Fabrication of integrated microelectrodes for electrochemical detection on electrophoresis microchip by electroless deposition and micromolding in capillary technique

A new method for the fabrication of an integrated microelectrode for electrochemical detection (ECD) on an electrophoresis microchip is described. The pattern of the microelectrode was directly made on the surface of a microscope slide through an electroless deposition procedure. The surface of the slide was first selectively coated with a thin layer of sodium silicate through a micromolding in capillary technique provided by a poly(dimethylsiloxane) (PDMS) microchannel; this left a rough patterned area for the anchoring of catalytic particles. A metal layer was deposited on the pattern guided by these catalytic particles and was used as the working electrode. Factors influencing the fabrication procedure were discussed. The whole chip was built by reversibly sealing the slide to another PDMS layer with electrophoresis microchannels at room temperature. This approach eliminates the need of clean room facilities and expensive apparatus such as for vacuum deposition or sputtering and makes it possible to produce patterned electrodes suitable for ECD on microchip under ordinary chemistry laboratory conditions. Also once the micropattern is ready, it allows the researchers to rebuild the electrode in a short period of time when an electrode failure occurs. Copper and gold microelectrodes were fabricated by this technique. Glucose, dopamine, and catechol as model analytes were tested.

The effect of light exposure on the degradation of latent fingerprints on brass surfaces: the use of silver electroless deposition as a visualization technique

We have studied the degradation of sebaceous fingerprints on brass surfaces using silver electroless deposition (SED) as a visualization technique. We have stored fingerprints on brass squares either (i) in a locked dark cupboard or (ii) in glass-filtered natural daylight for periods of 3 h, 24 h, 1 week, 3 weeks, and 6 weeks. We find that fingerprints on brass surfaces degrade much more rapidly when kept in the light than they do under dark conditions with a much higher proportion of high-quality prints found after 3 or 6 weeks of aging when stored in the dark. This process is more marked than for similar fingerprints on black PVC surfaces. Identifiable prints can be achieved on brass surfaces using both SED and cyanoacrylate fuming (CFM). SED is quick and straightforward to perform. CFM is more time-consuming but is versatile and can be applied to a wider range of metal surfaces than SED, for example brass surfaces which have been coated by a lacquer.

Nitrogen-assisted electroless assembling of 3D nanodendrites consisting of Pd and N-doped carbon nanoparticles as bifunctional catalysts

We report a facile synthesis of three-dimensional (3D) nanodendrites of Pd nanoparticles (NPs) and nitrogen-doped carbon NPs (N-CNPs) by electroless deposition of Pd2+ ions. N-CNPs being an electron-enriched material act as a reducing agent. Moreover, the availability of a variety of nitrogen species in N-CNPs promotes the open arm structure as well as stabilizes the oriented 3D assembly of primary Pd NPs. The dendrites exhibit superior catalytic activity for methanol (0.5 M) oxidation in alkaline media (1 M NaOH) which is ascribed to the large electrochemical active surface area and the enhanced mass activity with repeated use. Further mass activity improvement has been realized after acid-treatment of dendrites which is attributed to the increment in the -OH group. The dendrites show higher mass activity (J(f) similar to 653 A g(-1)) in comparison with a commercial Pt-carbon/Pd-carbon (Pt-C/Pd-C) catalyst (J(f) similar to 46 and 163 A g(-1), respectively), better operational stability, superior CO tolerance with I-f/I-b (similar to 3.7) over a commercial Pt-C/Pd-C catalyst (I-f/I-b similar to 1.6 and 1.75, respectively) and may serve as a promising alternative to commercial Pt-C catalysts for anode application in alkaline fuel cells. To ensure the adaptability of our 3D-nanodendrites for other catalytic activities, we studied 4-nitrophenol reduction at room temperature. The 3D-nanodendrites show excellent catalytic activity toward 4-nitrophenol reduction, as well.

