RESUMEN
We investigated the static charge generation by contact electrification between Au and polydimethylsiloxane (PDMS) and the redox reaction by the static charge in the aqueous phase, to reveal the mechanism of contact electrification and redox reaction which may be applied to mechanical-to-chemical energy harvesting. First, the static charge distribution on the equipotential Au was probed through Kelvin probe force microscopy (KPFM) in air after the contact with patterned PDMS. Positive charges are localized on the contact areas indicating the ion migration while the polarity becomes negative after water contact. Second, the redox reaction by the charged Au was electrochemically monitored using open circuit potential (OCP), stripping voltammetry, and copper underpotential deposition (UPD). All electrochemical experiments consistently resulted in the reduction of the reactant by the charged Au within the highly dielectric water media. We concluded that the reduction is not driven by the discharge of static charge on Au but by reducing radicals.
RESUMEN
Various R/Ar-functionalized tin 5,10,15-tris(pentafluorophenyl)corrolate derivatives are reported herein including the first ferrocenyltin corrolate species. The isopropyl, sec-butyl-, 2-methyl-n-butyl-, phenyl-, 2-thienyl-, and ferrocenyltin species have been prepared and characterized through (1)H, (13)C, and (119)Sn HMQC NMR spectroscopy, mass spectrometry, UV-vis and photoluminescent spectroscopy, and cyclic voltammetry studies. J(C/H-Sn) NMR spectroscopic couplings and ring-current effects (upfield shifting) were determined for the R-Sn axial hydrogen and carbon atoms. This report adds to older conceptually similar reports, by, i.e., Janson et al. (J. Am. Chem. Soc. 1969, 91, 5210) and Walker et al. (J. Am. Chem. Soc.1983, 105, 6923-6929), as discussed herein. Such NMR spectroscopic aspects are discussed for these model systems. Compound Sn-Ph bond cleavage was achieved by treatment with I(2).
Asunto(s)
Técnicas Electroquímicas , Compuestos Orgánicos de Estaño/química , Porfirinas/química , Estaño/química , Isótopos , Espectroscopía de Resonancia Magnética , Estructura Molecular , Compuestos Orgánicos de Estaño/síntesis química , Porfirinas/síntesis químicaRESUMEN
In this paper, we report the microelectrode array fabrication using selective wetting/dewetting of polymers on a chemical pattern which is a simple and convenient method capable of creating negative polymeric replicas using polyethylene glycol (PEG) as a clean and nontoxic sacrificial layer. The fabricated hole-patterned polypropylene film on gold demonstrated enhanced electrochemical properties. The chemical pattern is fabricated by microcontact printing using octadecanethiol (ODT) as an ink on gold substrate. When PEG is spin-cast on the chemical pattern, PEG solution selectively dewets the ODT patterned areas and wets the remaining bare gold areas, leading to the formation of arrayed PEG dots. A negative replicas of the PEG dot array is obtained by spin-coating of polypropylene (PP) solution in hexane which preferentially interacts with the hydrophobic ODT region on the patterned gold surface. The arrayed PEG dots are not affected the during PP spin-coating step because of their intrinsic immiscibility. Consequently, the hole-patterned PP film is obtained after PEG removal. The electrochemical signal of the PP film demonstrates the negligible leakage current by high dielectric and self-healing of defects on the chemical pattern by the polymer. This method is applicable to fabrication of microelectrode arrays and possibly can be employed to fabricate a variety of functional polymeric structures, such as photomasks, arrays of biomolecules, cell arrays, and arrays of nanomaterials.
