Department of Mechanical Engineering, University of Nevada, Las Vegas, Nevada 89154, USA.
Langmuir. 2010 Apr 20;26(8):5412-20. doi: 10.1021/la903842z.
Recently, there has been growing interest in utilizing electrical fields to position and separate rod-shaped particles such as DNA molecules, actin filaments, microtubules, viruses, bacteria, nanotubes, and nanorods. The polarization of the electrical double layer, enveloping the rod, plays a critical role in determining the magnitude and direction of the rod's dipole moment. We consider noninteracting, rod-shaped (spherocylinder) particles and calculate the induced dipole moment as a function of the electrical field frequency, the rod's aspect ratio (length/radius), the rod's free surface charge, and the double-layer thickness. To this end, we solve the Poisson-Nernst-Planck (PNP) equations for the ions' migration, diffusion, and convection. When the surface charge is small and the rod is short, the dipole moment is negative. As the rod's length increases, the dipole moment increases and eventually changes sign from negative to positive. The dipole coefficient of a rod, whose length is greater than some critical value, increases linearly with length. This latter observation simplifies the estimation of the dipole moment of particles with large aspect ratios (length/radius). The theoretical predictions are compared and favorably agree with experimental data for double-stranded, short DNA molecules.
最近，人们越来越感兴趣地利用电场来定位和分离棒状颗粒，如 DNA 分子、肌动蛋白丝、微管、病毒、细菌、纳米管和纳米棒。包围棒的电双层的极化在确定棒的偶极矩的大小和方向方面起着关键作用。我们考虑非相互作用的棒状（球柱）颗粒，并计算感应偶极矩作为电场频率、棒的纵横比（长度/半径）、棒的自由表面电荷和双层厚度的函数。为此，我们求解离子迁移、扩散和对流的泊松-纳斯特-普朗克（PNP）方程。当表面电荷较小且棒较短时，偶极矩为负。随着棒的长度增加，偶极矩增加，最终从负变为正。长度大于某个临界值的棒的偶极系数与长度呈线性增加。后一种观察结果简化了对大纵横比（长度/半径）颗粒偶极矩的估计。理论预测与双链短 DNA 分子的实验数据进行了比较，并得到了很好的一致性。
