Carbon nanotubes (CNTs) are remarkable novel synthetic nanomaterials with unique properties such as high surface area, hollow cavities, and excellent mechanical and electrical properties. Interfacing carbon nanotubes with biological materials could enable significant advances in biomedical applications such as disease diagnosis and treatment. In addition, the bioconjugated nanotubes combine with the sensitive nanotube-based electronic devices would enable sensitive biosensors toward medical diagnostics. This paper presents electronic sensing of antibodies that are specific to IGF-IR surface receptors in cancer cells with nanotube field effect transistor devices. This paper also presents antibody functionalization of carbon nanotubes and its potential applications for cancer diagnostics.