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To detect the target molecules, aptamers are currently focused on and the use of aptamers for biosensing is particularly interesting, as aptamers could substitute antibodies in bioanalytical sensing. So this paper describes the novel electrochemical system for protein in sandwich manner by using the aptamers and the scanning electrochemical microscope (SECM). For protein detection, sandwich system is ideal since labeling of the target protein is not necessary. To develop the electrochemical protein sensor system, thrombin was chosen as a target protein since many aptamers for it were already reported and two different aptamers, which recognize different positions of thrombin, were chosen to construct sandwich type sensing system. In order to obtain the electrochemical signal, the glucose oxidase (GOD) used for labeling the detection aptamers since it has large amount of stability in aqueous solution. One aptamer was immobilized onto the gold electrode and the other aptamer for detection was labeled with GOD for generation of the electric signal. Thrombin was detected in sandwich manner with aptamer immobilized onto the gold electrode and the GOD labeled aptamer. The enzymatic signal, generated from glucose addition after the formation of the complex of thrombin, was measured. The generation-collection mode of SECM was used for amperometric H2O2 detection.
RESUMEN
Thiol self-assembled monolayers (SAMs) have been widely used as a modification method to immobilize biomolecules to gold surfaces. However, the additional layers of SAM and biomolecules make electron transfer difficult, leading to a large overpotential in electrical signal. Electron transfer mediation is the most popular solution to overcome the problem of the overpotential for an electrochemical biosensor. We introduced mixed SAMs of mercapto-dodecanoic acid (MDA) and ferrocene-undecanthiol. Ferrocene-undecanthiol acts as an electron transfer mediator and MDA is used for immobilization of biomolecule. The electron transferability of mixed SAMs is affected by pH, kinds of electrolytes, and the composition of the thiol molecule. We optimized the carboxyl acid and ferrocene molecule ratio which is a crucial factor in the performance of mixed SAMs and electrochemically detected the avidin. The detection limit was 2.0 microg/mL of avidin concentration.
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Electroquímica/métodos , Compuestos Ferrosos/química , Compuestos de Sulfhidrilo/química , Electroquímica/instrumentación , MetalocenosRESUMEN
We report eight new A(2)B-type (M(n+)) corrolate compounds (two structural studies) that include the oxo[5,15-bis(pentafluorophenyl)-10-R-corrolatochromium(V)] [R = 2-/3-thienyl (1a/2a), 3-thianaphthyl (3a)] species. The first examples of meso-A(2) (thienyl)- and Cr-A(2)B-corrole types are represented herein. Characterization includes cyclic voltammetry, electron paramagnetic resonance, 2D ((1)H and (13)C) NMR, and UV-vis spectroscopy, mass spectrometry, and elemental analysis. Compounds 1a-3a have enabled analyte binding capacity studies. [Cu(2+)...O=Cr(cor)] binding represents a new selective mode of corrole-based detection, whereas free-base A(2)B-corroles exhibited limited M(n+) selectivity. The 10-position substitution affects optical profiles in analyte titrations. A limited amount of PPh(3) O-atom uptake from [O=Cr(cor)] was also demonstrated.
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Compuestos de Cromo/química , Porfirinas/química , Catálisis , Compuestos de Cromo/síntesis química , Cristalografía por Rayos X , Electroquímica , Espectroscopía de Resonancia por Spin del Electrón , Metales/química , Modelos Moleculares , Estructura Molecular , Porfirinas/síntesis química , Espectrofotometría UltravioletaRESUMEN
The handcrafted fabrication of a pyramidal mold on a silicon wafer for nanopatterning was investigated. This process started with the manual delivery of an aqueous glycerol solution onto the SiO2/Si wafer using a micropipette and subsequent drying to form a hemisphere whose diameter is in the range of hundreds of micrometers. A coating of polystyrene (PS) onto this wafer generates a circular hole caused by dewetting. Subsequently, anisotropic wet-etching with the PS film as a mask produces a pyramidal trench, whose apex approaches hundreds of nanometers. Various elastomeric materials were casted into this pyramidal mold. A pyramidal tip mounted on a simple micropositioner was used for electrochemistry and patterning of a protein. First, an agarose hydrogel was cast with a hydrogel pen for the electrochemical reaction (HYPER). The redox reaction at the HYPER-electrode interface demonstrated the characteristics of an ultramicroelectrode or bulk electrode based on the contact area. Second, the pyramidal polydimethylsiloxane served as a polymer pen for the contact printing of silane on a glass substrate. After the successive immobilization of biotin and avidin with fluorescence labeling, the resulting fluorescence image demonstrated the successful patterning of the protein. This new process for the creation of a pyramidal mold, referred to as a "do-it-yourself" process, offers advantages to nonspecialists in nanotechnology compared to conventional lithography, specifically simplicity, rapidity, and low cost.
