DNA-Directed Assembly of Nanophase Materials: An Updated Review - DNA Nanotechnology: From Structure to Function - page 158

Fig. 8.2 Site-specific strand-by-strand attachment of DNA linkers on a spherical gold nanoparticle
with well-defined 90 ı or 180 ı orientation angles (Copyright (2011) Wiley. Used with permission
from Ref. [ 32 ])
then detached from the silica surface by acidizing the solution with trifluoroacetic
acid (to protonate the carboxylic group on the silica particles). The resulting gold
nanoparticle bearing a single DNA ligand could be used as a starting nanoparticle
for a new round of DNA modification (to take up another DNA ligand from the silica
particle as the second ligand). This process went on until all the six DNA ligands
were decorated. During each step, the placement of a new DNA ligand would
self-adjust to minimize electrostatic repulsion and steric hindrance with all other
existing DNA ligands on the same nanoparticle. Following this logic, the researchers
succeeded in attaching DNA ligands on a spherical AuNP surface with up to sixfold
symmetry (linear, T-shape, square planar, square pyramidal, and octahedral). Note
that such a sequential modification will result in a “T”-shaped DNA arrangement
for a three-valence product (gold nanoparticle bearing three DNA ligands), which
is obviously different from the trigonal geometry determined by VSEPR theory. As
well, four or five steps of modifications resulted in square and square pyramidal
rather than tetrahedral and trigonal-bipyramidal geometries. Therefore, this method
will favor 90 ı or 180 ı orientation angle between adjacent DNA ligands. Such
a sequential modification strategy successfully avoided other possible geometries
for the same DNA coordination number, which happens during a simultaneous
modification of multiple ligands on a single nanoparticle in a homogeneous
solution.