Electroanalytical Applications Research Articles

Electrochemical applications of a Au nanoparticle array fabricated using highly ordered dimpled Ta templates

A large-area and high-density Au nanoparticle array (NPA) has been fabricated using highly ordered dimpled Ta (DT) templates. The array, with one Au nanoparticle (NP) per dimple, was formed by exploiting the instability of very thin (<5nm) films of Au at elevated temperatures, inducing the self-assembly of the Au NPs into an ordered structure mirroring that of the DT template. It is shown that the Au NPs can be electrochemically addressed, without interference from the underlying Ta oxide film, and that they are very stable, even in acidic media. In terms of their electroanalytical applications, cyclic voltammetry of the DT-supported Au NPA in neutral solutions containing [Fe(CN)6]3− showed nanoelectrode array behavior at very high scan rates, while coating of the Au NP array with glucose oxidase resulted in a significantly higher glucose oxidation signal than seen at a smooth Au surface, making the NPA quite promising as a glucose sensor.

Flavonoid electrochemistry: a review on the electroanalytical applications

Flavonoids are polyphenolic compounds widespread in vegetal kingdom. They present a C-15 skeleton, which is divided into three units A, B and C. Unit C is an oxygen containing heterocyclic, whose oxidation state and saturation level define major subclasses. Units A and B are aromatic rings, in which four major types of substituents, i.e. hydroxyl, methoxyl, prenyl and glycosides, lead to over 8000 different flavonoids. The great healthy-protecting value of these phytochemical biomarkers has attracted the attention of scientific community. Their main biological actions include anticancer and anti-inflammatory properties, which are strictly linked to antioxidant activities. So that, electroanalysis have been extensively applied on mechanistic studies and also for analytical determinations. This review presents the state of the art regarding the main applications of electroanalysis on the flavonoid research. The approaches on redox behavior characterization leading to a better understanding of structure antioxidant activity relationships are highlighted.

Preparation of new polymethylmethacrylate–silica gel anion exchange composite fibers and its application in making membrane electrode for the determination of As(V)

Polymethylmethacrylate–silica gel (PMMA–silica gel) organic–inorganic anion-exchange composite fibers were prepared by simple stirring with magnetic bar in different stoichiometric ratios of polymethylmethacrylate (PMMA) and silica gel. The structure and morphology of the prepared composite fibers were ascertained by Fourier transform spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and elemental analysis (CHN/O). The material was found to be highly desirable for electroanalytical application as ionic sensor, its membrane electrode has been developed for the detection of As(V) in solutions. The membrane electrode shows the best result with linear potential response in the concentration range of 1×10−1molL−1 to 1×10−8molL−1 of As(V) ion with a slope of 30.78mV/decade. The useful pH of the electrode is 5.5–10.0. The selectivity coefficient values for interfering ions indicate good selectivity for As(V) over interfering anions. The accuracy of the procedure has been tested on arsenic-free drinking water samples spiked with known amount of arsenate and results were comparable to those generated by Portable Coulometric Analyzer (PCA-Arsenomat).

Microfluidic thin-layer flow cell for conducting polymer growth and electroanalysis

