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The article is a continuation of the book chapter entitled Recent Advances in Antioxidant Capacity Assays published by IntechOpen in 2021. The various methods for determining antioxidant capacity in a variety of materials (plant extracts, biological material, foods, etc.) are discussed, with a special emphasis on articles published in recent years and especially on reviews. Both chemical methods for determining antioxidant capacity and cellular antioxidant capacity assays were presented. In addition to the review published in 2021, the following methods for the determination of antioxidant capacity were presented: crocin bleaching assay, Briggs-Rauscher reaction inhibition assay, ferricyanide-Prussian blue assay, cerric reducing antioxidant capacity assay and Anti Oxidant Power 1 (AOP1) assay. Several applications of the cellular antioxidant capacity assay were also presented in tabular form. [ABSTRACT FROM AUTHOR]

Ferri and ferro coordination polymers in sphere structure were synthesized. Scanning Electron Microscopy (SEM) Energy Dispersive X-Ray Spectroscopy (EDX), Gel Permeation Chromatography (GPC), elemental analysis, and Fourier Transform Infrared Spectroscopy (FT-IR) were performed for chemical and structural characterization of the coordination polymers. Glucose oxidase (GOD) enzyme immobilized to compare of kinetic parameters deal with glucano-1,5 lacton formation. Analyses results illustrate that structures coordination of ions Fe2+ and Fe3+ are different to the same support. It was seen that 2 mol of Fe2+ ion ((PS-N-([Fe(CN)4L]K3)2) was bound per unit structure while 1 mol of Fe3+ ion (PS-N- ([Fe(CN)2L]K)) is attaching. Km values of were found as 15.32 and 10.93 for (PS-NFe2+)- GOD and (PS-N-Fe3+)-GOD, respectively. Km value for (PS-N-Fe3+)-GOD was found to be 0.5 times higher, possible reason of such a case is the larger reduction potential of Fe3+. As the charge on the coordination structure increased, the enzyme's affinity for the substrate increased. After 20 repeated measurements, GOD immobilized on (PS-N-Fe3+) polymer retained 45.47% activity, while GOD immobilized on (PS-N-Fe2+) polymer retained 57.86% activity. [ABSTRACT FROM AUTHOR]

Understanding the factors that influence nitrite degradation in whole blood and developing methods for its stable preservation are crucial for ensuring accurate and reliable forensic identification in cases of nitrite poisoning. This study systematically monitored nitrite degradation and changes in hemoglobin proportions across different initial nitrite concentrations and blood samples. It was revealed that high nitrite concentrations rapidly reduced deoxyhemoglobin levels within the first 15 minutes and subsequently reacted with oxyhemoglobin at a slower rate. Therefore, the proportions of these two hemoglobin forms are key factors in determining nitrite degradation rates. Regarding preservation, the study examined the effects of low temperatures (4°C and −20°C) and various preservatives (potassium ferricyanide, N-ethylmaleimide) on nitrite stability. The results indicate that adding 6.6 g/L potassium ferricyanide can rapidly eliminate all deoxyhemoglobin and reduce oxyhemoglobin proportions to below 60 %, enabling stable preservation of high nitrite concentrations in whole blood for over 30 days at −20°C. The efficacy of potassium ferricyanide was further validated in forensic-acquired postmortem heart blood samples. • High nitrite levels reduce deoxyhemoglobin and react with oxyhemoglobin in the blood. • The hemoglobin ratio is the critical factor determining the rate of nitrite degradation. • Potassium ferricyanide removes deoxyhemoglobin and reduces oxyhemoglobin to below 60 % in 15 minutes. • Potassium ferricyanide preserves high nitrite concentrations in whole blood at −20°C for over 30 days. • The efficacy of potassium ferricyanide was further validated in forensic-acquired postmortem heart blood samples. [ABSTRACT FROM AUTHOR]

We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000 eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by grating spectrometers. These results show that soft-X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry, and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples. [ABSTRACT FROM AUTHOR]

Ferricyanide Fe(CN)6 3- is one of the most stable cyanometallic complexes present in the gold mining effluents. This cyanocomplex is hard to degrade by natural attenuation and generates a negative impact on aquatic environments. Although free cyanide (CN-) can be obtained by acidifying the solution, the CN- is lethal for all forms of life. The oxidation of Fe(CN)6 3- in a typical photocatalitic system was evaluated with the addition of H2O2. To verify the degradation, chemical parameters, such as free cyanide, the formation of ammonia, nitrate, and total iron were analyzed at the end of the process. Different parameters were evaluated to analyze the behavior of the degradation: 1. dark stage adsorption using the catalyst, 2. the TiO2 dosage, 3. Addition of H2O2, 4. UV radiation power (120 and 200W) and finally a test of TiO2 with solar radiation. The photolysis effect from a ferricyanide solution at 100 mg L-1 at alkaline pH 13, showed that the complex studied is highly stable since under UV irradiation conditions (λ> 300 nm), a low rate of dissociation was observed. After 24h of irradiation, the cyanocomplex was under 20%, whereas degradations up to 70% were obtained in a heterogeneous photocatalysis system with TiO2. The best result was achieved with the H2O2 and TiO2 photocatalytic system, and the stoichiometric concentration was about 2.5 times less than the peroxide used in the gold mining industry, reaching 83% degradation. The photocatalytic process obtained less toxic byproducts than the original synthetic ferricyanide used as mining wastewater. [ABSTRACT FROM AUTHOR]

Efficient electrode-electrolyte interaction is vital prerequisite for capacitive performance of supercapacitor. Herein, a novel capacitive system is proposed based on bare Ni foam electrode and ferricyanides (equal molar K 3 Fe(CN) 6 /K 4 Fe(CN) 6 pair) mediated alkali electrolyte free of any active electrode material. The efficient electrode-electrolyte interaction enables high faradic capacitance, considerable cycleability and slow self-discharge behavior. The hybrid supercapacitor based on the Ni foam electrode-ferricyanides electrolyte positive half-cell and activated carbon negative electrode delivers high energy, power and excellent cycleability, manifesting the significance of electrode-electrolyte interaction to capacitive performance. Image 1 • A facile bare Ni foam electrode-redox electrolyte capacitive system was proposed. • Efficient electrode-electrolyte interaction leads to high capacitive performance. • The hybrid supercapacitor based on this capacitive system offers high energy density. [ABSTRACT FROM AUTHOR]

Abstract The use of biosensors by using microorganisms such as bacteria have short life cycles and provide other advantages. One colorimetric biosensor technique that has been developed is the use of a biosensor utilizing the incorporation of Prussian blue formation reactions mediated by E. coli bioreactors with ferricyanide. Immobilization is a method that allows the bacteria can be used for long-term without reducing its ability as bioreceptor. This study aimed to develop a novel and rapid immobilized bacterial biosensor for the detection of toxic compound in water and to evaluate their analytical performances. Immobilization of E. coli performed by trapping method using alginate material support. The bacterial suspension was mixed with sodium alginate (1:1 v/v), and the mixture was continuously dropped in CaCl 2 solution to be a form of beads. The beads were used as bioreceptor to detect toxicants regarding cadmium, arsenic, mercury, chromium and lead solutions with Prussian blue as a colorimetric indicator. The linearity and sensitivity of detection of beads to the toxicants were tested, the stability of repeated use and storage were evaluated as well. The results showed that E. coli could be immobilized using alginate with response value was correlated with toxic concentration. The developed biosensor was more stable when used repeatedly and could be stored in a long time. The immobilization of E. coli in calcium alginate bead was successfully performed as a biosensor system for monitoring acute toxicity in water. Graphical abstract fx1 Highlights • A novel and rapid immobilized bacterial biosensor were successfully developed. • Biosensor developed have a good analytical performances. • Immobilization of E. coli with calcium alginate can be used more than one cycles. • Biosensor microbial beads seemed to be stable for storage up to 20 days. [ABSTRACT FROM AUTHOR]