RESUMEN
Gold electrode was modified with 3-mercaptopropionic acid (MPA) and further reacted with poly(amidoamine) (PAMAM) dendrimer (generation 4.0) then attached the nano-Au to obtain films on which Prussian blue (PB) was electrochemically deposited to afford much wider pH adaptive range, much better electrochemical stability and excellent electrochemical response. The microstructure and electrochemical behavior of Au/MPA/PAMAM/nano-Au/PB electrode were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The electrochemical response of the Au/MPA/PAMAM/nano-Au/PB-modified electrode for the electrocatalytic reduction of hydrogen peroxide was investigated, and it was found that the sensitivity as well as the corresponding detection limits were improved as compared to the voltammetric response of a Au/PB-modified electrode and Au/MPA/PAMAM/PB electrode. Based on this, a new electrochemical sensor for determination of hydrogen peroxide has been developed.
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Técnicas Biosensibles/instrumentación , Ferrocianuros/química , Oro/química , Peróxido de Hidrógeno/análisis , Peróxido de Hidrógeno/química , Microelectrodos , Nanoestructuras/química , Técnicas Biosensibles/métodos , Catálisis , Materiales Biocompatibles Revestidos/química , Dendrímeros , Conductividad Eléctrica , Electroquímica/instrumentación , Electroquímica/métodos , Diseño de Equipo , Análisis de Falla de Equipo , Nanoestructuras/ultraestructura , Tamaño de la Partícula , Poliaminas/química , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Redox cycling of enzymatically amplified electroactive species has been widely employed for high signal amplification in electrochemical biosensors. However, gold (Au) electrodes are not generally suitable for redox cycling using a reducing (or oxidizing) agent because of the high background current caused by the redox reaction of the agent at highly electrocatalytic Au electrodes. Here we report a new redox cycling scheme, using nicotinamide adenine dinucleotide (NADH), which can be applied to Au electrodes. Importantly, p-aminophenol (AP) redox cycling by NADH is achieved in the absence of diaphorase enzyme. The Au electrodes are modified with a mixed self-assembled monolayer of mercaptododecanoic acid and mercaptoundecanol, and a partially ferrocenyl-tethered dendrimer layer. The self-assembled monolayer of long thiol molecules significantly decreases the background current of the modified Au electrodes, and the ferrocene modification facilitates easy oxidation of AP. The low amount of ferrocene on the Au electrodes minimizes ferrocene-mediated oxidation of NADH. In sandwich-type electrochemical immunosensors for mouse immunoglobulin G (IgG), an alkaline phosphatase label converts p-aminophenylphosphate (APP) into electroactive AP. The amplified AP is oxidized to p-quinoneimine (QI) by electrochemically generated ferrocenium ion. NADH reduces QI back to AP, which can be re-oxidized. This redox cycling enables a low detection limit for mouse IgG (1 pg mL(-1)) to be obtained.
Asunto(s)
Aminofenoles/química , Técnicas Biosensibles , NAD/química , Electroquímica/métodos , Electrodos , Compuestos Ferrosos , Oro , Metalocenos , Oxidación-ReducciónRESUMEN
Human skin can perceive pressure, chemical compounds and temperature with a high spatial resolution via specific receptors. Inspired by human skin, we present a wet-chemistry based hydrogel sensing platform for 2D imaging sensitive to specific external stimuli, e.g., pressure, chemicals and temperature. This platform is composed of a hydrogel pyramidal array on a single electrode. Each pyramid serves as a spatially separated reservoir for chemical reactions, enabling independent pixels for sensing without individual electrodes. Depending on the electrochemiluminescence (ECL) electrolyte for specific stimuli, our platform possesses 2D imaging capabilities with high sensitivity for pH and temperature in addition to pressure via the deformation of the viscoelastic hydrogel. This work represents an important step toward the application of sensitive chemical reactions for various external stimuli to biocompatible electronic skins based on hydrogels without addressing circuit for each pixel.
