平鋪在基板(如:雲母片)上的脂質雙層 (supported lipid bilayer)，常被當成研究細胞膜的模型，且已被廣泛使用在生物物理相關領域。但雲母片 (mica) 對脂質雙層的影響少有研究。我們利用原子力顯微鏡探測在雲母片和在POPC塗佈雲母片 (POPC-coated mica) 上的1:1 DPPC/DOPC表面形貌，本研究中大部分的量測是在液體環境中進行。為了在液態環境中鋪平脂質雙層，我們使用不同方法製作脂質雙層，相較旋轉塗佈方法 (spin coating)，脂球融合方法 (vesicle fusion) 所製備的樣品在液態環境中有更好的品質。1:1 DPPC/DOPC 脂質雙層平鋪在POPC塗佈雲母片上的AFM影像，顯示出兩種脂質雙層厚度分布：較厚的脂質雙層推測對應到“富含DPPC的膠態區塊”(DPPC-rich gel phase domain) ; 較薄的脂質雙層推測對應到“富含DOPC的液態區塊”(DOPC-rich liquid crystalline phase domain)。且POPC塗佈雲母片上的脂質雙層和懸浮的多層脂球 (multilamellar vesicle) 有著相似的相變溫度 (gel-to-liquid crystalline transition temperature)，顯示在POPC塗佈雲母片上，脂質雙層可近似懸浮樣品。另一方面，在雲母片上的1:1 DPPC/DOPC有較高的相變溫度，此結果指出雲母片會迫使脂質雙層排列更緊密有序，而藉由預先塗佈一層POPC脂質雙層，夾在1:1 DPPC/DOPC 脂質雙層和雲母片之間，可減少此有序效應。此外，我們推測雲母片-脂質單層相互影響 (mica- leaflet interaction)和脂質雙層間相互影響 (inter-leaflet coupling) 可能是決定脂質雙層對稱性質 (bilayer symmetry) 的因素，這方面的研究還必須做更進一步的實驗驗證。 Supported planar lipid bilayers are versatile models of the biological membrane, which have been widely used in biophysical studies. However, limited consideration has been given to the effect of mica on the lipid bilayer. In this thesis, we study the morphology of the 1:1 DPPC/DOPC bilayer on mica and on POPC-coated mica using atomic force microscopy (AFM). Most of AFM images were acquired in buffer. To obtain a good-quality sample, bilayers prepared from different methods were compared. We found that the bilayer prepared from vesicle fusion yields better quality for imaging in buffer and shorter preparation time than that from spin coating. The images of 1:1 DPPC/DOPC bilayer on POPC-coated mica display two different bilayer thicknesses. The thicker and thinner bilayers, presumably correspond to the DPPC-rich gel phase and DOPC-rich liquid crystalline phase, respectively. We found that this bilayer on POPC-coated mica can be regarded as a free-standing bilayer effectively as it has a gel-to-liquid crystalline transition temperature close to that of the bilayers in multilamellar vesicle suspension. In contrast, the 1:1 DPPC/DOPC bilayer on mica exhibits a higher gel-to-liquid crystalline transition temperature, suggesting that mica induces an ordering effect on the lipid bilayer. This effect can be reduced by inserting a POPC bilayer between the 1:1 DPPC/DOPC bilayer and mica. Furthermore, there is a slight indication that the mica-leaflet interaction and and inter-leaflet coupling may dominate in bilayers on mica and on POPC-coated mica, respectively, which may result in different bilayer symmetry. Further studies will be needed to examine this in detail.