Polypyrrole films doped with sulfonated β-cyclodextrin (PPy/sβ-CD) and carboxymethyl β-cyclodextrin (PPy/CMβ-CD) were formed on electropolymerisation of pyrrole in a solution of the cyclodextrin sodium salts. Lower rates of electropolymerisation were evident with the carboxymethyl β-CD and this was attributed to protonation of the carboxylate groups due to an increase in the interfacial pH at the electrode-solution interface. The PPy/sβ-CD and PPy/CMβ-CD films showed cation exchange behaviour with the ingress of Na+ and its associated water molecules on reduction. The PPy/CMβ-CD film showed less electroactive behaviour which may be related to the lower number of anionic pendants on the CMβ-CD or to the possible precipitation of the less soluble neutral CD which arises due to the protonation of the carboxylate groups. The PPy/sβ-CD showed a high capacitance of 6.0 mF cm−2 corresponding to a specific capacitance of 71 F g−1 over a wide potential range extending from − 0.60 to 0.60 V vs SCE. Over-oxidation was observed at relatively low potentials, at about 0.60 V vs SCE. A diffusion coefficient of 6.47 × 10−6 cm2 s−1 and a rate constant of 3.73 × 10−2 cm s−1 were obtained for the ferricyanide redox couple at the PPy/sβ-CD, indicating little or no inhibition of the ferricyanide redox reaction.ᅟ [ABSTRACT FROM AUTHOR]

Abstract In this paper, a simple and sensitive immunosensor was fabricated for the detection of alpha-fetoprotein (AFP), which is based on a one-pot synthesized nanocomposite of gold nanoparticles-dextran-reduced graphene oxide (AuNPs-Dex-RGO). The AuNPs-Dex-RGO nanocomposite structure was confirmed by transmission electron microscope (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FT-IR). With ferricyanide as the electrochemical probe, this method achieved ultrasensitive detection of AFP antigen. The specific immunoreaction between AFP and AFP antibody resulted in a linear relationship between the redox peak current intensity of [Fe(CN) 6 ]4−/3- and AFP concentration. The detection range is 0.01–20 ng mL−1, and the detection limit is 0.05 pg mL−1. Moreover, the selectivity, reproducibility and stability of the proposed immunosensor were acceptable, which permitted the feasibility for the determination of AFP in human serum with satisfactory results, indicating the great potential for clinical application. Highlights • We proposed a new biosensor which novelly combines the advantages of both dextran and gold nanoparticles. • The AFP immunosensor has been successfully fabricated directly and simply by one-step synthesis based on AuNPs-Dex-RGO. • The AFP immunosensor exhibited outstanding performance with the wide linear range and low detection limit. • The AFP immunosensor has been successfully applied in the analysis of AFP in serum samples. • The AFP immunosensor exhibited high sensitivity and good stability. [ABSTRACT FROM AUTHOR]

In the existing study, the performance of (I2/I3 -) as the efficient redox catholyte for escherchia coli based microbial fuel cell (MFC) was investigated and compared with conventional ferricyanide based system. This studies also examined the effect of applied current density, linear sweep voltammetry, open circuit voltage, discharge capacitance, Impedance, Energy and power density of the microbial fuel cell. Linear sweep voltammetry studies revealed the higher current density (3.3768 mAcm-2) for(I2/I3 -)additive owing to its electro-reduction and this value is about 1.5 times higher in comparison to ferricyanide based system. The characteristics of (I2/I3 -)based MFC is attributed to its higher capacitive contribution, high conductivity, and high power, when compared to ferricyanide based MFC. The extreme power density of the MFC fabricated using (I2/I3 -)and ferricyanide additive at the measured current density of 50 µAcm-2were observed to be 1,140 and 1,670.8303mWm-2. Among the results, (I2/I3 -) basedMFCperformance displays excessive potential for enlightening the power generation of MFC. [ABSTRACT FROM AUTHOR]

Cyclic voltammetry was exploited to understand the interaction between chiral methyl-2-(5-fluorouracil-1-acetamide)-3-phenylpropionate molecules (denoted as (R)- or (S)-5FUPPM) and double-stranded (ds) or G-quadruplex (G4) DNAs. Using Fe(CN)63- as the redox mark, experiments illustrate that the anodic peak of Fe(CN)63- oxidation decreases as the concentration of 5FUPPM in the solution is increased. Calculation with the Langmuir equation yields the binding equilibrium constant of 9.1 × 10³ for the dsDNA and (S)-5FUPPM and of 3.3 × 103 for dsDNA and (R)-5FUPPM, suggesting that (S)-5FUPPM has more favorable interaction with dsDNA. On the other hand, the calculated binding constant between G4-DNA and (S)-5FUPPM is 1.6 × 104, as opposed to 3.2 × 104 between G4-DNA and (R)-5FUPPM. The results suggest that the binding selectivity of (R)-5FUPPM with DNAs, defined with (KG4-DNA/KdsDNA), is about 5 times larger than that of (S)-5FUPPM and DNAs, which is consistent with their inhibition rate on tumor cell. The information achieved here suggests that electrochemical characterization can provide useful information for the screening of new drug candidates. [ABSTRACT FROM AUTHOR]

Abstract In this study, activated red mud (ARM) was used as a new adsorbent for the removal of ferricyanide anions from aqueous solution. Based on the percentage of ferricyanide removal and ferricyanide adsorption capacity, optimum conditions were evaluated using the response surface method (RSM) and central composite design (CCD). In optimum conditions (pH = 5.6, adsorbent dosage of 2.59 g, ferricyanide concentration of 60 ppm and contact time of 60 min), the percentage of ferricyanide removal and ferricyanide adsorption capacity were obtained as 79.6% and 1.8 mg/g, respectively. The kinetics and equilibrium studies were evaluated by considering the effective parameters including pH and ferricyanide concentration. Kinetic studies were evaluated by kinetic models of pseudo first-order, pseudo-second-order (four different linearized forms), Elovich and intraparticle diffusion. The results of the kinetic study indicated that the mechanism of ferricyanide adsorption onto the ARM adsorbent is a chemisorption interaction by a fast ferricyanide adsorption onto ARM and subsequently the slow diffusion of ferricyanide ions into the ARM inner adsorption sites. The equilibrium studies showed that the adsorption process followed the Langmuir model in which ferricyanide adsorption onto ARM was homogeneous with monolayer adsorption. The results indicated that the activation process of red mud improved adsorbent efficiency and increased the adsorption capacity. Highlights • A novel adsorbent activated red mud was used for ferricyanide removal from wastewaters. • The process depends on solution pH, ferricyanide concentration and adsorbent dosage. • Ferricyanide adsorption follows the Langmuir model with homogenous monolayer adsorption. • Ferricyanide adsorption onto activated red mud is divided into two steps with chemisorption interaction. [ABSTRACT FROM AUTHOR]

