@loannis samaras thanks for elaboration and @Oleksiy Krupin for asking such a good question, it helped me alot

You may have a large uncompensated resistance.

Yurii V Geletii

Thank you, Yurii. So, from the electrochemical standpoint, it's not a proroblem? In other words, if I make a CE gold and 20x larges surface area, it should perform well? I apologies for trivial questions, I am just starting to dig into it.

Regards,

The classical and commonly used is the case with Pt working electrode and larger surface area Pt counter electrode. It should not be any problem with Au. Don't forget to use a rather high supprting electrolyte concentration, at least 0.1 M

why you should use two gold electrode@s.

is what you want to synthesize a polymer film in electrochemical way. it's another thing

dear scientist, you can do this method but the results may not accurate

Mohamed Damej We are developing a thin-film biosensor, using lithographic technique. The idea is to combine optical sensing (plasmonic Au waveguides) and electrochemicalo (doing CV or chronoamperometry). It would be much easier for us from the fabrication standpoint to have 2 Au electrodes. We can easily change the dimensions to have WE:CE 1:20 or so. And I was just inquiring what sort of problems I can get into in this case.

Ramin Farajpour "

this method but the results may not accurate

… 

Which method? Why results "may not accurate?" Please, explain

Ramin Farajpour I'm still waiting for your answer to my question.

Yurii V Geletii Dear Yurii, Thank you for your answers. I think I can make my question more precise: if I perform CV on ferrocyanide, would my results for CV-curve differ when a) I use Au WE and Au CE (with larger surface area than WE); and b) I use Au WE and Pt CE of the same configurations as in (a).

Thank you!

The standard CV ferrocyanide should be taken in 0.3 M KNO3 as electrolyte at neutral pH. Commonly CV depends on the nature of WE, but not on CE. It might be that CV on Au depends on preconditions of electrode. Don't apply too high or too low potentials. This could modify the electrode surface. The procedure of cleaning/polishing of Au WE can be found in the manufacture's website.

Dear Oleksiy Krupin ,

the identical WE, CE (Au-Au or even Au-Pt) electrodes' materials is not the main obstacle for your sensor.

A better re-focus on the geometry of the (WE, CE) micro-electrodes will help more the R&D of the sensor. The source of the major constraints on the (ferrocyanide and other) CV, chronoamperometry, as well as some possible EMI[1] (electromagnetic interference), ... etc., is, mainly, the flat (2D-constraint) geometric issue of the (WE, CE) micro-electrodes, formed on the same substrate.

a) What is the substrates' material ?

b) An example image (a possible photo or even a scheme) of the sensor under R&D might augment our feedback.

1. Functional integrated electromagnetic interference shielding in flexible micro-supercapacitors by cation-intercalation typed Ti3C2Tx MXene

https://www.sciencedirect.com/science/article/abs/pii/S2211285520302986

Yurii V Geletii, and Ioannis Samaras , thank you both very much for your responses. They also confirm my understanding of general concepts. Ioannis, I'll dig deeper into the EMI issues - it is new to me. Also, answering your question, our electrodes are ~ 5um wide, 35 nm thick, 1.5 mm long, on a dielectric fluoropolymer CYTOP, separation between the electrodes would range 500-1000 um.

Thank you!

Dear Oleksiy Krupin ,

let me propose a draft scheme[1,2] that is specific for your case of developing a thin-film biosensor, using lithographic technique.

1. bioSensorProbe__4_Oleksiy_Krupin.jpg

2. The 2nd metallic (Au) terminal line in each of the WE, CE electrode might be initially

a)ignored (or short-circuited for each one of the WE, CE),

or, later on, might be

b)useful for further (specific, EIS) measurements.

Thank you, Ioannis Samaras . I probably should've included the image of the system. We need electrodes to be straight - so that one can choose to use them either as optical waveguide or electrochemical electrode. Also, another interesting application we are looking into is to perform "plasmonic catalysis" - monitor redox reaction while exciting the plasmons on the waveguide with light, thus using a single stripe for both. But we will definitely consider your proposed scheme to have it as a non-optical electrode on the same (i.e. optical) chip - we actually haven't looked from this angle. Lithographically it is not a problem.

A standard electrochemical cell typically contains three electrodes: a working electrode, an auxiliary electrode, and a reference electrode. As a rule, the surface area of ​​the auxiliary electrode is much larger than the working one, so that when the electrodes are polarized, the current density on the auxiliary electrode would be much lower than on the working one. In this case, the auxiliary electrode is practically not polarized and its potential is close to the stationary potential. If a two-electrode cell is used, then the surface area of ​​the auxiliary electrode should be much larger than the working one, for example, in classical polarography with two mercury electrodes: one is a mercury drop and the other is a pool of mercury. The use of a reference electrode makes it possible to measure the potential of the working electrode relative to an electrode with a stable potential, as a rule, for the electrochemistry of aqueous solutions, this is a silver chloride electrode.

The experimental goal is to ensure that the current-voltage characteristics of your electrochemical cell are controlled by the working electrode reaction. If there is no chemically reversible redox reaction, then your counter electrode reaction will almost certainly be electrolysis of the solvent. This has a low exchange current density for both reduction and oxidation. You can increase the electrochemical area of your counter electrode by depositing e.g. Pt-black which will allow the projected area to be smaller, if this matters in your cell design.

Dr. Ioannis Samaras well responded.

Nice Contribution Danny O'Hare

@loannis samaras thanks for elaboration and @Oleksiy Krupin for asking such a good question, it helped me alot