Biomedical Engineering Reference
In-Depth Information
of oxygen. The detection of OP relied on the inhibition of AChE by OP compounds.
Hydrogen peroxide is then amperometrically detected with a CNT-modified electrode.
Owing to the remarkable catalytic activity of CNT to promote the oxidation of hydrogen
peroxide produced during the AChE-CHO enzymatic reaction with their substrate, the
biosensor exhibited a high sensitivity and low detection limit of 50 nM for OP pesticide,
methyl parathion. This result demonstrated the possibility of the field screening of OP
pesticides and nerve agents. Joshi et al. [31] demonstrated a very simple method for the
fabrication of OP biosensor. The degree of inhibition of AChE by OP pesticides was
determined by measuring the oxidation current of thiocholine generated by the AChE-
catalyzed hydrolysis of acetylthiocholine (ATCh). The CNT-modified screen-printed
electrode exhibited remarkable electrocatalytic activity toward thiocholine and lowered
oxidation overpotential to 200 mV. The biosensor can detect OP nerve agent paraoxon
with a detection limit of 0.5 nM (0.145 ppb).
13.3.2
Direct Electrochemistry of Redox Proteins and Enzymes
In general, direct electron transfer of redox proteins or enzymes at unmodified electrode sur-
face is not possible because redox-active sites of proteins or enzymes are shielded by glyco-
protein shells of proteins. However, direct electron transfers are possible for some proteins
and enzymes that are properly aligned to the electrode surface as shown in Figure 13.3.
Gooding et al. [32] reported on the direct protein electrochemistry using aligned SWCNT
arrays. An array of SWCNTs perpendicularly aligned on a gold electrode was fabricated by
covalently coupling the carboxylated SWCNT to a cystamine monolayer-modified gold
Redox proteins
GOx
HN
HN
HN
HN
C=O
C=O
C=O
C=O
e
−
e
−
O=C
O=C
O=C
O=C
NH
NH
NH
NH
FIGURE 13.3
(See color insert following page 330)
Direct electrochemistry of redox proteins (left) and enzymes (right).
