Biomedical Engineering Reference
In-Depth Information
Fig. 5.23
The structure of an
underlap FET with an
additional layer for
characterization in a wet
environment
Fig. 5.24
Experimental
results of an underlap FET in
a wet environment. The drain
current was decreased after
anti-AI binding due to its
negative charges at a pH
of 7.4
solution or kept in ambient air for characterization in watery or dry environment,
respectively.
As mentioned in Sect.
5.4.1
, the channel potential of the underlap region is highly
sensitive to the charge on it. An external charge on an open area will affect the
drain current. Thus, a change in the drain current can be observed after target
molecule binding in both wet and dry environments. The drain current reduction
in the dry environment was shown in Sect.
5.4.1
, and the result under the watery
environment is demonstrated in Fig.
5.24
. The drain current reduction in Fig.
5.24
can also explained by the electrical effect of the negatively charged biomolecules
(anti-AI) in the underlap region.
To ensure the specific binding of anti-AI and AIa on the underlap FET, false-
positive tests were performed in both watery and dry environments. First, a non-
AIa-functionalized device was immersed in an anti-AI solution for 1 h; after which
it was rinsed several times. As shown in Fig.
5.25
, there was no change in the drain
current for the nonfunctionalized device, even after anti-AI was added. In another
control experiment, an AIa-functionalized device was exposed to an anti-rabbit-IgG
antibody solution which showed nonspecific binding with AIa for 1 h; after which
