Self-Assembled DNA-Inorganic Nanoparticle Structures - DNA Nanotechnology: From Structure to Function - page 183

9.3 DNA-Directed Self-Assembly of 2-D Nanostructures

9.3.1 DNA as Smart Linker for Self-Assembly

In the field of self-assembly for 2-D nanostructures, the simplest method involves
the use of two complementary ssDNA strands spontaneously hybridizing into
a dsDNA double helix, which strictly follow the thermodynamically favorable
Watson-Crick base-pairing rules. In the past two decades, DNA nanotechnology has
experienced rapid development, and DNA has been used as an excellent structural
linker for controlled aggregation of NPs since the binding strength of DNA double
helices can be easily controlled.
AuNPs were most widely used for self-assembly because the strong Au-S bond
facilitates surface functionalization with thiolated DNA. Mirkin and Alivisatos were
the pioneers to report programmable aggregation of DNA-capped AuNPs. As early
as 1996, the two groups described two methods for assembling colloidal AuNPs
into aggregates using DNA as linkers, respectively [ 7 , 8 ]. Mirkin et al. employed the
AuNPs labeled with multiple copies of the same ssDNA as motif (Fig. 9.2 a), while
Alivisatos et al. attached ssDNA with defined length and sequence to individual
AuNP, which was subsequently assembled into dimers and trimers after addition
of a complementary single-stranded DNA template (Fig. 9.2 b). Afterwards, Mirkin
designed an AuNP satellite-like structure consisting of 8-nm and 31-nm AuNPs
coated with different 12-mer ssDNAs [ 20 ]. When a third complementary DNA
sequence (24-mer) was added, specific base pairing led to the association of particles
(Fig. 9.2 c). The geometry and optical property of the obtained nanostructures can be
tuned by simply varying the size of NPs and DNA ligand length. In 2010, Sleiman
group [ 21 ] introduced a facile method to site-specifically append an AuNP to either
the interior or terminal (5 0 or 3 0 ) position in DNA strand. It has the potential to enable
the construction of any number of discrete metal NPs. Such discrete structures will
be valuable as model systems for fundamental investigation of optical and electronic
properties of nanoparticles and as surface-enhanced Raman scattering substrates for
sensitive biological detection (Fig. 9.2 d). Capasso et al. reported another interesting
plasmonic heteropentamer clusters [ 22 ], in which a small AuNP was surrounded
by four larger AuNPs through surface-binding DNA base pairing, and the magnetic
and Fano-like resonances were observed in individual clusters. In this work, DNA
plays a dual role: it selectively assembles the clusters in solution and functions as
an insulating spacer between the AuNPs.
In addition to AuNPs, other self-assembled inorganic materials by means of DNA
linker have also been reported. In 1998, DNA was used for the assembly of fullerene
materials through electrostatic interactions with the phosphate groups along the
DNA backbone by Tour's group [ 23 ]. Stephen Mann first assembled anisotropic
nanomaterials, metallic nanorods (AuNRs) (Fig. 9.3 a), using the specific DNA
duplex formation [ 24 ]. Recently, Tang et al. have also assembled the gold nanorods
(AuNRs) through DNA hybridization and demonstrated that the hybrids of DNA
and AuNRs produce remarkable plasmonic CD signals at the visible light region