| 摘要: | 在本研究中，我們利用外加電場來輔助疊層組裝，控制聚電解質高分子
於基材上的吸附及其後的釋放行為。使用導電性高分子聚?咯為基材，分
別在堆疊DNA 或幾丁聚醣時施加電場，以進行電泳沉積。並使用幾丁聚醣
?將多層膜降解後，以分別定量在不同層數時DNA 及幾丁聚醣的堆疊量。
從吸附量的結果顯示，幾丁聚醣在低電場下(0.1V~0.2V)的疊層組裝確實增
加了DNA 與chitosan 的吸附，然而在0.5V 時吸附量卻開始有下降的趨勢，
推測是此時的電壓已到達水中溶氧的還原電位，所產生的氫氧根離子使溶
液產生pH值變化，因此減低了溶液中聚電解質的帶電量。而隨著電壓上升，
電解所造成的pH 改變及吸附減少的現象也更加明顯，然而當電壓5V 時，
可能pH 上升的幅度已超過而溶液中的幾丁聚醣的pKa 值，因此反而導致幾
丁聚醣析出而增加沉積量。而DNA 也有類似的現象，即在低電場下
(0.1V~0.2V)疊層組裝會增加吸附，但是隨著電壓增加，水開始氧化產生氫
離子，導致pH 值下降而造成DNA吸附減少。接著將通電組裝薄膜進行DNA
釋放實驗，發現DNA 通電所造成吸附量上升的多層膜，其釋放出來的DNA
質量也會較多。幾丁聚醣雖然也有類似的現象，但釋放提升程度並不如DNA
通電所帶來的效益。值得一提的是，針對電壓5V 擁有幾丁聚醣通電組中最
高的釋放量，這可能是因為幾丁聚醣是以析出的方式吸附於多層膜，導致
多層膜的結構鬆散，進而增加了DNA 的釋放量。最後將通電組裝薄膜進行
原子力顯微鏡(AFM)拍攝，觀察通電後薄膜表面粗糙度的變化，發現在DNA
低電壓的處理可以使膜表面趨於平滑，這可能是因為通電後膜上的電荷使
得高分子吸附更加的密合。然而在高電壓下，膜表面則會變得粗糙，推測
聚電解質由於pH 值的改變而減少帶電量，進而使其構型傾向蜷曲而導致膜
的粗糙度增加。然而幾丁聚醣的通電處理對於粗糙度並無明顯的趨勢，這
可能是因為與DNA 相比，幾丁聚醣分子量過小，因此電泳吸附對於膜表面
的影響不大。
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. |
