Week 1

Greetings!

Although this post is a little late, I have much to report. Last week was my first official week, and although I'm only beginning to delve into my projects I have already learned so much.

I am working on two projects, however the polymer synthesis project is the bigger project and I will dedicate this post solely to this project. At the end of this week however I will report on this weeks progress on both projects.

Composite polymer coating for electrodes:

       In the past few months and years, Dr. Heien's lab has been developing a polymer composite known as PEDOT:Nafion for the coating of carbon-fiber electrodes. This composite polymer is created like this. Acetonitrile (ACN), 3,4-Ethylenedioxythiophene (a monomer abbreviated as EDOT), and Nafion are combined in solution in very specific concentrations. The carbon fiber electrode, a chlorodized silver wire (the reference electrode) and a tightly coiled silver wire (the counter electrode) are then all lowered into the solution already created. Each of the the three electrodes are then hooked up to a potentiostat which applies a triangle wave form (1.5 V to -.8 V) for 15 seconds. This voltage causes the EDOT monomers around the electrode to form the polymer PEDOT. In addition under the correct voltage the PEDOT polymer also bonds to Nafion in the solution, forming the PEDOT:Nafion composite polymer (Figure 1). This composite Polymer then settles onto the carbon fiber electrode forming a uniform coat about 100 nm thick (Figure 2). 

      

Figure 1: EDOT (the monomer) is seen in the top left corner.
PEDOT:Nafion (the composite polymer) can be seen on the right side

       Why is it important that the electrodes are coated with the this PEDOT:Nafion composite polymer? This extra coating on the electrode has three purposes...

1. It makes the electrode more sensitive to Dopamine 
2. It increases the selectivity of the electrode for Dopamine (Figure 2)
3. It reduces the amount of biomaterial amassing on the electrode ( eg. bloodclots, etc.) (Figure 3) 

These three effects that the coating has makes neurotransmitter detection and uptake by an electrode much more accurate. 

Figure 2:
On the left is a picture showing the increase in Dopamine selectivity
On the right is an electron microscopy scan revealing the uniform coating
on the end of an electrode

Figure 3:
Left: Uncoated electrode left in brain
for 30 minutes (Lots of biomass present)
Right: Coated electrode left in brain
for 6 hours (Less biomass present)

Furthering this Research:

In my project I am particularly interested in the last purpose the composite polymer fulfills: it reduces the amount of "gunk" that attaches to the electrode when in the brain. I am interested in this because in Deep Brian Stimulation surgeries electrodes made of platinum are used to send electrical signals to affected parts of the brain. Since this electrode is in the brain for some time, biomaterial will naturally attach to it. Therefore, it would be useful to create a polymer that could coat the platinum electrodes as well. To do this however, I will change the concentration of ACN, EDOT, and Nafion, and I will also have to apply a different voltage range to it.

Last Wednesday, under the supervision of a graduate student I repeated the carbon-fiber electrode coating experiment to become familiar with how the process goes. I pipetted out the correct volumes of the 3 compounds in the solution and combined them in a 20mL vile. I then took the 20mL vile to the potentiostat, hooked up the Counter Electrode, the carbon-fiber Electrode, and the Reference Electrode, and ran the triangle wave form through the electrodes, allowing the reaction to take place around the electrode. This week, I'm taking things a step further and I am going to begin trying to coat the platinum electrodes.

After last week, I have a good grasp on the previous experiments that were conducted and now I have the necessary to knowledge to begin my actual project.

More coming on this project and my other one this weekend!

Thanks for reading!

Gil Wondrak


Sources: I learned most of this information from this article and the people who wrote it.

Michael Heien. "Biocompatible PEDOT:Nafion Composite Electrode Coatings for Selective Detection of Neurotransmitters in Vivo" Analytical Chemistry. Web. 24 February 2015.