The design and fabrication of a low cost and versatile poly(dimethylsiloxane) (PDMS)-glass microchip configured to house an electrochemical thin-layer flow cell is reported. The microchip contains an integrated electrochemical cell comprising a sputtered channel gold working electrode (110μmx5mm) and a reference and auxiliary electrode housed together in the channel outlet. The facile fabrication method allows for the production of fully disposable, gasket-free thin-layer cells for a range of channel depths (35–180μm), that are suitable for low-cost, chip-based electroanalytical applications. The microchip was found to exhibit thin-layer behaviour during a series of voltammetric experiments conducted in ferrocyanide/ferricyanide. The cell was observed to experience a high resistance to current, which was dependent on the distance from the channel working electrode to the auxiliary electrode.Polyaniline (PANI) monoliths were grown electrochemically onto the channel electrode (5mm in length). The thickness of these monoliths was shown to be uniform along the length of the electrode. This demonstrates that the IR drop along the channel was not significant over this electrode length. The growth behaviour of the PANI on-chip was further examined in terms of channel depth and flow rate. It was observed that, under certain flow conditions, PANI monolith thicknesses were limited to approximately half the channel depth being employed. This was attributed to increasing volumetric flow rates during PANI growth. Increasing flow and hence convection rates were due to the displacing of channel volume during voltammetric electropolymerisation of PANI.The microfluidic electrochemical cell incorporating the PANI-modified channel electrode was then used for the amperometric detection of ascorbic acid. When the working channel electrode was placed closest to the channel outlet, the microchip was capable of the detection of ascorbic acid at a sensitivity of 15.7μAmM−1cm−1 which is greater than reported previously under similar conditions.

Adsorption of Primary Substituted Hydrocarbons onto Solid Gallium Substrates

Adsorption of a series of primary substituted hydrocarbons (RX; C18H37PO(OH)2 (ODPA), C17H35COOH, C18H37OH, C18H37NH2, and C18H37SH) onto solid gallium substrates with and without UV/ozone treatment was studied using contact angle goniometry, spectroscopic ellipsometry, and cyclic voltammetry (CV). UV/ozone treatment offered a hydrophilic surface (water contact angle (θ(water)) less than 10°), reflecting the formation of a surface oxide layer with the maximum thickness of ca. 1 nm and possibly the removal of surface contaminants. Upon immersion in a toluene solution of a RX, θ(water) increased due to adsorption of the RX onto gallium substrates. In particular, UV/ozone-treated gallium substrates (UV-Ga) immersed in an ODPA solution exhibited θ(water) close to 105°. The ellipsometric thickness of the adsorbed ODPA layer was ca. 2.4 nm, and CV data measured in an acetonitrile solution showed significant inhibition of redox reaction on the substrate surface. These results indicate the formation of a densely packed ODPA monolayer on UV-Ga. The coverage of a C17H35COOH layer adsorbed onto UV-Ga was lower, as shown by smaller θ(water) (ca. 99°), smaller ellipsometric thickness (ca. 1.3 nm), and smaller electrode reaction inhibition. Adsorption of the other RX onto UV-Ga was weaker, as indicated by smaller θ(water) (82°-92°). ODPA did not strongly adsorb onto UV-untreated gallium substrates, suggesting that the ODPA adsorption mainly originates from hydrogen bond interaction of a phosphonate group with surface oxide. These results will provide a means for controlling the surface properties of oxide-coated gallium that play an essential role in monolayer conductivity measurements and electroanalytical applications.

Rhodium thin film-carbon nanotube nanostructures: Synthesis, characterization and electron transfer properties

Rh thin films have been synthesized onto carbon nanotubes by pulsed laser deposition under vacuum and under 266Pa of helium background pressure. Field emission scanning electron microscopy revealed two types of Rh films: (i) Rh film fabricated under vacuum was smooth and of closed structure and (ii) Rh prepared at 266Pa of He was porous. Transmission electron microscopy showed that the smooth Rh film was made of highly interconnected particles of 2nm diameter, whereas the porous film had a morphology of particles arranged into columns with particles having an average diameter of 5nm. In addition, using high resolution transmission electron microscopy images, the Rh film thickness could be estimated to be about 20nm. X-ray diffraction pattern showed well-crystallized thin films with a (111) intense orientation. X-ray photoelectron spectroscopy confirmed the presence of metallic Rh at the surface of the carbon nanotubes. Preliminary evaluation of the electron transfer properties showed that porous Rh-carbon nanotubes exhibited reduced oxophilicity than smooth Rh. In addition, the porous Rh film offered larger electrochemical stability window between the onset of hydrogen adsorption and Rh oxide formation. Such interesting properties have important implications in many electroanalytical applications.

