Gold–carbon three dimensional film electrode prepared from oppositely charged conductive nanoparticles by layer-by-layer approach

Gold–carbon three dimensional film electrode was prepared from oppositely charged conductive particles by layer-by-layer approach. This was done by alternative immersion of indium tin oxide plate into suspension of positive (gold) and negative (carbon) particles. The film formation is confirmed by scanning electron microscopy. The nanoparticulate film is stable and the obtained electrode exhibits catalytic current of dioxygen reduction connected with the presence of gold nanoparticles. After adsorption of bilirubin oxidase similar effect is observed with substantial decrease of overpotential – typical for bioelectrocatalytic reaction. Both catalytic currents are proportional to the number of immersion and withdrawal steps.     

Gold three dimensional film electrode prepared from oppositely charged nanoparticles

Nanoparticulate gold film electrodes were prepared from oppositely charged gold nanoparticles (c.a. 6 nm diameter) by a layer-by-layer approach without application of linker molecules. This was done by alternative immersion of indium tin oxide plates into suspensions of positively and negatively charged particles. The thickness of the film and the magnitude of the characteristic surface plasmon band are proportional to the number of immersion and withdrawal steps. Up to nine double immersions and withdrawal steps can be used to systematically increase the amount of nanoparticulate gold material. The capacitive current density and current density of hydrogen peroxide reduction are proportional to the number of immersion and withdrawal steps. Highly efficient and low overpotential glucose electrooxidation in alkaline solution is demonstrated.     

Three dimensional film electrode prepared from oppositely charged carbon nanoparticles as efficient enzyme host

Three dimensional carbon film electrodes were prepared from oppositely charged carbon nanoparticles (ca. 9 to 18 nm diameter) by a layer-by-layer approach. This was done by alternative immersion of indium tin oxide plates into suspension of positively and negatively charged particles. A stable film is formed already after single immersion and withdrawal step as confirmed by scanning electron microscopy. Up to ten immersion and withdrawal steps can be used to systematically increase the amount of nanoparticulate carbon material. The capacitive current density and current density of hydrogen peroxide reduction are proportional to the number of immersion and withdrawal steps. The same can be seen for adsorbed redox active 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate). After adsorption of bilirubin oxidase into the film efficient bioelectrocatalytic dioxygen reduction is observed.     

Electrostatic attachment of gold and poly(lactic acid) nanoparticles onto omega-aminoalkanoic acid self-assembled monolayers on 316L stainless steel

The assembly of poly(lactic acid) (PLA) nanoparticles on a 12-aminodecanoic acid (ADA) self-assembled monolayer (SAM) is described. Assembly is accomplished through electrostatic interactions between the positively charged SAM and the negatively charged PLA nanoparticles. The strategy used involves two steps in which a preliminary electrochemical coating of the ADA SAM is followed by a second step that involves immersing the SAM in a solution containing gold or PLA nanoparticles. The SAM was characterized by using cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy, and contact angle measurements, whereas scanning electron microscopy (SEM) was used to image the nanoparticles after electrostatic attachment was achieved. We found that the surface coverage of the nanoparticles could be controlled by modulating the electrostatic interactions between the negatively charged particles and the positively charged SAM surface by varying the pH of the nanoparticle solution, the immersion time, and the number of cyclic voltammetry scans under which the SAM was formed.     

Assembly of Gold Nanoparticles on a Molecular Ultrathin Film: Tuning the Surface Plasmon Resonance

A number of methodologies for immobilizing metal nanoparticles in 2‐dimensional aggregate structures on various substrates, some with concomitant tuning of the surface plasmon resonance (SPR), have been reported. Many of them involve special functionalization of the nanoparticles, multiple fabrication steps or lengthy procedures. The present study demonstrates that monolayer Langmuir–Blodgett (LB) film of a hemicyanine‐based amphiphile with cationic headgroup is an easily fabricated platform for harnessing citrate‐stabilized gold nanoparticles. It is shown that a single immersion step can be used to immobilize the nanoparticles uniformly on large area films and that systematic variation of the immersion time from 10 min to 6 h leads to controlled assembly of the particles and tuning of the SPR band over ～100 nm. A model for the structural reorganization in the LB film that facilitates the assembly of nanoparticles is presented and the advantages of the current methodology over earlier protocols are pointed out. The versatility of LB films in terms of the molecular level control of fabrication it enables and the variety of film structures that can be realized, point to the wide scope for future explorations, expanding upon the present observations.     