A spectrophotometric sensitive, selective and inexpensive method for the determination of phenolic drug phenylephrine hydrochloride. The method depended on the oxidation of phenylephrine hydrochlorideby potassium ferricyanide and coupling of the oxidized product with reagent 4-aminoantipyrine to give intensely coloredabsorbs light strongly in the spectral region of 503 nm. Beer's law was obtained in the concentration range of 5-100mgL-1.Good linearity (r2=0.9992) Under the optimum condition. calculation the standard error, limit of detection(LOD) (signal/noise = 3), Limits of Quantitation's, LOQ, Accuracy, and precision (R.S.D., %) better than 1%. Study the Effect of different parameter: order of addition, nature of the complex, temperature and effect of The concentration and type base. Results of theanalyses of pure drug and dosage forms by the proposed method are in good agreement with those of the official method. [ABSTRACT FROM AUTHOR]

We demonstrate the effect of varying the channel and land width dimensions of an interdigitated flow field experimentally and through computational modeling. Measured polarization curves (overpotential versus current density) are reported for a symmetric cell with a ferrocyanide-ferricyanide electrolyte in aqueous potassium chloride. A two-dimensional, coupled fluid dynamic and electrochemical model is developed to interpret polarization results from the symmetric cell. This model suggests that stagnant fluid zones above the center lines of the interdigitated channels negatively impact cell performance. A three-dimensional computational fluid dynamic model is used to calculate the pressure drop and power losses associated with flowing fluid through these flow fields. The voltage efficiency of the cell, corrected for pumping power losses, is evaluated and reported as a function of channel and land width to identify high-efficiency flow fields. The implications for the engineering of large-area flow fields are discussed. [ABSTRACT FROM AUTHOR]

The present work describes an electrochemical Hg 2+ ion biosensor which used Au nanoparticles decorated reduced graphene oxide (Au NPs-RGO) for generating electrochemical signal as indicator involving. Hg 2+ ions specifically captured two thymine bases (T) of DNA probe to form T-Hg 2+ -T stable base pairs, therefore, Hg 2+ ion solution induced the structure of Au NPs-RGO modified thiol-functionalized DNA probe from single-strand to hairpin. The DNA 1 modified on Au electrode is complementary with Au NPs-RGO modified single-stranded DNA probe. Therefore, the amount of Au NPs-RGO adsorbed on electrode is decreased when the concentrations of Hg 2+ ions increase. The current response of the fabricated biosensor is monitored on ferricyanide system, which exhibits a wide linear range of 0–2000 nM and a high selectivity towards Hg 2+ ion. Besides, there are no co-factors used in the process of fabricating biosensor. Moreover, the biosensor is applied for detecting Hg 2+ ions in water sample with satisfactory results. [ABSTRACT FROM AUTHOR]

We report a high energy density thermally chargeable supercapacitor (TCSC) based on the thermogalvanic effect, built by sandwiching a potassium ferrocyanide/ferricyanide gel electrolyte film between two high surface area carbon cloth electrodes. In addition to the characteristic Seebeck coefficient of −1.21 mV K −1 , the pseudocapacitive property of the ferrocyanide/ferricyanide redox couple endows the device with a high area-specific capacitance of 13 F cm −2 which finally leads to high thermally induced energy storage density. Furthermore, the all-solid-state and flexibility of the device allows it to accommodate different heat source shapes. Overall, the device offers a simple, scalable and cost-effective means to harvest energy from intermittent waste heat sources. Lastly, we propose an equivalent circuit model to elucidate the working mechanisms of energy conversion and storage applicable to thermally chargeable supercapacitor devices in general. A fitting analysis aids in the evaluation of model circuit parameters providing good agreement with experimental voltage and current measurements. [ABSTRACT FROM AUTHOR]

The integration of photocathodes with enzymatic label tracer for the development of amplified PEC immunoassays is attractive for different diagnosis applications. Herein, we induce a novel strategy for the construction of cathodic PEC immunoassay on the basis of enzymatic reaction inhibited exciton trapping for PbS quantum dots (QDs). The cathodic photocurrent of the PbS QDs sensitized NiO was inhibited by cupric ions due to the formation of exciton trapping centers of CuS on their surface. In the presence the model target of carcinoembryonic antigen (CEA), a sandwich-type immunoreaction occurred with the detection antibody labeled glucose oxidase (GOx) as the signal tracer. The enzymatic reduction of ferricyanide ([Fe(CN) 6 ] 3− ) by GOx produced ferrocyanide ([Fe(CN) 6 ] 4− ), which easily combined with cupric ions to form cupric hexacyanoferrate (CuHCF, Cu 2 [Fe(CN) 6 ]) aggregates, and thus interrupted the formation of the exciton trapping centers of CuS. The enhanced photocurrent of the system was linear with the CEA concentration ranging from 0.5 pg/mL to 30 ng/mL with a detection limit of 0.17 pg/mL. Moreover, the PEC immunosensor also displayed high specificity and good reproducibility toward the target protein. It was also evaluated to analyze CEA in real samples of human serum specimens, which gave well matched results with the commercially available enzyme-linked immunosorbent assay (ELISA) kits. [ABSTRACT FROM AUTHOR]

A simple electrochemical sensor platform for hydrogen peroxide (H2O2) using silver nanoparticles (Ag NPs) entrenched in silicate matrix (APS(SG)) is reported. The redox molecules such as potassium ferricyanide ([Fe(CN)6]3−), methyl viologen (MV2+) and ruthenium hexamine ([Ru(NH3)6]3+) were utilized to investigate the electron transfer behavior of the APS(SG)-Ag NPs. The glassy carbon (GC) electrode modified with amine-functionalized silicate sol-gel matrix (GC/APS(SG)) exhibited a complete suppression of the electrochemical response toward MV2+ and [Ru(NH3)6]3+. However, GC/APS(SG) electrode displayed a twofold increase in the peak currents and fast electron transfer kinetics toward [Fe(CN)6]3− in comparison with GC electrode, suggesting that GC/APS(SG) electrode demonstrated an excellent anion exchange property. The GC electrode modified with APS(SG)-Ag NPs (GC/APS(SG)-Ag NPs) showed an improved electron transfer kinetics when neither positive nor negative charge of the electroactive species in the electrolyte. The GC/APS(SG)-Ag NP electrode was effectively further applied for the electrocatalytic and sensor applications toward H2O2. The present sensor exhibited the reduction of H2O2 at less negative potential and showed the experimental low detection limit of 25.0 µM with the sensitivity of 0.042 µA/µM. In addition, the developed APS(SG)-Ag NP-based amperometric sensor presented fast response, good stability and reproducibility. [ABSTRACT FROM AUTHOR]

