Biomedical Engineering Reference
In-Depth Information
Fig. 5.17
A schematic explaining the effect of different V
G2
conditions on the V
T
shift in
biosensing applications. V
T
changes occur because the channel is electrostatically affected by the
charge of the analyte, which is bound to the receptor. (
a
) V
G2
<V
T;
DG
. Given that the channel
is formed close to the G1 side, G1 can easily control the channel, leading to a small V
T
shift.
(
b
) V
G2
>V
T;
DG
. The channel is induced on the G2 side. The V
T
shift increases due to the relatively
large distance between G1 and the channel (Copyright 2010 American Chemical Society)
Fig. 5.18
(
a
) A schematic of a double-gate nanowire FET with immobilized biomolecules and
(
b
) V
T
shift due to target molecule binding versus various V
G2
conditions (Copyright 2010
American Chemical Society)
As shown in Fig.
5.17
, charged analytes (e.g., antibodies) bound to receptors
immobilized on the nanowire attract/repel the inversion layer (channel) depending
on their charge polarity. In this way, the V
T
value is changed. As shown in Fig.
5.17
a,
because the channel is formed close to the G1 side under the condition of V
G2
<
V
T;
DG
, G1 can control the channel efficiently, resulting in a small V
T
value. Under
the condition of V
G2
>V
T;
DG
as shown in Fig.
5.17
b, however, the channel is
relatively far from the G1 side; hence, G1 loses its ability to control the channel
conductivity, leading to a large V
T
value [
44
].
To test sensing ability, bio-experiments using a specific analyte-receptor binding
system for the detection of the anti-AI were performed, as shown in Fig.
5.18
a. An
AI antigen (AIa) fused with silica-binding protein (SBP) was immobilized on the
surface of the nanowire via the SBP domain which serves as an anchor. The specific
binding between SBP-AIa and anti-AI was then accomplished by introducing anti-
AI onto an SBP-AIa immobilized device.
