利用微悬臂梁表面应力研究聚N-异丙基丙烯酰胺分子的构象转变

提出了一种基于微悬臂梁传感技术研究大分子折叠/构象转变的新方法.通过分子自组装的方法将热敏性的聚N-异丙基丙烯酰胺(PNIPAM)分子链修饰到微悬臂梁的单侧表面，用光杠杆技术检测温度在20—40℃之间变化时由于微悬臂梁上的PNIPAM分子在水中的构象转变所引起的微悬臂梁变形.实验结果显示：在升温过程中，微悬臂梁的表面应力发生了变化并且导致微悬臂梁产生了弯曲变形，这个过程对应着微悬臂梁上的PNIPAM分子从无规线团构象到塌缩小球构象的构象转变.在降温过程中，微悬臂梁发生了反方向的弯曲变形，这对应着PNIPA 关键词： 构象转变 聚N-异丙基丙烯酰胺分子链 表面应力 微悬臂梁

Investigation of conformation transition of poly(N-isopropylacrylamide) by surface stress detection using micro-cantilever

A new method based on micro-cantilever sensors was presented and used to investigate conformation transition of macromolecules. Poly(N-isopropylacrylamide)(PNIPAM)were grafted onto one surface of a micro-cantilever by self assemble monolayer method. Then the micro-cantilever was immersed into distilled water in which the temperature can be adjusted in the range of 20—40℃. The deflection of the micro-cantilever induced by conformation transition of PNIPAM chains was measured using optical lever technique. The results show that the micro-cantilever deflects upon heating and opposite deflection occurs upon cooling, which indicates that the surface stress of the micro-cantilever changes when the conformation of PNIPAM changes upon heating and cooling. The surface stress changes continuously over the range of 20—40℃. However, a sharp change appears around the low critical solution temperature (～32℃), at which a coil-globule transition occurs in free aqueous solution of PNIPAM. The whole process is irreversible and shows a clear hysteresis, which can be attributed to hydrogen bonding and the possible chain entanglement formed during the collapse process.