A new type of nanoporous carbon (NPC) was synthesized using dandelion pappus as a cost-effective carbon source through chemical activation with phosphoric acid. Notably, NPC is first considered to be used as an enhanced electrode material for the analysis of tryptophan (Trp). The high electrical conductivity of nanoporous carbon modified electrode (NPC/GCE) was better demonstrated by cyclic voltammetry using the ferricyanide system as a probe. Furthermore, the NPC/GCE exhibited an excellent electrocatalytic activity toward Trp oxidation with a decreased overpotential and improved current response, mainly due to the porous structure and large specific surface of nanoporous carbon. The electrocatalytic oxidation mechanism of Trp at the modified electrode was also investigated by cyclic voltammetry. The amperometric response of NPC-based sensor is linear in the 1 μM to 103 μM concentration range and the sensitivity is 171.43 μA mM −1  cm −2 . The proposed sensor was also successfully applied to the determination of Trp in real samples, and the satisfactory recoveries were obtained. [ABSTRACT FROM AUTHOR]

The present study explores the production, characterization, and application of a potentially stable melanin precursor from marine imperfect non-spore-forming Aspergillus nidulans sp. strain SG 28. Growth of the culture in artificial seawater with galactose and monosodium glutamate, pH at 7.2-7.5, and temperature at 35 ± 0.5 °C exhibits pigment production with the yield of 0.700- 0.800 g/L. The characterization studies revealed that the pigment is orange reddish pink in color, soluble in water, insoluble in both polar and non-polar organic solvents, and decolorized when exposed to H2O2, KMnO4, and K2Cr2O7. UV-visible spectrum exhibits maximum absorption peak at 330 nm and mild shoulders at 400 and 500 nm. The pigment displayed both antioxidant and reducing power properties when exposed with ABTS and ferricyanide, respectively. The sun protection factor of the pigment was determined as 9.9. The cytocompatibility of the obtained pigment studied using HaCaTcells revealed that the cells are viable up to 500 μM. Experiments on UVB protection of the pigment using HaCat cells demonstrated the appreciable protective effect by reducing the ROS generation upon UVB exposure. In conclusion, the pigment obtained from the marine imperfect fungus showed structural similarity with DHICA which is confirmed by LC-MS. The presence of metal ions in the growth medium mediates the reaction to proceed towards DHICA formation. The SPF analysis, antioxidant property, and the UVB protection studies authenticate the potential use of pigment for skin care. [ABSTRACT FROM AUTHOR]

Hypothesis Electrosynthesis of the MIP nano-film after binding of the separated domains or holo-cytochrome BM3 via an engineered anchor should result in domain-specific cavities in the polymer layer. Experiments Both the two domains and the holo P450 BM3 have been bound prior polymer deposition via a N-terminal engineered his6-anchor to the electrode surface. Each step of MIP preparation was characterized by cyclic voltammetry of the redox-marker ferricyanide. Rebinding after template removal was evaluated by quantifying the suppression of the diffusive permeability of the signal for ferricyanide and by the NADH-dependent reduction of cytochrome c by the reductase domain (BMR). Findings The working hypothesis is verified by the discrimination of the two domains by the respective MIPs: The holoenzyme P450 BM3 was ca. 5.5 times more effectively recognized by the film imprinted with the oxidase domain (BMO) as compared to the BMR-MIP or the non-imprinted polymer (NIP). Obviously, a cavity is formed during the imprinting process around the his 6 -tag-anchored BMR which cannot accommodate the broader BMO or the P450 BM3. The affinity of the MIP towards P450 BM3 is comparable with that to the monomer in solution. The his 6 -tagged P450 BM3 binds (30 percent) stronger which shows the additive effect of the interaction with the MIP and the binding to the electrode. [ABSTRACT FROM AUTHOR]

Schulman's titration (ST) and dynamic light scattering (DLS) were employed to obtain structural parameters of the reverse microemulsions formed by the functionalized surfactants cetyltrimethylammonium ferricyanide (CTAFeIII) and didodecyldimethylammonium ferricyanide (DDAFeIII). From the ST, the amount of surfactant and cosurfactant per droplet can be calculated, and if the droplets are spherical, it is possible to determine the droplet radius taking into account geometrical parameters. DLS measures the collective diffusion coefficient of the droplets, and then by means of the Stoke-Einstein equation, the droplets radius can be calculated. When the amount of water in the microemulsions is lower than 15 wt%, both techniques yield similar droplet radii, regardless of the functionalized surfactant used, which indicates that the microemulsions contain spherical droplets in this range of water concentration. When the amount of water reaches 20 wt% the radii obtained by DLS are larger than the one deduced from ST, suggesting that at this water concentration, the droplets are not spherical. These results are useful to understand the behavior of bulky functionalized surfactants and their possibility to be applied in the synthesis of nanoparticles based on ferricyanide ions. [ABSTRACT FROM AUTHOR]

For the first time, the preparation of leaf-like α-Fe 2 O 3 micron-particles via a pyrolysis method using potassium ferricyanide (K 3 [Fe(CN) 6 ]) as the precursor was reported in this work. The characterizations of the synthesized samples were mainly conducted by using XRD, XPS and SEM. The existence of α-Fe 2 O 3 in the final samples was effectively demonstrated by the XRD patterns and XPS spectra, and the SEM images indicated that the micron-particles with leaf-like crystal morphology as the main components were observed in sample b, and instead, more micron-particles with cubic crystal morphology were displayed in sample a. The electrochemical performances of the prepared samples as anode materials for lithium ion batteries (LIBs) were principally evaluated by using CV, galvanostatic charge-discharge tests and EIS. The results of electrochemical measurements demonstrated that at the current density of 100 mA g −1 , the initial specific capacity of sample b was about 741 mAh g −1 , much larger than that of sample a (564 mAh g −1 ). More importantly, after 10 cycles, at the current density of 500 mA g −1 , the capacity of sample b was maintained as high as 317 mAh g −1 , significantly larger than that of sample a (244 mAh g −1 ). [ABSTRACT FROM AUTHOR]

An amine-functionalized porous sol–gel silica film was shown to be an effective platform to immobilize small anionic redox mediators of high solubility on solid electrodes by electrostatic interaction. The highly soluble mediator hexacyanoferrate was used as a model. The film was grown and firmly anchored on a gold electrode surface via thiol groups of a self-assembled monolayer of (3-mercaptopropyl)trimethoxysilane. Film growth and thickness were controlled by electrochemical modulation of pH at the electrode/solution interface in a sol of a hydrolyzed solution of tetraethoxysilane and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane by the application of a negative potential to the electrode. Protonation of the amine groups made the amine-functionalized surface useful to immobilize hexacyanoferrate on gold. Thus, the immobilization is pH dependent, being highly effective in strongly acidic medium. Cyclic voltammetry and scanning electron microscopy were used to characterize the film and to optimize the experimental conditions. The stability of the film was demonstrated by applying the catalytic properties of the hexacyanoferrate containing surface for nitrite sensing using a flow injection analysis (FIA) system. Under the optimized conditions, the sensor exhibited high sensitivity, low detection limit, easy handling, and stability with a linear range from 1.0 to 40.0 µmol L−1and a detection limit of 0.53 µmol L−1based on a signal-to-noise ratio of 3. The sensor was successfully applied to nitrite determination in water samples using FIA with excellent recoveries. [ABSTRACT FROM PUBLISHER]

