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Photosynthesis
Photocatalytic Metal Deposition for
Nanolithography: Deposition of
Conductive Patterns
We are currently focusing on the synthesis of transducers for
selective photochemistry, such as deposition of conductive
metallic patterns (copper, silver or gold) by preassembling
nanoparticulate TiO2 on various supports. Preassembling of
the semiconductor particles into chains localizes deposition
of conductive metals on the chain domains and leaves the
rest of the surface nonconductive. This eliminates the need
for nanodimensional sources of energy such as X-ray or
electron beams for nanowriting, but allows the use of broad
light sources independent of their size or wavelength, and
eliminates the need for pattern specific masks. In this way,
a plurality of nanodimensional circuits can be prepared
simultaneously, significantly enhancing device throughput.
Oligonucleotides are being used as templating agents. One
strand of 16 base pair long oligonucleotides was selective
bound of TiO2 particles for particle assembling. During this
period we have synthesized different particle size colloids
(1.1; 1.9; 3.2 and 4.3 nm) of metal oxide particles (TiO2)
using controlled hydrolysis of titanium chlorides or alkoxides.
We have modified colloids with a series of surface modifiers
terminated with different groups (epoxy, silane or phosphine)
in order to prevent wrapping of the oligonucleotides around
TiO2 nanoparticles. We showed that ortho substituted
hydroxylated aromatic ligands have larger binding constants
for nanocrystalline TiO2 and replace other modifiers. This
finding allows irreversible binding of dopamine modified
oligonucleotides (coupling via N-hydroxy-succinimide ester
or carboimide complex) to some of the sites of surface modified
TiO2 nanoparticles. The sequence selective absorption of
TiO2 particles was observed as a result of the tentacle
binding of biologically functioned oligonucleotides strands
to TiO2 particle. The binding was quantified (number of
oligonucleotides per TiO2 particle) using calorimetric methods
(absorption at 450 NM) that we have developed.
Another approach was also pursued in which modified
particles act as transducers. Oligonucleotides will be used for
templating as well as for initiation of chemical transformations.
The particles are inactive photochemically until oligonucleotides
hybridize with its complementary strand which contains electron
donating groups. Following hybridization, the TiO2 nanoparticles
will generate electrical output or mediate photochemical reduction
of metal ions into conductive metal layers. In that respect the
photochemical respond of TiO2 particles in the presence of
different nucleic bases.
Contact:
T. Rajh
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