One of our ongoing projects is studying the behavior of Phytophthora oomycetes zoospores. Phytophthora is a plant pathogen, probably best known for causing the Irish Potato Famine in the 1800s. Part of the lifecycle of some species of Phytophthora involves the release of single-celled zoospores that have shown to respond to chemical signals. To study this behavior in the lab, we have designed and manufactured microfluidic chips at the Cornell NanoScale Science and Technology Facility (CNF).

The CNF has a fantastic program put together to assist in the engineering of nanotechnology. After a week-long training and assignment to an experienced staff member to provide guidance and insight, you are free to use the facilities. Each machine requires instruction to get started, but once complete; you are off to the races!

Phytophthora zoospores measure in around 10-15 microns. The channels we designed to assay them in have features 100 microns at the smallest. Believe it or not, this is rather large by the CNF’s standards. A lot of the work done there measures more in nanometers than micrometers. Because of this, we barely scratched the surface of the CNF’s capabilities, but it was more than enough to impress us.

To achieve our goal of making these microfluidics chips, we used a process known as photolithography. The general idea is to coat a silicon wafer in a substance, create a photomask of the chambers within the chip, and expose the coated wafer to light and leave behind a mold used to make PDMS assay chambers. You then fuse these chambers between two microscope slides using plasma treatment to create a microfluidic chip.

Single Choice Wafer Mold

Because of the size of our design, we ended up using SU-8 spun on a silicon wafer around a thickness of 150 microns. Now that the design is complete, we can continue the exploration of the chemical ecology of Phytophthora zoospores.