Properties of glucose sensors prepared by the electropolymerization of a positively charged pyrrole derivative

Amperometric glucose sensors were prepared by electropolymerization of a pyrrole derivative having the positively charged group, 3-(1-pyrrolyl)propyltrimethylammonium bromide, in the presence of glucose oxidase on bare and Nafion-coated platinum electrodes. Linear relationships between the glucose concentration and the response current for the electrode with and without Nafion inner film were up to 10.0 and 6.0 mmol dm⁻³, respectively. The introduction of Nafion inner film lowered the influence of electroactive compounds, such as ascorbic acid, uric acid, and acetoaminophen, on the sensor response, but was not able to eliminate the influence of these compounds sufficiently. However, Nafion inner film was effective in increasing the electrode stability. The response current of the electrode with Nafion film remained stable for more than 50 days, while that without Nafion film was significantly reduced after 20 days of use.     

Pt/十六烷基三甲基溴化铵纳米聚集体修饰玻碳电极促进析氢(英文)

A novel, cost‐effective, and simple electrocatalyst based on a Pt‐modified glassy carbon electrode (GCE), using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, is reported. Am‐phiphilic CTAB molecules were adsorbed on GCE by immersion in a CTAB solution. The positively charged hydrophilic layer, which consisted of small aggregates of average size less than 100 nm, was used for accumulation and complexation of [PtCl6]2? anions by immersing the electrode in K2PtCl6 solution. The modified electrode was characterized using scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, impedance spectroscopy, and electrochemical methods. The electrocatalytic activity of the Pt particles in the hydrogen evolution reaction (HER) was investigat‐ed. The results show that the CTAB surfactant enhances the electrocatalytic activity of the Pt parti‐cles in the HER in acidic solution.     

Evaluation of particle deposition in aqueous solutions by the quartz crystal microbalance method

Concerning the redeposition of particulate soils in the detergent process, particle deposition onto substrates in aqueous solutions was investigated by the application of the quartz crystal microbalance (QCM) technique, and the effects of the kinds of the particle and substrate and the addition of ethanol were discussed by the extended DLVO theory. The film of polyethylene, Nylon 6 or cellulose acetate as a substrate was prepared on the gold electrode of the QCM by a spin-coating method. The electrode with or without the polymer film was perpendicularly immersed in the aqueous dispersion of spherical polyethylene or nylon particles. The total mass of particles deposited onto the electrode was determined, in situ, from frequency change of the QCM. The deposited mass was also determined from the difference in frequency measured in air before and after the immersion in the dispersion. In both cases, the particle deposition increased with immersion time and attained apparent equilibrium after 30–60 min. Apparent equilibrium deposition was large for the polyethylene particle compared with the Nylon 12 particle. For either particle, a considerable difference in the deposited amount was observed among the substrates. In all systems, the particle deposition drastically decreased by addition of ethanol to the aqueous dispersion. The results were discussed in terms of the electrical double layer, the Lifshitz–van der Waals and acid–base interactions between the particle and the substrate, which were calculated using the experimentally determined surface free energy components and electrokinetic potentials.     

Polypeptide multilayer films on colloidal particles: an in situ electro-optical study

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on beta-FeOOH colloidal particles was investigated by means of electro-optics and electrophoresis. The films were built at different (acidic) pH in the absence of salt. We found that the thickness of the film grows linearly when the fully charged PLL (at pH 5.5) is combined with almost fully charged PGA (at pH 6.5), with a thickness of about 2 nm per single layer. When the fully charged PLL is combined with weakly charged PGA (at pH 4.5), the film thickness increases exponentially with the number of deposited layers. The thickness of the exponentially growing film increases to 300 nm after deposition of 16 layers. The exponential film growth is attributed to the ability of the PLL to diffuse "in" and "out" of the film bulk at each deposition step. The variation in the electrical polarizability of the film-coated particles was also monitored as a function of the number of adsorbed layers. The result reveals that the PLL chains, which can diffuse into the film bulk, have no measurable contribution to the electro-optical effect of the films terminated with PLL. It is only due to the polarization of counterions of the PLL adsorbed on the film surface.     

