Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 340

made from two or more constituents with significantly different physical or chemical
properties from their components, which remain separate and distinct within the finished
structure. A synergism results in material properties, which are unique prior to used con-
stituents, could be presented. Among the composites, organic-inorganic hybrid nanobio-
composites have attracted much interest as a new class of materials that utilize the synergy
of organic and inorganic components to obtain improved characteristics.
The benefits of using composites mainly include the following: (1) better mechanical
properties: organic-inorganic hybrid materials can effectively eliminate the brittleness of
pure inorganic materials and the swelling property of some pure polymers or hydrogels;
(2) enhancement of the surface biocompatibility of polymer materials or inorganic sup-
ports by the addition of biomaterials; (3) the existing problem of aggregation of inorganic
nanoparticles can be overcome by modifying these nanoparticles using polymers; (4) ease
of chemical modification via reactive functional groups in organic materials: in hybrid
nanobiocomposites, surface fuctionalization of nanoparticles allows their covalent attach-
ment and self-assembly on surfaces that can be used for loading the desired biomolecules
in a favorable microenvironment; (5) versatile enzyme immobilization methods: numer-
ous enzymes have been stabilized by entrapment in a composite support; (6) ease of prepa-
ration in different configurations: for example, composite films for biosensors were
fabricated by simple solvent evaporation.
For example, despite the many advantages of a silica sol-gel immobilization matrix, the
brittleness of the silica sol-gel matrix is a major obstacle in their wide adoption as an immo-
bilization matrix for biomolecules. In order to improve the performance of silica sol-gel hybrid
materials, some polymers such as poly(ethylene oxide) (PEO), polyhydroxyl, hydrophobic
poly(vinylpyridine), and poly(vinyl alcohol) (PVA) were hybridized into a silica sol-gel matrix.
Miao and Tan reported on the first attempt to develop an amperometric H 2 O 2 biosensor with
horseradish peroxidase (HRP) immobilized by the sol-gel/chitosan-inorganic-organic
hybrid film. It overcomes the shortcomings of a silica sol-gel matrix and the many amino
groups present in chitosan provide a biocompatible environment for enzyme immobilization
[16]. The carboxyl-containing nanofibers can be modified with chitosan or gelatin to build a
dual-layer biomimetic surface. The abundant reactive groups on the backbone of chitosan or
gelatin can provide sufficient bonding sites for enzyme immobilization. The tethering of chi-
tosan or gelatin increases the activity retention of immobilized lipase, with little sacrifice of
enzyme loading [17]. Immobilization of bioactive molecules onto surface-charged superpara-
magnetic nanoparticles (size ~25 nm) is of special interest, since the magnetic behavior of
these bioconjugates may result in improved delivery and recovery of biomolecules. Besides
this, the existing problem of aggregation and rapid biodegradation of Fe 3 O 4 nanoparticles
onto a given matrix containing biomolecules can perhaps be overcome by modifying these
nanoparticles using chitosan by preparing a hybrid nanobiocomposite (see Section 8.5.3.1).
8.2.3 Methods of enzyme immobilization on Chitosan-based Supports
Based on the characteristics of chitosan/chitin, methods of enzyme immobilization can be
divided into six groups:
I. Adsorption of the enzyme on the support: (I-i) physical adsorption; (I-ii) affinity
by the metal ion; (I-iii) affinity by the dye; and (I-iv) affinity by the chitin-binding
domain (ChBD).
II. Chemical cross-linking by covalent binding: (II-i) in the presence of an enzyme
solution; (II-ii) in the absence of an enzyme solution (the enzyme may be absorbed