Team:EPF-Lausanne/Tools/Microfluidics/HowTo2
From 2011.igem.org
Microfluidics how-to
To be done: describe how to design and make a chip. Or how to order one.
Microfludics chips are nothing but a piece of moulded rubber. To actually get anything out of them, an external setup of tubing, compressed air, and valves is needed to flow in fluids and actuate the on-chip valves. To see what's happening, you'll also need some form of microscope.
Contents |
Making a chip
A basic microfluidics control setup
Injecting fluids: mains pressure and tubing, pressure regulators
A microfluidic chip is a network of small channels for fluids. To inject fluid in, a small (.02" inner diameter) tube is filled, then plugged into the chip through one of the punched holes (connecting them with a tubular metal pin). On the other end, the tubes are plugged into a manifold, in turn supplied with air at about 0.2 bar (3 psi), as set by a pressure regulator. The fluid is thus forced into the channels by the compressed air. A syringe can also be used to fill the chip, but it is hard to keep an even pressure (plus you quickly run out of hands).
Controlling flow: microfluidic valves and 3-way valves.
Our chips have a second control layer above or below the main flow layer. The layers are separated by a thin membrane of PDMS, and their channels overlap in specific locations. When channels of the control layer are pressurized, the membrane bends into the flow layer and blocks it. This creates a microfluidic 'on-chip' valve.
The channels of the control layer are filled in the same way as the flow layer, but require much higher pressure to bend the membrane. We typically used about 2 bar or 30 psi. Each independant valve in the control layer is pressurised by a different tube, regulated by a three-way valve. These switch between high pressure (from mains pressure, and the pressure regulator) to low pressure (atmospheric pressure), and hence allow quick toggling of the microfluidic valve between the open (unpressurised) and closed (pressurised) state. Three way valves come in manually- or electrically-controlled flavours. The manual kind is simpler and more reliable; we use them for the MITOMI chips. The electric kind (more specifically solenoid valves) we use for the web-controlled setup.