Fabrication and Characterization of Cu/ZnO Nanocomposite Film for Advanced Electroanalytical Application

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Electroanalytical applications of screen printed microelectrode arrays

We report the fabrication of screen printed microelectrode arrays which are comprised of six working electrodes (50μm radii) which are separated from their nearest neighbour by an average distance of 2272 (±0.3)μm and arranged in a circular configuration around a common counter and reference electrode. Due to their facile fabrication, different inks can be used to give rise to both graphite- and gold-based screen printed microelectrode arrays. Additionally due to their fabrication design, the microelectrodes comprising the array are sufficiently separated to ensure no diffusional overlap which is commonly encountered by microelectrode arrays reported within the literature.The electrochemical sensing characteristics of the graphite screen printed microelectrode arrays are evaluated using acetaminophen, dopamine and nitrite giving rise to limits of detection (3σ) of 4.29, 3.24 and 5.24μM respectively. Further to this, the gold-based screen printed microelectrode arrays are explored towards the electroanalytical sensing of chromium (VI) yielding a limit of detection (3σ) of 8.28μM. Proof-of-concept is further demonstrated through the determination of chromium (VI) within an environmental (canal water) sample.Due to the analytically useful responses observed at the graphite and gold screen printed microelectrode arrays, these disposable and economical electrodes hold promise for in-the-field sensing applications. Additionally the working electrode composition can be readily changed through the use of the desired screen printing ink (i.e. Pd, Pt, Cu, etc.) allowing the tailoring of the electrode surface enabling electrocatalytic microelectrode arrays to be readily derived.

PEDOT-supported Pd nanoparticles as a catalyst for hydrazine oxidation

Composite poly-3,4-ethylenedioxythiophene (PEDOT)/palladium (Pd) films were obtained by chemical deposition of dispersed palladium nanoparticles into PEDOT conducting polymer matrix. The amounts of palladium particles incorporated into PEDOT films were estimated by electrochemical quartz crystal microbalance measurements. It was shown that palladium loading depends on the time a PEDOT film is exposed in the solution, containing Pd(II)-ions, on the concentration of Pd(II) ions and the film thickness. X-ray photoelectron spectroscopy data have confirmed the presence of metallic palladium in the polymer. The morphology of pristine and composite films as well as the size of Pd nanoparticles and their distribution were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). From SEM images, it was found that Pd particles decorated PEDOT globular structures as quasi-spherical particles, and their mean size was dependent on synthesis conditions. The nanoparticles were non-uniformly dispersed on the polymer surface. The comparison of TEM images of composite PEDOT/Pd films obtained for different times of metal loading was made. The remarkable effect of loading time on the size of particles has been established: the mean size of dominating palladium particles was close to 6–10 nm for 30 s of metal deposition, and it was getting larger with the increase of deposition time (close to 15–30 nm for 120 s). It is most likely that with prolongation of synthesis time, the deposition of palladium predominantly proceeds on the already deposited palladium clusters, resulting in the extension growth of their size. Catalytic properties of PEDOT/Pd composite films were studied in respect to hydrazine oxidation by cyclic voltammetry and voltammetry on rotating disk electrode. The obtained data allow to conclude that the process of hydrazine oxidation on PEDOT/Pd composites takes place predominantly on palladium particles, located on the surface or in the near-surface layers of the polymer. The diffusion nature of the limiting current of hydrazine oxidation on composite PEDOT/Pd film in phosphate buffer solution рН = 6.86 was confirmed, and hydrazine diffusion coefficient was calculated. The increase of the limiting currents of hydrazine oxidation with the increase of Pd deposition time was observed, resulting from the increase of the active surface area of palladium particles, acting as microelectrodes. The electroanalytical applications of these nanocomposite materials for the determination of hydrazine were demonstrated.

