Biomedical Engineering Reference
In-Depth Information
40
38
36
34
6
O
O
4
O
O
P
O
O
P
O
O
2
0
ABCDE
HN
HN
O
O
S
HS
S
1
2
3
SI
SI
SI
O
OH
OH
OH
O
O
O
O
O
O
O
O
(A)
(B)
(C)
(D)
FIGURE 12.15
Modification scheme of the SiNW surface for the DNA detector: (1) self-assembly of 3-mercaptopropyltrimethoxysi-
lane (MPTMS) by gas-phase reaction in Ar for 4 h; (2) covalent immobilization of DNA probes by exposing the pre-
vious surface to 5
M solution of oligonucleotide CCT AAT AAC AAT modified with acrylic phosphoramidite at the
5
-end for 12 h; (3) DNA detection based on hybridization between label-free complementary DNA target GGA TTA
TTG TTA and the immobilized DNA probes on the SiNW surfaces. The inset is the SPV signal on a p -type Si surface
at different stages of the modification; A, B, and C correspond to the schematic diagrams, D is with 25 pM solution
of complementary DNA target exposed to the surface C, and E is with 25 pM solution of noncomplementary DNA
(GGA TCA TTG TTA) exposed to the surface C. (From Li, Z., Chen, Y., Li, X., Kamins, T. I., Nauka, K., Williams, R.
S. (2004). Sequence-Specific Label-Free DNA Sensors Based on Silicon Nanowires. Nano Lett., 4(2), 245-247.)
Compared with noncovalent modification, the covalent anchoring of DNA on the SiNW
surface provided better stability and less nonspecific hybridization for DNA sensing.
Among the various materials of NWs, magnetic NWs are ideal candidates for applica-
tions in a magnetic cell separation system [210], which is an important step for biosensor
development. Cells (such as mammalian cells and human T-cells) have an affinity for
binding to the hydrophilic surface of the native nickel oxide layer or carboxylate groups
on the magnetic NWs. Thus, the binding of the cells makes the magnetic NWs accessible
for use in an immunomagnetic separation system based on a microfluidic device to auto-
mate and miniaturize sample preparation for biosensor application.
12.5
Design and Construction of Carbon Nanotube and Nanowire-Based
Biosensors
12.5.1
Approaches to Design and Assemble Biosensors Based on Carbon Nanotubes
12.5.1.1
Carbon Nanotubes-Based Electrochemical Biosensing Platforms
12.5.1.1.1 Directly Use Carbon Nanotubes as Electrodes
Carbon nanotubes are attractive as electrodes for electrochemical sensor devices because of
their high electronic conductivity, wide potential range, and the high electrochemically
assessable surface area. Since the first report using CNTs as electrodes to study the oxida-
tion of dopamine in 1996 by Britto et al. [130], CNTs have attracted many scientists in the
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