Dutta D, Leighton D T
Department of Chemical Engineering, University of Notre Dame, Indiana 46556, USA.
Anal Chem. 2001 Feb 1;73(3):504-13. doi: 10.1021/ac0008385.
Fluid is often moved about microetched channels in lab-on-a-chip applications using electrokinetic flows (electrophoresis or electroosmosis) rather than pressure-driven flows because the latter result in large Taylor dispersion. However, small pressure gradients may arise unintentionally in such systems due to a mismatch in electroosmotic flow rates or hydrostatic pressure differentials along the microetched channel. Under laminar flow conditions, Doshi et al. (Chem. Eng. Sci. 1978, 33, 795-804) have shown that for a channel with rectangular cross-section of width W and depth d, longitudinal diffusivities can attain values as large as approximately 8 K0 for small values of the aspect ratio d/W, where K0 is the value of the longitudinal diffusivity obtained by ignoring all variations across the channel. Microchannels in lab-on-a-chip geometries are often not rectangular in cross-section. Isotropic etching techniques, for example, lead to channels with quarter-circular ends. In this paper we examine the effect of this geometry on the magnitude of longitudinal dispersivity for pressure-driven flows and also investigate modifications to this design which may minimize such dispersion. Optimal channel profiles are shown to lead to dispersivities approaching K0, the theoretical minimum, for small values of d/W.
在芯片实验室应用中，流体通常利用电动流（电泳或电渗）在微蚀刻通道中流动，而非压力驱动流，因为后者会导致较大的泰勒色散。然而，由于沿微蚀刻通道的电渗流速不匹配或静水压力差，在这类系统中可能会无意地产生小的压力梯度。在层流条件下，多希等人（《化学工程科学》，1978年，第33卷，795 - 804页）表明，对于宽度为W、深度为d的矩形横截面通道，当宽深比d/W较小时，纵向扩散率可达到约8K0的值，其中K0是忽略通道内所有变化而得到的纵向扩散率值。芯片实验室几何结构中的微通道横截面通常不是矩形的。例如，各向同性蚀刻技术会导致通道两端为四分之一圆形。在本文中，我们研究了这种几何形状对压力驱动流纵向分散度大小的影响，并探讨了对该设计的改进措施，这些措施可能会使这种分散最小化。结果表明，对于较小的d/W值，最优通道轮廓会使分散度接近理论最小值K0。