Nafion® modified-screen printed gold electrodes and their carbon nanostructuration for electrochemical sensors applications

Screen printed electrodes are frequently used in electroanalytical applications because of their properties such as small size, low detection limit, fast response time, high reproducibility and disposable nature. On the other hand, since the discovery of carbon nanotubes there has been enormous interest in exploring and exploiting their properties, especially for their use in chemical (bio)sensors and nanoscale electronic devices. This paper reports the characterization of gold screen printed electrodes, modified with Nafion® and nanostructured with carbon nanotubes and carbon nanofibers dispersed on Nafion®. The dispersing agent and the nanostructure have a marked effect on the analytical signal that, in turn depends on the intrinsic characteristics of the analyte. Several model analytes have been employed in this study. Anionic, cationic and neutral species such as methylene blue, dopamine, iron (III) sulfate, potassium ferrycianide and urea were considered. The importance for the development of nanostructured sensors relies on the fact that depending on these factors the situation may vary from a notorious enhancement of the signal to a blocking or even decrease.

Graphene nanoplatelets supported metal nanoparticles for electrochemical oxidation of hydrazine

Graphene nanoplatelets have been applied as the support to electrodeposit monometallic Au and Pd nanoparticles as well as bimetallic Au–Pd nanoparticles. These nanoparticles have been characterized with scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, and electrochemical techniques. They are further utilized as the catalysts for electrochemical oxidation of hydrazine. The oxidation peak potential is −0.35 and 0.53V (vs. SCE) when monometallic Pd and Au nanoparticle are used as the catalysts. When bimetallic nanoparticles are applied as the catalyst, their composition affects the peak potential and peak current for the oxidation of hydrazine. Higher oxidation current is achieved when bimetallic Au–Pd nanoparticles with an atomic ratio of 3:1 are deposited on graphene nanoplatelets. Metal nanoparticle-loaded graphene nanoplatelets are thus novel platforms for electrocatalytic, electroanalytical, environmental, and related applications.

Multifunctional carbon nanoelectrodes fabricated by focused ion beam milling

We report a strategy for fabrication of sub-micron, multifunctional carbon electrodes and application of these electrodes as probes for scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM). The fabrication process utilized chemical vapor deposition of parylene, followed by thermal pyrolysis to form conductive carbon and then further deposition of parylene to form an insulation layer. To achieve well-defined electrode geometries, two methods of electrode exposure were utilized. In the first method, carbon probes were masked in polydimethylsiloxane (PDMS) to obtain a cone-shaped electrode. In the second method, the electrode area was exposed via milling with a focused ion beam (FIB) to reveal a carbon ring electrode, carbon ring/platinum disk electrode, or carbon ring/nanopore electrode. Carbon electrodes were batch fabricated (~35/batch) through the vapor deposition process and were characterized with scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and cyclic voltammetry (CV) measurements. Additionally, Raman spectroscopy was utilized to examine the effects of Ga(+) ion implantation, a result of FIB milling. Constant-height, feedback mode SECM was performed with conical carbon electrodes and carbon ring electrodes. We demonstrate the utility of carbon ring/nanopore electrodes with SECM-SICM to simultaneously collect topography, ion current and electrochemical current images. In addition, carbon ring/nanopore electrodes were utilized in substrate generation/tip collection (SG/TC) SECM. In SG/TC SECM, localized delivery of redox molecules affords a higher resolution, than when the redox molecules are present in the bath solution. Multifunctional geometries of carbon electrode probes will find utility in electroanalytical applications, in general, and more specifically with electrochemical microscopy as discussed herein.