Platinum electrode modified with polyterthiophene doped with metallic nanoparticles,as sensitive sensor for the electroanalysis of ascorbic acid (AA)

A novel electrochemical sensor for ascorbic acid (AA) detection based on platinum electrode modified with polyterthiophene (P3T) and doped with metallic particles (Cu, Co, Ag, Au, Pd) was constructed. The electrocatalytic performances of the modified electrode with polyterthiophene-metallic particles related to the detection of AA, showed a better catalytic activity compared to the modified electrode with polyterthiophene film. The obtained results demonstrate also that the use of P3T–Ag nanocomposite allows a good sensitivity; which gives a high response in oxidation peak of AA. In order to have a good performance using this sensor, several parameters such as polymerization time of the film and immersion time of the film in AgNO₃ solution were optimized.     

Reactivity of nanocolloidal particles gamma-Fe2O3 at charged interfaces. Part 2. Electrochemical conversion. Role of the electrode material

In this paper we are interested in the reactivity of magnetic nanoparticles at the electrode involved in the electrochemical synthesis of magnetic and conductive liquids. The reactivity of charged colloidal particles occurs in two steps, first the approach toward the electrode with a possible adsorption phenomenon and secondly the electron transfer. In this paper we focus on the electrochemical behaviour of well-defined gamma-Fe(2)O(3) nanoparticles at a gold and at a mercury electrode. Particles can be electrochemically reduced at the two electrodes and can be dispersed into mercury at a highly negative potential. Here, we probe in particular the properties of nanoreactor of the particles, that is to say, the possible conservation of their size after they have undergone the electrochemical process. By correlating complementary techniques (here atomic force microscopy (AFM) observations, Raman spectroscopy and cyclic voltammetry on gold electrode) and by studying the magnetic properties of the material obtained after reduction of the particles on a mercury electrode, we are able to probe both the chemical nature and the physical state of the particles once transformed. Experimental results show that under specific conditions, the particles are individually converted into iron, which justifies their use for preparing a liquid with both magnetic properties and properties of electron conduction.     

Electrocatalytic hydrogenation of 4-chlorophenol on the glassy carbon electrode modified by composite polypyrrole/palladium film

A polypyrrole/palladium composite film was prepared on a glassy carbon electrode by the electrochemical deposition method. The palladium particles were uniformly dispersed on a polypyrrole film that was previously electrodeposited on a glassy carbon electrode. By controlling the polymerization process of pyrrole, a highly porous polypyrrole film was obtained; this kind of structure provided more surface areas for depositing palladium particles. The sizes of Pd particles deposited on the porous polypyrrole film are about 15-30 nm. The X-ray photoelectron spectroscopy results showed there was strong interaction between polypyrrole film and palladium particles. This modified electrode showed excellent current efficiency (49.5%) for electrochemical hydrogenation of 4-chlorophenol and the phenol was the sole product. The potential effect on the dechlorination process was also investigated.     

Transport of alkaline cation and neutral species through the α-Ni(OH)2/γ-NiOOH film electrode

The transport of alkaline cation and neutral species through the α-Ni(OH)₂/γ-NiOOH film electrode has been investigated during the hydrogen extraction from and injection into the film electrode in 0.1 M LiOH, KOH and CsOH solutions by using the electrochemical quartz crystal microbalance technique combined with the potentiostatic current transient technique and cyclic voltammetry. From the ohmic relationship between the initial current density and the applied potential step, it is suggested that the hydrogen transport through the film electrode is exclusively governed by "cell-impedance". On the basis of the "cell-impedance-controlled" hydrogen transport, the mass change measured indicates that during the hydrogen extraction, the alkaline cation is slowly inserted into the film electrode before the finish of the current plateau. After the period of current plateau has finished, it is drastically inserted at an exponential rate. By contrast, during the hydrogen injection, the extraction of alkaline cation is nearly completed before the finish of the current plateau. Most of the neutral species are incorporated into the film electrode during the immersion prior to the hydrogen extraction. The minority is not incorporated until the finish of the current plateau during the hydrogen injection. Electronic Publication     