Photosynthesis converts solar energy into chemical energy. Photosystem II (PSII) oxidizes water to produce oxygen, electrons and protons under solar light irradiation. This light-driven water oxidation initiates a series of reactions in photosynthesis. Basic photoelectrochemical studies on PSII are directed toward the enzymatic applications of PSII for sustainable production of electricity or solar fuels. To maximize the photoelectrochemical catalytic activity of PSII on electrode substrates, interfacial designs between PSII and electrode substrates are important. Herein, we report bio-inorganic photoanodes of PSII and ferricyanide-intercalated layered double hydroxide (LDH) for visible-light-driven water oxidation. PSII is simply drop-cast onto a ferricyanide-intercalated cobalt–aluminum LDH and then shows a turnover frequency of 0.5 ± 0.1 s −1 and a turnover number of 920 ± 40 for 1 h at pH 6.5 at +0.5 V vs. NHE under visible light irradiation. Photoelectrochemical experiments using a PSII inhibitor or a bio-engineered PSII suggest that interfacial electron transfer from the plastoquinone Q A site of PSII to ferricyanide may play an important role in improving the photo-electrocatalytic activity and stability of PSII. Our studies will open up new possibilities in fundamental or advanced photoelectrochemical studies of PSII. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman scattering (SERS) is a powerful technique based on the intensification of the Raman signal because of the interaction of a molecule with a nanostructured metal surface. Electrochemically roughened silver has been widely used as SERS substrate in the qualitative detection of analytes at the ultra-trace level. However, its potential for quantitative analysis has not been widely exploited yet. In this work, the combination of time-resolved Raman spectroelectrochemistry with silver screen-printed electrodes (SPE) is proposed as a novel methodology for the preparation of SERS substrates. The in situ activation of a SERS substrate is performed simultaneously with the analytical detection of a probe molecule, controlling the process related to the preparation of the substrate and performing the analytical measurement in real time. The results show the good performance of silver SPE as electrochemically-induced surface-enhanced Raman scattering substrates. Raman spectra were recorded at fairly low integration times (250 ms), obtaining useful spectroelectrochemical information of the processes occurring at the SPE surface with excellent time-resolution. By recording the microscopic surface images at different times during the experiment, we correlated the different data obtained: structural, optical and electrochemical. Finally, the in situ activation process was used to obtain a suitable in situ SERS signal for ferricyanide and tris(bipyridine)ruthenium (II) quantification. The detection of the analytes at concentrations of a few tens of nM was possible with a low integration time (2 s) and good precision, demonstrating the exceptional performance of the Raman spectroelectrochemical method and the possibility to use cost-effective screen-printed electrodes for applications where a high sensitivity is needed. [ABSTRACT FROM AUTHOR]

We examined the feasibility of using handheld mid-infrared (MIR) Fourier-Transform infrared (FT-IR) instrumentation for detecting and analysing cyanide (CN) contamination in field contaminated soils. Cyanide spiking experiments were first carried out, in the laboratory, to test the sensitivity of infrared Fourier transform (DRIFT) spectrometry to ferro- and ferricyanide compounds across a range of reference soils and minerals. Both benchtop and handheld diffuse reflectance infrared spectrometers were tested. Excellent results were obtained for the reference soils and minerals, with the MIR outperforming the near-infrared (NIR) range. Spectral peaks characteristic of the –C≡N group were observed near 2062 and 2118 cm -1 in the MIR region for the ferro- and ferricyanide compounds spiked into soils/minerals, respectively. In the NIR region such peaks were observed near 4134 and 4220 cm -1 . Cyanide-contaminated samples were then collected in the field and analyzed with the two spectrometers to further test the applicability of the DRIFT technique for soils containing aged CN residues. The prediction of total CN in dry and ground contaminated soils using the handheld MIR instrument resulted in a coefficient of determination (R 2 ) of 0.88–0.98 and root mean square error of the cross-validation (RMSE) of 21–49 mg kg -1 for a CN range of 0–611 mg kg -1 . A major peak was observed in the MIR at about 2092 cm -1 which was attributed to “Prussian Blue” (Fe 4 [Fe(CN) 6 ] 3 · x H 2 O). These results demonstrate the potential of handheld DRIFT instrumentation as a promising alternative to the standard laboratory method to predict CN concentrations in contaminated field soils. [ABSTRACT FROM AUTHOR]

Materials science offers new perspectives in the clinical analysis of antimicrobial sensitivity. However, a biomaterial with the capacity to respond to living bacteria has not been developed to date. We present an electrochromic iron(III)-complexed alginate hydrogel sensitive to bacterial metabolism, here applied to fast antibiotic-susceptibility determination. Bacteria under evaluation are entrapped –and pre-concentrated- in the hydrogel matrix by oxidation of iron (II) ions to iron (III) and in situ formation of the alginate hydrogel in less than 2 min and in soft experimental conditions (i.e. room temperature, pH 7, aqueous solution). After incubation with the antibiotic (10 min), ferricyanide is added to the biomaterial. Bacteria resistant to the antibiotic dose remain alive and reduce ferricyanide to ferrocyanide, which reacts with the iron (III) ions in the hydrogel to produce Prussian Blue molecules. For a bacterial concentration above 10 7 colony forming units per mL colour development is detectable with the bare eye in less than 20 min. The simplicity, sensitivity, low-cost and short response time of the biomaterial and the assay envisages a high impact of these approaches on sensitive sectors such as public health system, food and beverage industries or environmental monitoring. [ABSTRACT FROM AUTHOR]

Abstract: Cell immobilization is an effective method to prolong the lifetime of a microorganism and has proven feasibility in some other biosensors. Thus, we studied the use of Escherichia coli immobilized by agar, gelatin, an agar/gelatin mixture, chitosan, and polyvinyl alcohol (PVA) to screen toxicity electrochemically. The E. coli immobilized by PVA gel showed the highest apparent bioactivity and the longest storage time in pH 7.0 phosphate‐buffered saline solution. Furthermore, the E. coli immobilized by different gels was applied in the toxicity determination via a reported ferricyanide‐mediated electrochemical method, where 3,5‐dichlorophenol (DCP) was used as a model toxin. The E. coli immobilized by PVA showed the highest sensitivity to DCP, and the corresponding value of 50% inhibition concentration was 9.62 mg L−1. Inhibition concentrations were in the range of 6.32 to 13.75% when the E. coli immobilized by PVA was challenged by wastewater, which were comparable with values obtained with the standard luminescent bacteria method (effective inhibition were in the range 7.96–25.42% for the same samples). Given the apparent bioactivity, storage ability, and sensitivity to toxin, PVA was the best polymer to confine cells among the polymers used in the present study. Environ Toxicol Chem 2018;37:329–335. © 2017 SETAC [ABSTRACT FROM AUTHOR]

In this study, waste solids of the alumina industry (red mud) have been modified and utilized as a ferricyanide adsorbent which is characterized by XRD, XRF, FTIR, SEM, EDX, ICP and BET analysis. The four modification methods including the processes of washing with seawater (B), acid treatment Bauxsol (ATB), activated ATB using ammonia (ABA), and activated Bauxsol using cetyltrimethylammonium bromide (CTAB) (ABC) were evaluated to increase the reactivity of red mud (RM) for ferricyanide removal. The ferricyanide adsorption capacity was obtained at 12.40, 6.84, 2.95, 2.50 and 0.44 (mg/g) for ABC, ATB, ABA, B and RM, respectively. The CTAB with a concentration above the critical micelle concentration changed the negative charge of red mud to positive charge. It decreased the negative charge repulsion force between the Bauxsol surface and ferricyanide ions. The adsorption capacity of ferricyanide was decreased from 12.40 to 2.75 (mg/g) with increasing the adsorbent amount from 0.5 to 5 (g). The results showed that the activated Bauxsol using CTAB could be effectively used as a new adsorbent for ferricyanide ions from wastewaters. [ABSTRACT FROM AUTHOR]

