Biomedical Engineering Reference
In-Depth Information
surface area of nanomaterials is likely to provide a better matrix for the immobilization of
the desired enzyme, leading to increased enzyme loading per unit mass of particles. The
enzyme-attached nanoparticles facilitate enzymes to act as free enzymes in solution that in
turn provide enhanced enzyme-substrate interaction by minimizing potential aggregation
of the free enzyme.
8.5.4.1 Magnetic Chitosan Support
In recent years, magnetic particles have shown great potential in protein and enzyme
immobilization, bioseparation, immunoassays, and so on. Used as the support material,
magnetic carriers can be quickly separated from the reaction medium and effectively
controlled by applying a magnetic field, and thus the catalytic efficiency and stability
properties of enzyme can be greatly improved. Moreover, magnetic nanoparticles exhibit
large surface-to-volume ratio, high surface reaction activity, high catalytic efficiency,
strong adsorption ability and unique fast electron transfer between the electrode and the
active site of an enzyme that can be helpful for obtaining improved stability and sensitiv-
ity of a biosensor. To date, magnetic nanoparticles have been used for the immobilization
of many enzymes, such as lipase, protease, glucoamylase, α-amylase, penicillin G acylase
and GOx.
The preparations of magnetic chitosan were mostly prepared by two steps with the sus-
pension cross-linking technique: the first step is the synthesis of Fe
3
O
4
particles and the
second one is the binding of Fe
3
O
4
and chitosan; the size of the particles with this method
was mostly on the micrometer scale. For biosensors, a mixture of Fe
3
O
4
nanoparticles and
chitosan solution could be directly dried and cast into a composite film [101]. Moreover,
several methods have been developed to synthesize magnetic chitosan nanoparticles such
as emulsion polymerization and
in situ
polymerization. For
in situ
polymerization, a con-
stitution of microemulsion containing chitosan and ferrous salt was suggested as the reac-
tion system. With the microemulsion system, the magnetic chitosan nanoparticles were
in
situ
prepared by controlling the precipitation of chitosan and Fe
3
O
4
with an NaOH solution
as the solidification solution [102].
8.5.4.1.1 Nanobiocomposite Films by Solvent Evaporation
One very simple preparation method of magnetic chitosan supports for biosensors is the
solvent evaporation/casting method. It was reported that Ur and GLDH are co-immobi-
lized onto a superparamagnetic iron oxide (Fe
3
O
4
) nanoparticles-chitosan-based nanobio-
composite film deposited onto an indium-tin oxide (ITO)-coated glass plate via physical
adsorption for urea detection. Fe
3
O
4
nanoparticles (<22 nm) are prepared using the copre-
cipitation method. Chitosan-Fe
3
O
4
hybrid nanobiocomposite films have been fabricated by
uniformly dispersing a solution of chitosan and Fe
3
O
4
nanoparticles onto an ITO surface
and allowing it to dry at room temperature. It is shown that the presence of iron oxide
nanoparticles results in increased active surface area of the nanobiocomposite for immobi-
lization of enzymes, enhanced electron transfer, and increased shelf-life of the nanobio-
composite electrode [101].
Ferrites are a group of important magnetic materials for technological applications
and fundamental studies. Nickel ferrite (NiFe
2
O
4
) with an inverse spinel structure
shows ferrimagnetism that originates from the magnetic moment of antiparallel spins
between Fe
3+
ions at tetrahedral sites and Ni
2+
ions at octahedral sites. The quantitative
cytotoxicity test verified that both uncoated and chitosan-coated NiFe
2
O
4
nanoparticles
had noncytotoxicity. Luo et al. fabricated a glucose biosensor by integrating GOx with
Search WWH ::
Custom Search