Minimum irradiances necessary to chemically modify carbon nanohorns by microwave radiation were investigated using XPS, TEM, and Raman spectroscopy. Only 150 W min, equivalent of operating a home-use microwave oven for less than 10 s, is sufficient to oxidize nanohorns, with the result that nearly all materials used for this study become dispersible in polar solvents. Also, irradiation of less than 250 W min is enough to deposit Pt particles on the nanohorns by the polyol method, with a unique property that Pt particles are deposited mostly at the horn ends. (c) 2006 Elsevier B.V. All rights reserved.