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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]

Deferoxamine (DFO), an iron chelator, is used therapeutically for the removal of excess iron in multiple clinical conditions such as beta thalassemia and intracerebral hemorrhage. DFO is also used as an iron chelator and hypoxia-mimetic agent in in vivo and in vitro basic research. Here we unexpectedly discover DFO to be a nitric oxide (NO) precursor in experiments where it was intended to act as an iron chelator. Production of NO from aqueous solutions of DFO was directly observed by ozone-based chemiluminescence using a ferricyanide-based assay and was confirmed by electron paramagnetic resonance (EPR). DFO also produced NO following exposure to ultraviolet light, and its incubation with sheep adult and fetal blood resulted in considerable formation of iron nitrosyl hemoglobin, as confirmed by both visible spectroscopy and EPR. These results suggest that experiments using DFO can be confounded by concomitant production of NO, and offer new insight into some of DFOs unexplained clinical side effects such as hypotension.

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]

Silver oxide doped iron oxide (Ag 2 O-Fe 2 O 3 ) nanocatalyst was prepared and coated on cotton cloth (CC) as well as wrapped in sodium alginate (Alg) hydrogel. Ag 2 O-Fe 2 O 3 coated CC (Ag 2 O-Fe 2 O 3 /CC) and Ag 2 O-Fe 2 O 3 wrapped Alg (Ag 2 O-Fe 2 O 3 /Alg) were utilized as catalysts in reduction reaction of 4-nitrophenol (4-NP), congo red (CR), methylene blue (MB) and potassium ferricyanide (K 3 [Fe(CN) 6 ]). Ag 2 O-Fe 2 O 3 /CC and Ag 2 O-Fe 2 O 3 /Alg were found to be effective and selective catalyst for the reaction of K 3 [Fe(CN) 6 ]. Further amount of catalyst, K 3 [Fe(CN) 6 ] quantity, amount of NaBH 4 , stability of catalyst and recyclability were optimized for the reaction of K 3 [Fe(CN) 6 ] reduction. Ag 2 O-Fe 2 O 3 /Alg and Ag 2 O-Fe 2 O 3 /CC were appeared to be the stable catalysts by maintaining high activity during recyclability tests showing highest reaction rate constants (k app ) of 0.3472 and 0.5629 min -1 , correspondingly. However, Ag 2 O-Fe 2 O 3 /CC can be easily recovered as compared to Ag 2 O-Fe 2 O 3 /Alg by simply removing from the reaction which is the main advantage of Ag 2 O-Fe 2 O 3 /CC. Moreover, Ag 2 O-Fe 2 O 3 /Alg and Ag 2 O-Fe 2 O 3 /CC were also examined in real samples and found useful for K 3 [Fe(CN) 6 ] reduction involving real samples. The Ag 2 O-Fe 2 O 3 /CC nanocatalyst is a cost and time saving material for economical reduction of K 3 [Fe(CN) 6 ] and environmental safety., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Pathogen-triggered infections are the most severe global threat to human health, and to provide their timely treatment and prevention, robust methods for rapid and reliable identification of pathogenic microorganisms are required. Here, we have developed a fast and inexpensive electrocatalytic aptamer assay enabling specific and ultrasensitive detection of E. coli. E. coli, a biomarker of environmental contamination and infections, was captured on the mixed aptamer/thiolated PEG self-assembled monolayers formed on electrochemically pre-treated gold screen-printed electrodes (SPE). Signals from aptamer - E. coli binding were amplified by electrocatalytic reduction of ferricyanide mediated by methylene blue (MB) adsorbed on bacterial and aptamer surfaces. PEG operated as an antifouling agent and inhibited direct (not MB-mediated) discharge of ferricyanide. The assay allowed from 10 to 1000 CFU mL -1 E. coli detection in 30 min, with no interference from B. subtilis, in buffer and artificial urine samples. This electrocatalytic approach is fast, specific, sensitive, and can be used directly in in-field and point-of-care applications for analysis of bacteria in human environment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

