Facilitated electron transfer for myoglobin in surfactant–polymer 2C12N+PVS− composite films on pyrolytic graphite electrodes

Direct electrochemistry and electrocatalysis of myoglobin immobilized on a hexagonal mesoporous silica matrix

The direct electrochemistry of myoglobin (Mb) immobilized on a hexagonal mesoporous silica (HMS)-modified glassy carbon electrode was described. The interaction between Mb and HMS was investigated by using Fourier transfer infrared spectroscopy, nitrogen adsorption isotherm, and cyclic voltammetry. Two couples of redox peaks corresponding to Fe(III) to Fe(II) conversion of the Mb intercalated in the mesopores and adsorbed on the surface of the HMS were observed with the formal potentials of -0.167 and -0.029V in 0.1M, pH 7.0, phosphate buffer solution, respectively. The electrode reaction showed a surface-controlled process with one proton transfer. The immobilized Mb displayed good electrocatalytic responses to the reduction of both hydrogen peroxide (H(2)O(2)) and nitrite (NO(2)(-)), which were used to develop novel sensors for H(2)O(2) and NO(2)(-). The apparent Michaelis-Menten constants of the immobilized Mb for H(2)O(2) and NO(2)(-) were 0.065 and 0.72mM, respectively, showing good affinity. Under optimal conditions, the sensors could be used for the determinations of H(2)O(2) ranging from 4.0 to 124microM and NO(2)(-) ranging from 8.0 to 216microM. The detection limits were 6.2x10(-8) and 8.0x10(-7)M at 3 sigma, respectively. The HMS provided a novel matrix for protein immobilization and the construction of biosensors via the direct electron transfer of immobilized protein.

Assembly of electroactive layer-by-layer films of myoglobin and ionomer poly(ester sulfonic acid)

Layer-by-layer films were assembled on solid substrates by alternate adsorption of negatively charged ionomer poly(ester sulfonic acid) or Eastman AQ55 from its aqueous dispersion and positively charged myoglobin (Mb) from its solution at pH 4.5. The film assembly process was monitored by cyclic voltammetry (CV), UV-vis spectroscopy, and quartz crystal microbalance (QCM). [AQ/Mb](n) films grown on pyrolytic graphite (PG) electrodes showed a pair of well-defined and nearly reversible CV peaks at about -0.20 V vs Ag/AgCl in pH 5.5 buffers, characteristic of the Mb heme Fe(III)/Fe(II) redox couple. Although the amount of Mb adsorbed in each bilayer was essentially the same, the fraction of electroactive Mb decreased dramatically with an increase of bilayer number (n). Soret absorption bands of [AQ/Mb](n) films on glass slides suggest that Mb in the films retains its native state in the medium pH range. Trichloroacetic acid, oxygen, and hydrogen peroxide were electrochemically catalyzed by [AQ/Mb](6) films with significant lowering of reduction overpotential.

Direct electrochemistry and electrocatalysis with horseradish peroxidase in Eastman AQ films

Stable films made from ionomer poly(ester sulfonic acid) or Eastman AQ29 on pyrolytic graphite (PG) electrodes gave direct electrochemistry for incorporated enzyme horseradish peroxidase (HRP). Cyclic voltammetry of HRP-AQ films showed a pair of well-defined, nearly reversible peaks at about -0.33 V vs. SCE at pH 7.0 in blank buffers, characteristic of HRP heme Fe(III)/Fe(II) redox couple. The electron transfer between HRP and PG electrode was greatly facilitated in AQ films. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (k(s)) and formal potential (E(o')) were estimated by fitting the data of square-wave voltammetry (SWV) with nonlinear regression analysis. Reflectance absorption infrared (RAIR) and UV-Vis absorption spectra demonstrated that HRP retained a near native conformation in AQ films. The embedded HRP in AQ films retained the electrocatalytic activity for oxygen, nitrite and hydrogen peroxide. Possible mechanism of catalytic reduction of H(2)O(2) with HRP-AQ films was proposed.