The active site behaviour of electrochemically synthesised gold nanomaterials

Even though gold is the noblest of metals, a weak chemisorber and is regarded as being quite inert, it demonstrates significant electrocatalytic activity in its nanostructured form. It is demonstrated here that nanostructured and even evaporated thin films of gold are covered with active sites which are responsible for such activity. The identification of these sites is demonstrated with conventional electrochemical techniques such as cyclic voltammetry as well as a large amplitude Fourier transformed alternating current (FT-ac) method under acidic and alkaline conditions. The latter technique is beneficial in determining if an electrode process is either Faradaic or capacitive in nature. The observed behaviour is analogous to that observed for activated gold electrodes whose surfaces have been severely disrupted by cathodic polarisation in the hydrogen evolution region. It is shown that significant electrochemical oxidation responses occur at discrete potential values well below that for the formation of the compact monolayer oxide of bulk gold and are attributed to the facile oxidation of surface active sites. Several electrocatalytic reactions are explored in which the onset potential is determined by the presence of such sites on the surface. Significantly, the facile oxidation of active sites is used to drive the electroless deposition of metals such as platinum, palladium and silver from their aqueous salts on the surface of gold nanostructures. The resultant surface decoration of gold with secondary metal nanoparticles not only indicates regions on the surface which are rich in active sites but also provides a method to form interesting bimetallic surfaces.

Reduction of Au3+ ions by activated surface atoms of platinum

In this work it is demonstrated that Pt electrodes can be activated by cathodic polarisation in the hydrogen evolution region which makes it prone to oxidation at potentials below that of bulk oxide formation. When an activated Pt electrode is placed in an aqueous HAuCl4 solution the electroless deposition of Au onto the surface of the electrode is observed and confirmed by cyclic voltammetry and XPS measurements. It is demonstrated that the oxidation of active Pt surface atoms provides the driving force for the spontaneous reduction of Au3+ ions into metallic Au to generate a Pt/Au surface which is highly active for the electro-oxidation of ethanol.

Robust nanostructured silver and copper fabrics with localized surface plasmon resonance property for effective visible light induced reductive catalysis

Inspired by high porosity, absorbency, wettability and hierarchical ordering on the micrometer and nanometer scale of cotton fabrics, a facile strategy is developed to coat visible light active metal nanostructures of copper and silver on cotton fabric substrates. The fabrication of nanostructured Ag and Cu onto interwoven threads of a cotton fabric by electroless deposition creates metal nanostructures that show a localized surface plasmon resonance (LSPR) effect. The micro/nanoscale hierarchical ordering of the cotton fabrics allows access to catalytically active sites to participate in heterogeneous catalysis with high efficiency. The ability of metals to absorb visible light through LSPR further enhances the catalytic reaction rates under photoexcitation conditions. Understanding the mode of electron transfer during visible light illumination in Ag@Cotton and Cu@Cotton through electrochemical measurements provides mechanistic evidence on the influence of light in promoting electron transfer during heterogeneous catalysis for the first time. The outcomes presented in this work will be helpful in designing new multifunctional fabrics with the ability to absorb visible light and thereby enhance light-activated catalytic processes.

Using an Office Inkjet Printer to Define the Formation of Copper Films on Paper

A low-cost fabrication process for forming conductive copper lines on paper is presented. An office inkjet printer was used to deposit desired patterns of silver nitrate and tannic acid solutions sequentially on paper. Silver nitrate was instantaneously reduced in situ on paper by tannic acid at room temperature to form silver nanoparticles, which acted as catalysts for the subsequent electroless deposition of copper. The copper films were 1.8 mu m thick, and the sheet resistance of the copper film on paper was 9 Omega/square. A dual monopole ultrawide band antenna was fabricated on paper and its performance was equivalent to that of a similar antenna fabricated on a copper-film covered Kapton substrate using conventional lithographic processes. The paper-based conductive copper films fabricated using the facile process presented herein will aid the development of low-cost flexible circuits and sensors.

Formation of low surface energy separators with undercut structures via a full-solution process and its application in inkjet printed matrix of polymer light-emitting diodes

In this paper, low surface energy separators With undercut structures were fabricated through a full solution process, These low Surface energy separators are more suitable for application in inkjet printed passive-matrix displays of polymer light-emitting diodes. A patterned PS film was formed on the P4VP/photoresist film by microtransfer printing firstly. Patterned Au-coated Ni film was formed on the uncovered P4VP/photoresist film by electroless deposition. This metal film was used as mask to pattern the photoresist layer and form undercut structures with the patterned photoresist layer. The surface energy of the metal film also decreased dramatically from 84.6 mj/m(2) to 21.1 mJ/m(2) by modification of fluorinated mercaptan self-assemble monolayer on Au surface. The low surface energy separators were used to confine the flow of inkjet printed PFO solution and improve the patterning resolution of inkjet printing successfully. Separated PFO stripes, complement with the pattern of the separators, formed through inkjet printing.

Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchips

We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 muM to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument.

