Rapid electrokinetic patterning (REP) is an emerging microfluidic tweezer which can dynamically trap and manipulate micro- and nanoparticles via modulation of electrothermal vortices with optical patterns. By analyzing the trajectory of trapped particles with subpixel resolution, we show that the transverse trapping force in REP originates due to axisymmetric Stokes drag experienced by the particles in toroidal electrothermal vortices. The trapping force scales linearly with radial distance from the trap center and trap stiffness is on the order of femtonewtons/μm in the transverse plane. This low trap stiffness is a direct feature of the fluidic nature of the REP trapping and would be useful for measuring femtonewton-scale forces.

中文翻译：

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光诱导电热涡流镊子中的俘获力性质

快速电动图案化（REP）是一种新兴的微流镊子，它可以通过调制具有光学图案的电热涡旋来动态捕获和操纵微颗粒和纳米颗粒。通过以亚像素分辨率分析捕获粒子的轨迹，我们发现REP中的横向捕获力是由于环状电热涡流中粒子经历的轴对称斯托克斯阻力引起的。捕集力与到捕集器中心的径向距离成线性比例，并且捕集器的刚度在横向平面上约为femtonewtons /μm。这种低的捕集器刚度是REP捕集器的流体性质的直接特征，对于测量毫微牛顿级力很有用。