RESUMEN
Iron is accumulated in Arabidopsis embryos during seed maturation. Where iron localizes in seed and embryo is important information for seed research. Iron detection can be performed in an inexpensive manner using Perls staining, based on the Prussian blue complex formation. After this first step, DAB intensification can be performed in order to visualize easily where iron pools are located in isolated embryos.
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Arabidopsis , Hierro , Coloración y Etiquetado , Semillas , FerrocianurosRESUMEN
The Zika virus (ZIKV) is a great concern for global health due to its high transmission, including disseminating through blood, saliva, urine, semen and vertical transmission. In some cases, ZIKV has been associated with microcephaly, neurological disorders, and Guillain−Barré syndrome. There is no vaccine, and controlling the disease is a challenge, especially with the co-circulation of the Dengue virus, which causes a severe cross-reaction due to the similarity between the two arboviruses. Considering that electrochemical immunosensors are well-established, sensitive, and practical tools for diagnosis, in this study we developed a sensor platform with intrinsic redox activity that facilitates measurement readouts. Prussian blue (PB) has a great ability to form electrocatalytic surfaces, dispensing redox probe solutions in voltammetric measurements. Herein, PB was incorporated into a chitosan−carbon nanotube hybrid, forming a nanocomposite that was drop-casted on a screen-printed electrode (SPE). The immunosensor detected the envelope protein of ZIKV in a linear range of 0.25 to 1.75 µg/mL (n = 8, p < 0.01), with a 0.20 µg/mL limit of detection. The developed immunosensor represents a new method for electrochemical measurements without additional redox probe solutions, and it is feasible for application in point-of-care diagnosis.
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Técnicas Biosensibles , Infección por el Virus Zika , Virus Zika , Técnicas Biosensibles/métodos , Ferrocianuros , Humanos , Inmunoensayo , Oxidación-Reducción , Infección por el Virus Zika/diagnósticoRESUMEN
A laser-induced graphene (LIG) surface modified with Prussian blue (iron hexacyanoferrate) is demonstrated as a novel electrochemical sensing platform for the sensitive and selective detection of hydrogen peroxide. Electrochemical Prussian blue (PB) modification on porous graphene films engraved by infrared laser over flexible polyimide was accomplished. Scanning electron microscopy images combined with Raman spectra confirm the formation of porous graphene and homogenous electrodeposition of PB over this porous surface. Electrochemical impedance spectroscopy reveals a substantial decrease in the resistance to charge transfer values (from 395 to 31.4 Ω) after the PB insertion, which confirms the formation of a highly conductive PB-graphene composite. The synergistic properties of PB and porous graphene were investigated for the constant monitoring of hydrogen peroxide at 0.0 V vs. Ag|AgCl|KCl(sat.), under high-flow injections (166 µL s-1) confirming the high stability of the modified surface and fast response within a wide linear range (from 1 to 200 µmol L-1). Satisfactory detection limit (0.26 µmol L-1) and selectivity verified by the analysis of complex samples confirmed the excellent sensing performance of this platform. We highlight that the outstanding sensing characteristics of the developed sensor were superior in comparison with other PB-based or LIG-based electrochemical sensors reported for hydrogen peroxide detection.
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Grafito , Técnicas Electroquímicas/métodos , Electrodos , Ferrocianuros , Grafito/química , Peróxido de Hidrógeno/análisis , Rayos LáserRESUMEN
Thallium (TI) is one of the most toxic heavy metals. Human exposure to Tl occurs through contaminated drinking water and from there to food, a threat to health. Recently, environmental contamination by Tl has been reported in several countries, urging the need for studies to determine the impact of endogenous and exogenous mechanisms preventing thallium toxicity. The cytoprotective effect of metallothionein (MT), a protein with high capacity to chelate metals, at two doses (100 and 600 µg/rat), was tested. Prussian blue (PB) (50 mg/kg) was administered alone or in combination with MT. A dose of Tl (16mg/kg) was injected i.p. to Wistar rats. Antidotes were administered twice daily, starting 24h after Tl injection, for 4 days. Tl concentrations diminished in most organs (p < 0.05) by effect of PB, alone or in combination with MT, whereas MT alone decreased Tl concentrations in testis, spleen, lung and liver. Likewise, brain thallium also diminished (p < 0.05) by effect of PB and MT alone or in combination in most of the regions analyzed (p < 0.05). The greatest diminution of Tl was achieved when the antidotes were combined. Plasma markers of renal damage increased after Tl administration, while PB and MT, either alone or in combination, prevented the raise of those markers. Only MT increased the levels of reduced glutathione (GSH) in the kidney. Finally, increased Nrf2 was observed in liver and kidney, after treatment with MT alone or in combination with PB. Results showed that MT alone or in combination with PB is cytoprotective after thallium exposure.
