Although advances are being made in covalent and
noncovalent modification of the nanodiamond surface,
imaging of nanodiamond particles has largely centered on
optical imaging with fluorescence spectroscopy.19,20,31 Ion
beam irradiation has been used to form fluorescent centers
with red and green emission visible at the cellular level.19,20
Blue fluorescent nanodiamonds (5 nm in diameter) have
been produced by covalent attachment of octadecylamine
(ODA) to the carboxylate groups of the nanodiamond surface.
31 While these fluorescent nanodiamonds provide an
alternative to toxic quantum dots, they suffer from the
similar limitations in tissue penetration as other optical
imaging techniques, restricting their use to primarily histological
applications. To our knowledge, there are no published
reports of nanodiamonds being visualized by other
imaging technologies.