Biomedical Engineering Reference
In-Depth Information
reported on cholesterol biosensor based on the cholesterol oxidase-sol-gel film on a pla-
tinized CNT electrode. Owing to the high electrocatalytic activity of the platinized CNT
electrode toward the reduction of hydrogen peroxide, the biosensor can detect as low as
1.6
M cholesterol.
Ruianes and Rivas [26] reported on lactate and phenol biosensors based on carbon nan-
otube paste electrodes containing lactate oxidase or polyphenol oxidase. The promoted
electron-transfer reaction of hydrogen peroxide at the CNT-based paste electrode offered
a rapid low-potential (-0.10 V) detection of the substrate. CNT-based lactate biosensor can
detect as low as 0.3 mM lactate; it covers not only physiological values of lactate but also
pathological values. In addition, CNT-based phenol biosensor can sensitively detect phe-
nol with a detection limit of 500 nM; this reflects that the CNT-modified electrode
enhanced electrocatalytic detection of the enzymatically generated catechol-quinone.
13.3.1.3 Dehydrogenase-Based Biosensors
Dehydrogenase-based biosensor relies on the coimmobilization of dehydrogenase enzyme
and their nicotinamide adenine dinucleotide (NAD
) cofactor on an electrode. The enzy-
matically liberated NADH in the presence of substrates is electrochemically detected.
Problems associated with the anodic detection of NADH are the large overpotential
required for its oxidation at ordinary carbon electrode and surface fouling associated with
the accumulation of the reaction products. Therefore, CNT-based electrode can take
advantages of excellent electrocatalytic activity and minimized surface-fouling effect asso-
ciated with CNTs. As discussed previously, the CNT-modified electrodes exhibit substan-
tial decreases in the anodic peak potential as well as increases in current signals. Wang and
Musameh [27] reported on a CNT-based ethanol amperometric biosensor based on the
coimmobilization of ADH and its NAD
cofactor within the CNT-Teflon composite
matrix. The marked decrease in the overvoltage for the oxidation of the liberated NADH
facilitates the development of low-potential ethanol biosensor with good selectivity and
sensitivity. Similar advantages are expected pertaining to the biosensing of lactate or glu-
cose in connection with lactate dehydrogenase or glucose dehydrogenase, respectively.
Gorski group [28] reported on the MWCNT-chitosan composite for glucose biosensor
based on dehydrogenase enzyme. MWCNTs were solubilized in aqueous solution of
biopolymer chitosan and the resulting solution was cast onto GC electrode. The
MWCNT-chitosan composite films facilitated the electrooxidation of NADH, and thus
required 0.3 V less overpotential than the GC for the NADH oxidation. The glucose dehy-
drogenase was covalently immobilized in the MWCNT-chitosan films using glutaric
dialdehyde. The resulting biosensor responded to glucose over the range 5-300
M with
a detection limit of 3
M. Gorski group [29] further developed the MWCNT-chitosan sys-
tem by covalently coimmobilizing the redox mediator of toluidine blue (TBO). Such inte-
gration of CNT and redox mediator in the dehydrogenase-based biosensor provided a
remarkable synergistic augmentation of the current because of the oxidation of redox-
active species.
13.3.1.4 Other Enzyme-Based Biosensors
Lin et al. [30] reported on a disposable CNT-modified screen-printed electrode for
amperometric detection of organophosphorus (OP) pesticides and nerve agents. The
biosensor involved the use of acetylcholinesterase (AChE) and choline oxidase (CHO)
enzymes covalently attached to MWCNT-modified screen-printed electrode. The AChE
works as a catalyst for the rapid hydrolysis of the acetylcholine into acetate and choline.
The choline is subsequently converted by CHO into hydrogen peroxide in the presence
