Use Of Ferricyanide Research Articles

Chemoorganotrophic electrofermentation by Cupriavidus necator using redox mediators

The non-pathogenic β-proteobacterium Cupriavidus necator has the ability to switch between chemoorganotrophic, chemolithoautotrophic and electrotrophic growth modes, making this microorganism a widely used host for cellular bioprocesses. Oxygen usually acts as the terminal electron acceptor in all growth modes. However, several challenges are associated with aeration, such as foam formation, oxygen supply costs, and the formation of an explosive gas mixture in chemolithoautotrophic cultivation with H2, CO2 and O2. Bioelectrochemical systems in which O2 is replaced by an electrode as a terminal electron acceptor offer a promising solution to these problems. The aim of this study was to establish a mediated electron transfer between the anode and the metabolism of living cells, i.e. anodic respiration, using fructose as electron and carbon source. Since C. necator is not able to transfer electrons directly to an electrode, redox mediators are required for this process. Based on previous observations on the extracellular electron transfer enabled by a polymeric mediator, we tested 11 common biological and non-biological redox mediators for their functionality and inhibitory effect for anodic electron transfer in a C. necator-based bioelectrochemical system. The use of ferricyanide at a concentration of 15 mM resulted in the highest current density of 260.75µAcm−2 and a coulombic efficiency of 64.1 %.

On the Effects of Ferricyanide as Cathodic Mediator on the Performance of Microbial Fuel Cells

This study provides an insight into the long-term influence of the use of ferricyanide in the cathode chamber of a microbial fuel cell (MFC) on the power generated and the COD removal attained. Two MFCs were operated in semicontinuous mode, using winery wastewater as fuel, activated sludge as the anodic inoculum, and concentrations of 0.05 and 0.25 M of ferrocyanide added in the cathode chamber as redox mediators. The MFC used had two chambers separated by a proton exchange membrane Sterion®. The results show that permeability of the membrane to mediators is a factor of the major significance. Under no crossover, the mediator produced a positive effect on the electricity generation and COD removal. However, as the experiments progressed, a significant concentration of mediator was detected in the anode chamber and the performance of the MFC gets worse. This work reports results that help to understand the main processes happening in the MFC.

Multilayer film of thiourea and gold nanoparticles as an effective platform for immobilization of activated non-labeled-DNA and construction of an ultrasensitive electrochemical DNA biosensor

In this work, self assembly of thiourea and gold nano-particle multilayer built up on a thiourea modified gold nanoparticles Au electrode, has been used as a platform for immobilization of activated ss-DNA. Two NH2 group of thiourea on a multilayer surface can interact with an activated phosphate group of non-labeled ss-DNA. Activated non-labeled ss-DNA was prepared using N-(3 dimethylaminopropyl)-N-ethyl-carbodiimide hydrochloride (EDC) and N-hydroxy-succinimide (NHS). The whole DNA biosensor fabrication process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods with the use of ferricyanide as an electrochemical redox indicator. Methylene Blue (MB) was used as the electrochemical indicator for monitoring the hybridization reaction after hybridized with the target ssDNA and the reduction current of MB intercalation decreased with increasing the concentration of target DNA, ranging from 7.9 × 10–13 to 1.2 × 10–8 M with a very low detection limit of 3.8 × 10–13 M (S/N = 3).

A label-free electrochemical immunosensor based on gold nanoparticles for direct detection of atrazine

A simple, selective, highly sensitive, and label-free electrochemical immunosensor for atrazine detection was developed by immobilizing gold nanoparticles (GNPs) on the gold electrode surface. The modified gold electrode exhibited good electrochemical activity. The high sensitive detection was achieved by increased the surface area of work electrode resulting in capturing more anti-atrazine monoclonal antibodies. The whole immunosensor fabrication process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with the use of ferricyanide as an electrochemical redox indicator, respectively. The signal was triggered based on the interaction between anti-atrazine monoclonal antibody and atrazine via differential pulse voltammetry (DPV). Under the optimal conditions, a limit of detection for atrazine as low as 0.016ng/mL was obtained in buffer, and the linear working range was between 0.05ng/mL and 0.5ng/mL. The recovery of 95.5–119.8% was obtained in maize. The proposed immunosensor has acceptable stability and reproducibility, thus could be applied to other pesticides analysis of crop samples in practice.

