I had performed CV for a DNA sample in DI (without buffer) with Ag/AgCl (ref), Pt wire (CE) and Gold working electrode with constant scan rate and exposing the setup to UV light during measurement.
i found that a peak for DNA had shifted towards lower potential from its initial position at a higher potential.
What could be the reason for this?
Thank you
Let's start with: why are you doing CV in DI water? Supporting electrolyte is needed to collapse the double layer to lower the energy barrier for electrochemistry (it also mitigates migration as a form of mass transport, and reduces uncompensated resistance, which is important on point 2). DI water isn't actually without [any] ions, so there is still a double layer that forms but electrochemistry will be...more difficult.
This brings me to the second point: I'm assuming this is an oxidation reaction based on the movement from more positive to less positive potentials, and most likely the answer is: you are using DI water. If you start doing electrochemistry in DI water you are starting with a fairly resistive solution, but the electrochemistry you do will generate ions (if you're oxidizing at your working electrode you are reducing at the counter electrode, plus there will be some ion diffusion through the reference electrode frit into your electrolyte). As the ionic strength of your solution increases, its resistance [impedance] decreases and the ohmic drop goes down as well shifting oxidative peaks to less positive potentials.
In general you want to do electrochemistry in solution with supporting electrolyte. That said, there are times when doing electrochemistry in low ionic strength solution is necessary, but the act of doing electrochemistry in those conditions has a much more dramatic effect on the solution and so needs to be accounted for.
Thank you for your answer Dr. Jacob,
The DNA used for this experiment has sodium ions which stabilize the helix, so i think Na-DNA is kind of an electrolyte of low ionic strength.
Hi Prathamesh,
Whats the origin of the oxidation peak. Are you using some electroactive tag like Fc or MB or it was due to the oxidation of G bases.
Regards
Hi,
I am on the same opinion, you should first record CV with supporting electrolyte. Is it possible that DNA adsorbs on the electrode? Which type of DNA you have, is it modified with thiol groups?
Best regards
Thank you for Your answer Dr. Chaker,
No i havent used any electroactive tag and i think the peak position may indicate oxidation of G bases
Hello Dr. Teresa,
Salmon sperm DNA with no modification was used for this study. Also i did observe a white film forming on the WE at times, but not always. This might be the adsorption you are indicating.
Hello Prathamesh,
What is the scan rate that you use? Do you observe the shift in the peak potential in between cycles or it's in between replicates? Can you attach the CV? Also, what is the purpose of the CV, what kind of information do you want to get from it?
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