Yanxia Xu

Single-chain surfactant monolayer on carbon paste electrode and its application for the studies on the direct electron transfer of hemoglobin

A variety of single-chain surfactants with different charge properties and tail lengths can spontaneously adsorb on the hydrophobic surface of carbon paste electrode and form stable monolayers on the electrode surface. Hemoglobin (Hb) was successfully immobilized on these surfactant monolayers to form stable protein-surfactant composite films regardless of the charge and the tail length of surfactants. The resulting surface-confined Hb exhibited well-defined direct electron-transfer behaviors in all positively, neutrally and negatively charged surfactant films, suggesting the important role of hydrophobic interactions in the adsorption of Hb on surfactant films. When the density of surfactant monolayers was controlled to be the same, Hb was found to possess a better direct electron-transfer behavior on monolayers of cationic surfactants with a longer tail length. This, in combination with the tunneling effect in the direct electron transfer of Hb on surfactant films, demonstrated that the adsorption of Hb on surfactant monolayers may be mainly achieved by the partial intercalation of Hb in the loose structures of surfactant films through hydrophobic interactions between the alkane chains of surfactants and the hydrophobic regions of Hb. The native conformation of Hb adsorbed on these surfactant films was proved to be unchanged, reflected by the unaltered ultraviolet-visible (UV-vis) and reflection-absorption infrared (RAIR) spectra, and by the catalytic activity toward hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) in comparison with the free Hb molecules.

Direct electrochemistry and electrocatalysis of heme-protein based on N,N-dimethylformamide film electrode.

The heme-protein including myoglobin (Mb), hemoglobin (Hb) and horseradish peroxidase (HRP) were immobilized on normal graphite electrode by using N,N-dimethylformamide (DMF). The proteins undergo direct electron-transfer reactions. The current is linearly dependent on the scan rate, indicating that the direct electrochemistry of heme-protein in that case is a surface-controlled electrode process. The E degrees s are linearly dependent on solution pH (redox-Bohr effect), indicating that the electron transfer was proton-coupled. Ultraviolet-visible (UV-vis) and reflection-absorption infrared (RAIR) spectra suggest that the conformation of proteins in the presence of DMF are little different from that proteins alone the conformation changes reversibly in the range of pH 3.0-10.0. The catalytic activity of proteins were examined by hydrogen peroxide and nitrite.

Direct electron-transfer of native hemoglobin in blood: Kinetics and catalysis

A novel approach that uses nature biological tissues, fish blood, for the study of the direct electron-transfer of hemoglobin and its catalytic activity for H(2)O(2) and NO(2)(-) is observed. The direct electron-transfer of hemoglobin in red blood cells in fish blood on glassy carbon electrode was observed for the first time. By simply casting fish blood on GC electrode surface and being air-dried, a pair of well-defined redox peaks for HbFe (III)/HbFe (II) appeared at about -0.36 V (vs SCE) at the fish blood film modified GCE in a pH 7.0 phosphate buffer solution. Ultraviolet visible (UV/VIS) characterization and the enhancement of the redox response of Hb by adding pure Hb in fish blood suggested that Hb preserved the native second structures in the fish blood film. Optical micrographs showed that the RBCs retained its integrity in blood. Hb in blood/GCE maintained its activity and could be used to electrocatalyze the reduction H(2)O(2) and NO(2)(-).

Direct electrochemistry and electrocatalysis of hemoglobin immobilized by methacrylic acid

The direct electrochemistry of hemoglobin (Hb) incorporated in methacrylic acid (MAA) film on a paraffin-impregnated graphite electrode (PIGE) was described. A pair of well-defined and quasi-reversible cyclic voltametric peaks are obtained. The formal potentials (E0′) linearly depend on the pH of solution, indicating that the electron transfer was proton-coupled. Ultraviolet-visible (UV-Vis) spectra showed that the secondary structure of Hb in the MAA film was similar to individual Hb. The immobilized Hb retained its biological activity well and exhibited a nice response to the reduction of both NO2−, and H2O2, on the basis of which a new biosensor has been developed.

Biosensors based on direct electron transfer of protein

This chapter focuses on the biosensors based on direct electron transfer of protein. In such biosensors, the absence of mediator is the main advantage that provides them with superior selectivity. They operate in a potential window closer to the redox potential of the enzyme and are therefore less prone to interfering reaction, and because of the lack of yet another reagent in the reaction sequence, the reaction system is simplified. Another attractive feature of such sensors is the possibility of modulating the desired properties of an analytical device by using protein modification with genetic or chemical engineering techniques on one hand and novel interfacial technologies on the other. The physical adsorption of protein onto the surface of an electrode is a simple immobilization method and the adsorption is obtained by volatilizing the buffers containing proteins. Protein is immobilized by combining with the surface of the electrode through a covalent bond, and this process requires low temperature (0oC), low ion intensity, and physiological pH conditions. Achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters has also enabled great accomplishments. A novel way to enhance the electron-transfer rates between Hemoglobin (Hb) and the electrode has been provided by nanotechnology, in which nanocrystalline TiO 2 film has been proposed as the interface for the immobilization of Hb. Biosensors based on direct electron transfer of proteins can determine many small molecules like H 2 O 2 , O 2 , NO, nitrite, and small organic peroxide and can also determine glucose, alcohol, and amino acids by coimmobilization of the corresponding oxidase on the electrode surface.