Enzyme-Activated Surfactants for Dispersion of Carbon Nanotubes

The ability of N-(Fluorenyl-9-methoxycarbonyl) (Fmoc) amino acids to disperse CNTs was demonstrated. Four Fmoc-protected aromatic amino acids, W, H, tyrosine (Y), and phenylalanine (F), were selected, with glycine (G) as a nonaromatic control. The interactions of these molecules with single and multiwalled nanotubes (SWNTs and MWNTs) were studied by examining their ability to disperse CNTs in phosphate buffer saline (PBS). The degree of dispersion was then assessed using UV-Vis spectroscopy, prepared with each vial containing CNTs (I mg) to which a solution of amino acid derivatives was added. The mixture was then ultrasonicated using a microprobe and a low power bath for 4 mm. Transmission electron microscopy (TEM) was used to examine morphological changes to the MWNT surface in the presence of Fmoc-W. High- resolution images revealed spherical features, thought to be Fmoc-W aggregates, ranging from 5 to 10 nm in diameter. The aromatic fluorenyl rings were found to stack on the surface of the CNT to maximize their π-stacking interactions.