RESUMEN
A programmable electrochemical rectifier based on thin-layer electrochemistry is described here. Both the rectification ratio and the response time of the device are programmable by controlling the gap distance of the thin-layer electrochemical cell, which is easily controlled using commercially available beads. One of the electrodes was modified using a ferrocene-terminated self-assembled monolayer to offer unidirectional charge transfers via soluble redox species. The thin-layer configuration provided enhanced mass transport, which was determined by the gap thickness. The device with the smallest gap thickness (â¼4 µm) showed an unprecedented, high rectification ratio (up to 160) with a fast response time in a two-terminal configuration using conventional electronics.
RESUMEN
In this study, for the first time, the anion dependency of Ag-deposition on self-assembled monolayers (SAMs) with alkyl chains long enough to meet the densely packed and well-organized surface is reported. Irrespective of pH, types of terminal groups of the SAMs, and the convective mass transfer condition, SAM structures show the "sieving behaviour" to the Ag deposition by the composition of the electrolytes.
RESUMEN
We demonstrate a protein micropatterning method based on electropolymerization of a monomer with two electroactive units, hydroquinone monoester and disulfide, which enables electrochemical ON-OFF switching for immobilization of bioligands on electrodes modified with the electropolymerized film.
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Polímeros/química , Proteínas/química , Disulfuros/química , Electroquímica , Hidroquinonas/química , Ligandos , Estructura MolecularRESUMEN
Asymmetric electrostatic interactions dependent on pH between the redox molecules and the terminal group on the top of the self-assembled monolayer (SAM) afford control of the electron transfer property of the SAM having the imidazole terminal group.
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Imidazoles/química , Membranas Artificiales , Electrodos , Electrones , Oro/química , Concentración de Iones de Hidrógeno , Cinética , Estructura Molecular , Oxidación-Reducción , Electricidad Estática , Propiedades de SuperficieRESUMEN
A hydrogel pen consisting of a microscopic pyramid containing an electrolyte offers a localized electroactive area on the nanometer scale via controlled contact of the apex with a working electrode. The hydrogel pen merges the fine control of atomic force microscopy with non-linear diffusion of an ultramicroelectrode, producing a faradaic current that depends on the small electroactive area. The theoretical and experimental investigations of the mass transport behavior within the hydrogel reveal that the steady-state current from the faradaic reaction is linearly proportional to the deformed length of the hydrogel pen by contact, i.e. signal transduction of deformation to an electrochemical signal, which enables the fine control of the electroactive area in the nanometer-scale regime. Combined with electrodeposition, localized electrochemistry of the hydrogel pen results in the ability to fabricate small sizes (110 nm in diameter), tall heights (up to 30 µm), and arbitrary structures, thereby indicating an additive process in 3 dimensions by localized electrodeposition.
RESUMEN
A novel Schiff base probe exhibited strong 'turn-ON' fluorescence for Cu(2+) at 345 nm, Al(3+) at 445 nm, and Cu(+) at 360 nm in the presence of Al(3+) in organic solvent (acetonitrile), which allowed for construction of molecular logic gates 'INH' and '1:2 DEMULTIPLEXING.' H(+) generated from Al(3+) contributed greatly to Cu(+) chemosensing based on a redox non-innocence mechanism.
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Aluminio/química , Técnicas de Química Analítica/instrumentación , Cobre/química , Lógica , Protones , Cobre/análisis , Colorantes Fluorescentes/química , Concentración de Iones de Hidrógeno , Bases de Schiff/química , Espectrometría de FluorescenciaRESUMEN
Self-assembled monolayers (SAMs) of a mu 3-eta 2:eta 2:eta 2-C60 triosmium cluster complex Os3(CO)8(CN(CH2)3Si(OEt)3)(mu 3-eta 2:eta 2:eta 2-C60) (2) on ITO or Au surface exhibit ideal, well-defined electrochemical responses and remarkable electrochemical stability being reducible up to tetranionic species in their cyclic voltammograms.
