what kind of adsorption method did you use to place the probe on erGO surface?may be the probe is not stable. you have to solve your anchoring chemistry before thinking any further application.

Hi Ahmed, the DNA probe immobilixation was done by interaction between the DNA bases and graphene through p-p interaction. There is no covalent immobilization in this case. 

Hi Chaker,

It may be that your probe interaction is not stable as Ahmed already suggested. Otherwise it could also be your redox label that is not stable. See this article about different redox labels for electrochemical sensors

Article Survey of Redox-Active Moieties for Application in Multiplex...

Hi Johannes,

Thanks for your answer. It could be that the redox tag is not really stable. But in the literature many reports used the Fc-tag.

Regards

Did you try to change the SWV's parameters? If the frequency, step amplitude and so on are not properly optimized, instable and unreproducible results can be obtained.

Regards

Hi Bernardo,

We tried to optimize such parameters as you mentioned but still the signal is not really stable.

Thanks for the help

Regards

Hi Chaker, physisorption of your DNA probe onto the erGO surface could be an issue which greatly rely on time of adsorption, pH and temperature. Therefore I believe the issues you faced are not related with the readout technique. Although during my PhD we reported similar works (see my publications), but despite its simplicity I found its difficult to control. I would suggest to choose another suitable probe immobilization chemistry for robustness of the sensor.

if you already optimized these parameters probably the problem is in the interaction between your electrode and the DNA, as suggested by Ahmed and Johannes.

Thanks Islam and Patella for answering this question. I think the problem is not coming from the interaction between the adsorbed DNA probe and the graphene layers. It looks like the erGO itself is not stable. We checked the CV of the modified electrode with erGO and it is not stable at all.

Regards