Electrochemistry of Microperoxidase-11 (MP-11) on Glassy Carbon Electrode Modified with Chitosan

In this paper, microperoxidase-11 (MP-11) was immobilized on glassy carbon electrode surface modified with chitosan by physical adsorption. The direct electrochemistry and the electrocatalytic behaviours to O-2 and the H2O2 of MP-11 on glassy carbon electrode modified with chitosan were characterized by cyclic voltammetry. The results indicate that MP-11 on modified electrode displays a quasi-reversible electrochemical process coupled with proton transfer in the phosphate buffer solutions(pH = 7.12). Direct electrochemical reaction of MP-11 on modified electrode has been realized. MP-11 on modified electrode can catalyze reduction for O-2 and H2O2. Both of the catalytic reductions are surface-controlled electrochemical process.

Label free electrochemiluminescence protocol for sensitive DNA detection with a tris(2,2'-bipyridyl)ruthenium(II) modified electrode based on nucleic acid oxidation

Label free electrochemiluminescence (ECL) DNA detection based on catalytic guanine and adenine bases oxidation using tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] modified glassy carbon (GC) electrode was demonstrated in this work. The modified GC electrode was prepared by casting carbon nanotubes (CNT)/Nafion/Ru(bpy)(3)(2+) composite film on the electrode surface. ECL signals of doublestranded DNA and their thermally denatured counterparts can be distinctly discriminated using cyclic voltammetry (CV) with a low concentration (3.04 x 10(-8) mol/L for Salmon Testes-DNA). Most importantly, sensitive single-base mismatch detection of p53 gene sequence segment was realized with 3.93 x 10(-10) mol/L employing CV stimulation (ECL signal of C/A mismatched DNA oligonucleotides was 1.5-fold higher than that of fully base-paired DNA oligonucleotides). Label free, high sensitivity and simplicity for single-base mismatch discrimination were the main advantages of the present ECL technique for DNA detection over the traditional DNA sensors.

Assembly of polyoxometalates on carbon nanotubes paste electrode and its catalytic behaviors

Carbon nanotubes paste (CNTP) electrode was prepared with multi-walled carbon nanotubes and methyl silicone oil. Polyoxometalates (POMs) were assembled on the electrode surface with different methods, and investigated by cyclic voltammetry and Raman spectroscopy. Experiments showed that POMs/CNTP electrode prepared by direct method had better performance. K6P2Mo18O62 center dot 14H(2)O (P2Mo18) assembled CNTP electrode (P2Mo18/CNTP) electrode possessed good reversibility and could catalyze the reduction of bromate and iodate in 0.1 M H2SO4 Solution. Further, the multilayer films of P2Mo18 assembled CNTP electrodes were fabricated by layer-by-layer technique, which showed higher electrocatalytic activities. All these POMs assembled CNTP electrodes prepared exhibited good stability.

Electrochemical characteristics of glucose oxidase adsorbed at carbon nanotubes modified electrode with ionic liquid as binder

Multiwall carbon nanotubes (CNTs)-modified electrode has been prepared by using ionic liquid (IL) as the binder. The as-prepared CNTs-IL composite modified electrode has good biocompatibility and is a suitable matrix to immobilize biomolecules. Glucose oxidase (GOx), containing flavin adenine dinucleotide as active site, stably adsorbed on modified electrode surface has resulted in the direct electron transfer. The electron transfer rate of 9.08 s(-1) obtained is much higher than that of GOx adsorbed on the CNTs papers (1.7 s(-1)), and the process is more reversible with small redox peak separation of 23 mV This may be due to the synergetic promotion of CNTs and IL to electron transfer of the protein, especially the IL as the binder, showing better electrochemical properties than that of chitosan and Nafion. Furthermore, GOx adsorbed at the modified electrode exhibits good stability and keeps good electrocatalytic activity to glucose with broad linear range up to 20 mM. Besides, the simple preparation procedure and easy renewability make the system a basis to investigate the electron transfer kinetics and biocatalytic performance of GOx and provide a promising platform for the development of biosensors.

Preparation of hybrid thin film modified carbon nanotubes on glassy carbon electrode and its electrocatalysis for oxygen reduction

A hybrid thin film containing Pt nanoparticles and [tetrakis(N-methylpyridyl)porphyrinato] cobalt (CoTMPyP) modified multi-walled carbon nanotubes (MWNTs) on a glassy carbon (GC) electrode surface was fabricated. This hybrid film electrode exhibited remarkable electrocatalytic activity for oxygen reduction and high stability with promising applications in fuel cells.

Surface charge influence on the surface plasmon absorbance of electroactive thiol-protected gold nanoparticles

Gold nanoparticles (3.1-5.0 nm in size) surface-derivatized with both electroactive and nonelectroactive self-assembled monolayers were synthesized. The surface-derivatized electroactive particles can be easily oxidized/reduced at an electrode surface based on the diffusion-controlled current-voltage curve observed in cyclic voltammetry measurements. Spectroelectrochemical investigation demonstrated that the maximum absorbance of the nanoparticles in their oxidized state red-shifted compared with their reduced state to a different extent according to their size distribution. In the case of the particles surface-derivatized with nonelectroactive monolayers, much less shift was observed. This study showed that surface plasmon absorbance of gold nanoparticles was not only related to core charge states but was also influenced by surface charge states as well.

