Glucose/O2 biofuel cell based on enzymes, redox mediators, and multiple-walled carbon nanotubes deposited by AC-electrophoresis then stabilized by electropolymerized polypyrrole.

In this study, we developed an automated strategy to manufacture an enzyme BFC powered by glucose/O(2). The bioanode consists of GOx enzyme and PQQ redox mediator adsorbed over night on MWCNTs then deposited by means of AC-electrophoresis at 30 Hz and 160 V(p-p) and, finally stabilized by electropolymerized polypyrrole. The biocathode is constructed from LAc enzyme and ABTS redox mediator adsorbed over night on MWCNTs, then electrophoretically deposited under AC-electric field at 30 Hz and 160 V(p-p) and, finally stabilized by electrodeposited polypyrrole. The BFC was studied under air in phosphate buffer solution pH 7.4 containing 10 mM glucose and in human serum with 5 mM glucose addition at the physiological temperature of 37°C. Under these conditions, the maximum power density reaches 1.1 µW · mm(-2) at a cell voltage of 0.167 V in buffer solution and 0.69 µW · mm(-2) at cell voltage of 0.151 V in human serum. Such automated BFCs have a great potential to be optimized, miniaturized to micro and nanoscale devices suitable for in vivo studies.

Neighboring amide participation in thioether oxidation: relevance to biological oxidation.

To investigate neighboring amide participation in thioether oxidation, which may be relevant to brain oxidative stress accompanying beta-amyloid peptide aggregation, conformationally constrained methylthionorbornyl derivatives with amido moieties were synthesized and characterized, including an X-ray crystallographic study of one of them. Electrochemical oxidation of these compounds, studied by cyclic voltammetry, revealed that their oxidation peak potentials were less positive for those compounds in which neighboring group participation was geometrically possible. Pulse radiolysis studies provided evidence for bond formation between the amide moiety and sulfur on one-electron oxidation in cases where the moieties are juxtaposed. Furthermore, molecular constraints in spiro analogues revealed that S-O bonds are formed on one-electron oxidation. DFT calculations suggest that isomeric sigma*(SO) radicals are formed in these systems.

In vivo biosensors.

Detailed understanding of the dynamics of living systems requires a means to monitor, in real time, changes in the levels of key components in response to specific stimuli. Applications involving cultured cells, tissue slices and implantation in living systems are discussed.

Neighboring π-Amide Participation in Thioether Oxidation: Conformational Control.

The electrochemical oxidation of thioethers is shown to be facilitated by neighboring amide participation. (1)H NMR spectroscopic analysis in acetonitrile solution of two conformationally constrained compounds with such facilitation shows that two-electron participation by the amide π2 orbital can occur to stabilize the developing sulfur radical cation.

Electrochemical and electrophoretic deposition of enzymes: principles, differences and application in miniaturized biosensor and biofuel cell electrodes.

Recent advances in nano-biotechnology have made it possible to realize a great variety of enzyme electrodes suitable for sensing and energy applications. In coating miniaturized electrodes with enzymes, there is no doubt that most of the available deposition processes suffer from the difficulty in depositing uniform and reproducible coatings of the active enzyme on the miniature transducer element. This mini-review highlights the promising prospects of two techniques, electrochemical deposition (ECD) and electrophoretic deposition (EPD), in enzyme immobilization onto miniaturized electrodes and their use as biosensors and biofuel cells. The main differences between ECD and EPD are described and highlighted in the sense to make it clear to the reader that both techniques employ electric fields to deposit enzyme but the conditions from which each process is achieved and hence the mechanisms are quite different. Many aspects dealing with deposition of enzyme under ECD and EPD are considered including surface charge of enzyme, its migration under the applied electric field and its precipitation on the electrode. Still all issues discussed in this mini-review are generic and need to be followed in the future by extensive theoretical and experimental research analysis. Finally, the advantages of ECD and EPD in fabrication of miniature biosensor and biofuel cell electrodes are described and discussed.

