Abstract: The electrochemical and diffusion behaviour of different redox probes in different ionic liquids is studied at gold nanoelectrode ensembles (NEEs) in comparison with millimetre sized gold (Au-macro) and glassy carbon (GC) disk electrodes. The redox probes are neutral ferrocene (Fc), the ferrocenylmethyltrimetylammonium cation (FA+) and the ferrocenylmonocarboxylate anion (FcCOO−). The ILs are the dicyanamide, [N(CN)2] or bis(trifluoromethylsulfonyl)amide), [N(Tf)2] salts of the following cations: 1-butyl-3-methylimidazolium, [BMIm], 1-butyl-3-methylpyrrolidonium, [BMPy], or tris(n-hexyl)tetradecylphosphonium [P14,666]. These ILs are characterized by different viscosities, ranging from 32 to 277 cP. The cyclic voltammetric behaviour of the redox probes is reversible and diffusion controlled at GC electrodes. Diffusion coefficients (D) calculated by the Randles–Sevcik equation scales inversely with the IL viscosity, ranging from 2 × 10−8 to 3 × 10−7 cm2 s−1. Ionic solutes, namely FA+ and FcCOO−, present slightly lower D values than neutral Fc. At the Au-macro the electrochemical behaviour of the redox probes is diffusion controlled in the ILs containing the [N(Tf)2] anion, while it involves relevant adsorption processes in the [N(CN)2] containing electrolyte. For this reason the diffusion at gold NEEs is studied only in the former ILs. The CVs of the redox probes at the NEEs are peak shaped at low scan rate ( v ), while they are sigmoidally shaped at high v , but with some shift between forward and backward patterns. This is indicative of the occurrence of a total overlap (TO) diffusion condition when v is low which becomes a mixed diffusion layers (MDL) regime, with only a partial overlapping of individual diffusion layers, at high v values. In the most viscous IL, namely [P14,666] [N(Tf)2], at v higher than 0.8 V s−1, a plateau current independent on the scan rate is achieved, indicating the tendency to reach the pure radial regime in this IL. The v values at which the transition between TO and MDL is observed scales directly with D and inversely with the IL viscosity. This behaviour is interpreted on the basis of the dependence of individual diffusion layers at each nanoelectrode on redox probe/IL interaction which fits with existing theoretical models very recently developed for nanoelectrode arrays.
TL;DR: The design of a novel immunosensor and its application for celiac disease diagnosis, based on an electrogenerated chemiluminescence (ECL) readout, using membrane-templated gold nanoelectrode ensembles (NEEs) as a detection platform, showing to be suitable to discriminate between healthy and celiac patients.
Abstract: We report here the design of a novel immunosensor and its application for celiac disease diagnosis, based on an electrogenerated chemiluminescence (ECL) readout, using membrane-templated gold nanoelectrode ensembles (NEEs) as a detection platform. An original sensing strategy is presented by segregating spatially the initial electrochemical reaction and the location of the immobilized biomolecules where ECL is finally emitted. The recognition scaffold is the following: tissue transglutaminase (tTG) is immobilized as a capturing agent on the polycarbonate (PC) surface of the track-etched templating membrane. It captures the target tissue transglutaminase antibody (anti-tTG), and finally allows the immobilization of a streptavidin-modified ruthenium-based ECL label via reaction with a suitable biotinylated secondary antibody. The application of an oxidizing potential in a tri-n-propylamine (TPrA) solution generates an intense and sharp ECL signal, suitable for analytical purposes. Voltammetric and ECL analy...
TL;DR: This review deals with recent advances in bioelectroanalytical applications of nanostructured electrodes, in particular nanoelectrode ensembles (NEEs) and arrays (NEAs), and nanofabrication techniques, principles of function, and specific advantages and limits of NEEs and NEAs.
Abstract: This review deals with recent advances in bioelectroanalytical applications of nanostructured electrodes, in particular nanoelectrode ensembles (NEEs) and arrays (NEAs). First, nanofabrication techniques, principles of function, and specific advantages and limits of NEEs and NEAs are critically discussed. In the second part, some recent examples of bioelectroanalytical applications are presented. These include use of nanoelectrode arrays and/or ensembles for direct electrochemical analysis of pharmacologically active organic compounds or redox proteins, and the development of functionalized nanoelectrode systems and their use as catalytic or affinity electrochemical biosensors.
