Biomedical Engineering Reference
In-Depth Information
mesoporous silica particles. More than 50% of gold nanoparticles are conjugated
on the surface of the bigger spheres but remain well separated from the surface, a
mesoporous silica particle containing 5-10 gold nanoparticles, while retaining its
mesopores, which are hexagonally arranged open channels with a 3 nm width.
The DNA-templated arrangement of nanoparticle arrays is not always restraint
to small sizes, such as a DNA strand or even a DNA architectural pattern. For
patterning self-assembly structures on large areas, the assembly technique can be
combined with lithography. In particular, electron-beam lithography can be used to
define with high-resolution domains on which self-assembly of specific biological
molecules from solution occurs (
Sabella et al. 2009
). A functionalized substrate with
a desired pattern is thus obtained after the removal of the resist and can be used as
template in a further site-specific assembly of probe species by hybridization with a
complementary DNA strand, for example, which become immobilized on desired
areas of the substrate. The remaining substrate area can be used to immobilize
another type of molecule, for example, a fluorophore which emits in another spectral
range than the initial probe fluorophore. The resolution of e-beam lithography and
thus of the DNA patterns is of the order of nanometers, but the method is costly and
time-consuming.
An inexpensive, large-area printing technique of DNA patterns called subtractive
printing has been developed in
Noh et al.
(
2009
) and is schematically represented
in Fig.
5.15
. Using this method, which involves adsorption of ssDNA solutions
on a polydimethylsiloxane (PDMS) substrate, followed by drying in a humidified
atmosphere, subtraction printing of DNA films on a silicon master, and finally
transfer of the remaining DNA on silicon substrates, it is possible to pattern DNA
a
b
Si
pattern
ssDNA
layer
PDMS
c
d
PDMS
Si
substrate
Fig. 5.15
Subtractive printing: (
a
) DNA film and the Si master, (
b
) subtraction printing of DNA
films on the silicon master, (
c
) transfer of the remaining DNA on silicon substrates, (
d
)the
transferred pattern
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