Fabrication of arrays of silver nanoparticle aggregates by microcontact printing and block copolymer nanoreactors

A combination of microcontact printing and block copolymer nanoreactors succeeded in fabricating arrays of silver nanoparticle aggregates. A complex solution of polystyrene-block-poly(4-vinylpyridine) micelles and silver salt was used as an ink to form thin films or droplets on polydimethylsiloxane stamp protrusions. After these complex aggregates were printed onto silicon substrates under controlled conditions, highly ordered arrays of disklike, dishlike, and dotlike complex aggregates were obtained. A Subsequent oxygen reactive ion etching treatment yielded arrays of silver nanoparticle aggregates.

Voltammetric studies of gold, protons, and [HCl2](-) in ionic liquids

The comparative study of the voltammetry of H[NTf2], HCl and H[AuCl4] in [C(4)mim][NTf2] has provided an insight into the influence of protons on the reduction of [AuCl4](-) at Au, Pt or glassy carbon (GC) electrodes, and has allowed the identification of an unprecedented proton-induced electroless deposition of Au on relatively inert GC surfaces. For the first time, clear evidence of the quantitative formation of [HCl2](-) has been obtained in HCl/[C(4)mim][NTf2] mixtures, and the electrochemical behavior of these mixtures analyzed. In particular, a significant shift of the dissociation equilibrium toward the formation of chloride and the solvated proton (H-IL(+)), following electrochemical reduction of H-IL(+) has been observed in the time-scale of the experiments.

Electroanalysis of urinary L-dopa using tyrosinase immobilized on gold nanoelectrode ensembles

The performance of an amperometric biosensor constructed by associating tyrosinase (Tyr) enzyme with the advantages of a 3D gold nanoelectrode ensemble (GNEE) is evaluated in a flow-injection analysis (FIA) system for the analysis of l-dopa. GNEEs were fabricated by electroless deposition of the metal within the pores of polycarbonate track-etched membranes. A simple solvent etching procedure based on the solubility of polycarbonate membranes is adopted for the fabrication of the 3D GNEE. Afterward, enzyme was immobilized onto preformed self-assembled monolayers of cysteamine on the 3D GNEEs (GNEE-Tyr) via cross-linking with glutaraldehyde. The experimental conditions of the FIA system, such as the detection potential (−0.200 V vs. Ag/AgCl) and flow rates (1.0 mL min−1) were optimized. Analytical responses for l-dopa were obtained in a wide concentration range between 1 × 10−8 mol L−1 and 1 × 10−2 mol L−1. The limit of quantification was found to be 1 × 10−8 mol L−1 with a resultant % RSD of 7.23% (n = 5). The limit of detection was found to be 1 × 10−9 mol L−1 (S/N = 3). The common interfering compounds, namely glucose (10 mmol L−1), ascorbic acid (10 mmol L−1), and urea (10 mmol L−1), were studied. The recovery of l-dopa (1 × 10−7 mol L−1) from spiked urine samples was found to be 96%. Therefore, the developed method is adequate to be applied in the clinical analysis.

Caratterizzazione di membrane metalliche e ionomeriche per applicazioni energetiche

