify the methodological aspects of comparative characterization of catalysts with various composition. The role of several important factors such as the methodology of electroactive surface area estimation, the nature of model acid electrolyte, polarization mode (potential range using in CV), polarization regime used for modeling of catalyst work in DMFC, medium pH and influence of methanol oxidation intermediates was discussed. It is shown that CO desorption is more appropriate method (with proposed modifications) for ECSA estimation; HClO4 is more favorable electrolyte for model experiments with catalysts when Nafion suspension is used as a binding agent. The polarization in CV mode in the potential range including the hydrogen adsorption region leads to local (near the electrode) pH changes, which results in increase in concentration (correlates with forward peak current density) of main electroactive species, gem-diolate, in methanol solution. The use of diluted methanol solutions allows to increase the efficiency of fuel consumption and decrease the overpotential of methanol oxidation reaction due to more favorable ratio of concentrations of electroactive and oxygen species adsorbed on the electrode surface.

Herein, a rapid electrochemical approach for testing of yeast cells damage using hydrogen peroxide spiking and Pd-NPs-based electrodes was proposed. The approach is based on the analyzing of electrochemical interactions between the droplets of yeast suspension spiked with hydrogen peroxide solutions (H2O2) and the surface of screen printed electrode modified by palladium nanoparticles (Pd-NPs). For the intact cells the characteristic anodic electrochemical signal recorded at 0.28 - 0.3 V remains at a constant level due to self-regulation processes regardless the spiked amount of hydrogen peroxide. In contrast, the increase of the anodic current corresponding to the added H2O2 concentration reflects the damage of yeast cells. Significantly, by introduction of peroxidesensitive oxidoreductase in the design of Pd-NPs, which led to the formation of hybrid oxidoreductase-Pd-NPs electrodes, it was possible to modify the electrochemical read-out of the proposed approach.

Herein, the impact of the chemical stability of RedOx mediator ferricyanide, K3[Fe(CN)6] (FC), a type of buffer solution used for bioreceptor preparation, gel composition (carboxymethylcellulose, CMC, Aerosile, AS, and alginate, ALG) on the long term stability of glucose test-strips and their analytical performance was examined. By simple addition of ALG to the functional gel aiming to improve its viscosity, we managed to enhance the sensitivity of conventional CMC-containing amperometric glucose test-strips from 3.3 µA/mM to 3.9 µA/mM and extend their shelf life from 8 months to 1.7 years. Moreover, during the course of investigations, it was revealed that the activity of enzyme in dependence with the used buffer did not linearly correlate with its activity in a dried functional layer, and the entire long-term electrochemical signal of glucose test-strips was determined by RedOx mediator FC chemical stability. The most stable and sensitive test-strips were obtained by the screen-printing approach from a gel containing 24 mg/mL GOx prepared in citrate buffer with pH 6, 200 mg/mL of FC and 10 mg/mL of CMC supplemented with 25 mg/mL of ALG.

Effects observed in the catalytic system are explained by a non-covalent interaction of the components of the system with the CNT surface.

During product isolation the received bioreceptors often do not exhibit a sufficient biochemical activity due to multistep dissociation and loss of cofactors. However, for bioelectrochemical applications the presence of cofactors is necessary for a successful oxidative or reductive conversion of the substrates to the products.Herein, we show how the immobilization of the required electroplated cofactors in a design of amperometric electrodes can in situ assist the activity of apo-enzymes. Compared to conventional approaches used in enzyme engineering this tailored nanoengineering methodology is superior from economic point of view, labor and time costs, storage conditions, reduced amount of waste and can fill the gap in the development of tuned bioelectrocatalysts.

PdRh/C catalyst and electrodeposited Pd, Rh and PdRh particles on glassy carbon electrode were studied in methanol and ethanol oxidation reactions in comparison with Pt-containing catalysts. Some features of this process have been described: (1) the appearance of oxidation peak in acidic and neutral media is possible only when polarization on CV is prolonged to hydrogen adsorption region where the surface OH-group formation occurred and surface oxides are reduced; (2) the CV-responses of model systems (electrodeposited Pd, Rh, PdRh) corresponding to alcohol oxidation increase and deform even during relaxation period when polarization is switched off; (3) experiments with addition of corresponding aldehydes (formaldehyde, acetaldehyde) to alcohol solution with stabilized CV responses showed that only increase in currents but not deformation of CV occurred. The addition of acid residue did not change the response noticeably. The formation of the same electroactive species, gem-diolate, for both alcohol and aldehyde electrooxidation mechanisms was supposed.