Research and fabricate a PDMS microfluidic chip which can implement the focusing quening experiment on different sizes of cells based on hydrodynamic focusing effect.The fabricating process of the chip is as follows:firstly

fabricate male mold of SU—8;secondly

make the PDMS microfluidic channel using soft photo-lithography;at last

bond and packge with the cover.Fluid focusing simulation is carried out under condition of different flow rate ratio between the sample flow and sheath flow via the COMSOL software and obtain focusing width of sample.Use Rhodamine B to carry out confirmatory experiment of focusing

focusing width is consistent with the simulation.The chip can be used for count and analysis of cells of

10

6

0 μm by adjusting the flow rate ratio.And the experiment of queuing of fluorescent microbeads is carried out

it is observed that microbeads pass through the focusing channel in a line.This fabrication method for microfluidic chip have the advantages of simple process（SU—8 male mold can reuse）

low cost

simple adjusting style and versatility.