去氧核糖核酸分子於交流電場下之響應研究

一般熟為人知的電泳技術是在直流電場之下，帶電顆粒由於所帶電荷量的不同，以及分子大小差異，而有不同速度的移動行為，從而彼此分離。然而在直流電場持續供應之下，可能會使得電荷累積在電極附近，意味著量測環境將隨之同時變化。因此，我們將直流電場更動為交流電場，以避免電荷持續累積之問題，希冀可使量測環境不隨時間而改變，在此條件之下觀察分子之運動行為。本實驗所選用之樣品為去氧核糖核酸分子。由於生物分子之信號微弱且雜訊嚴重，因此我們使用了鎖相放大器來擷取實驗數據。在實驗中，我們觀察了腺嘌呤、鳥糞嘌呤、胸腺嘧啶、胞嘧啶，四種分子之實部與虛部電流對頻率之關係，並同時將相位對頻率作圖。除此之外，亦量測了電流對電壓之關係。我們將解離這個行為，以彈簧做為類比，由此導出一個方程式，來解釋分子在交流電場下之運動行為。將理論值與實驗結果比對，發現曲線之趨勢相當地接近，可進一步找出未定參數之數量級範圍。在模擬的過程中，可以發現電流完全由去氧核糖核酸分子所主導。從物理出發，氫離子的質量比去氧核糖核酸分子小了三個數量級，移動速度較快；而水分子的組成為一個氧和兩個氫，氫離子在運動時遇到與自己匹敵的氫，散射機會亦提高許多。相較之下，質量大上許多的去氧核糖核酸分子，碰撞質量較小的水分子，反而受到的影響較小，雖然移動得較為緩慢，卻能穩定地形成電流，最後反而變成電流的主要貢獻來源。

關鍵字

交流電場；去氧核糖核酸分子；電泳；直流電場；散射

並列摘要

In general, the well-known electrophoresis is used under influence of an applied direct current field. By placing the particles in wells and applying an electric current, the particles will move through the matrix at different rates, usually determined by masses and the surface charges, toward the anode if negatively charged or toward the cathode if positively charged. However, the charges are probably to accumulate around the electrodes when the direct current electric field is being applied, meaning that the condition of measurement is somewhat changed as time goes by. Consequently, we applied an alternating current field instead of a direct current field to avoid the problem of charge accumulation by which the behavior of molecules in a time-invariant condition were observed. The deoxyribonucleic acid (DNA) molecules were used as specimens. According to the weakness and the noise of the signals from the biomolecules, the lock-in amplifier was used for measurement. In the experiment, we found the relations of real parts and imaginary parts of currents to time, and thus the relation of phase to time. Aside from these measurements, the I-V relationship was observed. In our model the behavior of dissociation is compared to a spring. The degree of dissociation is depicted by force constant. Based on this assumption, we made fittings compared with experimental results, attempting to find out the possible values of the three indeterminate variables. Later, we observed that the DNA molecules dominated the current by theoretical calculation which may be due to the small extent of scattering because that severe scattering might prevent current from producing.

並列關鍵字

DNA molecules ； alternating current field ； direct current field ； electrophoresis ； scattering

參考文獻

1 D. D. Eley and D. I. Spivey, Trans. Faraday Soc., 58, 411 – 415 (1962)

6 M. R. Bown and C. D. Meinhart, Microfluid Nanofluid, 2: 513-523 (2006)

7 Youdong Mao et al., Nucleic Acids Research, Vol. 35, No. 5 e33 (2007)

8 Noritada Kaji, Masanori Ueda, and Yoshinobu Baba, Biophysical Journal, Volume 82, 335-344 (2002)

9 Charles Polk, IEEE Transaction on Education, Vol. 34, No. 3 (1991)

國際替代計量

去氧核糖核酸分子於交流電場下之響應研究

主題瀏覽