I learned a lot about the physics behind Applied Biophysics' ECIS instrument this week. (As more of a biology person, I need a lot of visuals to understand the physics side of things, so get ready for a lot of pictures and diagrams!) Dr. Keese and Dr. Renken gave me an in-depth presentation on how cells located in each well of the electrode array are subjected to varying frequencies to measure their behavior. There are two types of current- AC (alternating current) and DC (direct current). The ECIS instrument sends an AC current through the electrode, allowing us to get a constant reading. Here is a diagram I made to explain the main idea of using AC current:

For our purposes, the capacitor represents the cells that are sitting on the electrode. They act just like a capacitor because cells are mostly saltwater, and do not let current flow through.

In my experiment from last week, I used the most basic ECIS instrument, the Z. It sent out super-low frequencies of 1000 hz, all the way up to 96000 hz. At low frequencies, we were able to see how tightly joined our cells were. This is because current always wants to follow the path of least resistance, and will therefore travel around and underneath the cells. At higher frequencies, the current will pass right through the cell, and therefore allows us to measure how many cells are in the vicinity of the electrode. It is important to note that cells don't sit flat on a surface. Instead, they have little anchors that connect the cell to the surface it is growing and spreading out on. Here is a diagram that illustrates this concept:

With all this new information, I was able to understand the basics of my own ECIS graphs that were produced from the experiment I ran last week. My cells responded just as they were supposed to, with the exception of my control well which was filled with only medium. Apparently, I somehow got a few cells into this well and began to grow. (Opps!) 

Here is a graph of my data at a medium frequency of 16000 Hz. This frequency gives you a good overview of how my cells were growing, but it doesn't measure specific things like cell density or cell junctions.