RESUMEN
Size reduction of neural electrodes is essential for improving the functionality of neuroprosthetic devices, developing potent therapies for neurological and neurodegenerative diseases, and long-term braincomputer interfaces. Typical neural electrodes are micromanufactured devices with dimensions ranging from tens to hundreds of micrometers. Their further miniaturization is necessary to reduce local tissue damage and chronic immunological reactions of the brain. Here we report the neural electrode with subcellular dimensions based on single-crystalline gold nanowires (NWs) with a diameter of â¼100 nm. Unique mechanical and electrical properties of defect-free gold NWs enabled their implantation and recording of single neuron-activities in a live mouse brain despite a â¼50× reduction of the size compared to the closest analogues. Reduction of electrode dimensions enabled recording of neural activity with improved spatial resolution and differentiation of brain activity in response to different social situations for mice. The successful localization of the epileptic seizure center was also achieved using a multielectrode probe as a demonstration of the diagnostics potential of NW electrodes. This study demonstrated the realism of single-neuron recording using subcellular-sized electrodes that may be considered a pivotal point for use in diverse studies of chronic brain diseases.
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Encéfalo/citología , Oro/química , Espacio Intracelular/metabolismo , Sondas Moleculares/química , Sondas Moleculares/metabolismo , Nanocables , Animales , Interfaces Cerebro-Computador , Electrodos Implantados , Masculino , Ratones , Ratones Endogámicos C57BLRESUMEN
An enzyme stimulated deposition of prussian blue onto the gold-coated magnetic microparticles is described. We propose to synthesize the continuous outer gold layer on the magnetic particle for a gold working electrode and its superparamagnetic property. In-depth characterization of the gold shell formation was studied with scanning electron microscopy, energy-dispersive X-ray spectroscopy, cyclic voltammetry. The gold-coated magnetic microparticles offered adhesive layer for the immobilization of glucose oxidase catalyzing the generation of prussian blue in the presence of glucose. The assembled prussian blue on the gold shell surfaces was detected with electrochemical measurements depending on the glucose concentration. With accomplishing the linear response range from 0.2 mM to 10 mM of glucose, this approach successfully proposed the applicability of the magnetic core-gold shell structures to the electrochemical bioassay area.
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Técnicas Biosensibles/instrumentación , Materiales Biocompatibles Revestidos/síntesis química , Ferrocianuros/química , Glucosa/análisis , Oro/química , Imanes/química , Técnicas Biosensibles/métodos , Catálisis , Precipitación Química , Materiales Biocompatibles Revestidos/química , Materiales Biocompatibles Revestidos/farmacología , Técnicas Electroquímicas/instrumentación , Técnicas Electroquímicas/métodos , Electrodos , Enzimas Inmovilizadas/química , Enzimas Inmovilizadas/metabolismo , Ferrocianuros/farmacocinética , Glucosa/farmacocinética , Glucosa Oxidasa/química , Glucosa Oxidasa/metabolismo , Nanopartículas de Magnetita/química , Microesferas , Tamaño de la Partícula , Reacción del Azul PrusiaRESUMEN
In tissue engineering, fabrication of 3D scaffolds with well-defined, inter-connected pores followed by culture of mammalian cells is a typical approach. In practice, however, hydrophobicity of scaffold surfaces is not suitable for cells to be adhered because of poor wettability. Especially, infiltration followed by adhesion of cells inside hydrophobic scaffolds remains as a challenge. Thus, hydrophilic conversions of the surfaces regardless of surface location are critical for success. Herein, a method to enhance infiltration and adhesion of preosteoblasts inside hydrophobic poly(ϵ-caprolactone) (PCL) scaffolds by a bio-inspired, hydroxyapatite formation is demonstrated. The approach can be a general method for controlling hydrophilicity of inner surfaces of scaffolds.