Abstract
Carbon nanotubes (CNTs) are among the most versatile nanomaterials, but their exploitation is hindered by limited dispersibility, especially in aqueous solvents. Here, we show that AP-LYS, a highly cationic soluble derivative of denatured hen egg lysozyme, is a very effective tool for the unbundling and solubilisation of CNTs. AP-LYS proved to mediate the complete and stable dispersion of CNTs at protein: CNT ratios ≥1: 3 (w:w) in very mild conditions (10–20 minutes sonication in ammonium acetate buffer, pH 5.0). Electrophoretic mobility and ζ-potential measurements confirmed that dispersed CNTs were coated by the protein, whereas molecular docking was used to study the interactions between AP-LYS and CNTs. AP-LYS-coated CNTs proved to be a very effective microbial cell-flocculating agent with an efficiency similar to that of chitosan, one of the best available flocculating agents, thus suggesting that this hybrid could find industrial applications in the treatment of wastewaters contaminated by microbial cells, or to remove microbial cells after fermentation processes. Moreover, we exploited the low stability of AP-LYS-coated CNT dispersions in eukaryotic cell culture media to prepare scaffolds with an extracellular matrix-like rough surface for the cultivation of eukaryotic cells.
Highlights
Carbon nanotubes (CNTs) are among the most versatile nanomaterials, but their exploitation is hindered by limited dispersibility, especially in aqueous solvents
We show that AP-LYS is able to promote the debundling of multiwalled CNTs (MWNTs) as well, providing very stable dispersions of positively charged CNTs
We demonstrated that AP-LYS coated MWNTs, even at very low concentrations, are able to mediate the flocculation of large amount of microbial cells, rendering this bioconjugate a very promising tool for water treatment, and for the removal of cells after industrial fermentation processes
Summary
Carbon nanotubes (CNTs) are among the most versatile nanomaterials, but their exploitation is hindered by limited dispersibility, especially in aqueous solvents. Chemical functionalization of the CNT surface is a very effective technique allowing both to improve dispersibility and to functionalize CNTs. For example, Borzooeian and colleagues, through the well-known carbodiimide chemistry, bound native hen egg lysozyme (LYS) to the surface of CNTs oxidized to generate free carboxylic groups[13]. Non-covalent strategies are generally based on the use of ultrasounds in the presence of a wide variety of water-soluble amphipathic (macro)molecules which, upon binding on the hydrophobic carbon surface, create a hydrophilic layer which will prevent their re-association Detergents, such as SDS and Tween, are cheap and effective but show low biocompatibility. In addition to an improved biocompatibility, biomacromolecules often provide the opportunity to functionalize the carbon surface, e.g. through the addition of enzymes or high specific binding modules (antibodies, cell attachment domains etc.)[20,23] In this context, it has been shown that proteins can effectively disperse carbon nanomaterials[20,24]. AP-LYS coated MWNTs are not toxic for human cells and precipitate in eukaryotic cell culture media, suggesting a possible use for the preparation of scaffolds for tissue engineering
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