Enzyme Immobilization on Chitosan-Based Supports - Chitosan Based Hydrogels: Functions and Applications - page 376

biosensor to H 2 O 2 concentration has long-range linearity. In addition, it was demonstrated
that the presence of methylene blue further enhances the sensitivity of the designed H 2 O 2
electrochemical biosensor [117].
8.5.4.2.4 Chitosan-CeO 2 Nanocomposite
CeO 2 nanoparticles as an important n-type semiconductor have attracted much interest
owing to their unique properties, including high mechanical strength, oxygen ion conduc-
tivity, high IEP, biocompatibility, and high adsorption capability and oxygen storage capac-
ity for the development of desired biosensors. NanoCeO 2 -chitosan nanocomposite film
was fabricated onto an ITO-coated glass plate to immobilize cholesterol oxidase (ChOx)
via physiosorption for cholesterol detection. Electrochemical studies reveal that the pres-
ence of NanoCeO 2 results in an increased electroactive surface area for ChOx loading,
resulting in enhanced electron transport between ChOx and the electrode [118].
Mixed ceria-based oxide systems have even higher electrocatalytic activities and oxy-
gen storage capacity. Such examples include binary and tertiary mixtures of CeO 2 /TiO 2 ,
CeO 2 /ZrO 2 , and CeO 2 /ZrO 2 /TiO 2 . These characteristics suggest that ceria and mixed
ceria-titania oxides could potentially be used as “oxygen-rich” electrode materials for
oxidase enzymes that could avoid or minimize the problems associated with variations
in the oxygen level for enzymes that are using oxygen as a cosubstrate, offering the pos-
sibility of operation in “oxygen-free” environments. Andreescu and coworkers first stud-
ied the electrochemical characteristics of the CeO 2 /TiO 2 -modiied GCE. They used a
positively charged natural biopolymer, chitosan, as a binder. The ceria and titania oxides
embedded within the chitosan film and the enzymatic reaction. It was demonstrated
that mixed TiO 2 /Ce O 2 hybrid composites provide enhanced analytical characteristics
to tyrosinase biosensors, including high sensitivity and the possibility of operation in
“oxygen-free” conditions [119].
8.5.4.3 Metal Nanoparticles-Chitosan Nanocomposite
Metal nanoparticles, such as silver (Ag), gold (Au), platinum (Pt), and palladium nano-
particles, have attracted much interest in the construction of biosensors due to their
unique chemical and physical properties. Gold nanoparticles, in particular, have been
widely used to construct biosensors because of their excellent ability to immobilize
biomolecules and at the same time retain the biocatalytic activities of those biomolecules.
Many kinds of biosensors, such as enzyme sensors, immunosensors, and DNA sensors,
with improved analytical performances have been prepared based on the application of
gold nanoparticles (GNPs).
It is well known that some functional groups such as cyano (-CN), mercapto (-SH), and
amino (-NH 2 ) groups have a high affinity for Au. Therefore, a nano-Au/chitosan compos-
ite was prepared via covalent bonds between GNPs (nano-Au) and the -NH 2 groups of the
chitosan. This material combined the advantages of inorganic nanoparticles and an organic
polymer. Moreover, GNPs have been shown to provide useful interfaces at which the redox
processes of molecules involved in biochemical reactions of analytical significance can be
electrocatalyzed.
8.5.4.3.1 Electrodeposition Method
Luo et al. have developed two kinds of biosensors based on the excellent properties of
chitosan and GNPs. Gold nanoparticles, which were prepared in advance through the
reduction of HAuCl 4 with citrate, can be self-assembled onto electrodeposited chitosan