Do you want to make modified electrodes with carbon on GC electrode surface ?

using chemical modification where Self assembly monolayer (SAM) technique is apply between APTES and carboxyl group

Carbon nanotube solution is prepared in DMSO solution and then dropped on a glassy carbon surface.

you can use carbon paint/epoxy (Electrodag) or even Ni print (MG Chemicals). Of course you will need to make sure that the solvent used in these adhesives/paint is compatible with your materials and electrolytes. I use both of these to attach carbon foams to Ni foil current collectors all the time and they work great. I use aqueous-based electrolytes.

Thank you all for your contributions, and I think Megan's suggestion is more related to my work!