Experimental and numerical analysis of the geometry effects of low-dispersion turns in microfluidic systems

This paper presents numerical and experimental investigations into the influence of the geometric bend ratio on turn-induced dispersion within U-shaped separation channels. The separation efficiency of an electrophoresis microfluidic device is known to be significantly influenced by the geometry and flow field conditions of the separation microchannel. Consequently, developing a thorough understanding of the effects of different geometries on the flow field physics in the separation microchannel is of fundamental concern in improving the design and operation of microfluidic chip systems. The turns in a microfabricated separation channel tend to induce a band-broadening effect which degrades the separation efficiency of the device. Consequently, the present study designs and tests various geometric bend ratios with the aim of reducing this so-called 'racetrack' effect. The effects on the band distribution in the detection area of the separation channel geometry, the fluid velocity profile and the bend ratio are investigated theoretically and experimentally for the case of a 100 bp DNA sizing ladder sample. A good agreement is obtained between the numerical and experimental results. It is shown that the serpentine U-shaped channel configuration is ideally suited to the efficient separation of this sample within miniature microfluidic devices. The results indicate that a bend ratio of 4 corrects band tilting and reduces the racetrack effect in the detection area, hence enabling an optimal separation performance.