论文标题
一种测量和定量纳米夹层液体中示踪剂扩散的新方法
A new method for measurement and quantification of tracer diffusion in nanoconfined liquids
论文作者
论文摘要
我们报告了一种新型仪器的开发，以测量纳米级限制下水中的示踪剂扩散。通过用金属将探针涂覆并打开一个小的光圈（0.1 $ $ $ m至1 $μm），可以使对限制水之间的直接光学通道限制在锥形纤维和扁平底物之间的限制区域。使用离子束进行良好控制的切割可确保所需的横向限制区域以及对限制间隙的充分照明。探针安装在基于调谐的力传感器上，以用NM精度控制探针和基板之间的分离。使用具有单个光子精确度的共聚焦排列记录，由于染料和样品之间限制在探针和样品之间的水中扩散荧光强度的波动。开发了一种蒙特卡洛方法，以确定从测量的强度波动的自相关的扩散系数，该相关的强度波动的自相关得出，该相关的特定几何形状和照明轮廓。该仪器允许在限制下测量扩散法。我们发现，对于5 nm及以下的探针 - 底物分离，示踪剂分子的扩散减慢了十倍以上。
We report development of a novel instrument to measure tracer diffusion in water under nano-scale confinement. A direct optical access to the confinement region, where water is confined between a tapered fiber and a flat substrate, is made possible by coating the probe with metal and opening a small aperture( 0.1 $μ$m to 1 $μ$m) at its end. A well-controlled cut using an ion beam ensures desired lateral confinement area as well as adequate illumination of the confinement gap. The probe is mounted on a tuning-fork based force sensor to control the separation between the probe and the substrate with nm precision. Fluctuations in fluorescence intensity due to diffusion of a dye molecule in water confined between probe and the sample are recorded using a confocal arrangement with a single photon precision. A Monte-Carlo method is developed to determine the diffusion coefficient from the measured autocorrelation of intensity fluctuations which accommodates the specific geometry of confinement and the illumination profile. The instrument allows measurement of diffusion laws under confinement. We found that the diffusion of a tracer molecule is slowed down by more than ten times for the probe-substrate separations of 5 nm and below.
