去氧核醣核酸(deoxyribonucleic acid,DNA)在生物學中是重要遺傳訊息的儲存基元。然而就目前而言，DNA還有許多未知特性需要被研究探討。本實驗利用雲母和金作為基板，以原子力顯微鏡(atomic force microscopy, AFM)研究吸附於基板的DNA結構。
雲母和DNA都帶有負電荷，可以藉由多價陽離子作為橋樑使DNA固定於雲母基板。於實驗中藉由改變離子濃度改善DNA吸附狀況。當以乙醇取代去離子水作為溶劑時，觀察DNA結構轉變。金和DNA鹼基都具有疏水性會產生強力鍵結，可以利用探針去拉伸同時鍵結金和探針的DNA，量測DNA的力曲線(force curve)。
DNA吸附在雲母上的效果不完全會隨陽離子濃度增加而提升，陽離子濃度介於0.5 mM ~ 10 mM時效果最好。當DNA溶於乙醇結構會由B構形轉變為A構形。量測DNA力曲線時探針的速度會影響所量測的曲線，當受力達到27 pN時DNA的螺旋狀結構會因為拉伸而解開。

Deoxyribonucleic acid (DNA) is the most important element for storing genetic information in biology. Until so far, there are still a lot of unknown properties which need to be investigated. In this study, we used mica and gold substrate for binding DNA and observed DNA structures by using atomic force microscopy (AFM).
Both mica and DNA have negative charges, so multivalent cations can be the bridge to link DNA and mica substrate. In our experiments, cation concentration is changed as the parameter to improve the DNA binding efficiency. We also observed the transition of DNA conformation when the liquor of deionized water was replaced by ethanol. Both Gold and the base on DNA backbone are hydrophobic, so DNA can be bound to gold substrate strongly. As the result, we used the tip to stretch DNA that is both bound to the gold substrate and the tip, and then we can measure the force curve of DNA during structure transformation.
The efficiency of DNA bound on mica is not really proportional to cation concentration. There are the best efficiency when the cation concentration is between 0.5 mM ~ 10mM. The conformation of DNA will change from B-form to A-form . During the stretching of DNA, The velocity of tip will affect the experiment data of force curve. The helical conformation of DNA will be unwinding under stretching with 27 pN.

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