Dear Jacob, you have to do a scan rate experiment using thiol derivatized gold electrode and to obtain the graph of ln(v)-Ep (v is scan rate). After calculating the slope of the line, put that value into laviron equation which can you infer the rate constant.

I don't think that the charge of your probe will make that much of a difference, especially with a good thiol cover... if you have a good thiol layer, you should have very little electron transfer, wheter it's positive or negative. If the layer is not complete, then the charge of the probe could have an effect if your thiol ending has a particular charge.... There are different ways of determining the rate constant, such as looking at how peak separation in voltammetry varies with scan rate (nicholson method - paper in analytical chemistry vol 37, p 1531) or impedance measurements, for example. A good reference for this type of measurements is Kissling et al Phys. Chem. Chem. Phys., 2011,13, 21175-21185 DOI: 10.1039/C1CP21996K (and the references they cite there).

well iagree with Danial ,however you should first check stabilty of your modified electrode and then test with Fe(II)/Fe(III) in 0.1 KCl by CV or impedance. then you may used laveron equation. Good luck.

An example is in attached publication.