In contrast to control sdAb, anti-IGFBP7 sdAb fluorescently tagged for detection was found to bind specifically to both human and mouse GBM tumour vessels ex vivo and to brain tumour vessels in mice after injection in vivo, creating high signal-to-noise ratio in orthotopic brain tumours easily detectable by in vivo optical imaging. The gene discussed is IGFBP7; the disease is brain neoplasm.