I am a phD student and since I started, I was using ferrocene carboxylic acid for CV and impedance scans, but now I started to use Ferri ferrocyanide in order to try the redox couple with a new polymer. The problem that I am having at the moment is that I am not be able to get a proper CV shape (as you can see in the Fig 1) in the bare gold. I tried:

1. Different current and potential

2. Checked the holders and connections

3. Use external counter, external reference and external working electrode to check the reaction in the internal reference and counter on chip.

4. Different scan rates,

5. Remove oxygen in the solution.

6. Use different concentration of ferri ferro and PBS.

7. Clean the surface with acid

8. Square wave voltammetry.

After try all this options is happening the same all time but just in the internal working electrode (if I use external one the scans are perfect. Another people in my lab were trying ferri ferrocyanide in the past and looks like they were having the same problem as me and them decided to use another type of ferrocene. But at the moment I think that if with a commercial electrode the solution works (fig 3), it should be the same with the internal electrode on the chips that we use.

When I did Square wave voltammetry, I Could realise that there are appear different peaks when I use the same electrode in different time (fig 4). And each one of the electrodes has different peaks. But what is weird is that each time its different on the same electrode, which means that there is a type of reaction happening on the surface.

Can anyone help me to understand what is happening here? I think that in the surface of the electrode there is ‘’something’’ that can be detected using ferri ferro but not with ferrocene carboxylic acid (because the reaction is mask for the groups OH during the oxidation of carboxylic groups).

I use a concentration of 1.5 mM of ferri ferrocyanide in PBS, but as I wrote before I tried different concentrations (of ferri ferro and PBS) and nothing works with the internal electrode but it works with the external working electrode (so the solution it’s not the problem in my opinion). Also I was reading about electro oxidation of methanol or ethanol or some surface with wax layer and the behaviour is a little bit similar, but I am not an expert on this…

Thanks in advance for your time and I hope get help on this.