了解高分子的型態對於生物技術中的許多面相有一定的重要性，譬如：處於膨鬆態的DNA較好與其他的分子配體或探針產生鍵結；相反地，緊縮態的DNA則較有利於基因傳遞。由於許多應用常在電場下進行，本文探討單一高分子鏈受外加電場極化作用下的構型變化。
在第二章中，我先從還未施加電場的高分子鏈行為開始探討。分析的依據是從經典的Flory-deGennes理論，本章重現了這一理論的結果，並提供單一高分子鏈的絨球-小珠轉變(Coil-Globule Transition, CGT)的一些基本特性。根據此理論，高分子鏈可為蓬鬆絨球或緊縮小珠，取決於溶劑的性質並反映於第二維里係數上。在優良溶劑中，第二維里係數大於零，單體與單體間彼此排斥，鏈表現得像一蓬鬆絨球，其絨球半徑(R)正比於鏈長(N)的3/5次方。相反的，在不良溶劑中，第二維里係數小於零，鏈因單體與單體間的吸引力而傾向收縮，導致R正比N的1/3次方。我還建立相圖，讓我可以知道絨球態、小珠態及共存時的條件。
根據第二章的結果，在第三章我延伸Flory-deGennes理論來檢視高分子鏈如何因AC電場而產生的極化作用來改變鏈的構型。我發現這電場極化作用足以拉伸或壓縮高分子鏈，取決於誘導電偶極的方向與強度。與靜態無電場作用下的經典絨球-小珠轉變(CGT)相比，所致的鏈構型變化可呈現出完全不同的表徵。結果表明：拉伸高分子鏈所需的電場強度會隨鏈長的-0.8至-0.75次方變化；若鏈所承受的是壓縮作用，處於膨鬆絨球態的高分子鏈反而會表現得像無電場作用時的緊縮小珠態。
在第四章中，我藉由微流變學的粒子追蹤來決定聚苯乙烯磺酸鈉在去離子水及lambda DNA在緩衝液，還未施加電場時的水力半徑(Rh)。實驗中，我使用微米等級的螢光粒子當追蹤物來決定均方位移(MSD)，再藉由Stoke-Einstein決定高分子溶液的黏度並使用Einstein-Batchelor方程式得出Rh。
在第五章中，我檢驗AC交流電場對第四章中的NaPSS和lambda DNA水力半徑的影響。首先先建立一會產生均勻電場的裝置，為了是確定鏈的壓縮及拉伸來自誘導電偶極而非介電泳(DEP)及交流電滲流(ACEO)。我發現NaPSS在20 Vpp及頻率為100-1000000 Hz的AC電場下似乎會減小它的尺寸，這表明NaPSS可能發生壓縮。然而，對lambda DNA而言，在上述電場的情況，鏈的尺寸似乎沒有顯著的變化。最後，我討論實驗和理論之間的差異以及可能影響實驗的問題。
在第六章中，我將裝置改為陣列式的微電極，這通常使得電場不均勻。在這種情況下，我研究lambda DNA(被yoyo-1標記)受交流電荷動力學如DEP和ACEO的影響。我使用不同的AC頻率並觀察到下列現象。當頻率大於1 MHz，些微lambda DNA被捕捉在相鄰電極對之間的較寬區域，這可能是由於負DEP導致。當頻率等於10 kHz，有大量的lambda DNA被捕捉於電極間的空隙中。此外，這些lambda DNA似乎也被延伸了，這觀察結果可能來自正DEP。然而，當我將頻率降低到100 Hz時，因為lambda DNA被ACEO帶走了，我發現上述捕獲現象消失了。儘管如此，在電極角落還是有捕捉一些lambda DNA。
本研究工作演示使用電場控制高分子構型的方法，從應用角度來看，也許可用於在奈米尺度下主動調控生物分子的活性。

Understanding conformational changes of a polymer chain is important to many aspects in biotechnology. As many applications are conducted under the actions of external electric fields, in this thesis I explore impacts of electric fields to investigate how a polymer chain changes its conformation due to polarization effects induced by electric fields. I begin by examining how a polymer chain behaves without electric fields. This is essentially described by the classical Flory-deGennes theory. According to this theory, a polymer chain can be either swollen coil or compact globule, depending on the solvent quality. Building on the results, I extend the Flory-deGennes theory to examine how a polymer chain changes its conformational state due to polarization effects generated by AC fields. I find that polarization effects can either stretch or compress a polymer chain, depending on the orientation and strength of an induced dipole moment. The results show that the critical electric field needed to stretch a polymer chain varies as the -0.8~-0.75 power of the chain length. On the contrary, if compression occurs to a polymer chain, even though the chain is immersed in a good solvent and situated at a swollen coiled state, it could behave like a compact globule, similar to that in a poor solvent without fields. My experimental results from microrheological experiments indicate that polystyrene sulfonate (NaPSS) in deionized water seems compressed at high frequency in AC electric fields. Tuning the conformation of a polymer chain with electric fields might provide an active mean for regulating the activity of a biomolecule at the nanoscale.

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