Preparation of poly(thionine) modified screen-printed carbon electrode and its application to determine NADH in flow injection analysis system

A poly(thionine) modified screen-printed carbon electrode has been prepared by an electrooxidative polymerization of thionine in neutral phosphate buffer. The modified electrodes are found to give stable and reproducible electrocatlytic responses to NADH and exhibit good stability. Several techniques, including cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), have been employed to characterize the poly(thionine) film. Further, the modified screen-printed carbon electrode was found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 5-100 muM.

Microperoxidase-11 modified electrode and its electrocatalytic activity on the reduction of O-2 and H2O2

Microperoxidase-11 (MP-11) was immobilized on the surface of a silanized glass carbon electrode by means of the covalent bond with glutaraldehyde. The measurements of cyclic voltammetry demonstrated that the formal redox potential of immobilized MP-11 was -170 mV. which is significantly more positive than that of MP-11 in a solution or immobilized on the surface of electrodes prepared with other methods. This MP-11 modified electrode showed a good electrocatalytic activity and stability for the reduction of oxygen and hydrogen peroxide.

Electrocatalytic oxidation of dopamine at a cobalt hexacyanoferrate modified glassy carbon electrode prepared by a new method

A stable electroactive thin film of cobalt hexacyanoferrate (CoHCF) was electrochemically deposited on the surface of a glassy carbon (GC) electrode with a new and simple method. The cyclic voltammograms of the CoHCF Film modified GC (CoHCF/GC) electrode prepared by this method exhibit two pairs of well-defined redox peaks, at scan rates up to 200 mV s(-1). The advantage of this method is that it is easy to manipulate and to control the surface coverage of CoHCF on the electrode surface. The modified electrode shows good electrocatalytic activity towards the electrochemical reaction of dopamine (DA) in a 0.1 mol dm (3) KNO3 + phosphate buffer solution (pH 7.0). The rate constant of the electrocatalytic oxidation of DA at the CoHCF/GC electrode is determined by employing rotating disk electrode measurements.

Toluidine blue modified self-assembled silica gel coated gold electrode as biosensor for NADH

A toluidine blue modified gold electrode was constructed using self-assembled silica gel technique. Firstly, toluidine blue was encapsulated within 3D network of silica self-assembly monolayer on the surface of gold electrode. Secondly, another layer of silica sol was further assembled to protect from leaching of mediator or possible contamination. The electrochemical characteristics of toluidine blue immobilized within self-assembled silica gel were studied in detail. The modified electrode was applied for electrochemical oxidation of NADH with satisfactory results.

Surface plasmon resonance studies on the electrochemical doping/dedoping processes of anions on polyaniline-modified electrode

The combination of in situ surface plasmon resonance (SPR) with electrochemistry was used to investigate the electrochemical doping/dedoping processes of anions on a polyaniline (PAn)-modified electrode. Electrochemical SPR characteristics of the PAn film before and after doping/dedoping were revealed. The redox transformation between the insulating leucoemeraldine, and the conductive emeraldine, corresponding to the doping/dedoping of anion, can lead to very distinct changes in both the resonance minimum angle and the shape of SPR curve. This is ascribed to the swelling/shrinking effect, and the change of the PAn film in the imaginary part of the dielectric constant resulted from the transition of the film conductivity. In situ recording the time evolution of reflectance change at a fixed angle permits the continuous monitoring of the kinetic processes of doping/dedoping anions. The size and the charge of anions, the film thickness, as well as the concentration of anions are shown to strongly influence the rate of ingress/egress of anions. The time differential of SPR kinetic curves can be well applied in the detecting electroinactive anion by flow injection analysis. The approach has higher sensitivity and reproducibility compared with other kinetic measurements, such as those obtained by amperometry.