Direct electrochemical sensor for label-free DNA detection based on zero current potentiometry

A direct electrochemical DNA biosensor based on zero current potentiometry was fabricated by immobilization of ssDNA onto gold nanoparticles (AuNPs) coated pencil graphite electrode (PGE). One ssDNA/AuNPs/PGE was connected in series between clips of working and counter electrodes of a potentiostat, and then immersed into the solution together with a reference electrode, establishing a novel DNA biosensor for specific DNA detection. The variation of zero current potential difference (ΔEzcp) before and after hybridization of the self-assembled probe DNA with the target DNA was used as a signal to characterize and quantify the target DNA sequence. The whole DNA biosensor fabrication process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy with the use of ferricyanide as an electrochemical redox indicator. Under the optimized conditions, ΔEzcp was linear with the concentrations of the complementary target DNA in the range from 10nM to 1μM, with a detection limit of 6.9nM. The DNA biosensor showed a good reproducibility and selectivity. Prepared DNA biosensor is facile and sensitive, and it eliminates the need of using exogenous reagents to monitor the oligonucleotides hybridization.

A novel and highly sensitive acetyl-cholinesterase biosensor modified with hollow gold nanospheres

In this work, a highly sensitive acetylcholinesterase (AChE) inhibition-based amperometric biosensor has been developed. Firstly, a glassy carbon electrode (GCE) was modified with chitosan (Chits). Then, hollow gold nanospheres (HGNs) were absorbed onto the surface of chitosan based on the strong affinity through electrostatic adsorption. After that, L-cysteine (L-cys) was assembled on HGNs through Au-S bond. The hollow gold nanospheres were prepared by using Co nanoparticles as sacrificial templates and characterized by scanning electron microscopy, transmission electron microscopy and ultraviolet spectra, respectively. Finally, AChE was immobilized with covalent binding via -COOH groups of L-cysteine onto the modified GCE. The AChE biosensor fabrication process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy methods with the use of ferricyanide as an electrochemical redox indicator. Under optimum conditions, the inhibition rates of pesticides were proportional to their concentrations in the range of 0.1-150 and 0.1-200μgL(-1) for chlorpyrifos and carbofuran, respectively, the detection limits were 0.06μgL(-1) for chlorpyrifos and 0.08μgL(-1) for carbofuran. Moreover, the biosensor exhibited a good stability and reproducibility and was suitable for trace detection of pesticide residues in vegetables and fruits.

Electrochemical synthesis of gold nanostructure modified electrode and its development in electrochemical DNA biosensor

In this article, gold nanostructure modified electrodes were achieved by a simple one-step electrodeposition method. The morphologies of modified electrodes could be easily controlled by changing the pH of HAuCl 4 solution. The novel nanoflower-like particles with the nanoplates as the building blocks could be interestingly obtained at pH 5.0. The gold nanoflower modified electrodes were then used for the fabrication of electrochemical DNA biosensor. The DNA biosensor fabrication process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy with the use of ferricyanide as an electrochemical redox indicator. The DNA immobilization and hybridization on gold nanoflower modified electrode was studied with the use of [Ru(NH 3) 6] 3+ as a hybridization indicator. The electrochemical DNA biosensor shows a good selectivity and sensitivity toward the detection of target DNA. A detection limit of 1 pM toward target DNA could be obtained.

Development of an electrochemical DNA biosensor with a high sensitivity of fM by dendritic gold nanostructure modified electrode

In this paper, dendritic gold nanostructure (DenAu) modified electrode was obtained by direct electrodeposition of planar electrode into 2.8 mM HAuCl 4 and 0.1 M H 2SO 4 solution under a very negative potential of −1.5 V. Scanning electron microscopy was used to characterize the growth evolution of DenAu with time. The whole DNA biosensor fabrication process based on the DenAu modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy methods with the use of ferricyanide as an electrochemical redox indicator. The probe DNA immobilization and hybridization with target DNA on the modified electrode could be well distinguished by using methylene blue as an electrochemical hybridization indicator. The DenAu modified electrode could realize an ultra sensitivity of 1 fM toward complementary target DNA and a very wide dynamic detection range (from 1 fM to 1 nM).

