DNA-Directed Assembly of Nanophase Materials: An Updated Review - DNA Nanotechnology: From Structure to Function - page 171

a new form of bio-conjugated carbon materials that may find important applications
in catalytic, sensing, and nanobiomedical applications, some of which have recently
been demonstrated in the literature.

8.4.3 Non-gold Metal Nanoparticles

Starting from Mirkin and Alivisatos groups' pioneering work [ 13 , 14 ], DNA-
conjugated gold nanoparticles have been one of the most enthusiastically pursued
subjects, resulting in a vast diversity of fundamental and technological applications.
Although DNA multifunctionalized gold nanoparticles (termed as spherical nucleic
acids—SNAs—by Mirkin et al.) have found important uses in sensors, biomedi-
cal materials, and crystalline colloidal superlattices, the capability of controlling
the number (valence) of DNA ligands on a nanoparticle brings much greater
opportunities in conjunction with structural DNA nanotechnology. Such a valence-
controllable nanoparticle is analogous to an atomic or molecular building block
that forms the structural basis of a chemical molecule or a crystalline solid. One
important breakthrough achieved more than 10 years ago was the separation of
monofunctionalized (monovalent) DNA-gold nanoparticle conjugates by agarose
gel electrophoresis [ 17 , 18 ], which has afforded precisely assembled discrete
nanostructures and ordered nanoparticle arrays by DNA-directed self-assembly.
However, in the following more than a decade pursuit, the gel electrophoresis-based
method has not succeeded in the case of other metal nanoparticles toward valence
separations of their DNA conjugates. The reasons are often attributed to the lack of
suitable chemical and colloidal stabilities of the nanoparticles and their relatively
broad size distributions. In addition, a chemical anchoring group that provides a
strong binding of DNA to nanoparticles is also required so that DNA detachment
can be thermodynamically or dynamically hindered.
We recently found that citrate-capped platinum nanoparticles (PtNPs)
with a diameter of 3-4 nm can be stabilized after ligand exchange with
bis( p -sulfonatophenyl) phenylphosphine dipotassium salt (BSPP) (Fig. 8.13 )[ 38 ].
The resulting BSPP-PtNPs could be stored at 4 ı C for more than a month, without
noticeable change of their stability. Importantly, the BSPP-PtNPs migrated in
a sharp band during agarose gel electrophoresis, which further allowed for an
electrophoretic sorting of PtNPs bearing a discrete number of DNA molecules [ 38 ].
As shown in Fig. 8.13 , the PtNPs, after being incubated with a suitable amount
of thiolated DNA, formed a ladder of separated gel bands during electrophoresis,
which could be easily assigned to PtNP-DNA complexes bearing up to 7 DNA
ligands. The products isolated from corresponding gel bands exhibited an excellent
stability against ligand detachment even in the presence of “bare” gold or platinum
nanoparticles (strong competitors for the DNA ligands). Benefiting from the good
compatibility between Au and Pt nanoparticles and the availability of their valence-
pure DNA adducts, discrete Au-Pt bimetallic assemblies and cross-link-free Au-Pt
core-satellites were finally assembled. Because Pt nanoparticles are especially