This paper describes the development of a label-free immunosensor using carbon nanotube array electrodes. Highly aligned multi-walled carbon nanotubes were grown by chemical vapor deposition using a metallic catalyst, Fe/Al2O3/SiO2, On Si wafers. Harvested towers were cast in epoxy and polished on both ends; one end being for electrical connection and the other being the electrode array surface. The nanotubes were functionalized electrochemically to form carboxyl groups and then coupled to antibodies. EIS was used to directly monitor the antibody-antigen binding.