Reactions of synthetic phenolic antioxidants with electrogenerated titrants and their analytical applications

Synthetic phenolic compounds (pyrogallol, catechol, hydroquinone, and their derivatives bearing heterocyclic fragments) react with electrogenerated titrants, halogens, and ferricyanide(III) ions. Stoichiometric coefficients of reactions are found. It is shown that the use of ferricyanide(III) ions as a titrant and a one-electron oxidant for the determination of this class of antioxidants offers advantages in comparison with titrants-halogens. The found amounts of pyrogallol, pyrocatechol, and hydroquinone derivatives in model solutions with the RSD 1–5% are fractions of milligrams. It is found that, in the series of the studied synthetic phenolic compounds, pyrocatechol derivatives possess the maximum antioxidant capacity (AOC).

Efficient Light Harvesting by Photosystem II Requires an Optimized Protein Packing Density in Grana Thylakoids

A recently developed technique for dilution of the naturally high protein packing density in isolated grana membranes was applied to study the dependence of the light harvesting efficiency of photosystem (PS) II on macromolecular crowding. Slight dilution of the protein packing from 80% area fraction to the value found in intact grana thylakoids (70%) leads to an improved functionality of PSII (increased antenna size, enhanced connectivity between reaction centers). Further dilution induces a functional disconnection of light-harvesting complex (LHC) II from PSII. It is concluded that efficient light harvesting by PSII requires an optimal protein packing density in grana membranes that is close to 70%. We hypothesize that the decreased efficiency in overcrowded isolated grana thylakoids is caused by excited state quenching in LHCII, which has previously been correlated with neoxanthin distortion. Resonance Raman spectroscopy confirms this increase in neoxanthin distortion in overcrowded grana as compared with intact thylakoids. Furthermore, analysis of the changes in the antenna size in highly diluted membranes indicates a lipid-induced dissociation of up to two trimeric LHCII from PSII, leaving one trimer connected. This observation supports a hierarchy of LHCII-binding sites on PSII.

Electrochemical DNA biosensor fabrication with hollow gold nanospheres modified electrode and its enhancement in DNA immobilization and hybridization

In this article, hollow gold nanospheres (HGN) were prepared by using Co nanoparticles as sacrificial templates and varying the stoichiometric ratio of HAuCl4 over the reductants. The HGN was then modified on the electrode surface via a 1,6-hexanedithiol linking agent to fabricate a novel electrochemical DNA biosensor. The whole DNA biosensor fabrication process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) methods with the use of ferricyanide as an electrochemical redox indicator. The probe DNA immobilization and hybridization on the modified electrode was further studied with CV and differential pulse voltammetry (DPV) methods by using Co(phen)33+ as an electrochemical hybridization indicator. Results revealed that the HGN modified electrode, especially for the HGN with the outer surface surrounded by densely spike-like nanocrystallites, could largely enhance the DNA hybridization ability. The fabricated DNA biosensor was proved to have a low detection limit (1pM) and a wide dynamic range (from 1pM to 10nM) with a high stability and reusability.

Total Antioxidant Capacity Assay Using Optimized Ferricyanide/Prussian Blue Method

The existing ferricyanide/Prussian blue assay of reducing capacity measurement was optimized so as to obtain a more reproducible, linear and additive response from antioxidants. The modification involved the simultaneous use of ferricyanide and iron(III) to regulate more favorable redox conditions for a greater variety of antioxidants. Prussian blue precipitation was hindered with the addition of sodium dodecyl sulfate, and the optimal pH was adjusted to 1.7 to maintain the redox activity of ferric ion while preventing its hydrolysis. Incubation of the reaction mixture at room temperature for 30 min enabled more complete oxidations than observed in the conventional ferricyanide method. The order of trolox equivalent antioxidant capacities was quercetin > rosmarinic acid > gallic acid > ferulic acid ≥ catechin > caffeic acid ≥ rutin ≥ ascorbic acid ≈ trolox. Synthetic antioxidant mixtures gave the theoretically expected total antioxidant capacities conforming to Beer’s law. The assay was nonresponsive to simple sugars and citric acid (which are not true antioxidants) but responsive to biologically important thiols which are not oxidized by other Fe(III)-based assays. The assay was used in real sample solutions by using the method of standard additions to green tea, nettle, and sage, and validated against other similar antioxidant assays.