Pyrene-anchored boronic acid receptors on carbon nanoparticle supports: fluxionality and pore effects

Pyrene-appended boronic acids self-assemble onto graphitic surfaces and are shown here to self-assemble also around negatively charged carbon nanoparticles of ca. 8–18 nm diameter (Emperor 2000, Cabot Corp.). The resulting boronic acid modified nanoparticles are water-insoluble and readily deposited onto graphite electrodes, for example for electroanalytical applications. Boronic acid binding to the ortho-quinol caffeic acid is demonstrated and the mechanism based on ligand fluxionality is further investigated. Electrodes based on nanoparticle aggregates are sensitive to caffeic acid with Langmuirian binding constants estimated as 106 mol−1 dm3. The molecular structure of the pyrene-appended boronic acid affects the ability to bind caffeic acid as well as, more importantly, the fluxional transformation of the strongly bound (high oxidation potential) into the weakly bound (low oxidation potential) form. The resulting design principles for improved boronic acid receptors are discussed.

Layered-double-hydroxide-modified electrodes: electroanalytical applications

Two-dimensional inorganic solids, such as layered double hydroxides (LDHs), also defined as anionic clays, have open structures and unique anion-exchange properties which make them very appropriate materials for the immobilization of anions and biomolecules that often bear an overall negative charge. This review aims to describe the important aspects and new developments of electrochemical sensors and biosensors based on LDHs, evidencing the research from our own laboratory and other groups. It is intended to provide an overview of the various types of chemically modified electrodes that have been developed with these 2D layered materials, along with the significant advances made over the last several years. In particular, we report the main methods used for the deposition of LDH films on different substrates, the conductive properties of these materials, the possibility to use them in the development of membranes for potentiometric anion analysis, the early analytical applications of chemically modified electrodes based on the ability of LDHs to preconcentrate redox-active anions and finally the most recent applications exploiting their electrocatalytic properties. Another promising application field of LDHs, when they are employed as host structures for enzymes, is biosensing, which is described considering glucose as an example.

The fabrication of novel screen printed single-walled carbon nanotube electrodes: Electroanalytical applications

Abstract Screen printed single-walled carbon nanotube sensors are presented which are fabricated upon flexible polyester substrates and are benchmarked against standard screen printed graphite electrodes and additionally commercially available single- and multi-walled carbon nanotube electrodes. The screen printed single-walled carbon nanotube sensors (SW-SPE) are benchmarked using potassium ferrocyanide (II), dopamine, hydrazine and capsaicin and are found to be analytically useful, in particular towards the sensing of capsaicin down to low micromolar levels with a limit of detection (3σ) of 1.9 μM improving on those determined utilising commercially available single- and multi-walled carbon nanotube sensors. These electrodes hold potential for those who have developed electroanalytical methodologies in the laboratory and wish to translate this into the field as the sensors are potentially disposable, highly reproducible and easily mass produced.

Nitrite determination at electrochemically synthesized polydiphenylamine-Pt composite modified glassy carbon electrode

Platinum nanoparticles found very wide application in electrocatalysis and sensor. However, Pt must be deposited in a stable matrix to increase stability and avoid fouling. In this work polydiphenylamine-Pt (PDPA-Pt) composite has been synthesized by electrochemical method on glassy carbon electrode. PDPA-Pt has been characterized by scanning electrochemical microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The SEM studies showed well dispersed Pt nanoparticles on PDPA surface. The electrocatalytic activity of PDPA-Pt film modified electrode toward the oxidation of NO2−was studied by cyclic voltammetry and amperometry. Cyclic voltammograms showed that NO2−undergoes irreversible oxidation at 0.85 V at PDPA-Pt modified electrode which is 0.33 V less than that of bare GCE. This shows the efficient electrocatalytic activity of the composite film. The electroanalytical application of the composite film was done by amperometric technique. The film shows a response time of less than 1 s and wide linear range of detection from 1 μM to 9.5 mM. PDPA-Pt is a promising material for electrochemical and biosensor applications. The good recoveries achieved in the various water samples for the determination of nitrite shows the practicality of the proposed sensor.