Electrochemical and Raman studies of the biointeraction between Escherichia coli and mannose in polydiacetylene derivative supported on the self-assembled monolayers of octadecanethiol on a gold electrode

Here, we describe a new method to study the biointeraction between Escherichia coli and mannose by using supramolecular assemblies composed of polydiacetylene supported on the self-assembled monolayer of octadecanethiol on a gold electrode. These prepared bilayer materials simply are an excellent protosystem to study a range of important sensor-related issues. The experimental results from UV-vis spectroscopy, resonance Raman spectroscopy, and electrochemistry confirm that the specific interactions between E. coli and mannose can cause conformational changes of the polydiacetylene backbone rather than simple nonspecific adsorption. Moreover, the direct electrochemical detection by polydiacetylene supramolecular assemblies not only opens a new path for the use of these membranes in the area of biosensor development but also offers new possibilities for diagnostic applications and screening for binding ligands.

Gold nanoparticles as fine tuners of electrochemical properties of the electrode/solution interface

Recently, a novel approach for preparing SERS and SPR substrates was developed, which indicates a potential application in tailoring the interfacial structure of an electrode surface. In this study, (3-mercaptopropyl)trimethoxysilane (MPTMS) was selected as a polymeric adhesive layer, and a low concentration of colloid Au solution was used to achieve a more accurate control over interface morphology at nanoscale dimensions due to slow self-assembling kinetics of gold nanoparticle's. Subsequent seeding growth of these MPTMS-supported submonolayers of gold nanoparticles in Au3+/NH2OH aqueous solution enlarges particle size and eventually results in the generation of conductive gold films (similar to previous (3-aminopropyl)trimethoxysilane-supported gold films). Such tunable interface structure was evaluated by atomic force microscopy (AFM). Also, ac impedance spectroscopy (ACIS) and cyclic voltammograms were performed to evaluate electrochemical properties of the as-prepared interfaces by using Fe(CN)(6) (3-/4-) couples as a probe. Furthermore, relevant theories of microarray electrodes were introduced into this study to explain the highly tunable electrochemical properties of the as-prepared interfaces. As a result, it is concluded that the electrochemical properties toward Fe(CN)(6) (3-/4-) couples are highly dependent on the active nanoelectrode (nanoparticles) area fraction and nanoparticles are fine-tuners of interfacial properties because the number density. (numbers/unit area) and size of nanoparticles are highly tunable by self-assembling and seeding growth time scale control. This is in agreement with the theoretical expectations for a microarray electrode if a single nanoparticle tethered to a blocking SAM is taken as a nanoelectrode and 2-D nanoparticle assemblies are taken as nanoelectrode arrays.

Direct electron transfer between hemoglobin and a glassy carbon electrode facilitated by lipid-protected gold nanoparticles

We synthesized a kind of gold nanoparticle protected by a synthetic lipid (didodecyidimethylammonium bromide, DDAB). With the help of these gold nanoparticles, hemoglobin can exhibit a direct electron transfer (DET) reaction. The formal potential locates at -169 mV vs. Ag/AgCl. Spectral data indicated the hemoglobin on the electrode was not denatured. The lipid-protected gold nanoparticles were very stable (for at least 8 months). Their average diameter is 6.42 nm. It is the first time to use monolayer-protected nanoparticles to realize the direct electrochemistry of protein.

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed, Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.

Fabrication of Au(111) single-crystal nanoisland-arrayed electrode ensembles by template-directed seeding growth

A new and simple approach for preparation of Au(111) single-crystal nanoisland - arrayed electrode ensembles, based on fine colloidal Au monolayer-directed seeding growth, is reported.

Voltammetric Behavior of ethambutol on a glassy carbon electrode and its application

The anodic voltammetric behavior of ethambutol in the presence of various electrolytes was studied by direct-current voltammetry, differential-pluse voltammetry and cyclic voltammetry at a glassy carbon electrode. In a medium of 0.039 mol/L Na2HPO4, an oxidative peak of ethambutol was obtained. The peak potential is at about 1.04 V( vs. Ag/AgCl). The height of the peak is linearly increased with the concentration of ethambutol over the range of 3 mg/Lsimilar to1000 mg/L. The method has been used for the direct determination of ethambutol in tablets. The average recovery of ethambutol in urine samples is 84.7%. Experimental results proved that the electrode reaction was diffusion controlled and irreversible.

