Biomedical Engineering Reference
In-Depth Information
oxide electrodes [95-96]. The electrochemical behavior is unstable and extremely
sensitive to the sample purity and the conditions of the electrode surface [97]. Great
efforts have been made to enhance its electron transfer by using mediators, promoters,
or some special modifi ed materials [98-102]. Among these, surfactant micelles have
been shown to be effi cient in promoting the electron transfer of Mb. Extensive studies
on electrochemistry of Mb using various surfactants such as DDAB, lipids, LB fi lms,
etc. [99, 102-103] demonstrate that the surfactant fi lm can effectively enhance the rate
of electron transfer between the protein and the electrode.
Polyelectrolyte-surfactant complex fi lms can be viewed as a new type of biomem-
brane-like fi lms, which promote the electron transfer of proteins. Such complexes
combine in unique ways the properties of amphiphilic surfactants with those of poly-
mers. The polymeric components can provide mechanical strength and good stability,
while the surfactants retain their tendency to assemble in bilayered structures [104-105].
Proteins in this kind of fi lm show well-behaved electrochemistry and good stability
[106-107]. Since these fi lms are amenable to a variety of electrochemical and other
experiments for a longer time than surfactant fi lms, they may have more practical
applications as biosensors or bioreactors. Wang and Hu [108] prepared the polyelec-
trolyte-surfactant complex DHP-PDDA by reacting the anionic surfactant dihexade-
cylphosphate (DHP) with polycationic poly(diallyldimethylammonium) (PDDA). Thin
fi lms made from DHP-PDDA on solid substrates demonstrated an ordered multibilayer
structure by XRD and DSC. Mb incorporated in DHP-PDDA fi lms on PG electrodes
showed a pair of well-defi ned and nearly reversible CV peaks for the Mb Fe(III)/Fe(II)
couple, which refl ected that the electron transfer between Mb and PG electrodes was
greatly facilitated in the fi lm microenvironment. Mb could act as an enzyme-like cat-
alyst in DHP-PDDA fi lms as demonstrated by catalytic reduction of trichloroacetic
acid, nitrite, and oxygen with a decrease in the electrode potentials required.
A series of inorganic porous materials, such as clay, montmorillonite, etc., have been
shown to be promising as immobilization matrices. They have the advantages of high
mechanical, thermal, and chemical stability and good adsorption and penetrability due
to their regular structures and appreciable surface areas. In addition, the unique struc-
tural and catalytic properties of molecular sieves for structuring an electrochemical/
electron-transfer environment and resistance to biodegradation have attracted considera-
ble attention. Among those protein immobilization matrices, molecular sieves can com-
bine with proteins through physical or chemical action. Ju and Dai [109] used a kind
of mesoporous silica material, hexagonal mesoporous silica (HMS), which processes
a porous size of nanoscale dimension to make it more suitable for enzyme intercala-
tion and loading. When it is immersed into aqueous solution, the vacancy of the hex-
agonal mesopores is diffi cult to be saturated by water due to its hydrophobic surface.
Thus, it can be used for the intercalation of protein. The direct electrochemistry of Mb
immobilized on an HMS-modifi ed glassy carbon electrode was described in their work.
Two couples of redox peaks corresponding to Fe(III) to Fe(II) conversion of Mb inter-
calated in the mesopores and adsorbed on the surface of the HMS were observed with
the formal potentials of
0.029 V in 0.1 M, pH 7.0, phosphate buffer solu-
tion, respectively. The electrode reaction showed a surface-controlled process with one
0.167 and
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