Shaolin Mu

Bioelectrochemical responses of the polyaniline horseradish peroxidase electrodes

Employing the electrochemical method, horseradish peroxidase (HRP) was immobilized on polyaniline films polymerized on the platinum foil and on glassy carbon to form two kinds of the enzyme electrode, which are designated as HRP/PAN/Pt and HRP/PAN|C, respectively. The HRP/PAN|Pt electrode potential was set at 0.20 V (vs. SCE), and that of HRP/PAN|C was set at 0.075 V (vs. SCE). They have a fast response. The response currents of both enzyme electrodes in 0.2 M phosphate buffer containing 1×10−5 M H2O2 increase with decreasing pH and potential. The apparent Michaelis-Menten constant >m′ is 3.2 × 10−5M for the HRP/PAN|Pt electrode, and is 2.8×10−5M for the HRP/PAN|C electrode. The activation energy of the enzyme-catalyzed reaction is 15.4 kJ mol−1 for the HRP/PAN|Pt electrode, and is 13.8 kJ mol−1 for the HRP/PAN|C electrode. The electrochemical reduction of hydrogen peroxidase was observed at both the bare platinum electrode and polyaniline film polymerized on platinum, but the current of the reduction of hydrogen peroxidase at the polyaniline film is very small. Hydrogen peroxidase cannot be reduced at either the bare glassy carbon or polyaniline film polymerized on the glassy carbon. Both enzyme electrodes have a linear relationship between the response current and concentration of hydrogen peroxidase below 5×10−6M in the mediator-free solution and at low potentials, so the polyaniline horseradish peroxidase electrodes can be used to determine low H2O2 concentrations.

Effect of inhibitors on Zn-dendrite formation for zinc-polyaniline secondary battery

Abstract The effects of Pb2+, sodium lauryl sulfate and Triton X-100 on inhibition of Zn-dendrite growth in Zn-polyaniline batteries were studied by scanning electron micrograph and cyclic voltammetry. The results show that Triton X-100 in the region of 0.02–500 ppm in the electrolyte containing 2.5 M ZnCl2 and 2.0 M NH4Cl with pH 4.40 can effectively inhibit zinc-dendrite growth during charge–discharge cycles of the battery and yield longer cycles.

Bioelectrochemical response of the polypyrrole xanthine oxidase electrode

Xanthine oxidase at pH values greater than its isoelectric point has been immobilized electrochemically in the polypyrrole film, which provides evidence for the doping mechanism of conducting polymers. The polypyrrole xanthine oxidase electrode formed in this manner has the kinetic behaviour of a free enzyme during the enzyme-catalysed reaction. The response current increases with increasing potential and temperature between 5 and 40°C. The activation energy of the enzyme-catalysed reaction is 88.7 kJ mol−1. The activity of the enzyme electrode is affected by pH. The optimum pH is 8.4. The result from the effect of pH on the maximum rate, i.e. maximum response current, indicates that the immobilized xanthine oxidase has two ionizing groups involved in the catalytic activity. The enzyme electrode has a fast response time and a high operational stability; its activity decreased by only 39% after 120 days. The response current increases linearly with increasing concentration of xanthine below 1.0 mmol dm−3. This enzyme electrode can be used to determine the concentration of xanthine in human blood.

A composite poly azure B /clay /enzyme sensor for the mediated electrochemical determination of phenols

Abstract The biosensor construction is based on the entrapment of polyphenol oxidase (PPO) within a laponite clay film coated on an underlying poly azure B film (PAB) modified electrode. The amperometric detection consists in the electrochemical reduction of o -quinone, the product of the PPO reaction. Upon oxidative electropolymerization of azure B in aqueous electrolyte, an electroactive PAB is formed on the electrode surface. This underlying poly azure B film acts as a highly efficient electron shuttle between the cathode and the enzymatically generated o -quinone. The resulting composite PAB/PPO–laponite biosensor enabled the direct determination of 4 nM ( −1 ) phenol, 0.4 nM (0.05 μg l −1 ) p -cresol and 0.2 nM (0.02 μg l −1 ) m -cresol in batch mode. Linearity of response over four orders of magnitude was achieved.

Bioelectrochemical response of the polyaniline ascorbate oxidase electrode

Abstract Ascorbate oxidase has been immobilized in the polyaniline film by an electrochemical method. The response current of the polyaniline ascorbate oxidase electrode is slightly affected by the applied potential from 0.36 to 0.45 V vs. SCE: also the response current of the enzyme electrode is a little sensitive to pH from 6.26 to 7.02, although thh immobilized ascorbate oxidase has an optimum pH at 6.8. The response current of the enzyme electrode at 0.40 V increases linearly with increasing concentration of ascorbic acid in the range 0.01–0.1 mM. Direct electrochemistry between the enzyme and the polyaniline film was observed. The narrow linear range between the response current and the substrate concentration is limited by the ascorbic acid diffusing through the polyaniline film at high concentration, then reacting on the underlying Pt. The response current of the enzyme electrode increases tremendously at both the phosphate buffer containing 0.125 mM ascorbic acid with pH 6.82, and phosphate buffer containing 0.1 mM ascorbic acid with pH 7.52. The enzyme electrode has a fast response time, and can be used to determine ascorbic acid at low concentrations.

