Biomedical Engineering Reference
In-Depth Information
be readily obtained by mixing citrate-stabilized AuNPs and alkylthiol deriva-
tizedDNAoligomers,andsubsequentincubationandpurification[69].
Alivisatos and coworkers showed for the first time that a discrete num-
ber of gold nanocrystals with one ssDNA strand ligand can be organized into
spatially defined structure by base pairing [70]. Oligonucleotides modified at
either the 3
-or5
-terminus with a free sulforyl group were coupled with an
excess of nanoparticles. After being combined with suitable ssDNA templates,
parallel (head-to-tail) and antiparallel dimers (head-to-head) were obtained
(Fig. 11a). UV/vis absorbance measurements indicated changes in the spec-
tral properties of the nanoparticles as a consequence of the supramolecular
organization [71]. Following this approach, Mao et al. reported a new chal-
lenge to build larger arrays by DNA-encoded self-assembly, which assembled
AuNPs into 4
m-long ssDNA strand templates produced from “rolling-circle
DNA polymerization” [72]. In the rolling-circle DNA polymerization, a DNA
polymerase uses a short (less than 100 bases long), circularized, single DNA
strand as a template to synthesize long (more than 10 000 bases), linear,
tandemly repetitive single DNA strands under isothermal conditions [73].
The 5 nm gold nanoparticls modified by ssDNA strands with a thiol group at
5
end were introduced into the resulting long ssDNA strand.
To arrange AuNPs into a monolayer, Simon and coworkers [74] reported
a simple protocol via the oligonucleotides complementary immobilization. 5
-
Amino-modified oligonucleotide was immobilized on the substrate surface
first, and then, 15 nm gold particles modified with thiolated DNA oligomers
were coupled to the surface through DNA base pairing. The resulted nanopar-
ticle monolayers were demonstrated to have a thermally activated conduc-
tivity. A similar approach has been used to insert a liposome into a DNA
chip [75] (Fig. 11b).
Three-dimensionally linked nanoparticle assemblies have been successful
prepared by DNA hybridization. Mirkin's group initially described a method
µ
Fig. 11
Process of the DNA-based colloidal nanoparticle assembly.
a
Base-pairing interac-
tions induced assembly in 1D template.
b
Immobilization by DNA hybridization onto 2D
surface.
c
3D assembly by duplex DNA interconnects