Combination of laccase and catalase in construction of H2O2-O2 based biocathode for applications in glucose biofuel cells.

In this study, we propose a new strategy to boost the power density of glucose biofuel cells (GBFCs) biocathodes. By combining laccase with catalase enzymes electrophoretically deposited by means of AC electric fields on multiple walled carbon nanotubes modified platinum black and, then stabilized by an outer layer of polypyrrole in the construction of GC/MWCNTs/Ptb/LAc-CAt/PPy biocathode, we can take advantage of the H(2)O(2) present in the solution or body tissue to increase the level of the dissolved O(2). The results from cyclic voltammetry, amperometry and electrochemical impedance spectroscopy demonstrate that the deposited enzymes laccase and catalase by means of AC-EPD did not inhibit each other and carry out ∼90% of the catalytic reduction process of O(2)-H(2)O(2). The power density of the non-compartmentalized GBFC constructed from GC/MWCNTs/Ptb/LAc-CAt/PPy biocathode and GC/MWCNTs/GOx/PPy bioanode in phosphate buffer containing 10mM glucose and equal amounts of dissolved O(2) and H(2)O(2) (0.3mM) is almost doubled because of the presence of catalase enzyme in the constructed biocathode. The latter might be of great interest for in vivo studies of GBFCs where the concentration of dissolved O(2) in the body tissues or biological fluids is very low compared to in vitro conditions (buffers under air).

Performance of SLS/MWCNTs/PANI capacitor electrodes in a physiological electrolyte and in serum.

We report a stainless steel/multi walled carbon nanotubes/polyaniline (SLS/MWCNTs/PANI) capacitor electrode capable of operating in a physiological electrolyte and in serum. The specific capacitance of SLS/MWCNTs/PANI reaches 401 F g(-1) in the physiological electrolyte and 326 F g(-1) in serum. The capacity loss at 6.4 µA mm(-2) over 2000 cycles is 10% in the physiological electrolyte and 21% in serum.

Neighboring pyrrolidine amide participation in thioether oxidation. Methionine as a "hopping" site.

Methionine residues have been shown to function as efficient "hopping" sites in long-range electron transfer in model polyprolyl peptides. We suggest that a key to this ability of methionine is stabilization of the transient sulfur radical cation by neighboring proline amide participation. That is, in a model system a neighboring pyrrolidine amide lowers the oxidation potential of the thioether by over 0.5 V by formation of a two-center three-electron SO bond.

Highly sensitive and selective glutamate microbiosensor based on cast polyurethane/AC-electrophoresis deposited multiwalled carbon nanotubes and then glutamate oxidase/electrosynthesized polypyrrole/Pt electrode.

A highly sensitive and selective glutamate microbiosensor based on polypyrrole (PPy), multiwalled carbon nanotubes (MWCNT) and glutamate oxidase (GluOx) deposited on the transducer platinum electrode (Pt) is described. The sensor consists of a permselective membrane of polypyrrole for the rejection of interferences, followed by a layer of multiwalled carbon nanotubes and glutamate oxidase deposited by asymmetrical alternating current electrophoretic deposition (AC-EPD). The biosensor has a high sensitivity (3.84 nA/(microMmm(2))), low response to interferences such as ascorbic acid, uric acid and acetaminophen, a fast response time (7s), low detection limit (approximately 0.3 microM), a linear range of 140 microM and a satisfactory stability. In order to improve the linear range and the stability, a thin layer of polyurethane (PU) was applied to the Pt/PPy/MWCNT/GluOx sensor. The resulting sensor with the PU outer membrane showed an increase in the linear range up to approximately 500 microM glutamate and has a better stability at the expense of a decrease in sensitivity (2.5 nA/(microMmm(2))) and an increase in the response time (15s).

Micro-biofuel cell powered by glucose/O2 based on electro-deposition of enzyme, conducting polymer and redox mediators: preparation, characterization and performance in human serum.