Electrochemiluminescent microoptoprobe with mini-grid working electrode and self-contained sample container

A new electrochemiluminescence (ECL) microoptoprobe with simple structure. small sampling volume and high efficiency was developed. It was constructed by fixing the transparent gold mini-grid on the end surface of the optical fiber, and by surrounding the fiber with the counter- and reference electrodes to form a self-contained three-electrode system. The use of mini-grid electrode increased the surface area and collection efficiency. which resulted in higher ECL signal and better sensitivity. The counter electrode together with one end of the fiber formed a mini-vessel, which eliminated the need of additional container and allowed to perform ECL detection in a very small volume (about 10 mul). The microoptoprobe obtained was characterized with the Ru(bpy)(3)(2-)-tripropylamine system and was applied for the determination of oxalate and chlorpromazine (CPZ). Detection limits (S/N = 3) were 5 x 10(-7) and 1 x 10(-6) mol l(-1) for oxalate and CPZ. respectively. The linear range for oxalate and CPZ extended from 1 x 10(-6) to 1 x 10(-3) mol l(-1), and from 5 x 10(-6) to 5 x 10(-4) mol l(-1). respectively.

Novel tris(2,2-bipyridine)ruthenium(II) cathodic electrochemiluminescence in aqueous solution at a glassy carbon electrode

A novel approach of generating cathodic electrochemiluminescence lof Ru(bpy)(3)(2+) at -0.4 V triggered by reactive oxygen species is reported for detecting alkylamines and some organic acids.

Electrochemiluminescent determination of glucose with a sol-gel derived ceramic-carbon composite electrode as a renewable optical fiber biosensor

A sol-gel derived ceramic-carbon composite electrode is used for fabrication of a new type of optical fiber biosensor based on luminol electrochemiluminescence (ECL). The electrode consists of graphite powder impregnated with glucose oxidase in a silicate network. In this configuration, the immobilized enzyme oxidizes glucose to liberate hydrogen peroxide and graphite powder provides percolation conductivity for triggering the ECL between luminol and the liberated hydrogen peroxide. Both of the reactions occur simultaneously on the surface of the composite electrode, thereby the response of the biosensor is very fast. The peak intensity was achieved within only 20 s after glucose injection. In addition, the electrode could be renewed by a simple mechanical polishing step in case of contamination or fouling. The linear range extends from 0.01 to 10 mM for glucose and the detection limit is about 8.16 muM. The renewal repeatability and stability of the biosensor are also investigated in detail.

Sol-gel derived carbon ceramic electrode containing methylene blue-intercalted alpha-zirconium phosphate micro particles

Methylene blue-intercalated a-zirconium phosphate (MBZrP) micro particles in deionized water were deposited onto the surface of graphite powder to prepare graphite powder-supported MBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite. The composite was used as electrode material to fabricate a surface-renewable, rigid, leak-free carbon ceramic composite electrode, bulk-modified with methylene blue (MB). In the configuration, alpha-zirconium phosphate was employed as a solid host for MB, which acted as a catalyst. Graphite powder ensured conductivity by percolation, the silicate provided a rigid porous backbone and the methyl groups endowed hydrophobicity and thus limited the wetting section of the modified electrode. Peak currents of the MBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled at high scan rates. Square-wave voltammetric study revealed that MBZrP immobilized in carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution with pH ranged from 0.44 to 2.94. In addition, the chemically modified electrode showed an electrocatalytic activity toward nitrite reduction at +0.15 V (vs. Ag/AgCl) in acidic aqueous solution (pH=0.44). The linear range and detection limit are 1 x 10(-6)-4 x 10(-3) mol L-1 and 1.5 x 10(-7) mol L-1, respectively.