Cites background from "Diffusion regimes at nanoelectrode ..."
...) Bioelectroanalysis with nanoelectrode arrays 3721...
...It has recently been shown that, for NEE, transition from the total overlap to the pure radial diffusion can be observed on increasing electrolyte viscosity ....
TL;DR: Electrochemical results showed satisfactory agreement between experimental voltammograms and suitable theoretical models, and the peculiarities of NEAs versus ensembles of nanoelectrodes, obtained by membrane template synthesis, are critically evaluated.
Abstract: Ordered arrays of nanoelectrodes for electrochemical use are prepared by electron beam lithography (EBL) using polycarbonate as a novel e-beam resist. The nanoelectrodes are fabricated by patterning arrays of holes in a thin film of polycarbonate spin-coated on a gold layer on Si/Si3N4 substrate. Experimental parameters for the successful use of polycarbonate as high resolution EBL resist are optimized. The holes can be filled partially or completely by electrochemical deposition of gold. This enables the preparation of arrays of nanoelectrodes with different recession degree and geometrical characteristics. The polycarbonate is kept on-site and used as the insulator that separates the nanoelectrodes. The obtained nanoelectrode arrays (NEAs) exhibit steady state current controlled by pure radial diffusion in cyclic voltammetry for scan rates up to approximately 50 mV s − 1. Electrochemical results showed satisfactory agreement between experimental voltammograms and suitable theoretical models. Finally, the peculiarities of NEAs versus ensembles of nanoelectrodes, obtained by membrane template synthesis, are critically evaluated.
Abstract: Herein, combined the synergetic effects and excellent adsorption of binary oxides, a novel sensor interface was designed by using porous Ce-Zr oxide nanospheres modified glassy carbon electrode (Ce-Zr oxide/GCE), which has successfully realized high sensitivity and anti-interference detection of Pb(II). The electrochemical determination of Pb(II) has been investigated by square wave anodic stripping voltammetry (SWASV) range from 0.02 to 0.5 μM, and a high sensitivity per unit area of 1666.02 μA μM−1 cm−2 was obtained with a limit of detection of 0.006 μM (3σ method). The enhancement of Pb(II) stripping signal is attributed to the excellent adsorption performance of porous Ce-Zr oxide nanospheres, which has been confirmed with X-ray photoelectron spectroscopy (XPS). Importantly, Ce-Zr oxide/GCE possesses highly anti-interference ability against the influence of Hg(II), Cd(II), Cu(II), and Zn(II) in the determination of Pb(II). Meanwhile, the remarkable stability and reproducibility were obtained. Finally, the accurate analysis of Pb(II) in wastewater collected from Wangtang sewage disposal plant was achieved. These results indicate that porous Ce-Zr oxide nanospheres are identified as promising modifier for the reliable and accurate determination of Pb(II).
Abstract: Determination of arsenite [As(III)] without interference in mild condition is crucial for portably assessing arsenic contamination using electrochemical method. We have developed high-surface area nanoporous gold (np-Au) with a three dimensional, interconnected ligaments and nanoporous structure for the electrochemical detection of As(III) in 0.1 M HAc-NaAc solution (pH 5.0) without using strong acidic electrolyte. Square wave anodic stripping voltammetry (SWASV) using the np-Au modified glassy carbon electrode (GCE) confirms the successful detection of As(III) with almost no interference from some commonly coexisting ions. Furthermore, the sensitivity of the np-Au modified GCE exhibited approximately 10-fold enhancement as compared to Au nanoparticles (Au NPs) modified GCE. Finally, the proposed method is successfully applicable for analysis of As(III) in real water samples with satisfactory recoveries. The np-Au modified GCE shows enhanced anti-interference and excellent sensing performance may be attribute to its special surface structure and the fast transports of analytes and electron in the interface of electrode.
TL;DR: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophilic anions and thus water-soluble.
