Biomedical Engineering Reference
In-Depth Information
Filtration of
GOx (12.5 μM) +
0.1% chitosan
1% chitosan
(Protective layer)
Al
2
O
3
/GOx/Chit
membrane
Al
2
O
3
membrane
GOx
Al
2
O
3
Chitosan network
Cross-sectional view of the
Al
2
O
3
/GOx/Chit membrane
Figure 8.10
Immobilization of GOx in nanoporous alumina membranes. (From Darder, M. et al. 2006.
Thin Solid Films
495:
321-326. With permission.)
the pore size and the membrane thickness by changing the anodizing voltage and the
amount of transferred charge, respectively. These membranes were used to encapsulate
GOx by procuring an external coverage with a thin layer of the biopolymer chitosan, which
avoids enzyme leaching. The enzyme-modified membranes have been attached to the sur-
face of a platinum electrode for the biosensor construction. GOx was immobilized on
nanoporous alumina membranes by following the steps depicted in Figure 8.10.
A relatively higher amount of enzyme is retained within the pores of the membrane as
the surface area of the asymmetric porous structure of the membrane increases. The thin
film incorporating the enzyme is displayed on the electrode surface, without interrupt-
ing the diffusion of the product of the enzymatic reaction toward the electrode surface
due to its thickness on the micrometer level and the suitable properties of the chitosan
matrix. Experimental results indicate that the control of membrane dimensions, pore
diameter, and thickness is a key factor in the performance of these GOx/thin film-based
biosensors [88].
8.5.3 Chitosan-based Polyelectrolyte Complexes
Many investigators have suggested ionic complexation of chitosan (having a positive
charge) with polyanion to form PECs and LBL self-assembly films/microcapsules for
enzyme immobilization. Gel beads/microcapsules were achieved by adding an anionic
polyelectrolyte solution dropwise into an acidic chitosan solution. Enzyme immobili-
zation is achieved here by preparing an enzyme-containing anionic polyelectrolyte
solution prior to gelation. Of course, reversed chitosan polyanions, such as chitosan-
alginate, a PEC for enzyme immobilization, have also been reported. Complexation
network/films were obtained by precipitating a mixture of chitosan and polyanion.
The technique of LBL self-assembly is based on the sequential deposition of interactive
polymers from their solutions by electrostatic, van der Waals, hydrogen bonding, and
charge-transfer interactions. The development of LBL self-assembly on colloidal tem-
plates has attracted considerable attention in biotechnology and promises solutions to
many problems in the fields of drug delivery, biosensors, and microreactors, as well as
bioseparations.
Search WWH ::
Custom Search