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Metalotioneína , Talio , Animales , Ferrocianuros , Masculino , Metalotioneína/metabolismo , Estrés Oxidativo , Ratas , Ratas Wistar , Talio/metabolismo , Talio/toxicidadRESUMEN
Considered one of the most promising building blocks of life on primitive Earth, cyanide and its complexes are likely to have played an important role in the emergence of life on the planet. Investigation into cyanide on Earth has primarily considered high concentrations, but the cyanide concentration in the oceans of prebiotic Earth was exceptionally low. Thus, Bernal's hypothesis has allowed investigators to work around this problem. We observed, however, that cyanide does not adsorb onto several minerals; therefore, ferrocyanide could be used as a cyanide source when adsorbed onto mineral surfaces to promote the synthesis of molecules of biological significance. When adsorbed onto bentonite, a mineral that has Fe3+ atoms in its interlayers, the formation of Prussian blue analog complexes occurs through endothermic reaction and with increased entropy. The adsorption of ferrocyanide onto kaolinite indicates an exothermic and outer-sphere interaction, which results in degeneracy breakdown for C ≡ N stretch energy into two new bands of FTIR-ATR spectrum. Magnetite, which has iron atoms in its structure, and ferrocyanide interactions have been observed by outer-sphere coordination as well as the formation of Prussian blue analogs, as confirmed by the appearance of a new doublet in the Mössbauer spectra and a broadband close to 750 nm at UV-visible spectroscopy. Magnetite and kaolinite experiments presented relevant results only when performed in seawater, which suggests the importance of seawater composition for prebiotic experiments. These obtained results prove that ferrocyanide interacts with minerals differently according to structure and composition and show that this complex, like the Prussian blue analogs, may have played a crucial role as a source of cyanide on primitive Earth.
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Ferrocianuros , Adsorción , Planeta Tierra , MineralesRESUMEN
Zika virus (ZIKV) is a mosquito-borne infection, predominant in tropical and subtropical regions causing international concern due to the ZIKV disease having been associated with congenital disabilities, especially microcephaly and other congenital abnormalities in the fetus and newborns. Development of strategies that minimize the devastating impact by monitoring and preventing ZIKV transmission through sexual intercourse, especially in pregnant women, since no vaccine is yet available for the prevention or treatment, is critically important. ZIKV infection is generally asymptomatic and cross-reactivity with dengue virus (DENV) is a global concern. An innovative screen-printed electrode (SPE) was developed for amperometric detection of the non-structural protein (NS2B) of ZIKV by exploring the intrinsic redox catalytic activity of Prussian blue (PB), incorporated into a carbon nanotube-polypyrrole composite. Thus, this immunosensor has the advantage of electrochemical detection without adding any redox-probe solution (probe-less detection), allowing a point-of-care diagnosis. It was responsive to serum samples of only ZIKV positive patients and non-responsive to negative ZIKV patients, even if the sample was DENV positive, indicating a possible differential diagnosis between them by NS2B. All samples used here were confirmed by CDC protocols, and immunosensor responses were also checked in the supernatant of C6/36 and in Vero cell cultures infected with ZIKV.
