Biomolecular Architecture for Nanotechnology - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 168

a b c

DNA

PDMS

Fig. 5.16 Double subtraction method: ( a ) initial DNA layer on PDMS, ( b ) the pattern after the
first subtraction and ( c ) after the second subtraction process

Fig. 5.17 Electric-field-
directed self-assembly

streptavidin
nanoparticles

biotin nanoparticles

streptavidin

Pt

- - - + + + - - - + + +

Si

strands over areas of 4 mm, with a resolution of 50 nm. Colloidal conjugated gold
nanoparticles with dimensions of 10 nm can then bind on the DNA patterns and
show long-range order if confined in sub-100-nm domains. The method relies on
the fact that DNA is transferred to the silicon master only when there is conformal
contact between DNA and the master surface. In particular, it was shown that silicon
masters with holes with diameters of 180 nm produce dot patterns of ssDNA with
the same diameter on silicon, arrays of ssDNA lines with widths of 50 nm, and
crossed ssDNA line patterns with widths of 100 nm can be generated.
A two-dimensional large-area DNA-templated nanoparticle pattern, with long-
range order over 1-2m, can be obtained by confining the nanoparticles to surfaces
covered by patterns of DNA molecules ( Noh et al. 2010 ) that can be formed by the
double subtraction method. This method involves a double subtraction printing on
two silicon masters with orthogonal groove directions (see Fig. 5.16 ). Such two-
dimensional DNA patterns have sharp edges and corners, can be as thin as 4-5 nm,
and can be fabricated on PDMS substrates, with a resolution better than 200 nm.
Inside such parallelogram-shape DNA features with dimensions ranging from 3 to
200 nm, 10-nm functionalized gold nanoparticles are arrange in hexagonally packed
superlattices due to a combination of thermal annealing and interparticle DNA
hybridization.
One of the problems of self-assembly is the formation of undesired nonspecific
binding, particularly important for high concentrations of analytes which, however,
speed the assembly process. A solution to avoid nonspecific binding and to fabricate
multilayer structures in a relatively short time interval is the electric-field-directed
self-assembly ( Dehlinger et al. 2007 ). In this case, positive and negative voltages are
applied on adjacent Pt electrodes patterned over a Si substrate, as shown in Fig. 5.17 ,
the electrodes being embedded in a covering layer that contains streptavidin on