Carbon nanotubes (CNTs) have many unique properties such as high surface area, hollow cavities, and excellent mechanical and electrical properties. Solubilization and biological functionalization of carbon nanotubes have greatly increased the usage of carbon nanotubes in biomedical applications such as biosensors and nanoprobes. This paper presents biofunctionalization of single wall carbon nanotubes (SWNT) with antibodies, which are specific to insulin-like growth factor 1 receptor (IGF1R) in breast cancer cells, for their potential applications as carriers in drug or gene delivery systems. A high degree of binding (~ 80%) between antibodies and SWNTs has been successfully demonstrated via confocal microscopy and further verified by transmission electron microscopy (TEM). Control experiments revealed that non-specific binding of antibodies onto SWNTs could be prevented through pre-treatment with a biocompatible polymer, polyethylene glycol (PEG) which could open up new opportunities for future generation biosensors with superior specificity and selectivity.