Carbon nanotubes come into contact with complex biological fluid phases in a variety of scenarios in the fields of nanotoxicology and nanomedicine. Of immediate interest are their interactions with cells in culture, which are fundamental to toxicity assays and to biomedical research on nanostructured surfaces. In addition to direct interactions between cells and nanotubes (endocytosis, phagocytosis, cell attachment), the high-surface-area nanotubes may influence cell behavior indirectly by adsorbing, deactivating, or destroying biological solutes in extracellular fluid or cell culture medium.

In this paper, we present new experimental results on the interaction of single-wall nanotubes with cell culture media through multicomponent amino acid and vitamin profiling. We show that nanotubes cause dose-dependent depletion of cell culture medium with respect to some amino acids, the pH indicator dye phenol red, and a range of vitamins, especially those with aromatic or polyaromatic core structure. The mechanism of this interaction is investigated by correlating the adsorption with molecular physical properties and through separate single-component experiments on tyrosine and phenol red. The single components experiments yield equilibrium isotherms and provide information on reversibility, multicomponent competitive effects, and the dependence on nanotube surface chemistry. The combined results suggest that the dominant mechanism is competitive multicomponent physical adsorption on hydrophobic nanotube surface patches, and the implications for biological assays and cell behavior is discussed.

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