Yoshina-Ishii Chiaki, Boxer Steven G
Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
Langmuir. 2006 Feb 28;22(5):2384-91. doi: 10.1021/la0526277.
We recently introduced methods to tether phospholipid vesicles or proteoliposomes onto a fluid-supported lipid bilayer using DNA hybridization (Yoshina-Ishii, C.; Miller, G. P.; Kraft, M. L.; Kool, E. T.; Boxer, S. G. J. Am. Chem. Soc. 2005, 127, 1356-1357). These intact tethered vesicles diffuse in two dimensions parallel to the supporting membrane surface. In this article, we report the dynamic response of individual tethered vesicles to an electric field applied parallel to the bilayer surface. Vesicles respond to the field by moving in the direction of electro-osmotic flow, and this can be used to reversibly concentrate tethered vesicles against a barrier. By adding increasing amounts of negatively charged phosphatidylserine to the supporting bilayer to increase electro-osmosis, the electrophoretic mobility of the tethered vesicles can be increased. The electro-osmotic contribution can be modeled well by a sphere connected to a cylindrical anchor in a viscous membrane with charged headgroups. The electrophoretic force on the negatively charged tethered vesicles opposes the electro-osmotic force. By increasing the amount of negative charge on the tethered vesicle, drift in the direction of electro-osmotic flow can be slowed; at high negative charge on the tethered vesicle, motion can be forced in the direction of electrophoresis. The balance between these forces can be visualized on a patterned supporting bilayer containing negatively charged lipids that reorganize in an externally applied electric field to create a gradient of charge within a corralled region. The charge gradient at the surface creates a gradient of electro-osmotic flow, and vesicles carrying similar amounts of negative charge can be focused to a region perpendicular to the applied field where electrophoresis is balanced by electro-osmosis, away from the corral boundary. Electric fields are effective tools to direct tethered vesicles and concentrate them and to measure the tethered vesicle's electrostatic properties.
我们最近介绍了利用DNA杂交将磷脂囊泡或蛋白脂质体拴系到流体支撑脂质双层上的方法（吉纳-石井，C.；米勒，G. P.；克拉夫特，M. L.；库尔，E. T.；博克瑟，S. G.《美国化学会志》2005年，127卷，1356 - 1357页）。这些完整的拴系囊泡在平行于支撑膜表面的二维空间中扩散。在本文中，我们报告了单个拴系囊泡对平行于双层表面施加的电场的动态响应。囊泡通过沿电渗流方向移动来响应电场，这可用于将拴系囊泡可逆地浓缩到障碍物上。通过向支撑双层中添加越来越多带负电荷的磷脂酰丝氨酸以增加电渗作用，可以提高拴系囊泡的电泳迁移率。电渗贡献可以通过一个连接到粘性膜中带电荷头部基团的圆柱形锚的球体很好地建模。带负电荷的拴系囊泡上的电泳力与电渗力相反。通过增加拴系囊泡上的负电荷量，可以减缓其在电渗流方向上的漂移；在拴系囊泡上负电荷很高时，可以迫使它沿电泳方向移动。这些力之间的平衡可以在含有带负电荷脂质的图案化支撑双层上可视化，这些脂质在外部施加的电场中重新排列，在一个围栏区域内形成电荷梯度。表面的电荷梯度产生电渗流梯度，携带相似负电荷量的囊泡可以聚焦到垂直于施加电场的区域，在该区域电泳与电渗达到平衡，远离围栏边界。电场是引导和浓缩拴系囊泡以及测量拴系囊泡静电性质的有效工具。