Use of ferricyanide for gold and silver cyanidation

Low gold and silver leaching kinetics has been commonly observed in traditional gold-silver cyanidation process, especially in heap leaching and in situ leaching operations. The different mineralogy of gold and silver in the ores is suspected to be the main reason, e.g., the occurrence of low solubility acanthite (Ag 2S) typically results in low overall silver extraction. Due to the low solubility of oxygen in cyanide solution, the reactivity and availability of oxidant is believed to be the critical limitation for gold and silver dissolution. The use of ferricyanide as the auxiliary oxidant for gold and silver cyanidation has been examined. The rotating disc test results prove the assistant effect of ferricyanide on increasing the dissolution rate of gold and silver. The potential use of ferricyanide in gold/silver cyanidation process is proposed based on the leaching results of actual ores.

Cyano-bridged Fe(II)–Cu(II) bimetallic assemblies: honeycomb-like and pentanuclear structures

A 2D honeycomb-like compound [Fe(CN)6{Cu(apn)}3]n(ClO4)2n(H2O)4n (1) (apn=N-(3-aminopropyl)-1,3-propanediamine) and a pentanuclear compound [Fe(CN)6{Cu(dmen)2}4](ClO4)4 (2) (dmen=N,N-dimethylethylenediamine) have been prepared and characterized. In the synthesis, the use of ferricyanide or ferrocyanide yielded identical products due to reduction of Fe(III) ion to Fe(II) in water. For 1, all cyanide groups of ferrocyanide are bonded to six Cu(II) ions of which two symmetry-related Cu atoms are linked to nitrogen atoms of cyanide ligands bound to the neighboring Fe(II) center, resulting in the honeycomb structure. The variations of the geometries around Cu(II) centers are between ideal trigonal bipyramidal and square pyramidal structures, which may arise from the relative structural arrangements of flexible apn ligands. For 2, all the Cu(II) ions can be seen as square pyramidal geometries composed of basal least-squares planes from four dmen nitrogen atoms and apical nitrogen atoms from cyanide bridge. The Cu–NC angle around Cu centers in 2 is 127.9(7)°, much acuter than that of 1, which is presumably associated with steric interactions between the bulky methyl groups of the dmen ligands on the neighboring Cu ions. Both compounds exhibit very weak antiferromagnetic interactions in the low temperature range.

Ferricyanide mediated biochemical oxygen demand – development of a rapid biochemical oxygen demand assay

The use of an artificial electron acceptor in microbial respiration was investigated with a view to developing a rapid assay for biochemical oxygen demand (BOD). The use of ferricyanide resulted in a significant increase in the rate of the biochemical reaction and allowed for biodegradative conversion efficiencies similar to the 5-day BOD assay to be achieved in 1 h. The extent and rate of the ferricyanide mediated microbial reaction was determined by monitoring the concentration of the microbially produced ferrocyanide during or after incubation of microorganisms in the presence of ferricyanide and organic substrate. Spectrophotometry, potentiometry and amperometry using microelectrodes were evaluated as detection methods, with the latter providing the most convenient, stable and reproducible results. Experimental parameters investigated included incubation time, incubation temperature, microbial concentration, ferricyanide concentration and substrate concentration. In all cases, the results obtained were analogous to that expected in conventional aerobic microbial oxidation of organic material, with the major difference being the considerable increase in rate. The microorganisms used in this study were Escherichia coli and Pseudomonas putida. Results showed that while E. coli could successfully catabolise a standard BOD solution containing glucose and glutamic acid, its use for other substrates was limited. Preliminary investigations into the use of P. putida, however, showed significantly improved performance and demonstrated the promise of this approach for rapid BOD determinations.

Determination of lead in calcium carbonate by flow-injection hydride generation with dc plasma atomic emission detection

Flow-injection hydride generation, coupled with dc plasma atomic emission spectrometry has been used for the determination of trace lead concentrations in calcium carbonate matrices. The use of ferricyanide combined with sodium tetrahydroborate(III) enable the production of plumbane from acid solution. The plumbane is separated in a new gas–liquid separator and delivered to the plasma for determination. Detection limits for the technique are 0.7 ng ml −1. Precision of measurements at the 20 ng ml −1 level was 1.6% RSD. In an investigation of interferences, it was found that Fe(II), Fe(III), Cd(II), Co(II), Mn(II), Ni(II) and Zn(II) do not interfere. The presence of copper(II) at 1 μg ml −1 reduced the signal from lead by 50%. Samples can be analyzed at a rate greater than 60 h −1.