Formation of polyelectrolyte multilayers from polysaccharides at low ionic strength

Layer-by-layer deposition of sodium carboxymethylcellulose (NaCMC) and chitosan (CHI) was used to create polyelectrolyte multilayers on ellipsoidal beta-FeOOH particles at low ionic strength. Using electro-optics, we investigated the formation of films in dependence on the polyelectrolyte charge density by controlling pH of the dipping solutions. We found out a linear growth of the CMC/CHI films when they are constructed from highly charged CHI (at pH 4.0) and weakly charged NaCMC (at pH 4.0 and 5.5). The hydrodynamic thickness of the film constructed at pH 4.0/4.0 is unusually large for a linearly growing film (ca. 220 nm after deposition of 8 bilayers), but it strongly decreases (ca. 4 times) with increasing ionization of NaCMC (at pH 5.5). In both cases, the multilayer buildup proceeded through a series of adsorption-desorption steps. This was explained by a partial loss of CHI from the film surface on exposure to the solution of longer NaCMC molecules. The irregular film growth correlated quite well with the variations in the electrical polarizability of the polymer-coated particles. This correlation enabled us to conclude that the adsorption of both polymers occurs only on the film surface, with no diffusion in and out of the film bulk during deposition of each CMC/CHI bilayer.     

A PDDA/poly(2,6-pyridinedicarboxylic acid)-CNTs composite film DNA electrochemical sensor and its application for the detection of specific sequences related to PAT gene and NOS gene

2,6-Pyridinedicarboxylic acid (PDC) was electropolymerized on the glassy carbon electrode (GCE) surface combined with carboxylic group-functionalized single-walled carbon nanotubes (SWNTs) by cyclic voltammetry (CV) to form PDC-SWNTs composite film, which was rich in negatively charged carboxylic group. Then, poly(diallyldimethyl ammonium chloride) (PDDA), a linear cationic polyelectrolyte, was electrostatically adsorbed on the PDC-SWNTs/GCE surface. DNA probes with negatively charged phosphate group at the 5' end were immobilized on the PDDA/PDC-SWNTs/GCE due to the strong electrostatic attraction between PDDA and phosphate group of DNA. It has been found that modification of the electrode with PDC-SWNTs film has enhanced the effective electrode surface area and electron-transfer ability, in addition to providing negatively charged groups for the electrostatic assembly of cationic polyelectrolyte. PDDA plays a key role in the attachment of DNA probes to the PDC-SWNTs composite film and acts as a bridge to connect DNA with PDC-SWNTs film. The cathodic peak current of methylene blue (MB), an electroactive label, decreased obviously after the hybridization of DNA probe (ssDNA) with the complementary DNA (cDNA). This peak current change was used to monitor the recognition of the specific sequences related to PAT gene in the transgenic corn and the polymerase chain reaction (PCR) amplification of NOS gene from the sample of transgenic soybean with satisfactory results. Under optimal conditions, the dynamic detection range of the sensor to PAT gene target sequence was from 1.0x10(-11) to 1.0x10(-6) mol/L with the detection limit of 2.6x10(-12) mol/L.     

Discrete electrostatic charge transfer by the electrophoresis of a charged droplet in a dielectric liquid

We have experimentally investigated the electrostatic charging of a water droplet on an electrified electrode surface to explain the detailed inductive charging processes and use them for the detection of droplet position in a lab-on-a-chip system. The periodic bouncing motion of a droplet between two planar electrodes has been examined by using a high-resolution electrometer and an image analysis method. We have found that this charging process consists of three steps. The first step is inductive charge accumulation on the opposite electrode by the charge of a droplet. This induction process occurs while the droplet approaches the electrode, and it produces an induction current signal at the electrometer. The second step is the discharging of the droplet by the accumulated induced charge at the moment of contact. For this second step, there is no charge-transfer detection at the electrometer. The third step is the charging of the neutralized droplet to a certain charged state while the droplet is in contact with the electrode. The charge transfer of the third step is detected as the pulse-type signal of an electrometer. The second and third steps occur simultaneously and rapidly. We have found that the induction current by the movement of a charged droplet can be accurately used to measure the charge of the droplet and can also be used to monitor the position of a droplet under actuation. The implications of the current findings for understanding and measuring the charging process are discussed.     

