In this study, fluorescently labeled affibody molecules (Affibody, Solna, Sweden) targeting EGFR have been developed for human use. Affibody molecules are small proteins (derived from a 58 amino acids long Z-domain scaffold) . The EGRF-binding affibody molecules were engineered with a maleimide linker for site-specific cysteine conjugation with a fluorescent dye such that fluorophore labeling does not interfere with the binding domain site for a receptor, thereby maintaining binding affinity. These molecules have high affinity (approximately K d ~ 2.8 nM) and demonstrate localization in glioma tumors [13, 26]. Due to their small size, affibody molecules present fast clearance from the blood and reasonable diffusion through tissue, which are the desirable features for a high-contrast surgical imaging agent .