In photosynthetic bacteria, the absorbed light drives the canonical cyclic electron transfer between the reaction center and the cytochrome bc 1 complexes via the pools of mobile electron carriers. If kinetic or structural barriers hinder the participation of the bc 1 complex in the cyclic flow of electrons, then the pools of mobile redox agents must supply the electrons for the multiple turnovers of the reaction center. These conditions were achieved by continuous high light excitation of intact cells of bacterial strains Rba. sphaeroides and Rvx. gelatinosus with depleted donor side cytochromes c 2 (cycA) and tetraheme cytochrome subunit (pufC), respectively. The gradual oxidation by ferricyanide further reduced the availability of electron donors to pufC. Electron transfer through the reaction center was tracked by absorption change and by induction and relaxation of the fluorescence of the bacteriochlorophyll dimer. The rate constants of the electron transfer (~ 3 × 10 3  s ‒1 ) from the mobile donors of Rvx. gelatinosus bound either to the RC (pufC) or to the tetraheme subunit (wild type) were similar. The electrons transferred through the reaction center dimer were supplied entirely by the donor pool; their number amounted to about 5 in wild type Rvx. gelatinosus and decreased to 1 in pufC oxidized by ferricyanide. Fluorescence yield was measured as a function of the oxidized fraction of the dimer and its complex shape reveals the contribution of two competing processes: the migration of the excitation energy among the photosynthetic units and the availability of electron donors to the oxidized dimer. The experimental results were simulated and rationalized by a simple kinetic model of the two-electron cycling of the acceptor side combined with aperiodic one-electron redox function of the donor side., (© 2023. The Author(s).)

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]

In the acidic medium, hydrosulfuryl(-SH) in cysteine hydrochloride can reduce Fe3+ to Fe2+, then Fe2+ react with potassium ferricyanide to form KFe[Fe(CN)6](soluble Prussian blue). Prussian blue has a maximum absorption at 727 nm, Bill's law is observed between mass concentration of cysteine hydrochloride and absorbance of Prussian blue, the content of cysteine hydrochloride is indirectly determinated by measuring the absorbance of Prussian blue. An accurate, simple, fast spectrophotometric method for the determination of cysteine hydrochloride content by ferric chloride-potassium ferricyanide has been established. The optimal determination conditions of cysteine hydrochloride content are explored. The cysteine hydrochloride content is determinate by this method.

The photoassembly of the Mn 4 CaO 5 cluster in Mn-depleted photosystem II preparations (photoactivation) was studied under the influence of oxidants, reductants and pH. New data on the effect of these factors on the photoactivation yield are presented. The presence of the oxidant, ferricyanide, negatively affected the photoactivation yield over the entire concentration range studied (0-1 mM). In contrast to ferricyanide, the addition of the reductant, ferrocyanide, up to 1 mM resulted in an increase in the photoactivation yield. Other reductants either did not significantly affect (diphenylcarbazide) or suppressed (ascorbate) the photoactivation yield. The effect of ferrocyanide on photoactivation were found to be similar dichlorophenolindophenol. Investigation of the photoactivation yield as a function of pH revealed that the maximum yield was observed at pH 6.5 in the presence of ferrocyanide and DCPIP, and at pH 5.5 without additives. In addition, the photoactivation yield at pH 5.5 was the same without and with the addition of ferrocyanide or dichlorophenolindophenol. Although ferricyanide suppressed the photoactivation, the photoactivation yield increased in the presence of ferricyanide by shifting the pH to the acidic region. The samples contained approximately 25 % of the HP cyt b 559 , which was in the reduced state, as the absorbance at 559 nm was decreased upon addition of ferricyanide and subsequent addition of ferrocyanide returned the spectrum to the baseline. A possible relationship between the effect of factors on the photoactivation and the involvement of cyt b 559 in the protection of PSII from oxidative damage on the donor side is discussed., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

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]