Single-Walled Carbon Nanotube Dispersion in Tryptic Soy Broth

There has been little research on the dispersion of carbon nanotubes in dispersions of standard microbiological media. We report that tryptic soy broth (TSB) containing casein digest disperses single-walled carbon nanotubes (SWNT) at concentrations similar to those achieved in lysozyme (LSZ), one of the best known biomolecular SWNT dispersants. Similar to LSZ, the proposed mechanism for SWNT dispersion in TSB is favorable π-π stacking interactions with l-tryptophan. This is supported by similar SWNT concentrations in both LSZ and TSB supernatants, and the absence of appreciable dispersion in TSB that does not contain a source of l-tryptophan. Since l-tryptophan alone is insufficient to enable dispersion, it was previously hypothesized that LSZ's macromolecular structure created steric hindrance that was critical for SWNT dispersion. These new results show that intermediately sized l-tryptophan containing species can also enable dispersion. In addition, since TSB is a commonly used growth medium for microbiological research, its dispersive ability presents new research avenues for studying the effect of SWNT on prokaryotic cells without the need to oxidize SWNT or add dispersants that may induce microbial stress.