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Team:UC Davis/Electrochemistry Electrode Choice
From 2014.igem.org
Which electrode to use?
Selecting the electrode was the first step in building our electrochemical system. In the selection process, many features were considered including price, portability, accuracy, solution volume, and compatibility with our hardware and software signal processing device. Our initial idea was to build our own electrode. However, after reviewing many literatures, we have concluded that purchasing one would be the smarter choice for our short time constraints and enhancing accuracy of chemical detection. We narrowed down our choice to one of the commercial electrodes which already has been proved to detect small concentration of NADH. One was DropSens, and the other was Pine Instrument. These two electrode have features which may or may not be suitable for our system.
Electrode Schema and Diagram
DropSens Vs. Pine Instrument:
| DropSens | Pine Instrument |
|---|---|
Pros:
Cons:
|
Pros:
Cons:
|
| D119L;Y296F;N455A | Increase hydrophobicity at far end of tunnel |
| D456L;D458L | Change far pocket polar residues to posess more nonpolar characteristics |
Importance of Mediator & Polymerization
The electrode system consists of a screen-printed chip embedded with three electrodes: the counter, working, and reference electrodes. Though the potential of the reference electrode is kept constant, a voltage bias is applied across the working and counter electrodes to facilitates a buildup of excess positive charge on the working electrode. This buildup induces the directional diffusion of NADH toward the working electrode. The working electrode consists of a carbon ink infused with polymer. Since some polymers have selective oxidative affinity for NADH, we decided to test two polymers that would work the best for our electrode.
Azure A vs. Meldola's Blue comparison Table goes here
Comparison experiment result:
Polymerization with both compounds, Azure A and Meldola’s Blue both gives some selective oxidative affinity for NADH by lowering the potential required to oxidize NADH at the electrode; therefore, expanding the voltage range favorable for us to conduct experiments at.
Both AA and MB has a selective oxidative affinity for NADH, reducing the over potential necessary for NADH oxidation at the working electrode. Although both are advantageous in terms of selectivity for detecting NADH, we have decided to use a polycyclic aromatic monomer dye, Meldola’s Blue (MB) for the following reason:
1. MB facilitates greater electron deposition and flow.
2. Azure A demonstrated second order responses, which can be possible indicative of non-trivial chemical interactions at the electrode surface.
3. MB gave us more reliable readings, especially showed no second order responses.
4. We can specifically ordered MB-infused electrodes from Dropsens.
