Biomolecular Architecture for Nanotechnology - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 166

a b

ssDN A 1

ssDNA

+

Au

+

ssDNA 2

Au

+ +

Fig. 5.13 Self-assembled groups for plasmonic applications containing ( a )twoand( b )three
nanoparticles with different diameters

Si

Au

+ +

ssB

ssA

ssC

Fig. 5.14 Formation of satellite structures

field, nonperiodic assembly of nanoparticles can show also plasmon resonances
if the distances between particles are of only few nanometers. In this case, the
plasmonic modes of individual nanoparticles hybridize analogously to hybridization
of electron orbitals in molecules. Such groups of nanoparticles, consisting of
groups of Au particles with diameters of 5, 8, and 18 nm, can be obtained
by self-assembling on a DNA scaffold ( Bidault et al. 2008 ). More precisely, if
phosphine-coated gold nanoparticles with different diameters are functionalized
either with a 5 0 -thiolated ssDNA or with a 3 0 -thiolated ssDNA with complementary
strands, strand hybridization forms asymmetric groups of two particles, whereas
a group of three particles forms when one type of nanoparticle is sequentially
functionalized with different ssDNA molecules (see Fig. 5.13 ). Estimates show that
these groups of particles locally enhance electromagnetic fields up to four orders of
magnitude, depending on the interparticle spacing, particle diameters, and the angle
between the particles in the three-particle group.
One of the successes of DNA-driven self-assembly processes is the fabrication
of congregations of nanoparticles with different properties and sizes. In particular,
small metallic particles, with a diameter of 11 nm, can link to the surface of large,
mesoporous silica, with diameters of 100 nm, such that a satellite structure forms
( Sadasivan et al. 2005 ). In this assembly, shown schematically in Fig. 5.14 , both
components can be accessed and multifunctionality can be achieved. Moreover,
the structure is reversible. To form satellite nanostructures, the mesoporous silica
particles are functionalized with a 12-bp single-strand oligonucleotide ssA and the
gold particles are functionalized by another 12-bp ssDNA, ssB, self-assembly being
initiated when a target 24-bp single-strand nucleotide ssC, complementary with both
ssA and ssB, is introduced in the solution containing the functionalized gold and