In this study we report a new simple process to manufacture a biofuel cell consisting of a glucose oxidase (GOx) based anode and a laccase (LAc) based cathode. The process is based on the electro-deposition of the enzymes, conducting polymer and redox mediators from ultrapure water at a potential of 4V vs. AgCl/Ag. Contrary to the conventional electro-deposition from high ionic strength (buffer solution) at low applied potential (1V vs. AgCl/Ag) where only thin films could be deposited, leading to BFC with moderate power, the electro-deposition from ultrapure water at 4V allows the growth of thick films leading to BFC with high power output. It was observed that the combination of polypyrrole (PPy), with ferrocenium hexafluorophosphate (FHFP) and pyrroloquinoline quinone (PQQ) to be appropriate for the electron transfer at the GOx bioanode, while the combination of polypyrrole with bis-(bipyridine)-(5-amino-phenanthroline) ruthenium bis (hexafluorophosphate)(RuPy) and 4,4-sulfonyldiphenol (SDP) to be effective for the electron transfer at the LAc biocathode. The working biofuel cell was studied at 37 degrees C in phosphate buffer solution at pH 7.4 containing 10 mM glucose and in human serum. Under these conditions, the maximum power density reached 3.1 microW mm(-2) at a cell voltage of 0.28 V in buffer solution and 1.6 microW mm(-2) at a cell voltage of 0.21 V in human serum. This study offers a new route to the development of enzymatic BFCs with high performance and provides information on enzymatic BFCs as in vivo power sources.

Nitrite sensor based on multilayer film of Dawson-type tungstophosphate alpha-K7)[H4PW18O62]x18H2O immobilized on glassy carbon.

A nitrite sensor based on immobilized Dawson-type tungstophosphate alpha-K(7)[H(4)PW(18)O(62)].18H(2)O (PW(18)) in multilayers of charged polyelectrolyte poly(allylamine hydrochloride) (PAH) on a glassy carbon electrode is described. A nitrite sensor manufactured with 10 layers has a sensitivity of approximately 4 nA/microM nitrite, fast response time (<6s), low detection limit ( approximately 0.1 microM), high selectivity towards endogenous interferences such as nitrate and molecular oxygen, a linear range from 0.1 microM to at least 20mM nitrite and was stable for at least 2 months. In addition, such nitrite sensors can operate in a pH range from 1 to 9, and the sensitivity can be increased by increasing the number of layers at the expense of increasing the response time.

AC-electrophoretic deposition of glucose oxidase.

The electrophoretic deposition of glucose oxidase from water using asymmetrical alternating voltages is investigated. Using asymmetric voltages, glucose oxidase layers with a thickness of 7 microm could be deposited on a platinum electrode in 20 min time as verified with a microbalance, carbon analysis and scanning electron microscopy. In contrast, if a symmetrical alternating signal is used under the same conditions, a layer of 0.5 microm is formed. We believe the deposition is due to two effects: the electrophoretic migration of the enzyme towards the deposition electrode and the pH induced precipitation of the enzyme near the deposition electrode. The electrophoretic migration is due to the non-linear dependence of the electrophoretic mobility on the electric field caused by the asymmetry of the applied alternating current signal. In addition, pH changes near the deposition electrode drive the enzyme towards its point of zero charge (PZC), perhaps causing the precipitation of GOx on the substrate. The effect of amplitude, frequency, deposition time and GOx concentration on the deposition rate was studied. An amplitude of 160 V(p-p) and a frequency of 30 Hz was found to be optimal for the formation of thick enzyme layers, which excludes a big part of the interferences.

Interactions of arenes and thioethers resulting in facilitated oxidation.

Synthesis of 6-endo and 6-exomethylthio-2-endoarylbicyclo[2.2.1]heptanes was accomplished stereoselectively. The ionization energies, determined by photoelectron spectroscopy, and electrochemical oxidation potentials, determined by cyclic voltammetry, were lower for the 6-endomethylthio compounds than for their 6-exomethylthio analogues. Calculations supported the notion that facilitation of electron transfer in the 6-endomethylthio compounds results from through-space S...pi interaction.