Abstract: New, hydrophobic ionic liquids with low melting points (<−30 °C to ambient temperature) have been synthesized and investigated, based on 1,3-dialkyl imidazolium cations and hydrophobic anions. Other imidazolium molten salts with hydrophilic anions and thus water-soluble are also described. The molten salts were characterized by NMR and elemental analysis. Their density, melting point, viscosity, conductivity, refractive index, electrochemical window, thermal stability, and miscibility with water and organic solvents were determined. The influence of the alkyl substituents in 1, 2, 3, and 4(5)-positions on these properties was scrutinized. Viscosities as low as 35 cP (for 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide (bis(triflyl)amide) and trifluoroacetate) and conductivities as high as 9.6 mS/cm were obtained. Photophysical probe studies were carried out to establish more precisely the solvent properties of 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)amide). The hydrophobi...
Abstract: Salts having a low melting point are liquid at room temperature, or even below, and form a new class of liquids usually called room temperature ionic liquids (RTIL). Information about RTILs can be found in the literature with such key words as: room temperature molten salt, low-temperature molten salt, ambient-temperature molten salt, liquid organic salt or simply ionic liquid. Their physicochemical properties are the same as high temperature ionic liquids, but the practical aspects of their maintenance or handling are different enough to merit a distinction. The class of ionic liquids, based on tetraalkylammonium cation and chloroaluminate anion, has been extensively studied since late 1970s of the XX century, following the works of Osteryoung. Systematic research on the application of chloroaluminate ionic liquids as solvents was performed in 1980s. However, ionic liquids based on aluminium halides are moisture sensitive. During the last decade an increasing number of new ionic liquids have been prepared and used as solvents. The general aim of this paper was to review the physical and chemical properties of RTILs from the point of view of their possible application as electrolytes in electrochemical processes and devices. The following points are discussed: melting and freezing, conductivity, viscosity, temperature dependence of conductivity, transport and transference numbers, electrochemical stability, possible application in aluminium electroplating, lithium batteries and in electrochemical capacitors.
Abstract: A review. Physicochem. properties of ionic liqs. are discussed. Chem. and electrochem. reactivity in ionic liqs. is described including electrode reactions, electrode reaction kinetics, electrosynthesis, etc.
Abstract: Non-linear diffusion effects induced by partial blocking of an electrode surface toward electron transfer are analyzed in the case where the blocking film is sprinkled with a large number of microscopic, active sites. Under such conditions, the average size of the active sites and the average distance between them are small compared to the total diffusion layer. As a result, non-linear diffusion is confined to a layer adjacent to the electrode surface which is thin compared to the total diffusion layer. It follows that, in the framework of relaxation electrochemical techniques, non-linear diffusion can be regarded as occurring under stationary conditions while linear diffusion is time-dependent. The resolution of the diffusion problem is thus greatly simplified, leading to the description of the polarization as a function of only two dimensionless parameters which are simply related to the experimental parameters: fractional coverage, distance between active sites, standard rate constant of electron transfer and time-range. The formulations thus obtained give evidence for a formal similarity with the polarization problem corresponding to the coupling of electron transfer with preceding and following chemical reactions. According to the values of these parameters, two main types of behavior are obtained: in one of them, the polarization curves show a quasi-reversible behavior, while in the other, kinetic-type waves are obtained. The effect of the various parameters on the characteristics of these waves and on the passage from one type of behavior to the other is described. Procedures for deriving estimates of the size of the active sites and the distance between them from the polarization curves are proposed.
Abstract: : An electroless deposition procedure for filling the pores in nanoporous filtration membranes with metal (gold) nanowires is described. This method allows us to routinely prepare ensembles of gold nanodisk electrodes in which the nanodisks have diameters as small as 10 nm. Results of electrochemical experiments at ensembles of 30 nm-diameter and 10 nm-diameter gold-disk electrodes are described. The electrochemical response characteristics of these nanoelectrode ensembles are in agreement with predictions of the relevant electrochemical theories. Cyclic voltammetric detection limits for electroactive species at ensembles containing 10 nm-diameter gold disks can be as much as 3 orders of magnitude lower than at a large-diameter gold-disk electrode.