  Various proteins adsorb spontaneously on the sidewalls of acid-oxidized
single-walled carbon nanotubes. This simple non-specific binding scheme can be
used to afford non-covalent protein-nanotube conjugates. The proteins are found
to be readily transported inside various mammalian cells with nanotubes acting
as the transporter via the endocytosis pathway. Once released from the
endosomes, the internalized protein-nanotube conjugates can enter into the
cytoplasm of cells and perform biological functions, evidenced by apoptosis
induction by transported cytochrome c. Carbon nanotubes represent a new class
of molecular transporters potentially useful for future in-vitro and in-vivo
protein delivery applications.
