以扭轉模式原子力顯微鏡量測磷脂雙層膜之研究

Abstract

由於原子力顯微鏡(Atomic force microscope, AFM)有著能夠在不同溶液中得到樣本奈米級表面形貌以及微尺度機械性質的能力，一直是研究生物樣本的一大利器。其中磷脂雙層膜(Lipid bilayer)是組成細胞膜結構的代表性樣本之一。儘管使用原子力顯微鏡對磷脂雙層膜的各種研究不勝枚舉，卻鮮少有對其平面方向(In-plane)性質的研究。本論文使用扭轉(Torsion)以及輕敲(Tapping)的混和模式對1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)及1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)兩種磷脂質進行量測，結果顯示振幅、相位訊號能在雲母及兩種磷脂雙層膜上得到明顯差異。此外，相較於輕敲膜是，扭轉模式在相位上能夠得到更高的對比。實驗也對兩種磷脂雙層膜進行了力體積模式(Force volume)掃描。透過分析逐點力圖計算探針與樣本接觸點位置得到磷脂雙層膜厚度約為2至4 nm，而利用探針刺穿磷脂雙層膜時之振幅、偏折力圖資訊則計算出平均膜厚約為5 nm。此外，由力圖變化之斜率差異可以辨別材料軟硬度。

Atomic force microscope (AFM) has the ability to measure surface morphology and mechanical properties at nano-scale, which is a powerful tool for studying biological samples. Lipid bilayer is one of the typical biological samples, which is the basic structure of the cell membrane. Although lipid bilayer has been widely studied by using AFM, it’s in-plane mechanical properties are still rarely discussed. In this thesis, a hybrid mode of torsion and tapping modes AFM was used to measure two types of the lipid bilayers, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The results show that significant contrast can be obtained on both amplitude and phase signal between mica and the lipid bilayers, and the phase signal of the torsion mode provided a higher contrast comparing with the tapping mode. Moreover, by using the force volume mode, the contact point positions between the cantilever tip and sample were calculated at each image pixels, and the thickness of the lipid bilayers was about 2 to 4 nm. By analyzing both amplitude and deflection force curve, an average thickness of 5 nm was obtained. Furthermore, the slope of the force curve cab be utilized to distinguish the material stiffness.