於改良式漸縮微流道拉伸DNA之研究

Abstract

本研究以實驗驗證Hsieh and Lin利用有限元素法及布朗動態模擬法所設計以電場拉伸DNA之裝置。此裝置藉由特殊設計的微流道改變DNA之初始形狀，使DNA能以有利於拉伸之型態進入漸縮通道進行拉伸。我們希望能將這種新設計應用於基因圖譜技術。根據模擬結果我們測試三種不同設計之微流道: Case I是Randall and Doyle所設計的單純漸縮通道；case II的通道是先漸擴再漸縮之通道，漸擴部分有預拉伸DNA之效果，使DNA的初始狀態有利於拉伸；case III是case II的改良式通道，可以減少case II通道中，DNA對半折疊造成不利於拉伸的情形。利用電場實際拉伸DNA後，發現實驗結果不如預期，DNA在高電場下會「自纏繞」成球狀型態。我們利用COMSOL計算在通道之流場分布，發現和電場分布相似，再經由實驗初步評估後，我們便嘗試以流場在同樣的微流道中拉伸DNA。 流場拉伸DNA的結果與電場模擬有相似的情形；1.Case II與case III中皆有產生旋轉預拉伸的效果。2.由於體積排斥力的關係，DNA在case III中無沿中心線進入漸擴通道之情形。3.case III的拉伸效果最好，其次為case II，最後為case I。另外，在case I中，當黛博拉數為20以上，DNA在經過漸縮流道時，有些碰到通道邊界的DNA會有「翻轉」的情形，我們推斷此情形是由於壁邊流速為零的邊界條件所造成，而case II與case III則較少發生此情形。由於產生「翻轉」情形，造成case I中從黛博拉數從10上升至20時，其平均最大拉伸率上升幅度會比從黛博拉數由20上升至30時為低。若與Randall and Doyle在漸縮微流道中以電場拉伸DNA之結果相比，本實驗在case II與case III中利用流場拉伸DNA之平均最大拉伸率明顯優於在case I中利用電場拉伸DNA之平均最大拉伸率。

We experimentally test two microfluidic devices for stretching DNA using electric field and flow field. The microfluidic devices were designed with the help of computer simulations for electrophoretic stretching of DNA, and both were predicted to outperform a simple contraction. We first electrophoretically stretch DNA using DC field while the experimental results were not even in qualitative agreement with our simulations. Detailed investigation in experiments reveals that DNA adapts a compressed conformation in high DC field and thus becomes more difficult to stretch. Due to the similarity between flow field and electric field, we use the same microfluidic devices with flow field to stretch DNA. The experimentally observed DNA behavior in flow field is similar to the prediction based on electric field. The rotation-extension motion of DNA that is the key to the preconditioning effect is also observed in flow field. As to the performance for DNA stretching, case III is better than case II, and case II is better than case I. The result is again consistent with our prediction.