Biomedical Engineering Reference
In-Depth Information
FIGURE 12.14
Attachment of DNA to carbon nanotubes. (a,b) N -hydroxysuccinimide (NHS) esters formed on carboxylated, sin-
gle-walled carbon nanotubes (SWNTs) are displaced by PNA, forming an amide linkage. ( c) A DNA fragment
with a single-stranded, “sticky” end hybridizes by Watson-Crick base-pairing to the PNA-SWNT. (d,e) Atomic
force microscope (TappingMode) images of PNA-SWNTs. SWNTs appear as bright lines; the paler strands rep-
resent bound DNA. Scale bars: 100 nm; nanotube diameters: (d) 0.9 nm; (e) 1.6 nm. (From Williams, K. A.,
Veenhuizen, P. T. M., De La Torre, B. G., Eritja, R., Dekker, C. (2002). Nanotechnology: Carbon Nanotubes With
DNA Recognition. Nature , 420 (6917), 761.)
massive redundancy in nanosensor arrays, so that a large number of sensing elements can
be densely packed onto a small footprint of an array device. Biological functionalization
of NW surfaces is also a key point for NW-based biosensor applications [65]. The most
direct approach to functionalizing NWs is to transfer the well-developed surface chem-
istry at planar metal interfaces to the NW geometry [124,125]. It is well known that thiols,
dithiols, and thioacetates have a high affinity for gold surfaces and carboxylic acid groups
strongly interact with metal oxide surfaces to form stable self-assembled monolayers
[126,127]. The reactivity provides several convenient routes for functionalization of the
NW surface. For example, gold nanorods can be modified by a thiol-derivatized DNA
(ssDNA) [201] or a thioacetate-terminated porphyrin via an Au-S covalent bond [128].
DNA hybridization has been effectively monitored by fluorescence quenching due to the
aggregation of DNA functionalized nanorods [202]. Recent advances in surface modifica-
tion of silicon nanowires (SiNWs) to generate hydrophilic surface have made it possible to
facilitate biofunctionalization (such as DNA, protein, and cells) of SiNWs (Figure 12.15).
For example, SiNWs have been functionalized with a phosphoramidite-terminated DNA
monolayer. Using the SiNWs functionalized with DNA probes, a label-free DNA analysis
system was developed with a high sensitivity and selectivity [129]. The method of func-
tionalization is based on the gas-phase method to generate a self-assembled monolayer of
mercaptopropyltrimethoxysilane on silicon oxide surface. Then the functionalized silicon
oxide NWs were used for covalent coupling with phosphoramidite-modified DNA.
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