Light-assisted oxidation of carbon nanohorns for enhancing bio-compatibility

Single-wall carbon nanohorn (SWNH) has a structure similar to single-wall carbon nanotubes but with a larger diameters (2-5 nm) and shorter lengths (40-50 nm), and about 2000 of them assembled to form a spherical aggregate with a diameter of about 100 nm. For various applications of SWNHs, the chemical modification is the crucial issue. To chemically modify SWNHs, the --COOH groups at the holes edges are useful. We show in this report that --COOH groups are formed abundantly when SWNHs were oxidized with H$_{2}$O$_{2}$ under the light irradiation (Xe lamp). SWNHox thus obtained well dispersed by themselves in water, which was even more enhanced by attaching proteins to SWNHox. The modification with proteins effectively enhance the bio-compatibility of SWNHox, which was confirmed through in vitro assay using the mammalian cells.