When designing your microfluidic circuit, you should consider which type (or types) of valve is most appropriate for your design. The three available valve types are: 1) Push-down, 2) Push-up, and 3) Sieve valve. The following briefly describes these valves and when it is appropriate to use them.

Push-down Valves

Configuration : Control lines pass over the flow channels. Pneumatic/hydraulic pressure in the control lines flattens the membrane valve downwards to create a seal.  This geometry is suitable only for low aspect ratio (1:10), shallow (approx 10µm) flow-structures and does not allow for deep reaction chambers to be integrated on the flow layer.

 

Standard Flow Geometry :  Standard flow features for the push-down valve is 100µm wide by 13µm tall.  

Standard Control Geometry :  Standard control channels are 100µm wide and either 10µm or 25µm tall. This results in a valve junction area of 100µm * 100µm. 

Applications : This geometry is particularly well suited to applications where the flow structure must be in direct contact with the substrate (e.g. spotting DNA, patterned substrate, etc.)

Sealing to Substrate :  The chip flow structures may be sealed either directly onto a glass cover-slip / glass slide, or onto a glass substrate coated by a thin layer of PDMS.  Devices sealed to glass are only rated to approximately 6psi flow pressures before delamination occurs.  Devices sealed with a third layer of PDMS are rated to 20psi flow pressure. The chip may also be bonded to a glass substrate directly via plasma bonding.

Push-up Valves

Configuration : Control lines pass under the flow channels. Pneumatic pressurization of the control line causes a membrane to deflect up into the flow structure, sealing the channel. Deep reaction chambers may be integrated into the flow layer (upwards).  

Standard Flow Geometry : 

a. Shallow Channel Option : Flow features are similar to push-down valves (100µm wide, 13µm tall). 

b. Deep Channel Option : Maximum flow channel heights at a valve junction is approximately 45µm. For 45µm tall flow channels, a valve junction area should be 200µm * 200µm.

Standard Control Geometry :  

a. Shallow Channel Option :  Standard control channels are 100µm wide and either 10µm or 25µm tall. This results in a valve junction area of 100µm * 100µm.    

b. Deep Channel Option :  Control channels are 200µm wide and 25µm tall.  For 45µm tall flow channels, a valve junction area should be 200µm * 200µm.

Applications : Deep channel push-up valves are suitable for applications that require suspensions of large particles (eukaryotic cells, large beads ...). 

Sealing to Substrate :  It is recommended to bond this type of chip to a glass substrate coated with a thin layer of PDMS or directly to a glass substrate via plasma bonding.

Seive Valves

Configuration : Sieve valves are different from push-down and push-up valves in that they intentionally do not create a tight seal. The flow channel has a rectangular profile instead of a rounded profile. When the valve is closed, the edges of the valve are not sealed and allows liquid to pass through along the channel edges. Most commonly, sieve valves are of the ‘push-up variety' (the control channels pass underneath the flow channels) and the membrane deflects upwards.

Applications: Sieve valves are useful for creating affinity columns of beads by blocking the movement of beads, but allowing reagents to flow through. The beads can then be released by opening the valve and allowing them to flow to another part of the chip. The sieve valve may also be used for filtering purposes.

Sealing to Substrate :  It is recommended to bond this type of chip to a glass substrate coated with a thin layer of PDMS or directly to a glass substrate via plasma bonding.