On-chip valving has been widely applied in polydimethylsiloxane (PDMS) microfluidics due to the fast response,low dead volume and high integration density.However,the technique is difficult to migrate to thermoplastic microfluidics [1,2],which is the better candidate in many lab-on-a-chip and diagnostics applications.In this work,we are developing a novel on-chip valving solution for thermoplastic microfluidic devices,demonstrating the pneumatic-driven and magnet-actuated valves which are reliable,easy to implement,scalable,and low-cost.The on-chip valving is realized by a miniaturized valve,which can be mounted onto a microfluidic chip.The valve is separately fabricated from polymethylmethacrylate (PMMA) with a sandwiched structure.A piece of thermoplastic polyurethane (TPU) membrane is partially joined with the PMMA part around the centre,and can be deformed vertically in the centre under external force.As shown in Figure 1,on the PMMA microfluidic chip,there are two open holes vertically link to the microfluidic circuits inside.Mounting the valve onto the PMMA chip,the two open holes together with the lower cavity under the valve membrane form a flow path,which can be pinched off when the valve membrane is deformed downwards and block one of the open holes on PMMA chip,and realize the valving function.The pneumatic-driven valve can be actuated by air pressure,which realizes the programmable switching by controlling the air pressure.In the other configuration,it can be magnet-actuated through applying mechanical force directly on the membrane.Both actuation mechanisms have been successfully demonstrated in this work.The geometrical design of valve was guided by COMSOL Multiphasic simulation as shown in Figures 2.As shown in Figure 3,the pneumatic valve has overall size of 8mm×8mm×4mm,including the build-in air connector.The TPU membrane has a size of 4mm diameter and 0.15mm thickness.During the liquid flow test,the air-actuated valve can withstand up to 600 kPa flow pressure in switch-off status without any leakage.Also,the magnet-actuated valve was fabricated and tested,as shown in Figure 4,which demonstrated gauge pressure up to 85 kPa of flow pressure in switch-off status.