We successfully expressed the l-aspartate oxidase homolog gene (accession no: OCC_06611) of Thermococcus litoralis DSM 5473 in the soluble fraction of Escherichia coli BL21 (DE3) using a pET21b vector with 6X His tag at its C-terminus. The gene product ( Tl-LASPO) showed l-aspartate oxidase activity in the presence of FAD in vitro, and this report is the first that details an l-aspartate oxidase derived from a Thermococcus species. The homologs of Tl-LASPO existed mainly in archaea, especially in the genus of Thermococcus, Pyrococcus, Sulfolobus, and Halobacteria. The quaternary structure of Tl-LASPO was homotrimeric with a subunit molecular mass of 52 kDa. The enzyme activity of Tl-LASPO increased with temperature up to 70 °C. Tl-LASPO was active from pH 6.0 to 9.0, and its highest activity was at pH 8.0. Tl-LASPO was stable at 80 °C for 1 h. The highest k / K value was observed in assays at 70 °C. Tl-LASPO was highly specific for l-aspartic acid. Tl-LASPO utilized fumaric acid, 2,6-dichlorophenolindophenol, and ferricyanide in addition to FAD as a cofactor under anaerobic conditions. The absorption spectrum of holo- Tl-LASPO exhibited maxima at 380 and 450 nm. The FAD dissociation constant, K , of the FAD- Tl-LASPO complex was determined to be 5.9 × 10 M. [ABSTRACT FROM AUTHOR]

The Franz diffusion cell is one of the most widely used devices to evaluate transdermal drug delivery. However, this static and nonflowing system has some limitations, such as a relatively large solution volume and skin area and the development of gas bubbles during sampling. To overcome these disadvantages, this study provides a proof of concept for miniaturizing models of transdermal delivery by using a microfluidic chip combined with a diffusion cell. The proposed diffusion microchip system requires only 80 μL of sample solution and provides flow circulation. Two model compounds, Coomassie Brilliant Blue G-250 and potassium ferricyanide, were successfully tested for transdermal delivery experiments. The diffusion rate is high for a high sample concentration or a large membrane pore size. The developed diffusion microchip system, which is feasible, can be applied for transdermal measurement in the future. [ABSTRACT FROM AUTHOR]

The reductase domains of neuronal NOS, endothelial NOS and two constitutive nitric oxide synthase (cNOS) share higher sequence similarity (>60%). In order to evaluate the role of ferredoxin-NADP+ reductase (FNR) module in adjusting NOS catalytic activities, chimeras were by interchanging the FNR-like module between endothelial NOS and neuronal NOS in the present study. The assays of steady-state enzymatic activities for cytochrome c and ferricyanide reduction, NO synthesis and NADPH oxidation were performed spectrophotometrically. The two NOS FNR modules transferred their ferricyanide reductase character to the chimera enzymes. Results showed that the FNR module was important in adjusting electrons flow through the reductase domain and out of the FMN module. Results indicated that the FNR module was critical in controlling the electron transfer capacities of the FMN module. [ABSTRACT FROM AUTHOR]

An electrochemical sensor based on molecularly imprinted polymer (MIP) film for dodecyl gallate detection at the surface of a glassy carbon electrode (GCE) was proposed in this paper. The GCE was modified with f-MWCNT and the MIP synthesis was performed in situ by means of electropolymerization using ortho-phenylenediamine as the monomer. The stepwise preparation of the MIP and NIP (non-imprinted polymer) was characterized electrochemically by means of cyclic and square wave voltammetry employing ferrocyanide/ferricyanide as a redox probe. The selective capacity performance of the MIP and its imprinted effect to the template molecule (analyte) was compared to the NIP. They were also characterized by scanning electron microscopy technique (SEM). The analytical performance of the MIP sensor performed using square wave voltammetry showed linear range from 0.50 to 8.0 × 10 −9 mol L −1 , with a correlation coefficient of 0.9921. The sensor presented detection and quantification limit of 0.22 × 10 −9 and 0.67 × 10 −9 mol L −1 , respectively. The apparent dissociation constant (K D ) calculated was of 1.26 × 10 −4 mol L −1 and 5.27 × 10 −1 mol L −1 for the MIP and NIP respectively. [ABSTRACT FROM AUTHOR]

Monitoring blood lactate concentration is important in clinical diagnosis and evaluation of fitness care. Electrochemical enzyme sensors are commonly used for the measurement of lactate owing to their simplicity and sensitivity. Lactate oxidases (LOxs) are widely used for the construction of lactate enzyme sensors, especially the LOx derived from Aerococcus viridans (AvLOx). To minimize interference from redox substances, most lactate sensors utilize artificial mediators. However, reports on the comparison of different mediators in lactate measurements are limited. In this study, the preferences of AvLOx for electron mediators were investigated electrochemically. We concluded that the charge of the mediator plays a significant role in determining its suitability as a mediator for AvLOx. The relatively uncharged 1-methoxy-5-methyl phenazinium methylsulfate (mPMS) was the preferred mediator for AvLOx, the strongly negative ferricyanide was a less preferential mediator, and the strongly positive hexaammineruthenium(III) was not utilized as a mediator by AvLOx. This suggests that the protein scaffold of AvLOx can almost completely block the access to the co-factor for very small electron acceptors, depending on their charge. [ABSTRACT FROM AUTHOR]

Most commercially available electrochemical enzyme sensor strips for the measurement of blood glucose use an artificial electron mediator to transfer electrons from the active side of the enzyme to the electrode. One mediator recently gaining attention for commercial sensor strips is hexaammineruthenium(III) chloride. In this study, we investigate and compare the preference of enzyme electrodes with two different FAD-dependent glucose dehydrogenases (FADGDHs) for the mediators hexaammineruthenium(III) chloride, potassium ferricyanide (the most common mediator in commercial sensor strips), and methoxy phenazine methosulfate (mPMS). One FADGDH is a monomeric fungal enzyme, and the other a hetero-trimeric bacterial enzyme. With the latter, which contains a heme-subunit facilitating the electron transfer, similar response currents are obtained with hexaammineruthenium(III), ferricyanide, and mPMS (6.8 μA, 7.5 μA, and 6.4 μA, respectively, for 10 mM glucose). With the fungal FADGDH, similar response currents are obtained with the negatively charged ferricyanide and the uncharged mPMS (5.9 μA and 6.7 μA, respectively, for 10mM glucose), however, no response current is obtained with hexaammineruthenium(III), which has a strong positive charge. These results show that access of even very small mediators with strong charges to a buried active center can be almost completely blocked by the protein. [ABSTRACT FROM AUTHOR]