Electrocatalytic reduction of oxygen at multi-walled carbon nanotubes and cobalt porphyrin modified glassy carbon electrode

The multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode exhibited electrocatalytic activity to the reduction of oxygen in 0.1 M HAc-NaAc (pH 3.8) buffer solution. Further modification with cobalt porphyrin film on the MWNTs by adsorption, the resulted modified electrode showed more efficient catalytic activity to O-2 reduction. The reduction peak potential of O-2 is shifted much more positively to 0.12 V (vs. Ag/AgCl), and the peak current is increased greatly. Cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were used to characterize the material and the modified film on electrode surface. Electrochemical experiments gave the total number of electron transfer for oxygen reduction as about 3, which indicated a co-exist process of 2 electrons and 4 electrons for reduction of oxygen at this modified electrode. Meanwhile, the catalytic activities of the multilayer film (MVVNTs/CoTMPyP)(n) prepared by layer-by-layer method were investigated, and the results showed that the peak current of O-2 reduction increased and the peak potential shifted to a positive direction with the increase of layer numbers.

Immunosensors based on layer-by-layer self-assembled Au colloidal electrode for the electrochemical detection of antigen

Colloidal Au particles have been deposited on the gold electrode through layer-by-layer self-assembly using cysteamine as cross-linkers. Self-assembly of colloidal Au on the gold electrode resulted in ail easier attachment of antibody, larger electrode surface and ideal electrode behavior. The redox reactions of [Fe(CN)(6)]-/[Fe(CN)(6)](3-) on the gold surface were blocked due to antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.0 with various concentrations of antigen at 37degreesC for 30 min. Further, an amplification strategy to use biotin conjugated antibody was introduced for improving the sensitivity of impedance measurements. Thus, the sensor based oil this immobilization method exhibits a large linear dynamic range, from 5 - 400 mug/L for detection of Human IgG. The detection limit is about 0.5 mug/L.

Electrooxidation of COad intermediated from methanol oxidation on polycrystalline Pt electrode

The poisonous intermediate of methanol oxidation on a Pt electrode was validated to be COad by electrochemical method. An approximate treatment to bimolecular elementary reactions on an electrode was advanced and then was applied to the stripping normal pulse voltammetry (NPV) for complex multistep multielectron transfer processes on plane electrodes to study the kinetics of completely irreversible process Of COad oxidation to CO2. The kinetic parameters for this process, such as standard rate constant (0) and anodic transfer coefficient (alpha) for this irreversible heterogeneous electron-transfer process at electrode/solution interface and apparent diffusion coefficient (D-app) for charge-transfer process within the monolayer of COad on electrode surface, were obtained with stripping NPV method. The effect of the approximate treatment on the kinetic parameters was also analyzed.

Self-assembly of 4-ferrocene thiophenol capped electroactive gold nanoparticles onto gold electrode

Gold nanoparticles capped by 4-ferrocene thiophenol with an average core size of 2.5 nm and surface plasmon absorbance at 522 nm were place-exchanged with 1,8-octanedithiol, and then self-assembled onto the gold electrode via tail SH group. The self-assembly was characterized by X-ray photoelectron spectroscopy. Cyclic voltammograms examined the coverage fraction of the self-assembled monolayers of the electroactive gold nanoparticles and the formal potential of the indicated SAMs. Further experiments exhibited that the electrode process was controlled by surface confined faradic reactions.

Electrochemical detection of DNA immobilized on gold colloid particles modified self-assembled monolayer electrode with silver nanoparticle label

The target DNA was immobilized successfully on gold colloid particles associated with a cysteamine monolayer on gold electrode surface. Self-assembly of colloidal An onto a cysteamine modified gold electrode can enlarge the electrode surface area and enhance greatly the amount of immobilized single stranded DNA (ssDNA). The electrontransfer processes of [Fe(CN)(6)](4)-/[Fe(CN)(6)](3-) on the gold surface were blocked due to the procedures of the target DNA immobilization, which was investigated by impedance spectroscopy. Then single stranded target DNA immobilized on the gold electrode hybridized with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution, and the indirect determination of the released solubilized Ag-1 ions by anodic stripping voltammetry (ASV) at a carbon fiber microelectrode. The results show that this method has good correlation for DNA detection in the range of 10-800 pmol/1 and allows the detection level as low as 5 pmol/1 of the target oligonucleotides.

