Team:UC Davis/Electrochemistry Electrode Choice

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
• compatibility

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 two of the commercial electrodes which already have 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.

DropSens Vs. Pine Instruments:

Both electrodes gave us huge advantage of built-in counter, reference, and working electrode. However, we still had to select one that will be more suitable for our experimental environment. Both Dropsens and Pine instrument provides light-mass, inexpensive, and disposable electrode. However, Pine Instrument comes with its closed solution container which requires solution volume of 10mL; while Dropsens only requires 50µL-60µL of solution, which is 200 times less solution volume required from Pine Instrument. Another difference was that the electrode from Pine Instrument comes with bare electrode without pre-polymerized surface. It gives us more option to choose chemicals to polymerize our electrode surface; however, it gives us a disadvantage that we have to polymerize the surface each time before we start our general experiments. Dropsens, on the other hand, comes with the working electrode consists of a carbon ink infused with a choice of polymer. Considering each characteristic on both electrodes, we have decided that Dropsens electrodes are more suitable for our experimental system.

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
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1. Showed selective oxidative affinity for NADH
2. Dissolved and activated in hydrochloric acid and sodium nitrate
3. Electropolymerized onto surface

Meldola's Blue
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1. Showed selective oxidative affinity for NADH
2. Dissolved and activated in Phosphate buffer
3. Electropolymerized onto surface
4. Displayed greater electron deposition and flow
5. Demonstrated more reliable signals
   (NO indication of major chemical interference at the electrode surface)

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:

• MB facilitates greater electron deposition and flow.
• Azure A demonstrated second order responses, which can be possible indicative of non-trivial chemical interactions at the electrode surface.
• MB gave us more reliable readings, especially showed no second order responses.
• We can specifically ordered MB-infused electrodes from Dropsens.