Introduction to Microfluidics
Imagine that you’re sick and need to get some blood tests done. Today, you would have to go to the hospital, get your blood drawn, and have the blood sent to a lab for analysis. In the near future, all of this could be done at home, with a device the size of a postage stamp. Prick your finger on one end of the device, and a tiny amount of blood is drawn. Your blood flows through microfluidic channels, going through various preparations and ending up in contact with some chemical – _____ for example. The ____ turns red, showing you have a deficiency in ____. Throw the device away like an old band-aid and you’re all set.
This kind of upcoming technology is called lab-on-a-chip, and it is based on using microfluidic channels to transport small quantities of fluids. In the example above, the microfluidic channels brought blood to a chemical for testing. While most of microfluidic research is done in laboratories, there are a few ways you can do it at home for a small cost.
Paper Microfluidics
One great quality of paper is that it allows capillary action, like how plants can draw water from the ground. If you could somehow make barriers in the paper where fluids could not go, spaces in between the barriers would be the channels. Drop some liquid at one end of the channel, and through capillary action, the liquid automatically flows through the paper to the other side. The key problem with this method is how to make these barriers.
So far, wax has shown to be a good way of making these barriers. Wax can be deposited on the paper, melted using an oven or hot plate, causing the wax to penetrate the paper and form barriers where fluids can’t cross. Wax can be put on paper precisely through a printer using wax-based ink, or by hand with a wax pen.
Printing the wax also opens another door – printing chemicals. A standard color printer has four ink reservoirs – black, cyan, magenta, and yellow. The blank ink can be refilled with the wax ink, and the three colored reservoirs can be refilled with chemical indicators. That way, creating a lab on a chip would be as simple as printing it on a piece of paper and heating it to melt the wax. This process would be excellent for low cost mass production of the devices.
PDMS Microfluidics ( Silicon based microfluidics)
A common type of microfluidics is called PDMS (polydimethylsiloxane) microfluidics. PDMS is simply a silicone that is easily molded – like Jell-O, but stronger (and less tasty). PDMS is hydrophobic and transparent, making it an ideal material to make microfluidic channels. PDMS is commercially sold as Sylgard 184 by Dow chemical – you can find it on eBay as many people use it in the process of building solar panels.
The way PDMS microfluidics works is tiny channels are molded into the PDMS where the liquid can flow. PDMS does not allow capillary action, so the fluids in these will be pressure driven – a syringe will push in the fluid from one end, forcing the liquid to flow through the device.