Biomedical Engineering Reference
In-Depth Information
Fig. 13.7
Real-time
responses of 1hOR-CPNT
FET B-nose measured
at
V
sd
= 50 mV:
a
target
odorant (AB),
b
non-target
(BB, HB, and PB) and
target odorant (AB). The
sensitivity was recalculated
as normalized
I
sd
changes.
(Reprinted with permission
from ref. [
34
]. Copyright
2009 Wiley-VHC Verlag
GmbH @ Co. KGaA)
butyrate (AB), a common reagent for fruit flavor, is particularly sensitive to the
hOR, leading to a rapid response time. Figure
13.7a
displays the real-time response
of the B-nose to AB. The current values from the B-nose were achieved with a con-
centration-dependent increase in
I
sd
upon exposure to AB. To avoid electro-chemi-
cal oxidation of AB, the applied gate voltage was below the oxidation potential. The
highly selective hOR interaction to AB leads to the lowest MDL (
ca
. 400 fM) for
the B-nose compared with the conventional B-nose using 1D nanomaterials. The
real-time responses of the B-nose were fast (< 1 s) and clearly saturated. Pristine
CPNTs were also introduced as an identical experiment: no significant current sig-
nals were observed. This was attributed to the ultrasmall olfactory receptor (diame-
ter < 4 nm) being expressed in the insoluble fraction of
E. coli
. It is believed that the
sensing mechanism originates from a change in the charge-transport behavior of the
CPNTs induced by the binding event of hOR-AB. Specifically, the hOR has both an
uncharged (RSH) state and a negatively charged (RS
-
) state through the acid-to-base
transition of the sulfhydryl group. The structural rearrangement of hORs occurred,
due to the interaction of AB, which induced negative point charge formation on
the liquid-ion gate dielectric near the CPNTs. Finally, the accumulation of positive
charge carriers in the CPNT channel allowed the increasing current to be monitored.
Such a molecular gating effect is similar to a p-type doping effect acting indirectly
on the liquid-ion gate dielectric, rather than directly affecting the semiconducting
layer. Moreover, the B-nose has excellent selectivity with highly specific atomic-
level resolution at femto-molar concentrations, as shown Fig.
13.7b
. There were no
changes in the current from the non-targeted molecules which only differed by the
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