The bioelectrochemical response of the polyaniline sarcosine oxidase électrode

Sarcosine oxidase has been immobilized in the polyaniline film by the electrochemical doping method. The response current of the polyaniline sarcosine electrode is a function of the applied potential, and increases with increasing pH in the region 7.0 to 8.75 and with increasing ionic strength of the buffer. The optimum pH of the immobilized sarcosine oxidase is 8.75. The optimum temperature is 39.6°C. The activation energy of the enzyme-catalyzed reaction is 32.0kJmo1. The apparent Michaelis-Menten constant K′m is 1.7mM. The enzyme electrode has a high operational stability. The response current of the enzyme electrode increases linearly with increasing concentration of sarcosine in the range below 1.0 mM, and is not affected by formaldehyde at concentrations less than 0.01 mM. Thus, the polyaniline sarcosine oxidase electrode can be used to determine sarcosine concentration.

Interconversion of polarons and bipolarons of polyaniline during the electrochemical polymerization of aniline

Abstract An in situ electron spin resonance (ESR)-electrochemical method was employed to study the interconversion of polarons and bipolarons of polyaniline during the electrochemical polymerization of aniline. The ESR signal was hardly observed for the first scan during electrolysis of the solution containing 20 mM aniline and 1 M HCl when the potential was swept from 0 to 1.07 V (vs saturated calomel electrode). However, an ESR signal with a single line was clearly observed when the potential was swept to about 0.95 V for the first scan during electrolysis of the solution containing 0.2 M aniline and 1 M HCl. For the second scan, from 0 V in the positive direction at the same potential range, the ESR intensity first increased and then a peak of the ESR signal, i.e. a maximum value of the ESR intensity, occurred at 0.26 V. This was caused by polyaniline polymerized on platinum due to the first scan; over the peak, the intensity of the ESR signal decreased quickly with increasing potential. The change in the ESR intensity with potential shows that a transfer of polarons in polyaniline to bipolarons occurs from 0.26 to 0.95 V. As the potential increased further, the intensity of the ESR signal increased again from 0.95 to 1.07 V, although this increment is small compared with the intensity change from 0 to 0.26 V. This is caused by the oxidation of aniline, since the intensity of the ESR signal of polyaniline in 1 M HCl solution in the absence of aniline always decreased with increasing potential from 0.26 to 1.07 V. After stopping electrolysis at 1.07 V, the intensity of the ESR signal increased quickly with decreasing potential of polyaniline and then increased slowly when the potential of polyaniline reached an equilibrium value. This indicates that bipolarons in polyaniline immediately transferred to polarons, followed by the establishment of an equilibrium between polarons and bipolarons. The potential range for formation of the ESR signal in the first scan during electrolysis of aniline is extended in the presence of NaCl.

The electrocatalytic characteristics of polyaniline synthesized in the presence of ferrocenesulfonic acid

Polyaniline(PAnFc) synthesized in the presence of ferrocenesulfonic acid can effectively catalyze the oxidation of catechol in the solution of pH 5.0. Evidence is that the anodic peak current on the cyclic voltammogram of the PAnFc electrode is 10 times as high as that on the bare platinum electrode and 4.7 times as high as that on the polyaniline (PAn) electrode synthesized in the absence of ferrocenesulfonic acid; the oxidation current of catechol on the PAnFc electrode is 20 times as high as that on the bare platinum electrode and 2 times as high as that on the PAn electrode at the constant potential; and the potential of the PAnFC electrode decreases with time during the electrolysis of catechol at the constant current.

Improvement in selectivity and storage stability of a choline biosensor fabricated from poly(aniline-co-o-aminophenol)

A choline biosensor was fabricated by using electrochemical doping to immobilize choline oxidase in poly(aniline-co-o-aminophenol) film that exhibits a good electric activity over a wide pH range. Using cyclic voltammetry, impedance measurement and scanning electron microscopy characterized the poly(aniline-co-o-aminophenol) film doped with choline oxidase. The amperometric detection of choline is based on the oxidation of the H2O2 enzymatically produced on the choline biosensor. The choline biosensor has a lower potential dependence. Thus, its operational potential was controlled at a low potential of 0.40 V (vs.SCE). The response current of the choline biosensor increases with increasing temperature from 277.1 to 308.1 K. An apparent activation energy of 30.8 kJ mol(-1) was obtained. The choline biosensor has a wide linear response range from 1x10(-7) to 1x10(-4) M choline with a correlation coefficient of 0.9999 and has a high sensitivity of 127 microA cm(-2), at 0.40 V and pH 8.0. The response time of the biosensor is 15-25 s, depending on the applied potentials. An apparent Michaelis constant and an optimum pH for the immobilized enzyme are 1.8 mM choline and 8.4, respectively, which are very close to those of choline oxidase in solution. The effect of selected organic compounds on the response of the choline biosensor was studied. Together, these findings show that the choline biosensor exhibits a better selectivity to interfering species and a better storage stability.

Electrochemical oxidation of glucose on gold nanoparticle-modified reduced graphene oxide electrodes in alkaline solutions

A given amount of gold is electrodeposited on the reduced graphene oxide (RGO)/glassy carbon (GC) electrodes to form Au/RGO/GC electrodes, which are carried out at different potentials. The Au/RGO/GC electrode with Au loading of 250 μg cm-2 prepared at a constant potential of -0.30 V exhibits the best electrocatalytic activity to glucose oxidation in alkaline solutions because of homogeneous dispersion of gold nanoparticles with smaller sizes. This electrode shows long-term stability, rapid charge transfer ability, and higher current density compared to other gold electrodes reported previously.