Flow-delay Control Units For Microfluidic Devices

The technology of point-of-care-test(POCT) has been more and more used in chemical analysis, medical diagnosis and environmental testing.The need for the advanced methods of microfluidic control is becoming more and more urgent as the integration of biochemical sensors, mixer, post-processing system on platform of lab-on-a-chip is advanced. However,there is still many challenges in the integration of microfluidic operation units.Many active microfluidic units which is driven by external device have been studied at present.It's often hard to integrate or take along those devices as they are too bulky.Passive microfluidic chips driven by capillary force provides a new chance to integration of microfluidic units.However,there are still many problems to be solved for the automatic liquid flow along the specific path controlled by capillary force.In this paper,the microfluidic delay flow control unit based on capillary force are studied.The capillary force of different areas of the channel was controlled by changing size of micro structure on the surface of channel.So the flow direction and time can be controlled accurately.The finished works are as follow:(1)Two delay flow control units are designed.Based on the theory of capillary pressure, three micro structures are designed separately to control the liquid flow horizontally, and vertically.The comb tooth and maze shaped microfluidic delay control unit are formed by combination and array of three micro structures mentioned above.The flow direction and time can be controlled accurately by these two unit.(2)The experimental chips are fabricated by the process of UV-LIGA and hot embossing.The silicon mold is fabricated by UV-LIGA first.Then the microfludic channel and units designed are hot embossed on the PMMA substrate by silicon mold.The deviation of the channel's depth between the actual and design is-1.59?m?-0.41?m.As for delay flow control unit,the deviation is-0.35?0.22?m.The substrate and cover was bonded last.(3)The liquid experiment is conducted on the two units.X1 and X2 are the two design size of the comb tooth microfluidic delay control unit.X1 is the distance between rectangular convex platform and channel wall and X2 is the longitudinal spacing of adjacent two rectangular convex platform.X3,X4 and X5 are the three design size of maze shaped microfluidic delay control unit.X3 is the distance between rectangular convex platform and channel wall. X4 is the longitudinal spacing of adjacent two rectangular convex platform.X5 is the longitudinal spacing of adjacent two rectangular convex platform that control the liquid flow in the middle.The liquid experiment indicated that the delay time of XI is 2.36s-4.24s,and for X2 is 2.12s-13.96s,3 is 3.76s-5.44s,X4 is 7.56s-15.84s,X5 is 0.52s-0.88s.