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Técnicas Biosensibles , Inmunoensayo , Virus Zika/aislamiento & purificación , Ferrocianuros , Humanos , Nanotubos de Carbono , Polímeros , Pirroles , Virus Zika/inmunología , Infección por el Virus Zika/diagnóstico , Infección por el Virus Zika/virologíaRESUMEN
This communication shows the electrochemical synthesis of Prussian blue (PB) films on additive manufactured (3D-printed) electrodes from iron impurities found at the graphene-polylactic acid (G/PLA) substrate and its application as a highly selective sensor for H2O2. The 3D-printed G/PLA electrode was immersed in dimethylformamide for 30 min to exposure the iron impurities within the PLA matrix. Next, cyclic voltammograms (200 cycles) in the presence of potassium ferricyanide in 0.1 mol L-1 KCl + 0.01 mol L-1 HCl were performed to grow the PB films. The sensing properties of this novel PB/G/PLA platform were evaluated for the amperometric detection of H2O2 using batch-injection analysis, with a limit of detection of 0.56 µmol L-1 under the application of 0.0 V (vs Ag/AgCl/KClsat.). The applicability of the sensor was demonstrated for the analysis of milk samples (10-fold diluted in the supporting electrolyte), resulting in proper recovery values (94-101%).
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Grafito , Peróxido de Hidrógeno , Electrodos , Ferrocianuros , Hierro , Impresión TridimensionalRESUMEN
Small-molecule fluorescent probes having optimized optical properties, such as high photostability and brightness, local microenvironment sensitivity and specific subcellular localizations, are increasingly available. Although the basis for designing efficient fluorophores for bioimaging applications is well established, implementing an improvement in a given photophysical characteristic always tends to compromise another optical property. This problem has enormous consequences for in vivo imaging, where ensuring a specific localization and precise control of the probe response is challenging. Herein we discuss a fluorescent probe, CC334, as a case study of the chromenylium-cyanine family that commonly exhibits highly complex photophysical schemes and highly interfered bioanalytical responses. By an exhaustive and concise analysis of the CC334 optical responses including detailed spectroscopic calibrations, steady-state microenvironment effects, ultrafast photophysics analysis and computational studies, we elucidate a new strategy to apply the probe in the singlet oxygen reactive oxygen species (1O2-ROS) monitoring using in vitro and in vivo models. The probe provides a new avenue for designing fluorescent probes to understand the dynamic behavior of subcellular environments.
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Benzopiranos/química , Colorantes Fluorescentes/química , Colorantes Fluorescentes/metabolismo , Cobalto/química , Ferrocianuros/química , Quinolinas/química , Especies Reactivas de Oxígeno/química , Análisis EspectralRESUMEN
The use of ultraviolet light in photoreactors for wastewater treatment has become popular as an alternative of known chemical oxidative substances. UV LED light represents cheaper, robust, and versatile alternative to traditional UV lamps. In this study, it was designed and evaluated a photoreactor with an approach of chemical fluid dynamics (CFD) and experimental validation. The evaluation consisted of (1) CFD velocity profile analysis, (2) characterization of the average light distribution with potassium ferrioxalate actinometry, (3) degradation of a typical recalcitrant metallic cyanocomplex Fe(CN)63-, and (4) scavenger effect analysis in the photodegradation using potassium persulfate. Actinometrical essay concluded that the system was able to receive 1.93 µE/s. The reactor operated under turbulent regime and best result for Fe(CN)63- degradation was obtained at 4 h of operation, using 5-W UV-A LEDs, with pH ~ 7 and 10 mM de S2O82-. Baffled photoreactor demonstrated to be useful for this type of illumination and wastewater treatment.
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Minería , Eliminación de Residuos Líquidos/instrumentación , Eliminación de Residuos Líquidos/métodos , Diseño de Equipo , Ferrocianuros/química , Hidrodinámica , Oxalatos/química , Oxidación-Reducción , Fotólisis , Compuestos de Potasio/química , Sulfatos/química , Rayos Ultravioleta , Aguas Residuales/químicaRESUMEN
In this work nanostructured film composites of the monoamine oxidase B (MAO-B) enzyme, free or encapsulated in liposomes, were fabricated by the layer-by-layer (LbL) self-assembly technique, employing polyethylene imine (PEI) as polycation. Initially, the MAO-B enzyme was incorporated into liposomes in order to preserve its enzymatic structure ensuring their activity and catalytic stability. The LbL film growth was monitored by surface plasmon resonance (SPR) by gold resonance angle shift analysis after each bilayer deposition. Subsequently, the films were applied as amperometric biosensors for dopamine detection using Prussian Blue (PB) as the electron mediator. The biosensor fabricated by MAO-B incorporated into liposomes composed of DPPG:POPG in the ratio (1:4) (w/w) showed the best performance with a sensitivity of 0.86 (µA cm(-2))/(mmol L(-1)) and a detection limit of 0.33 mmol L(-1).