Enhancement of response by incorporation of platinum microparticles into a polypyrrole-glucose oxidase electrode

Platinum was incorporated into a polypyrrole/glucose oxidase electrode by immersion in a hexachloroplatinate(IV) solution after electrochemical oxidation of the polypyrrole film; dispersed platinum was then formed by electrochemical reduction. The platinized electrode reproducibly yielded a response to glucose (20 mM) which was typically about 40% higher than that obtained in the absence of platinum microparticles in the polypyrrole/glucose oxidase film.     

Particles at the airway interfaces of the lung

Inhaled particles may land on the surface of the lung’s airspaces. Upon making contact with the airway wall, the processes of retention and clearance begin. Particle retention depends on many factors; among these are: (1) particle size, shape, solubility, surface chemistry and elastic properties of both the particles and the lung surface. (2) The anatomical location of the deposition site. (3) The structures with which the particle interacts at the site of deposition, including the surfactant film at the air–liquid interface, the aqueous phase, free cells like macrophages, lymphocytes and granulocytes, the epithelial cells and dendritic cells that reside at the basal side of the epithelium. Particles, after their deposition are wetted and displaced towards the epithelium by the surfactant film during the retention process. In vitro experiments have demonstrated that the extent of particle immersion depends on the surface tension of the surfactant film. The lower the surface tension, the greater is the immersion of the particles into the aqueous phase. Experimental results demonstrate consistently greater immersion of smaller particles into a liquid substrate covered with a surfactant film than that for larger particles. The exact mechanism, especially the initial wetting process, is not yet understood and requires further experiments. Line tension is a possible explanation for the dependence of particle displacement on particle size.     

Assembly of Electroactive Ordered Multilayer Films of Cobalt Phthalocyanine Tetrasulfonate and Polycations

Films with alternating layers of the anion cobalt phthalocyanine tetrasulfonate (CoIIPcTS4-) and cationic polydimethyldiallylammonium chloride (PDDA) were prepared by electrostatic layer-by-layer adsorption. Quartz crystal microbalance and optical studies demonstrated formation of smooth ultrathin films with a linear increase in thickness with the number of deposition steps. Films containing 1, 2, 3, 4, and 5 bilayers of CoIIPcTS4-/PDDA on a gold electrode gave reversible, reproducible steady state cyclic voltammetry for the CoII/CoI redox couple with midpoint potential at -0.28 V vs a saturated calomel reference electrode. Voltammetry was controlled predominantly by charge transport processes in the film, even for films containing only a bilayer of PDDA/CoIIPcTS4-. The peak reduction current increased with the number of layers and showed a tendency to saturation after a deposition of 4-5 bilayers. Copyright 1999 Academic Press.     

Electrocatalytic oxidation and flow-injection determination of ascorbic acid at a graphite electrode modified with a polyaniline film containing electrodeposited palladium

A method for forming a composite film on the surface of a graphite electrode is proposed. Conditions for detecting the maximum catalytic current under batch and flow conditions are determined. A procedure for the electrocatalytic determination of ascorbic acid at the graphite electrode modified with a polyaniline film containing palladium particles is proposed. The catalytic effect of this electrode manifests itself by a ～300-mV decrease in the peak potential of ascorbic acid oxidation and by a multiple increase in the peak current of ascorbic acid oxidation as compared to the unmodified electrode. The linear dependence of the electrocatalytic response of the composite electrode on the concentration of ascorbic acid is observed down to 1 × 10^?8 M and 2.5 nmol of ascorbic acid under batch and flow-injection analysis conditions, respectively.