Biomedical Engineering Reference
In-Depth Information
suitable biosensing matrix due to its good conductivity, high stability, and good
biocompatibility.
8.5.4.5.1 Solvent Evaporation
The CNTs-chitosan-enzyme nanobiocomposite-modified electrode was fabricated by
casting CNTs-chitosan-enzyme mixture solution on the surface of a GCE and evaporat-
ing the solvent under room temperature in air. A facilely fabricated amperometric biosen-
sor by entrapping laccase into MWCNTs-chitosan composite film has been developed by
Liu et al. The system is in favor of accessibility of the substrate to the active site of laccase,
and thus the affinity to the substrate is improved greatly. On the other hand, the system
can be applied in the fabrication of biofuel cells as the cathodic catalyst on the basis of its
good electrocatalysis for oxygen reduction. More importantly, operation of the biosensor
in pH 6.0 solution overcomes the restriction of fungi laccase exhibiting bioactivity in a
solution of pH < 5.0 [138].
Tsai et al. used a composite of multiwalled CNTs-chitosan as a matrix for the entrap-
ment of lactate dehydrogenase (LDH) onto a GCE in order to fabricate an amperometric
biosensor. It was shown that the enzyme is homogeneously immobilized within
MWCNT-CHIT-LDH. The inclusion of MWCNT within MWCNT-CHIT-LDH exhibits the
abilities to raise the current responses, to decrease the electrooxidation potential of
β-nicotinamide adenine dinucleotide, reduced form (NADH), and to prevent the electrode
surface fouling [139].
The application of the composites of MWNTs and core-shell organosilica-chitosan-
cross-linked nanospheres as an immobilization matrix for the construction of an ampero-
metric hydrogen peroxide (H
2
O
2
) biosensor was described by Chen et al. MWNTs and
positively charged organosilica-chitosan nanospheres were dispersed in acetic acid solu-
tion (0.6 wt%) to achieve organosilica-chitosan-MWNTs composites, which were cast
onto a GCE surface directly. And then, HRP, as a model enzyme, was immobilized onto it
through electrostatic interaction between oppositely charged organosilica-chitosan
nanospheres and HRP. The direct electron transfer of HRP was achieved at HRP/
organosilica-chitosan/MWNTs/GCE, which exhibited excellent electrocatalytic activity
for the reduction of H
2
O
2
. Moreover, the proposed biosensor displayed a rapid response
to H
2
O
2
and possessed good stability and reproducibility. When used to detect H
2
O
2
con-
centration in disinfector samples and sterilized milks, respectively, it showed satisfactory
results [140].
8.5.4.5.2 Chemical Cross-Linking Methods
Further stabilization of the chitosan film containing SWNT (CHIT-SWNT) was performed
by chemical cross-linking with GA, and free aldehyde groups produced a substrate used
for covalent immobilization of galactose oxidase [141]. The use of dispersed CNTs as a
transducer allows a very rapid detection of galactose with a sample throughput of 150 h
−1
while retaining high selectivity and sensitivity. Moreover, the biosensor is mechanically
robust, reliable and has been successfully used for the detection of galactose in blood
plasma.
A graphite-epoxy resin composite electrode modified with functionalized MWCNTs
immobilized by EDC and NHS in a chitosan matrix was prepared by Ghica et al. It was
then used as a base for GOx immobilization by the simple method of cross-linking with
GA using BSA as a carrier protein. The biosensor showed good reproducibility and
good stability under continuous use and storage conditions. Selectivity against a
number of interferences, such as wines, juices, or blood, was also good and the ascorbic
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