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Técnicas Biosensibles , Dopamina/análisis , Monoaminooxidasa/metabolismo , Nanoestructuras/química , Dicroismo Circular , Técnicas Electroquímicas , Enzimas Inmovilizadas/química , Enzimas Inmovilizadas/metabolismo , Ferrocianuros/química , Humanos , Límite de Detección , Liposomas/química , Monoaminooxidasa/química , Polietileneimina/química , Resonancia por Plasmón de SuperficieRESUMEN
UNLABELLED: Folin-Ciocalteu colorimetric assay (FC) is the most widely used assay to estimate the total phenolic content in foods, beverages, herbs and other plant extracts, but many chemical compounds may act as interfering agents, producing inaccurate estimations of the real concentration of phenolic compounds in the matrix. Based on this limitation, the objective of this study was to compare, quantitatively, the Folin-Ciocalteu and Prussian Blue (PB) assays in estimating the total phenolic content in purple grape juices (n = 20; Vitis labrusca L.) and teas (n = 25) from different botanical origins using 96-well microplates. PB assay presented a low limit of detection (PB = 0.27 mg/L; FC = 0.25 mg/L) and quantification (PB = 0.92 mg/L; FC = 0.82 mg/L), showing its suitability in screening the total phenolic content in grape juices and teas. FC and PB assays presented a high association (P < 0.0001) for teas (r = 0.887) and grape juices (r = 0.923). The advantages of PB over FC assay are its simplicity, low time consumption (15 min reaction as compared to 60 min reaction for the FC assay), lower usage of reagents (solutions are prepared in a mM base), and higher selectivity. Additionally, PB assay was proven to be reproducible and repeatable and, therefore, may be used as an alternative to FC assay. PRACTICAL APPLICATION: Prussian Blue assay (PB) has been used as an alternative to Folin-Ciocalteu assay (FC) to estimate the total content of phenolic compounds in herbs and some natural products. In our study we showed that the advantages of PB assay over FC are its simplicity, low time consumption (15 min reaction as compared to 60 min reaction for the FC assay), lower usage of reagents (solutions are prepared in a mM base) and higher selectivity as compared to FC assay. Additionally, PB assay was proven to be reproducible and repeatable and, therefore, may be used as an alternative to FC assay.
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Bebidas/análisis , Camellia sinensis/química , Ferrocianuros , Análisis de los Alimentos/métodos , Fenoles/análisis , Extractos Vegetales , Vitis/química , Frutas/química , HumanosRESUMEN
Supramolecular self-assembly has been demonstrated to be a useful approach to developing new functional nanomaterials. In this work, we used a cobalt Prussian blue analogue (PBA, Co3[Co(CN)6]2) compound and a ß-cyclodextrin (CD) macrocycle to develop a novel host-guest PBA-CD nanomaterial. The preparation of the functional magnetic material involved the self-assembly of CD molecules onto a PBA surface by a co-precipitation method. According to transmission electronic microscopy results, PBA-CD exhibited a polydisperse structure composed of 3D nanocubes with a mean edge length of 85 nm, which became shorter after CD incorporation. The supramolecular arrangement and structural, crystalline and thermal properties of the hybrid material were studied in detail by vibrational and electronic spectroscopies and X-ray diffraction. The cyclic voltammogram of the hybrid material in a 0.1 mol · L(-1) NaCl supporting electrolyte exhibited a quasi-reversible redox process, attributed to Co2+/Co3+ conversion, with an E1/2 value of 0.46 V (vs. SCE), with higher reversibility observed for the system in the presence of CD. The standard rate constants for PBA and PBA-CD were determined to be 0.07 and 0.13 s(-1), respectively, which suggests that the interaction between the nanocubes and CD at the supramolecular level improves electron transfer. We expect that the properties observed for the hybrid material make it a potential candidate for (bio)sensing designs with a desirable capability for drug delivery.
