View - DSpace UniPR

PNA Microcontact Printing
5.2.2 PNA microcontact printing
The chemical strategy adopted for the fabrication of PNA monolayers was based on the
reaction between the PNA primary amino group and an aldehyde monolayer on the surface,
obtaining a Schiff base that could be reduced to secondary amine by NaBH 15 4 . The
microcontact printing strategy was used to print PNA full layers or to pattern them in well
defined structures. Since the material used to make the stamp, polydimethylsyloxane (PDMS),
is hydrophobic, it had, first to be modified by oxygen plasma oxidization, in order to be
compatible with more polar molecules such as PNA. Then, the oxidized PDMS stamps were
inked with a 10µM solution of PNA 1 (Table 5-1) in CH 3 CN for 5 minutes, then dried and
printed over an aldehyde-derivatized substrate for 15 min applying a pressure of 15g. The
samples thus obtained were reduced with a solution of NaBH 4 , sonicated for two minutes in a
solution of sodium carbonate 0.1M and SDS 2% (pH=9) in order to remove non reacted
molecules, and finally washed with a 1mM solution of sodium carbonate. The samples were
imaged using a fluorescence microscope.
Figure 5-4: Pattern obtained printing increasing concentration of PNA 1 and hybridizing with DNA c1
labeled with TAMRA. Samples were imaged using a green filter (fluorescein) and a red one
(TAMRA)
In figure 5-4 (first row) a printing test performed using different concentration of PNA is
reported. The figure shows the quality of the patterning process, which allowed to obtain well
defined structures with high fluorescence intensity. In order to verify the specificity of the
bond between PNA and the aldehyde group of the surface, a blank experiment was performed
97