Biomedical Engineering Reference
In-Depth Information
only facilitate the stabilization of the enzymes but also ensure diffusion of substrate
and efficient electron transfer [32]. Many methods have been employed in the immobi-
lization of enzymes, but it is difficult to control the amount and spatial distribution of
these biocatalysts. Compared with these methods, the LBL method presents great advan-
tages. For instance, the amount of enzyme immobilized can be controlled by adjusting the
number of layers, and as all the adsorption steps are conducted in aqueous solution
and no chemical reactions are involved, enzymes can be immobilized without being
denatured.
Appropriate pH values relative to the isoelectric point of enzymes to be immobilized
result in net positive or negative charges as required, to facilitate the LBL method. Several
works have been devoted to the immobilization of enzymes by LBL method [4,16,33-36].
A monomolecular layer was formed after each adsorption step, and the enzymes incorpo-
rated in these multilayer films showed long-term storage stability and relatively high ther-
mostability after heat treatment [33]. The applications of LBL adsorption for biosensors are
listed in Table 8.1.
8.5
Conclusions
The LBL technique has many potential applications in the biosensor area. Alternate
adsorption of various enzymes and synthetic or natural polyions on an electrode surface
has been used to fabricate biosensor systems. Finely controlled multilayer films
were constructed that were composed of enzymes and redox polyelectrolytes, and
the enzymes retained their activities in a multilayer assembly formed by using the
LBL method.
TABLE 8.1
The Application of Layer-by-Layer Adsorption for Biosensors
Substrate
Electrode
Polyanion
Polycation
Reference
Fructose
Au
Fructose dehydrogenase
Poly[(vinylpyridine)Os(bpy)
2
Cl
[36]
Horseradish peroxidase (HRP)
Glucose
ITO
Glucose oxidase
Poly(allylamine)hydrocloride
[37]
Prussian Blue
Cholesterol
Au
Cholesterol oxidase
Microperoxidase
[38]
Poly(styrenesulfonate)
Catechol
Glassy carbon
Polyphenol oxidase
Chitosan
[39]
Poly(styrenesulfonate)
IgG
Choline
Pt
Choline oxidase
Poly(ethyleneimine)
[40]
Poly (diallyldimethylammonium
chloride)
Cholesterol
ITO
Cholesterol oxidase
Poly(ethyleneimine)
[41]
Cholesterol esterase
Poly(styrenesulfonate)
DNA
Carbon
Algnic acid
Poly(ethyleneimine)
[42]
Streptavidin
Polyethyleneimine)-ferrocene