The work of this thesis has been focused on the characterization of metallic membranes for the hydrogen purification from steam reforming process and also of perfluorosulphonic acid ionomeric (PFSI) membranes suitable as electrolytes in fuel cell applications. The experimental study of metallic membranes was divided in three sections: synthesis of palladium and silver palladium coatings on porous ceramic support via electroless deposition (ELD), solubility and diffusivity analysis of hydrogen in palladium based alloys (temperature range between 200 and 400 °C up to 12 bar of pressure) and permeation experiments of pure hydrogen and mixtures containing, besides hydrogen, also nitrogen and methane at high temperatures (up to 600 °C) and pressures (up to 10 bar). Sequential deposition of palladium and silver on to porous alumina tubes by ELD technique was carried out using two different procedures: a stirred batch and a continuous flux method. Pure palladium as well as Pd-Ag membranes were produced: the Pd-Ag membranes’ composition is calculated to be close to 77% Pd and 23% Ag by weight which was the target value that correspond to the best performance of the palladium-based alloys. One of the membranes produced showed an infinite selectivity through hydrogen and relatively high permeability value and is suitable for the potential use as a hydrogen separator. The hydrogen sorption in silver palladium alloys was carried out in a gravimetric system on films produced by ELD technique. In the temperature range inspected, up to 400°C, there is still a lack in literature. The experimental data were analyzed with rigorous equations allowing to calculate the enthalpy and entropy values of the Sieverts’ constant; the results were in very good agreement with the extrapolation made with literature data obtained a lower temperature (up to 150 °C). The information obtained in this study would be directly usable in the modeling of hydrogen permeation in Pd-based systems. Pure and mixed gas permeation tests were performed on Pd-based hydrogen selective membranes at operative conditions close to steam-reforming ones. Two membranes (one produced in this work and another produced by NGK Insulators Japan) showed a virtually infinite selectivity and good permeability. Mixture data revealed the existence of non negligible resistances to hydrogen transport in the gas phase. Even if the decrease of the driving force due to polarization concentration phenomena occurs, in principle, in all membrane-based separation systems endowed with high perm-selectivity, an extensive experimental analysis lack, at the moment, in the palladium-based membrane process in literature. Moreover a new procedure has been introduced for the proper comparison of the mass transport resistance in the gas phase and in the membrane. Another object of study was the water vapor sorption and permeation in PFSI membranes with short and long side chains was also studied; moreover the permeation of gases (i.e. He, N2 and O2) in dry and humid conditions was considered. The water vapor sorption showed strong interactions between the hydrophilic groups and the water as revealed from the hysteresis in the sorption-desorption isotherms and thermo gravimetric analysis. The data obtained were used in the modeling of water vapor permeation, that was described as diffusion-reaction of water molecules, and in the humid gases permeation experiments. In the dry gas experiments the permeability and diffusivity was found to increase with temperature and with the equivalent weight (EW) of the membrane. A linear correlation was drawn between the dry gas permeability and the opposite of the equivalent weight of PFSI membranes, based on which the permeability of pure PTFE is retrieved in the limit of high EW. In the other hand O2 ,N2 and He permeability values was found to increase significantly, and in a similar fashion, with water activity. A model that considers the PFSI membrane as a composite matrix with a hydrophilic and a hydrophobic phase was considered allowing to estimate the variation of gas permeability with relative humidity on the basis of the permeability in the dry PFSI membrane and in pure liquid water.

Grenzflächenverhalten und Strukturierung von dünnen, amphiphilen Blockcopolymerfilmen

Die Oberfläche von Blockcopolymerfilmen wird aus denjenigen Blöcken gebildet, die gegenüber dem benachbarten Medium die geringste Oberflächenenergie besitzen. Durch eine gezielte Änderung des Mediums kann man Einfluss auf die chemische Zusammensetzung nehmen und einen Wechsel der Oberflächenlamelle erzwingen. Das Ziel dieser Arbeit war es, das Grenzflächenverhalten von dünnen, amphiphilen Blockcopolymerfilmen näher zu untersuchen, die Filmoberflächen in einem lösungsmittelfreien Prozess lateral zu strukturieren und anschließend chemisch zu modifizieren. Zu diesem Zweck wurden zunächst neuartige hydrophile und hydrophobe Styrenderivate mit kurzen Seitenketten dargestellt, die anschließend durch kontrollierte radikalische Polymerisation („stable free radical polymerisation“ SFRP) mit dem TEMPO Unimer zu amphiphilen Diblockcopolymeren polymerisiert wurden. Funktionelle Gruppen in den hydrophilen Blöcken sollen zusätzlich eine chemische Modifizierung der Oberflächen dünner Blockcopolymerfilme ermöglichen. Der Nachweis der Reorientierung der Oberflächenlamelle unter dem Einfluss angrenzender polarer und unpolarer Medien gelang im Folgenden sowohl indirekt durch Kontaktwinkelmessungen, als auch direkt durch „Near edge X-ray Absorption Fine Structure“ Spektroskopie (NEXAFS). Durch Letztere konnten auch kinetische Informationen über den Prozess der Reorientierung gewonnen werden. In AFM Studien konnten weiterhin Zwischenstufen des von Senchu et al. postulierten Mechanismus nachgewiesen werden, der die Reorientierung als eine Art Reißverschlussmechanismus beschreibt, bei dem sich die energetisch günstigere Lamelle über die ungünstigere Oberflächenlamelle stülpt. Die laterale Strukturierung der Oberflächen dünner Blockcopolymerfilme erfolgte abweichend von der bekannten Technik, die auf der Verwendung von hydrophoben PDMS Stempeln und einem polaren Lösungsmittel zurückgreift, durch einen lösungsmittelfreien Prozess mit hydrophilen PDMS Stempeln. Auf die hydrophilen Bereiche der so strukturierten Blockcopolymeroberflächen konnte dann mittels einer Templatstrategie selektiv elementares Kupfer abgeschieden werden. Durch die Erzeugung leitfähiger Strukturen auf Blockcopolymerfilmen konnte exemplarisch die Eignung dieser zum Aufbau von Sensorstrukturen gezeigt werden.