Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 372

chitosan-NiFe 2 O 4 nanoparticles on a GCE. Because of the excellent biocompatibility of
the film with GOx, the catalytic activity of the immobilized GOx was well retained and
the direct electron transfer with the underlying GCE could be realized. The resulting
glucose biosensor exhibited a fast response, high sensitivity, low detection limit, and
long-term stability [103].
Pure magnetic particles are likely to form a large aggregation, alter magnetic proper-
ties, and can undergo rapid biodegradation when they are directly exposed to the biologi-
cal system. It has been demonstrated that the formation of a passive coating of inert
materials such as silica on the surfaces of iron oxide nanoparticles could prevent their
aggregation in liquid and improve their chemical stability. Qiu et al. developed a novel
amperometric glucose biosensor by entrapping GOx in a chitosan composite doped with
ferrocene monocarboxylic acid-modified magnetic core-shell Fe 3 O 4 /SiO 2 nanoparticles. It
is shown that the obtained magnetic bionanoparticles attached to the surface of a CPE
with the employment of a permanent magnet showed excellent electrochemical charac-
teristics and at the same time acted as a mediator to transfer electrons between the enzyme
and the electrode [104].
8.5.4.1.2 Magnetic Chitosan Beads/Microspheres by the Phase-Inversion Technique
Bayramoglu et al. prepared cross-linked magnetic chitosan beads by the phase-inver-
sion technique in the presence of ECO under alkaline conditions, and used it for cova-
lent immobilization of laccase. The magnetic chitosan beads were in spherical form
mostly in the size range of ca. 1.0 mm and had a porous surface structure. The porous
surface properties of the magnetic chitosan beads would favor a higher immobilization
capacity for the enzyme due to an increase in the surface area. The laccase immobilized
on magnetic chitosan beads was very effective in removal of textile dyes from aqueous
solution, which creates an important environmental problem in the discharged textile
dying solutions [105].
Similarly, magnetic chitosan microspheres were prepared with reversed-phase suspen-
sion methodology (combining the phase-inversion technique with the emulsification pro-
cess) using GA as a cross-linking reagent for the enzyme immobilization. The microspheres
have well-shaped spherical form with a smooth surface, and their mean particle size was
5.0 μm with a narrow size distribution. Laccase was immobilized on magnetic chitosan
microspheres by adsorption and cross-linking with GA. The thermal, operational, and
storage stabilities of the enzyme were improved greatly after they were immobilized on
the surface of magnetic chitosan microspheres [106].
8.5.4.1.3 Magnetic Chitosan Nanoparticles Prepared by the Ionization Gelation Method
The preparation processes of magnetic particles in the water/oil system might impose
limitations on practical applications in water systems. The problem with this method is
that productivity is low; in addition, it uses a number of surfactant and cosurfactant com-
pounds that are harmful to the environment. An efficient immobilization of β-d-
galactosidase from Aspergillus oryzae has been developed by using magnetic chitosan
nanoparticles as the support, which were prepared by electrostatic adsorption of chitosan
on the surface of Fe 3 O 4 nanoparticles and subsequently adding TPP. Fe 3 O 4 nanoparticles
could adsorb chitosan molecules on their surface due to the high surface energy. β-d-
Galactosidase was covalently immobilized onto the nanocomposites using GA as an acti-
vating agent. As a result, the immobilized enzyme presented a higher storage, pH, and
thermal stability than the soluble enzyme [107].