Metallic nanoparticles have been studied intensively during the last decades because of their
intriguing optical properties: Due to collective oscillations of the conducting electrons - the
so called plasmonic oscillations - they absorb light in the visible spectrum. The resonance
frequency thereby sensitively depends on parameters such as the particle size and shape as well
as the dielectric constant of the medium. DNA exhibits outstanding recognition properties and
can be modified easily. Thus template-directed material synthesis along synthetic DNA is a
promising route to grow nanoparticles of defined shape and size and with defined
interparticle-spacing. In this study two different methods are used to deposit silver on
oligonucleotides of different lengths ranging from 23 to 96 basepairs in order to synthesize
metallic nanorods of controlled aspect ratios. The first method involves the specific labeling
of nucleotides with aldehyde groups followed by exposure to a Tollens reagent and a developer.
The second method relies on the photoinduced deposition of silver onto unmodified DNA samples.
Several preparation parameters such as the DNA sequence buffer salt type silver concentration
and UV illumination time are varied systematically. The metallized DNA molecules are
characterized concerning their optical and structural properties. Absorption spectra show
plasmon peaks around 420nm. Peak positions intensities and bandwidths are analyzed. Dynamic
Light Scattering studies in solution provide information about the particle sizes as well as
their structural asymmetry. Both optical techniques are used to observe the temporal evolution
of the nanoparticle growth in the Tollens metallization process. Structural information is
inferred from Atomic Force Microscopy for that purpose the particles are deposited on
single-crystalline silicon substrates.