Nickel-based ferricyanides have attracted much attention as cathode materials for aqueous sodium-ion batteries, owing to their room-temperature synthesis and open structural framework. However, factors affecting their electrochemical performance are still not clear. Herein, the effect of electrolyte concentrations on electrochemical properties of the ferricyanide cathode has been investigated by combining cyclic voltammetry, charge/discharge tests, and electrochemical impedance microscopy. It is found that high-concentration electrolyte can not only raise the working potential, owing to increased activity of Na+ ions, but also increase the initial coulombic efficiency due to suppression of side reactions. The optimized electrolyte enables it cycling with an initial coulombic efficiency of 99.3 %, excellent high-rate capability (68.1 mAh g−1 at 0.5 C and 63.1 mAh g−1 at 10 C), and outstanding cycling stability (96.3 % capacity retention after 1000 cycles at 10 C). The finding indicates that designing high-concentration electrolytes is an effective strategy to improve electrochemical performance of ferricyanide cathodes for aqueous sodium-ion batteries. [ABSTRACT FROM AUTHOR]

The application of nanodiamond (ND) in the preparation of an electrochemical sensor for the determination of pyrazinamide (PZA), one of the most consumed antibiotics for the treatment of tuberculosis, is proposed. The electrochemical sensor was constructed by the modification of a glassy carbon electrode (GCE) with an aqueous ND dispersion. The morphological characterization of the obtained ND film was carried out by scanning and transmission electron microscopy (SEM and TEM), and the electrochemical characterization assays were performed for the bare GCE and modified ND-GCE using potassium ferricyanide as redox probe. This redox probe showed an enhanced response on the ND-GCE, a higher electroactive surface area and a higher heterogeneous electron transfer rate constant ( k 0 ). The ND-GCE was employed in the PZA determination using square-wave voltammetry, and the obtained analytical curve was linear from 7.9 × 10 −7 to 4.9 × 10 −5 mol L −1 , with a limit of detection of 2.2 × 10 −7 mol L −1 . The proposed voltammetric method was successfully applied in the PZA determination in biological samples, with excellent recovery percentages. The proposed sensor architecture was notable for its simplicity of preparation and sensitivity towards the PZA drug, representing an interesting achievement in the preparation of nanodiamond-based electrochemical sensors. [ABSTRACT FROM AUTHOR]

The paper presents an electrochemical flow meter. It is based on a principle of measuring a response to chemical reaction which depends on the flow. The ferro/ferricyanide redox couple has reliable and robust electrochemical kinetics. The reaction consists of transfer of one electron and change of solvation structure without any change of complex structure. If the geometry of electrochemical cell is not changed the output current depends only on the flow through the cell. This device enables measurement of extremely low flows which is important in microsystem hydrodynamic studies. Measured flow limit of detection is 100 pl/min. The flow resolution is better than 1 pl/min. Time resolution of flow is better than 1 s. The device was used in study of peristaltic pump and movable piston pump flow. Sensitive measurement of flow and use of Fast Fourier Transform (FFT) has proved that noise generated by pump is periodic and correlates with the flow. The signal after pump pulsation elimination has white noise. The analysis of sensor signals with FFT in systems with peristaltic pumps or movable piston pumps enables to split the signal to periodic component correlating with the flow and non-periodic component correlating with the measured concentration. [ABSTRACT FROM AUTHOR]

In this study, we developed a screen-printed carbon−graphene-based electrochemical biosensor for EN2 protein detection. The engrailed-2 (EN2) protein, a biomarker for prostate cancer, is known to be a strong binder to a specific DNA sequence (5′-TAATTA-3′) to regulate transcription. To take advantage of this intrinsic property, aptamer probes with TAATTA sequence was immobilized onto the screen-printed carbon−graphene electrode surface via EDC−NHS coupling approach. Cyclic voltammetry (CV) of the electrochemical measurement technique was employed for the quantitative detection of EN2 protein. The hindrance to the redox reaction of potassium ferricyanide on the biosensor surface due to the binding of the immobilized aptamer with its target EN2 protein quantified the protein concentration. Under optimum conditions, the aptamer biosensor can detect EN2 protein over a linear range from 35 to 185 nM with a detection limit of 38.5 nM. [ABSTRACT FROM AUTHOR]

The high spatial resolution provided by synchrotron generated infrared (IR) radiation has been used to map spatiotemporal concentration profiles in the diffusion layer around a working electrode. An IR spectroelectrochemcial cell employing an inlaid band electrode has been developed that eliminates geometric issues with previous designs. The new cell was used to follow the diffusion layers produced by the reduction of ferricyanide and the oxidation of hydroquinone. Differences between the diffusion coefficients of ferricyanide and ferrocyanide determined here and the accepted literature are caused by the water-structure forming properties of different supporting electrolytes. The diffusion coefficients of hydroquinone and p- benzoquinone determined by diffusion layer mapping have been shown to be self-consistent with independently determined diffusion coefficients as measured using hydrodynamic linear sweep voltammetry. The consistency of the diffusion coefficients achieved for all species demonstrates that the spectroelectrochemical cell design allows for accurate monitoring of concentration profiles of species within electrochemical diffusion layers. [ABSTRACT FROM AUTHOR]

The mineral sperrylite (PtAs 2 ), unlike other Pt minerals, has shown to be resistant to cyanide leaching, even at elevated temperatures of 50 °C. This has prevented further development of a two-stage heap leaching process, of which the second stage is cyanide leaching for a Platreef ore, due to a considerable portion of the Pt being present as sperrylite. Through a comprehensive set of leaching tests, this study has shown that sperrylite leaches slowly in cyanide due to eventual passivation. The addition of ferricyanide to the cyanide solution results in significantly more Pt being leached (up to 16 times) than with cyanide only under identical process conditions. However, over time passivation occurred in this system also, but can be seemingly be overcome by filtering, rinsing and re-suspending the sperrylite. This was further investigated using a reactor system continuously fed with a ferricyanide-cyanide to leach a fixed bed of sperrylite mineral. Again, gradual passivation of the mineral phase was observed, which was fully reversible following a day of feeding with distilled water. XPS analysis of fresh and leached mineral indicated a depletion of As on the mineral surface, which tallied with an observed preferential leaching of As during leaching, at least initially. As a result, it is postulated that a less cyanide-soluble compound of the form PtAs (X) forms, where x is < 2. The ease with which the leaching process can be restarted after rinsing the mineral indicates that the adsorption of solution species is the key step in forming a passivating layer. This adsorption is potentially favoured by the gradual surface transformation. Finally, an electrochemical study confirmed that the ferricyanide-cyanide system facilitated an electron transfer reaction at the sperrylite surface with the likely oxidation of As and reduction of the ferricyanide. Gradual passivation of the surface was also observed in this system. [ABSTRACT FROM AUTHOR]

The quality of exported canned citrus sinensis and citrus limetta degrades slowly owing to the excess liberation of methanol from the pectin of canned citrus sinensis and citrus limetta. To detect the methanol liberation, an electroactive inorganic-organic nanocomposite modified working electrode was fabricated by immobilizing reduced graphene oxide/ferricyanide (rGO/Fe(CN) 6 3− ) on the surface of Pt electrode via chitosan membrane. The electrocatalytic oxidation of methanol by Fe(CN) 6 3− was observed at the anodic potential of 243 mV (vs Ag/AgCl), which was shifted negatively to almost 36 mV when compared with that of direct electrochemical oxidation of Fe(CN) 6 4− in the Pt/Chitosan/rGO/Ferricyanide electrode. The developed amperometric sensor could detect methanol concentration down to 12 nM with a linearity of 1–7 mM, sensitivity of 0.479 μA mM −1 , reproducibility of 1.2% RSD, repeatability of 1.1% RSD, response time of less than 10 s with the stability of 98% over a period of 20 days. [ABSTRACT FROM AUTHOR]