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Cobalto/química , Ciclodextrinas/química , Ferrocianuros/química , Nanopartículas/química , Compuestos Organometálicos/síntesis química , Compuestos Organometálicos/química , Oxidación-Reducción , PolimerizacionRESUMEN
A thiophene-modified screen printed electrode (SPE) for detection of the Dengue virus non-structural protein 1 (NS1), an important marker for acute phase diagnosis, is described. A sulfur-containing heterocyclic compound, the thiophene was incorporated to a carbon ink to prepare reproducible screen printed electrodes. After cured, the thiophene SPE was coated by gold nanoparticles conjugated to Protein A to form a nanostrutured surface. The Anti-NS1 antibodies immobilized via their Fc portions via Protein A, leaving their antigen specific sites free circumventing the problem of a random antibodies immobilization. Amperometric responses to the NS1 protein of dengue virus were obtained by cyclic voltammetries performed in presence of ferrocyanide/ferricyanide as redox probe. The calibration curve of immunosensor showed a linear response from 0.04 µg mL(-1) to 0.6 µg mL(-1) of NS1 with a good linear correlation (r=0.991, p<0.05). The detection limit (0.015 µg mL(-1) NS1) was lower than conventional analytical methods. In this work, thiophene monomers incorporated in the carbon ink enhanced the electroanalytical properties of the SPEs, increasing their reproducibility and sensitivity. This point-of-care testing represents a great potential for use in epidemic situations, facilitating the early diagnosis in acute phase of dengue virus.
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Virus del Dengue/metabolismo , Técnicas Electroquímicas/métodos , Tiofenos/química , Proteínas no Estructurales Virales/análisis , Animales , Anticuerpos/química , Anticuerpos/inmunología , Anticuerpos Inmovilizados/química , Anticuerpos Inmovilizados/inmunología , Técnicas Biosensibles/instrumentación , Técnicas Biosensibles/métodos , Carbono/química , Línea Celular , Técnicas Electroquímicas/instrumentación , Electrodos , Ferricianuros/química , Ferrocianuros/química , Oro/química , Tinta , Nanopartículas del Metal/química , Reproducibilidad de los Resultados , Espectroscopía Infrarroja por Transformada de Fourier , Proteínas no Estructurales Virales/química , Proteínas no Estructurales Virales/inmunologíaRESUMEN
This paper reports the magnetic control of nanoparticle collisions on gold ultramicroelectrode surface. Magnetite nanoparticles with diameters of 10 nm and modified with Prussian blue (Fe3O4-NPs-PB) were directed by gravitational force on the electrode surface, and spikes in current-time transients were observed. By modulating a magnetic field parallel to the electrode surface, the number of nanoparticle collisions and the nanoparticle positions could be controlled.
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Ferrocianuros/química , Oro/química , Nanopartículas de Magnetita/química , Campos Magnéticos , Nanopartículas de Magnetita/ultraestructura , Microelectrodos , Propiedades de SuperficieRESUMEN
Label-free immunosensor based on amine-functionalized carbon nanotubes screen-printed electrode is described for detection of the cardiac troponin T, an important marker of acute myocardial infarction. The disposable sensor was fabricated by tightly squeezing an adhesive carbon ink containing carbon nanotubes onto a polyethylene terephthalate substrate forming a thin film. The use of carbon nanotubes increased the reproducibility and stability of the sensor, and the amine groups permitted nonrandom immobilization of antibodies against cardiac troponin T. Amperometric responses were obtained by differential pulse voltammetry in presence of a ferrocyanide/ferricyanide redox probe after troponin T incubation. The calibration curve indicated a linear response of troponin T between 0.0025 ng mL(-1) and 0.5 ng mL(-1), with a good correlation coefficient (r=0.995; p<0.0001, n=7). The limit of detection (0.0035 ng mL(-1) cardiac troponin T) was lower than any previously described by immunosensors and was comparable with conventional analytical methods. The high reproducibility and clinical range obtained using this immunosensor support its utility as a potential tool for point-of-care acute myocardial infarction diagnostic testing.
