Biomedical Engineering Reference
In-Depth Information
13.3.4
Fabrication of OR Conjugated-CPNT Substrate
as a B-nose Sensing Platform
An interdigitated microelectrode array (IMA) was patterned on a glass wafer using
a photolithographic process and consisted of a pair of gold interdigitated micro-
electrodes (source and drain) with more than 50 fingers (
W
/
L
= 1000,
L
= 2 μm
channel length). The IMA glass substrate was modified using aminosilane
((3-aminopropyl) triethoxysilane, APS) to introduce amine groups. The CPNTs
were attached on the modified surface of IMA
via
the covalent bonding between
the carboxylic acid groups of the CPNTs and the amine groups of IMA. To con-
struct stable covalent bonding, an efficient condensing agent, 4-(4,6-dimethoxy-
1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM), was added. The
DMT-MM facilitates the conjugation reaction at room temperature. The immobi-
lization process of the CPNTs on the IMA stabilizes the electrical properties and
induces mild reactions in the liquid state. Consecutively, the ORs were immobi-
lized on the CPNTs
via
similar conjugation reactions. The overall reactions are
given as follows (Fig.
13.3
):
(
)
(
)
+
Reaction 1 HydrolysisHNCH iOCH
.
:
3H O
2
2
3
3
3
2
(
)
(
)
+
→
HNCH S
iiOH
3CHOH
2
2
3
3
3
(
)
(
)
+
CondensationHNCH iOH
:
3OH ubstrat
−
e
2
2
3
3
(
)
()
−
→
HNCH Si Osubstrate
2
2
3
3
− +
( )
()
− ubstrate
pyrrole CONH CH Si Osubstrate
2
3
Reaction 2 Condensation pyrrole COOH
.
:
H NCH iO s
2
2
3
3
(
)
()
−
→−
3
Reaction 3 Condensation
.
:
pyrrole COOH
−
+ −−
H N ys OR
2
→
pyrro
le CONH lysOR
−
−
−
The FE-SEM image of OR-conjugated CPNTs deposited on the IMA was dis-
played, as shown Fig.
13.4a
. It was clearly observed that the surface of CPNTs had
considerably more rugged by the immobilized ORs compared to pristine CPNTs
(Fig.
13.2d
). Interestingly, no significant evidences of ORs on the surface of IMA,
indicating the ORs were selectively immobilized on the surface of the CPNTs
through covalent bonding. Compared with conventional physical adsorption, this
immobilization process offers several advantages, including mild reaction condi-
tions, stable electrical contact, and successful chemical bonding. Therefore, this
sensing platform using immobilization will allow highly selective and sensitive
sensing capabilities in B-nose.
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