Biomedical Engineering Reference
In-Depth Information
v, v
s
v
B
=
0.1
==
0
V
D
30
pH=1.2
6.0
9.8
CALOMEL
REF.PROBE
20
D
S
V
D
V
G
I
D
10
0
0.5
1.0
1.5
2.0
V
G
(VOLTS)
Fig. 5.4
Drain current (I
D
) versus gate voltage (V
G
) characteristics and their changes with pH.
The aqueous solution with the higher pH shows the higher threshold voltage
Fig. 5.5
Conductance versus time, recorded for a PSA antibody-modified p-type silicon nanowire
for (1) 9 pg/ml PSA, (2) 0.9 pg/ml PSA, (3)0.9 pg/ml PSA and 10g=ml bovine serum albumin
(BSA), (4) 10g=ml BSA, and (5) 9 pg/ml PSA (Copyright 2005 Nature Publishing Group)
Silicon nanowire biosensors have been used to detect ions [
24
], small molecules
[
25
], proteins [
26
], DNA [
27
], and viruses [
28
] by taking advantage of the changes
in surface charge, depending on the binding of target molecules. Surface charges
serve as a gate and induce a potential change in the nanowire channel, thus leading
to a conductance change in the nanowire. For example, as shown in Fig.
5.5
,when
prostate specific antigen (PSA), a cancer marker protein, binds to a nanowire coated
with the PSA antibody, the conductance is increased because PSA carries a negative
charge at pH 7.4.