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Técnicas Biosensibles , Infarto del Miocardio/sangre , Nanotubos de Carbono/química , Tereftalatos Polietilenos/química , Troponina T/sangre , Animales , Anticuerpos Inmovilizados/química , Anticuerpos Inmovilizados/aislamiento & purificación , Calibración , Técnicas Electroquímicas , Electrodos , Ferricianuros/química , Ferrocianuros/química , Humanos , Límite de Detección , Ratones , Infarto del Miocardio/diagnóstico , Infarto del Miocardio/patología , Miocardio/química , Miocardio/metabolismo , Miocardio/patología , Impresión , Reproducibilidad de los Resultados , Troponina T/aislamiento & purificaciónRESUMEN
AIMS: The survival rate of freeze-dried cultures is not enough information for technological applications of micro-organisms. There could be serious metabolic/structural damage in the survivors, leading to a delay time that can jeopardize the design of a rapid biochemical oxygen demand (BOD) metabolic-based bioassay. Therefore, we will study the metabolic activity (as ferricyanide reduction activity) and the survival rate (as colony-forming units, CFU) of different Klebsiella pneumoniae freeze-dried cultures looking for stable metabolic conditions after 35days of storage. METHOD AND RESULTS: Here, we tried several simple freeze-drying processes of Kl. pneumoniae. Electrochemical measurements of ferrocyanide and survival rates obtained with the different freeze-dried cultures were used to choose the best freeze-drying process that leads to a rapid metabolic-based bioassay. CONCLUSIONS: The use of milk plus monosodium glutamate was the best choice to obtain a Kl. pneumoniae freeze-dried culture with metabolic stable conditions after storage at -20°C without the need of vacuum storage and ready to use after 20min of rehydration. We also demonstrate that the viability and the metabolic activity are not always directly correlated. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows that the use of this Kl. pneumoniae freeze-dried culture is appropriate for the design of a rapid BOD bioassay.
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Análisis de la Demanda Biológica de Oxígeno/métodos , Liofilización/métodos , Klebsiella pneumoniae/metabolismo , Animales , Ferrocianuros/química , Klebsiella pneumoniae/crecimiento & desarrollo , Leche/metabolismo , Oxígeno/metabolismo , Glutamato de Sodio/químicaRESUMEN
Bone marrow mesenchymal stem cells (MSC) have been tested and proven effective in some neurodegenerative diseases, but their tracking after transplantation may be challenging. Our group has previously demonstrated the feasibility and biosafety of rat MSC labeling with iron oxide superparamagnetic nanoparticles (SPION). In this study, we investigated the therapeutic potential of SPION-labeled MSC in a rat model of Huntington's disease, a genetic degenerative disease with characteristic deletion of striatal GABAergic neurons. MSC labeled with SPION were injected into the striatum 1h after quinolinic acid injection. FJ-C analysis demonstrated that MSC transplantation significantly decreased the number of degenerating neurons in the damaged striatum 7 days after lesion. In this period, MSC transplantation enhanced the striatal expression of FGF-2 but did not affect subventricular zone proliferation, as demonstrated by Ki67 proliferation assay. In addition, MSC transplantation significantly reduced the ventriculomegaly in the lesioned brain. MRI and histological techniques detected the presence of the SPION-labeled cells at the lesion site. SPION-labeled MSC produced magnetic resonance imaging (MRI) signals that were visible for at least 60 days after transplantation. Our data highlight the potential of adult MSC to reduce brain damage under neurodegenerative diseases and indicate the use of nanoparticles in cell tracking, supporting their potential as valuable tools for cell therapy.
