We have developed a simple and efficient method for the covalent functionalization of detonation nanodiamond. After homogenization of the surface by borane reduction, the surface was modified with (3-aminopropyl)trimethoxysilane. Subsequent grafting of biotin yielded covalently biotinylated nanodiamond, which was characterized by FTIR spectroscopy, X-ray powder diffractometry, thermogravimetry, and elemental analysis. The activity was tested with horseradish peroxidase-labeled streptavidin. The surface loading of biotin was found to be 1.45 mmol g(-1). The new material opens the way to covalently bonded diamond bioconjugates for labeling, drug delivery, and other applications.