The unique physical and chemical properties of conventional room temperature ionic liquids (RTILs) render them highly deployable materials in electrochemical devices performing functions such as solvent-free electrolytes in capacitors, batteries and sensors. However, these non-faradaic applications can be complimented by incorporating faradaic redox functionality into the ionic liquid structure which facilitates access to a large array of new electrochemical applications such as dye sensitised solar cells, redox batteries, hydrid capacitors and selective amperometric sensor applications which are all reliant on heterogeneous or homogenous electron-transfer processes. This paper presents and discuses some examples of redox active ionic liquids base on the ferri-/ferro- functionality. These functional electro-materials which are already known [Ref. [18]] exhibit simple reversible one-electron electrochemistry at very negative potentials (by at least −1 V relative to aqueous systems) in anhydrous media. Glass transition temperatures lower than −50 °C were also observed along with an overall thermal stability up to at least 400 °C under dry N 2 atmosphere conditions. Opportunities and challenges for these types of electro-materials are discussed. [ABSTRACT FROM AUTHOR]

In this work we have developed an amperometric enzymatic biosensor in a paper-based platform with a mixed electrode configuration: carbon ink for the working electrode (WE) and metal wires (from a low-cost standard electronic connection) for reference (RE) and auxiliary electrodes (AE). A hydrophobic wax-defined paper area was impregnated with diluted carbon ink. Three gold-plated pins of the standard connection are employed, one for connecting the WE and the other two acting as RE and AE. The standard connection works as a clip in order to support the paper in between. As a proof-of-concept, glucose sensing was evaluated. The enzyme cocktail (glucose oxidase, horseradish peroxidase and potassium ferrocyanide as mediator of the electron transfer) was adsorbed on the surface. After drying, glucose solution was added to the paper, on the opposite side of the carbon ink. It wets RE and AE, and flows by capillarity through the paper contacting the carbon WE surface. The reduction current of ferricyanide, product of the enzymatic reaction, is measured chronoamperometrically and correlates to the concentration of glucose. Different parameters related to the bioassay were optimized, adhering the piece of paper onto a conventional screen-printed carbon electrode (SPCE). In this way, the RE and the AE of the commercial card were employed for optimizing the paper-WE. After evaluating the assay system in the hybrid paper-SPCE cell, the three-electrode system consisting of paper-WE, wire-RE and wire-AE, was employed for glucose determination, achieving a linear range between 0.3 and 15 mM with good analytical features and being able of quantifying glucose in real food samples. [ABSTRACT FROM AUTHOR]

Motion tracking of microorganisms is useful to investigate the effects of chemical or physical stimulation on their biological functions. Herein, we describe a novel electrochemical imaging method for motion tracking of microorganisms using a large-scale integration (LSI)-based amperometric device. The device consists of 400 electrochemical sensors with a pitch of 250 μm. A convection flow caused by the motion of microorganisms supplies redox species to the sensors and increases their electrochemical responses. Thus, the flow is converted to electrochemical signals, enabling the electrochemical motion tracking of the microorganisms. As a proof of concept, capillary vibration was monitored. Finally, the method was applied to monitoring the motion of Daphnia magna. The motions of these microorganisms were clearly tracked based on the electrochemical oxidation of [Fe(CN)6]4− and reduction of O2. [ABSTRACT FROM AUTHOR]

Despite complex molecular and atomic doping, efficient post-functionalization strategies for graphene quantum dots (GQDs) are of key importance to control the physicochemical properties and broaden the practical applications. With ionic liquid as specific modification agents, herein, the preparation of ionic liquid-capped GQDs (IL-GQDs) and its application as label-free fluorescent probe for direct detection of anion were reported. Hydroxyl-functionalized GQDs that could be easily gram-scale synthesized and possessed single-crystalline were chosen as the model GQDs. Also, the most commonly used ionic liquids, water-soluble 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIMBF 4 ) was chosen as the model IL. Under the ultrasonic treatment, BMIMBF 4 easily composited with GQDs to form IL-GQDs. The synthesized IL-GQDs were characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and fluorescence (FL) spectrum. After successful combination with IL, the excitation-independent photoluminescence behavior of GQDs presented almost no change, whereas, the anion responsiveness of IL-GQDs drastically improved, which afforded the IL-GQDs a sensitive response to Fe(CN) 6 3− . Based on the strong fluorescence quench, a facile and sensitive detection of Fe(CN) 6 3− was achieved. A wide linear range of 1.0×10 −7 to 2.5×10 −3 mol l −1 with a low detection limit of 40 nmol l −1 was obtained. As the composition and properties of IL and GQDs could be easily tuned by varying the structure, ionic liquids-capped GQDs might present promising potential for their applications in sensing and catalysis. [ABSTRACT FROM AUTHOR]

We introduce dual kinetic chronoamperometry, in which reciprocal relations are established between the kinetic curves of electrochemical reactions that start from symmetrical initial conditions. We have performed numerical and experimental studies in which the kinetic curves of the electron-transfer processes are analyzed for a reversible first order reaction. Experimental tests were done with the ferrocyanide/ferricyanide system in which the concentrations of each component could be measured separately using the platinum disk/gold ring electrode. It is shown that the proper ratio of the transient kinetic curves obtained from cathodic and anodic mass transfer limited regions give thermodynamic time invariances related to the reaction quotient of the bulk concentrations. Therefore, thermodynamic time invariances can be observed at any time using the dual kinetic curves for reversible reactions. The technique provides a unique possibility to extract the non-steady state trajectory starting from one initial condition based only on the equilibrium constant and the trajectory which starts from the symmetrical initial condition. The results could impact battery technology by predicting the concentrations and currents of the underlying non-steady state processes in a wide domain from thermodynamic principles and limited kinetic information. [ABSTRACT FROM AUTHOR]

In this work T4, also known as thyroxine, a thyroid hormone with many relevant roles in human metabolism, was determined with an antibody-based biosensor, consisting on a multi thiol self-assembled monolayer (SAM) whereas a selective antibody was attached. Electroanalytical measurements were performed by impedance on a ferricyanide redox probe. A limit of detection of 1.5 ng mL-1 and limit of quantification (LOQ) of 4.0 ng mL-1 were obtained. This biosensor is a proof-of-concept for the creation of point-of-care electrochemical approach for the quantification of T4. [ABSTRACT FROM AUTHOR]

This work presents a novel method for the full fabrication of electrochemical paper-based cells by screen-printing technology. Firstly, a mixture of ultraviolet curable inks was used for patterning hydrophobic barriers into chromatography paper. Afterwards three-electrode systems were coupled for electrochemical detection by printing successively carbon and silver/silver chloride inks over the hydrophilic areas. The resulting electrochemical cells were characterized by cyclic voltammetry in different redox systems and used for amperometric detection of ferricyanide. [ABSTRACT FROM AUTHOR]