The effect of divalent metal ions on the performance of a glucose-sensitive ENFET using potassium ferricyanide as an oxidising substrate

A glucose-sensitive ENFET was fabricated by immobilising glucose oxidase (GOD) on the gate of a pH-sensitive field-effect transistor. The operation of the ENFET using ferricyanide as an oxidising substrate is based on the production of H + ions during reoxidation of the reduced FADH 2 fragment of glucose oxidase. The use of ferricyanide as an alternative to oxygen permits the measurements to be taken in highly buffered solutions and extends the dynamic range of the biosensor. The addition of divalent metal ions, such as Ca 2+ and Mg 2+ , to the solution in a concentration from 10 to 150 mM substantially increases the response and extends the dynamic range of the biosensor. The increase in ionic strength associated with these additions does not account for such effects, in fact increasing ionic strength by other means slightly reduces the biosensor response. The results obtained are consistent with an increase of the rate of FADH 2 oxidation by ferricyanide. It seems that the metal ions facilitate the electron exchange between ferricyanide and the active centre of GOD that is similar in a way to the effect of multicharged cations on the reduction of anions on a mercury electrode. The latter phenomenon is usually explained in the framework of the Frumkin's slow discharge theory. The observed effect is strongly pH dependent with a maximum between pH 7 and 8. When a layer of reticulated lysozyme has been deposited on top of the layer of immobilised glucose oxidase, the addition of Ca 2+ ions to the solution had an even more dramatic effect on the calibration curve extending the ENFET dynamic range to more than 100 mM glucose, but in this case the ions, probably, affected not only the rate of FADH 2 oxidation but the permeability of the additional protein layer to ferricyanide as well.

Glucose-sensitive ENFET using potassium ferricyanide as an oxidizing substrate: the effect of an additional lysozyme membrane

A glucose-sensitive field-effect transistor is fabricated by immobilizing glucose oxidase on the gate of a ph-sensitive field-effect transistor. An additional membrane of reticulated lysozyme is formed on top of the enzymatic layer. Calibration curves of the biosensor are measured in phosphate and Tris buffers in the presence of potassium ferricyanide as an oxidizing substrate alternative to oxygen. The use of ferricyanide leads to an increase of the acidification rate of the solution inside the enzymatic layer, because now two protons are produced during recycling the redox state of the glucose oxidase active centre. This permits the biosensor to be used even in highly buffered solutions. Under air-saturated conditions, the enzyme field-effect transistor (ENFET) calibration curves in both buffers used have a sigmoidal shape at any concentration of ferricyanide and extend up to a glucose concentration of ≈ 30 mM in 50 mM buffers. The sigmoidal form of the curves is mainly due to the competition between oxygen and ferricyanide as oxidizing substrates. In solutions saturated with nitrogen, the curves look as usual: they start with a linear part at lower and level off at greater glucose concentrations. The additional lysozyme membrane also suppresses the contribution o the variation of the buffer capacity of the solution inside the enzymatic layer during the biosensor operation to the sigmoidal appearance of the calibration curves.

Estimation of NADH oxidation in human skeletal muscle mitochondria

Assay procedures are described for the detection of defects in the process of NADH oxidation by the respiratory chain in human skeletal muscle biopsy specimens. The procedures allow determination of rotenone-sensitive NADH : O 2 oxidoreductase and NADH : ubiquinone-1 oxidoreductase activity not only in isolated mitochondria but also in post-nuclear supernatants. The use of ferricyanide as electron acceptor for estimation of NADH dehydrogenase activity is inadequate when only applied on a disrupted mitochondrial preparation.

Demonstration of succinic dehydrogenase in mitochondria of fern egg cells at electron microscope level.

The use of ferricyanide in the presence of Cu++ to capture the ferrocyanide generated proved a reliable method for the location of succinic dehydrogenase in fern egg cells. The response of mitochondria-like nuclear evaginations was largely negative, but small patches of apparently authentic reaction product, absent in the controls, were occasionally encountered in their envelopes. From the point of view of deciding the nature of the nuclear evaginations the results were therefore equivocal.