| dc.description.abstract | To regulate the adsorption and the following release of polyelectrolyte on
substrate, we developed external electric field to assist layer-by-layer (LbL)
assembly in this study. Conductive polymer, polypyrrole, was utilized as the
substrate, and DNA as well as chitosan was applied to deposit on the surfaces.
To elucidate the effect of electricophoretic deposition, the electric field was
solely administrated to chitosan or DNA adsorption. Chitosanase was used to
degrade polyelectrolyte multilayers (PEMs) at different bilayer numbers, and the
adsorbed chitosan and DNA may thus be quantified. The adsorption results
demonstrated that LbL assembled DNA and chitosan can both be augmented
under low electric field (0.1~0.2V). However, for the groups using electrical
field during chitosan deposition, the improvement began to reduce at 0.5 V. It
should be due to that the voltage approach to the reduction potential of dissolved
oxygen in solution, and the increased hydroxyl ions decreased the charges on
chitosan molecules to inhibit their adsorption. But when the voltage increased to
5V, the adsorption of chitosan was increased. It probably due to that the
electrolysis significantly increased pH value to close to the pKa of chitosan,
which chitosan precipitation on PEMs. The electrical field treatment during
DNA deposition also revealed similar trends that using low voltage can increase
deposition. However, the oxidization occurred when the voltage was high which
resulted in proton release to decrease pH. Therefore, the charged density of DNA
was decreased which decline DNA adsorption to PEMs. Then we soaked PEMs
to PBS to determine their DNA release efficiency. Because electric-assisted LbL
during DNA deposition highly increased DNA adsorption, their releases were
thus also improved. However, this trend was not obvious to the chitosan groups.
Interestingly, the group using 5V during chitosan deposition demonstrated
highest release. It was consistent to our deduction that 5V led chitosan
participation, which weakened the stability of PEM that the DNA can be
released easily from loose structure. Finally, these films were illustrated by
atomic force microscopy (AFM). When films were treated low voltage (0.1V
and 0.2V) for chitosan deposition, surfaces were smoothened, suggesting that
surface potential of substrate increased the contact of polyelectrolyte to surfaces
that the defects of PEMs can thus be reduced. However, using high voltage
increased the roughness of the films. It should be due to that the reduction of
charge density of polylelectrolyte on PEM caused their configuration as
coiled-form and thus the microstructure of PEMs was not as smooth as those
using low voltages. In contrast, for electric field-treated DNA deposition, there
was no obvious trend between voltage and roughness. We deduced that chitosan
was extremely small compared to DNA, so the surface roughness mainly
depended on DNA but not chitosan. | en_US |