Dispersability of carbon nanotubes in biopolymer-based fluids and their potential biotechnological applications

The dispersability of carbon nanotubes in aqueous solutions containing proteins or nucleic acids is discussed. In the mentioned systems different dispersion modes occur, depending on the type and concentration of biopolymer, and on the amount of dispersed nanotubes, as well. The phase behavior depends on how much biopolymers are adsorbing, and, naturally, on their molecular details. Modulation of the nanotube/biopolymer interactions helps switching between repulsive and attractive regimes between surface-functionalized particles. Accordingly, dispersion or phase separation take place, and the formation of nematic phases, or gels, may prevail with respect to dispersions. We report on systems containing DNA-stabilized and lysozyme-stabilized carbon nanotubes, since the two cases are representative of largely different adsorption modes. In the former case, ss-DNA uniformly rolls around CNTs and ensures significant surface coverage; conversely, lysozyme poorly, randomly and non-cooperatively adsorb onto nanotubes. A fine tuning of temperature, nano-tube content, added polymer, pH and/or ionic strength conditions induces the formation of different dispersion modes and different phases, as well.