Probing UPD-induced surface atomic rearrangement of polycrystalline gold nanofilms with surface plasmon resonance spectroscopy and cyclic voltammetry

Silver underpotential deposition (UPD)-induced surface atomic rearrangement of polycrystalline gold nanofilms was probed with use of surface plasmon resonance spectroscopy (SPRs) as a novel probe tool in combination with cyclic voltammetry. Interestingly, upon repetitive electrochemical UPD and stripping of Ag, the surface structure of the resulting bare Au film is rearranged due to strong adatom-substrate interactions, which causes a large angle shift of SPR R-theta curves, in a good linear relationship with the number of UPDs, to a lower SPR angle. The n, K values of the surfacial Au monolayers before and after the repetitive Ag UPD and stripping for 27 times are found to be 0.133, 3.60 and 0.565, 9.39, respectively, corresponding to the huge shift of 1.61degrees to the left of the SPR minima. Cyclic voltammetry experiments in 0.10 M H2SO4 are carried out before and after the UPD treatment to examine the quality of the whole electrode surface and confirmed this change. To correlate the angle change in SPRs with the profile change in the cyclic voltammogram, the UPD treatment was also performed on a Au(111) textured thin film. It was therefore confirmed that the resonance position of the SPR spectrum is very sensitive to the surface crystallographic orientation of the bare Au substrates. Some surface atomic rearrangement can cause a pronounced SPR angle shift.

Direct electrochemistry and surface plasmon resonance characterization of alternate layer-by-layer self-assembled DNA-myoglobin thin films on chemically modified gold surfaces

Alternate layer-by-layer (L-by-L) polyion adsorption onto gold electrodes coated with chemisorbed cysteamine gave stable, electroactive multilayer films containing calf thymus double stranded DNA (CT ds-DNA) and myoglobin (Mb). Direct, quasi-reversible electron exchange between gold electrodes and proteins involved the Mb heme Fe2+/Fe3+ redox couple. The formation of L-by-L (DNA/Mb), films was characterized by both in situ surface plasmon resonance (SPR) monitoring and cyclic voltammetry (CV). The effective thickness of DNA and Mb monolayers in the (DNA/Mb)l bilayer were 1.0 +/- 0.1 and 2.5 +/- 0.1 mn, corresponding to the surface coverage of similar to65% and similar to89% of its full packed monolayer, respectively. A linear increase of film thickness with increasing number of layers was confirmed by SPR characterizations. At pH 5.5, the electroactive Mb in films are those closest to the electrode surface; additional protein layers did not communicate with the electrode. CV studies showed that electrical communication might occur through hopping conduction via the electrode/base pair/Mb channel, thanks to the DNA-Mb interaction. After the uptake of Zn2+, a special electrochemical behavior, where MbFe(2+) acts as a DNA-binding reduction catalyst in the Zn2+-DNA/Mb assembly, takes place.

Preparation of multilayer films containing pt nanoparticles on a glassy carbon electrode and application as an electrocatalyst for dioxygen reduction

In this paper, a simple route for the preparation of Pt nanoparticles is described. PtCl62- and [tetrakis-(N-methylpyridyl)porphyrinato] cobalt (CoTMPyP) were assembled on a 4-aminobenzoic acid modified glassy carbon electrode through the layer-by-layer method. The three-dimensional Pt nanoparticle films are directly formed on an electrode surface by electrochemical reduction of PtCl62- sandwiched between CoTMPyP layers. Regular growth of the multilayer films is monitored by UV-vis spectroscopy. X-ray photoelectron spectroscopy verifies the constant composition of the multilayer films containing Pt nanoparticles. Atomic force microscopy proves that the as-prepared Pt nanoparticles are uniformily distributed with average particle diameters of 6-10 nm. The resulting multilayer films containing Pt nanoparticles on the modified electrode possess catalytic activity for the reduction of dissolved oxygen. Rotating disk electrode voltammetry and rotating ring-disk electrode voltammetry confirm that Pt nanoparticle containing films can catalyze an almost four-electron reduction of O-2 to water in 0.5 M H2SO4 solution.

Synthesis, characterization and fabrication on a glassy carbon electrode of a tetra-iron substituted sandwich-type pentadecatungstodiarsenate heteropolyanion

A novel sandwich-type compound, Na-12[Fe-4(H2O)(2)(As2W15O56)2].41H(2)O, has been synthesized. The compound was well-characterized by means of IR, UV-vis, W-183 NMR and elemental analyses. The compound crystallizes in the triclinic, P (1) over bar symmetry group. The structure of the compound is similar to that of Na-16[M-4(H2O)(2)(As2W15O56)(2)].nH(2)O (M = Cu, Zn, Co, Ni, Mn, Cd), and consists of an oxo-aqua tetranuclear iron core, [(Fe4O14)-O-III(H2O)(2)], sandwiched by two trivacant alpha-Wells-Dawson structural moieties, alpha-[As2W15O56]. Redoxelectrochemistry of the compound has been studied in buffer solutions at pH = 4.7 using polarography and cyclic voltammetry ( CV). The compound exhibited four one-electron couples associated with the Fe(III) center followed by three four-electron redox processes attributed to the tungsten-oxo framework. The compound-containing monolayer and multilayer films have been fabricated on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternating deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)(2)Cl](2+/-). CV, X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy and atomic force microscopy (AFM) have been used to characterize the multilayer films.