Porphyrins are an important class of macrocycles that regulate many biological processes such as the transport and activation of dioxygen. Free-base porphyrins display intense fluorescence and are readily derivatized with functional groups that bind tenaciously to solid state surfaces, but do not affect the fluorescent properties. To functionalize magnetic nanowires with fluorescent porphyrins, we chose Hematoporphyrin IX, [8,13-bis(1-hydroxyethyl)-3,7,12,17-tetra-methyl-21H,23H-porphine-2,18-dipropionic acid], which has two intense, red fluorescence bands, and two carboxylic acid groups that are known to bind strongly to metal oxides and to the native oxide films on metals, such as nickel.

The upper panel of this figure shows an optical microscope image, and the bottom panel shows the corresponding fluorescence image of a single, 22-micron-long porphyrin-functionalized nickel nanowire. Such nanowires remain fluorescent for weeks when stored in hexadecane/octadecane, water, or air.