Recent Developments in the Synthesis, Characterization and Applications of Zirconium(IV) Based Composite Ion Exchangers

This article provides a review in the area of zirconium(IV) based organic–inorganic composite ion exchange materials used in analytical, pharmaceutical and environmental protection processes. It focuses on the synthesis, characterization and electroanalytical applications of various Zr(IV)-based composite ion exchangers in detail. The results obtained in different studies have also been critically reviewed. Also reviewed are the various composite cation exchange materials used as electroactive materials for the fabrication of ion-selective membrane electrodes. The ion exchange kinetic parameters of Zr(IV) based composite ion exchangers have been discussed, which provide the preliminary idea before the selection of the material for a particular application.

Novel synthesis of Prussian blue nanoparticles and nanocomposite sol: Electro-analytical application in hydrogen peroxide sensing

This paper reports a new method for the synthesis of Prussian blue nanoparticles (PBNPs) sol of homogeneous dispersion with average particle size to the order of 15.8nm. The new method of PBNPs sol synthesis is based on the interaction of active concentrations of 3-aminopropylalkoxysilane, cyclohexanone and single precursor potassium ferricyanide under ambient conditions. The PBNPs sol shows excellent electrochemistry with electron transfer rate constant to the order of 32.1s−1. The resulting PBNPs sol has been found highly stable for practical applications and shows functional activity for making nanocomposite sol with tris(2,2′-bipyridyl) ruthenium (Rubpy). The PB-Rubpy nanocomposite shows high sensitivity for H2O2 electrochemical sensing to the order of 1102.0μAmM−1cm−2 and storage stability of the materials for more than 3 months. In addition, these nanocomposite exhibits excellent electrocatalytic property for hydrogen peroxide (H2O2) sensing with catalytic rate constant to the order of 3.14×103M−1s−1. The PB-Rubpy nanocomposite sol, apart from electrocatalytic application, shows photoluminiscent ability for many opto-electroanalytical applications. In addition to that functional property of PBNPs sol for making nanodispersion with several known nanoparticles of gold, silver, palladium along with in situ synthesis of mixed metal hexacyanoferrate have also been observed.

Spontaneously Synchronized Electrochemical Micro-oscillators with Nickel Electrodissolution

We investigate the dynamical behavior of oscillatory electrodissolution of two nickel microwires in an on-chip integrated microfluidic flow cell. With equivalent circuit analysis, an equation is derived that shows that the electrical coupling strength between the electrodes can be intensified by increasing the distance from the downstream electrode to the reference/counter electrodes, increasing the electrode size, and decreasing the total resistance within the cell. Experiments and numerical simulations with an ordinary differential equation model show that by intensifying the coupling between the electrodes spontaneously synchronized oscillations occur due to large potential (IR) drop in the small flow channel. Experiments with different distances, electrode diameters, and total resistances confirm a correlation between the statistical entropy based synchrony index and the theoretically derived coupling strength formula. The findings thus show that dynamical features of the chemical reaction that have been previously seen with macroelectrodes with application of external coupling resistances can occur spontaneously with microwires. The delineation of coupling effects in the reaction system could facilitate kinetic and electroanalytical applications in design of microchip-based setups that require collector-generator multielectrode wires: the accuracy of the measurement can be improved by proper cell design that diminishes electrical cross talk.

Voltammetric determination of Rutin at Screen-Printed carbon disposable electrodes

Abstract Rutin is a flavonoid commonly employed for many therapeutic purposes. Although the electroactive phenolic groups of rutin might be oxidized at low applied potential, the adsorption of oxidized species changes the electrode surface. As a consequence, the repeatability and reproducibility of the method decreases, which limits electroanalytical applications. This paper describes the use of disposable screen-printed electrodes as an alternative to improve the electrochemical quantification of rutin in commercial and standard samples. The electrochemical behavior was consistent to what is observed using other carbon electrodes: an adsorption-involved step and a pH-dependent oxidation process. The replacement of the electrodes between the analyses ensured rapid analysis, good intermediate precision and repeatability. The proposed method was successfully applied to rutin determination in pharmaceutical samples of capsules, with the limit of quantification being 0.30 µM.