Turbulence is commonly viewed as a type of macroflow, where the Reynolds number (Re) has to be sufficiently high. In microfluidics, when Re is below or on the order of 1 and fast mixing is required, so far only chaotic flow has been reported to enhance mixing based on previous publications since turbulence is believed not to be possible to generate in such a low Re microflow. There is even a lack of velocimeter that can measure turbulence in microchannels. In this work, we report a direct observation of the existence of turbulence in microfluidics with Re on the order of 1 in a pressure driven flow under electrokinetic forcing using a novel velocimeter having ultrahigh spatiotemporal resolution. The work could provide a new method to control flow and transport phenomena in lab-on-a-chip and a new perspective on turbulence.

Separation of cancer cells from the other biological cells is important for clinical cancer diagnosis and cancer treatment. In this presentation, we use conventional dielectrophoresis (c-DEP) in a microfluidic chip to manipulate and collect colorectal cancer HCT116 cell. It is noticed that at particular AC frequency band, the HCT116 cell are deflected to a side channel from a main channel clearly after the electric activation. This motion caused by negative DEP can be used to separate the cancer cell from others. In this manuscript, we report the chip design, flow condition, the DEP spectrum of the cancer cell, and the separation and collection efficiency as well.