Team:TU Delft-Leiden/Project/Gadget/Microfluidics

Microfluidics

Intro paragraph about microfluidics

Mother Machine

Dropsens

Paper Microfluidics

Paper microfluidics offer a simple, low cost method for employing some of the advantages of microfluidics for analytics purposes. Disposable analytical devices can be made easily and quickly with no specialised equipment. We plan to combine a paper microfluidic device with our Electrace e coli, and printed electrodes, to create a “test strip” for our analyte, which can be used to measure the voltage output of our biosensor. There are several methods that can be employed to create a paper microfluidic device. The two we chose to look at due to their simplicity and potential for good results were FLASH (Andres W. Martinez et al) - which utilises a form of photolithography, and a method utilising Parafilm, by E. M. Dunfield et al.

Parafilm Method

We first tested the Parafilm method, as described here. This involves stacking a piece of filter paper, a heat resistant mask (in the shape of the desired fluid channels) and a layer of parafilm, and applying heat and pressure to this stack. The principle is that the parafilm melts, and is forced into the filter paper, creating a hydrophobic area. The mask prevents the parafilm entering the paper, thus this area remains hydrophilic - providing the fluid channels. A regular clothes iron was used to provide heat, and pressure was provided by simply pressing down on the iron. We tested several types of paper, including tissue paper, coffee filter, filter paper (?) and Whattman grade 1) thicker grades of paper resulted in failure, as the parafilm would not fully penetrate the paper. Best results were had with the coffee filter paper.

With a heat press, such as those used to print images on to t-shirts, more heat and pressure could be applied in a consistent manner, likely improving results even in thicker grades of paper, however such a device was not accessible. Whilst we has some degree of success with this method, it had several shortcomings which made us move onto the second method, namely:
- Didn’t work with thicker grade of pressure (with our methods)
-Some parafilm “leakage” across the edges of the mask, results in a degree of imprecision in the creation of the channels.
-The need to cut out the mask limits its ability to be used for complex shapes and small dimensions, particular if access to a laser cutter or similar is not possible.