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Dextranos/uso terapéutico , Enfermedad de Huntington/terapia , Imagen por Resonancia Magnética/métodos , Nanopartículas de Magnetita/uso terapéutico , Trasplante de Células Madre Mesenquimatosas , Células Madre Mesenquimatosas/metabolismo , Nanopartículas/uso terapéutico , Fármacos Neuroprotectores/farmacología , Animales , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Proliferación Celular/efectos de los fármacos , Modelos Animales de Enfermedad , Ferrocianuros/metabolismo , Factor 2 de Crecimiento de Fibroblastos/metabolismo , Enfermedad de Huntington/patología , Masculino , Células Madre Mesenquimatosas/citología , Neostriado/efectos de los fármacos , Neostriado/patología , Degeneración Nerviosa/patología , Degeneración Nerviosa/terapia , Ratas , Ratas Wistar , Coloración y EtiquetadoRESUMEN
The aquapentacyanoferrate(II) ion, [Fe(II)(CN)(5)H(2)O](3-), catalyzes the disproportionation reaction of O-methylhydroxylamine, NH(2)OCH(3), with stoichiometry 3NH(2)OCH(3) â NH(3) + N(2) + 3CH(3)OH. Kinetic and spectroscopic evidence support an initial N coordination of NH(2)OCH(3) to [Fe(II)(CN)(5)H(2)O](3-) followed by a homolytic scission leading to radicals [Fe(II)(CN)(5)(â¢)NH(2)](3-) (a precursor of Fe(III) centers and bound NH(3)) and free methoxyl, CH(3)O(â¢), thus establishing a radical path leading to N-methoxyamino ((â¢)NHOCH(3)) and 1,2-dimethoxyhydrazine, (NHOCH(3))(2). The latter species is moderately stable and proposed to be the precursor of N(2) and most of the generated CH(3)OH. Intermediate [Fe(III)(CN)(5)L](2-) complexes (L = NH(3), H(2)O) form dinuclear cyano-bridged mixed-valent species, affording a catalytic substitution of the L ligands promoted by [Fe(II)(CN)(5)L](3-). Free or bound NH(2)OCH(3) may act as reductants of [Fe(III)(CN)(5)L](2-), thus regenerating active sites. At increasing concentrations of NH(2)OCH(3) a coordinated diazene species emerges, [Fe(II)(CN)(5)N(2)H(2)](3-), which is consumed by the oxidizing CH(3)O(â¢), giving N(2) and CH(3)OH. Another side reaction forms [Fe(II)(CN)(5)N(O)CH(3)](3-), an intermediate containing the nitrosomethane ligand, which is further oxidized to the nitroprusside ion, [Fe(II)(CN)(5)NO](2-). The latter is a final oxidation product with a significant conversion of the initial [Fe(II)(CN)(5)H(2)O](3-) complex. The side reaction partially blocks the Fe(II)-aqua active site, though complete inhibition is not achieved because the radical path evolves faster than the formation rates of the Fe(II)-NO(+) bonds.
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Ferrocianuros/química , Hidroxilaminas/química , Catálisis , Radicales Libres/química , Cinética , Análisis EspectralRESUMEN
Here we report the derivatization of mesoporous TiO2 thin films for the preparation of H2O2 amperometric sensors. The coordination of the bifunctional ligand 1,10 phenantroline, 5,6 dione on the surface Ti(IV) ions provides open coordination sites for Fe(II) cations which are the starting point for the growth of a layer of Prussian blue polymer. The porous structure of the mesoporous TiO2 allows the growth, ion by ion of the coordination polymer. Up to four layer of Prussian blue can be deposit without losing the porous structure of the film, which results in an enhanced response of these materials as H2O2 sensors. These porous confined PB modified electrodes are robust sensors that exhibit good reproducibility, environmental stability and high sensitivity towards H2O2 detection.
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Técnicas Biosensibles/instrumentación , Conductometría/instrumentación , Electrodos , Ferrocianuros/química , Peróxido de Hidrógeno/análisis , Titanio/química , Catálisis , Diseño de Equipo , Análisis de Falla de Equipo , Peróxido de Hidrógeno/química , PorosidadRESUMEN
The uptake of ascorbate by neuroblastoma cells using a ruthenium oxide hexacyanoferrate (RuOHCF)-modified carbon fiber disc (CFD) microelectrode (r = 14.5 microm) was investigated. By use of the proposed electrochemical sensor the amperometric determination of ascorbate was performed at 0.0 V in minimum essential medium (MEM, pH = 7.2) with a limit of detection of 25 micromol L(-1). Under the optimum experimental conditions, no interference from MEM constituents and reduced glutathione (used to prevent the oxidation of ascorbate during the experiments) was noticed. The stability of the RuOHCF-modified electrode response was studied by measuring the sensitivity over an extended period of time (120 h), a decrease of around 10% being noticed at the end of the experiment. The rate of ascorbate uptake by control human neuroblastoma SH-SY5Y cells, and cells transfected with wild-type Cu,Zn-superoxide dismutase (SOD WT) or with a mutant typical of familial amyotrophic lateral sclerosis (SOD G93A), was in agreement with the level of oxidative stress in these cells. The usefulness of the RuOHCF-modified microelectrode for in vivo monitoring of ascorbate inside neuroblastoma cells was also demonstrated.