Biomedical Engineering Reference
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Fig. 5.9 Two-dimensional
pattern consisting of
alternating rows of Au
nanoparticles with different
diameters attached to
different tiles
a
b
c
DNA
metal
mica
Fig. 5.10 Negative replication of DNA structures: ( a ) DNA mask on mica substrate, ( b ) metal
deposition on top of the mask, ( c ) negative replica of the mask in metal, after lift-off
end binding, while the third direction terminates with a blunt end and so becomes
available for attachment of gold nanoparticles. The two-dimensional pattern has a
lattice constant of 27.4 nm for triangles with edges consisting of 84 nucleotide pairs.
The specificity of gold attachment is enhanced when it is linked with an ssDNA that
is part of the motif such that its 5 0 end is on a blunt end. Different gold nanoparticles
can be attached on the two tiles that form the lattice: nanoparticles with diameters
of 5 nm are attached on the gray tiles in Fig. 5.9 , and those with 10 nm diameter
bind to the black tiles.
DNA molecules can affect lithography also as masks. More precisely, negative
replica of self-assembled DNA structures can be directly reproduced in metal. The
sequence of processes, illustrated in Fig. 5.10 , involves evaporation of a 20-nm-thick
gold layer on a mica substrate on which DNA masks are first deposited followed by
lift-off, process in which the golf film is separated from the mica substrate ( Deng and
Mao 2004 ). The negative replica of the DNA mask is thus imprinted in the side of the
gold layer that was in contact with the substrate. After peeling off the metal film, the
DNA molecules are left intact on the mica substrate. The DNA mask can have any
form since it can self-assembly in designed patterns by simply cooling equimolar
mixtures of component strands, and its advantage is that the mask dimension is
of the nanometer scale, thinner than the currently used lithographic masks. One-
dimensional arrays of DX molecules with a width of 4 nm and two-dimensional
tetragonal arrays with a grid pitch of 18 nm, as well as more complex structures,
were successfully replicated.
Three-dimensional inorganic crystals with precise and controllable lattice con-
stant can be fabricated using synthetic biological scaffolds consisting of cationic
membranes and anionic DNA. These scaffolds self-assemble into a lamellar struc-
ture composed of one-dimensional lattices of parallel DNA chains sandwiched
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