Biomedical Engineering Reference
In-Depth Information
phosphate-buffered solution (PBS, pH 7.4). (ii) three electrodes were introduced as
source (
S
)/ drain (
D
) electrodes and gating electrodes (
G
). The gating electrodes
were applied with the Ag/AgCl reference electrode and platinum counter electrode
immersed in the PBS solution, leading to the efficient gating control. This liquid-ion
gating can induce effects that enhance efficiency, including intimate contact on the
CPNT surface and low-voltage operation, in the liquid state.
13.4.2.2
Characterization of the Liquid-Ion Gated FET-Type B-Nose
Before using the FET-type B-nose for liquid-phase odorant detection, the electrical
properties were characterized. Figure
13.6c
presents the
I
-
V
curves of hOR-con-
jugated CPNTs and pristine CPNTs without hOR deposited on the IMA substrate
(scan rate = 10 mVs
−1
). The d
I
/d
V
values of the B-nose sensing platform gradually
decreased with increasing concentrations of hOR attachment. Although the gradi-
ent of d
I
/d
V
decreased slightly due to hOR attachment, the linearity of the B-nose
sensing platform was continuously retained after the coupling reaction and washing
process. This result indicates that covalent immobilization of the CNPTs provided
stable electrical properties in the liquid state, leading to reliable electrical contact.
Moreover, the loading amount of hOR on the CPNT could be controlled by adjust-
ing the feed amount, which allowed to the maximum MDL for the B-nose using the
hOR-conjugated CPNT. The observed d
I
/d
V
values from smallest to largest are as
follows: hOR-to-CPNT weight ratios 1:4 (1hOR-CPNT) < 1:2 (2hOR-CPNT) < 1:1
(4hOR-CPNT).
To use the hOR-CPNT sensing platform as a signal transducing component of
B-noses, we constructed a liquid-ion gated FET system with a PBS solution as the
electrolyte. This was possible because the gating remote could be easily controlled.
The FET-type sensing geometry was also applied to enhance the sensing perfor-
mance through signal amplification. Figure
13.6b
shows the FET system with three
types of electrodes: source, drain, and gate electrodes. The gate potential (
V
g
) was
applied between the reference electrode and the drain electrode through the liquid-
ion solution. More than 100 sensing platforms were tested under ambient condi-
tions. Figure
13.6d
demonstrates the output curve characterization of the B-nose
using an hOR-CPNT sensing platform at room temperature. The source-to-drain
current (
I
ds
) negatively increased with negatively increasing gate voltage (
V
g
), in-
dicating p-type (hole-transporting) behavior. From these experimental results, the
binding of odorants to the B-nose was observed by monitoring the current changes
via
the liquid-ion gated FET system.
13.4.2.3
Real-Time Responses of Liquid-Ion Gated FET-Type B-Nose
To investigate the real-time sensing characteristics of the liquid-ion gated hOR-
CPNT FET, the
I
sd
was measured at
V
sd
= 50 mV (
V
G
= 0 mV, a low operating volt-
age) upon the addition of various odorant concentrations. Generally, odorant amyl
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