title: Controlled dispersion and purification of protein-carbon nanotube conjugates using guanidine hydrochloride.
abstract: For the development of biofunctional carbon nanotubes for biosensors, drug carriers, and nanobiocatalysts, their aggregation and biofouling in aqueous solutions are crucial problems because this behavior leads to a reduction of their excellent optical and electrical properties and nanoscale size effects. This paper presents a new method for enhancing the dispersibility of protein-carbon nanotube conjugates and for exfoliating the protein from the carbon nanotube sidewalls through controlling the concentration of guanidine hydrochloride (Gdn·HCl) in the solution. In medium concentrations (2-3 M) of Gdn·HCl, the dispersibility of protein-carbon nanotube conjugates was found to be substantially increased without denaturation or aggregation of the proteins. At higher concentrations (>6 M) of Gdn·HCl, pristine carbon nanotubes were precipitated instantly as a result of dissociation of the protein. These phenomena indicate that Gdn·HCl functions not only as a dispersion adjuvant for biofunctional protein-carbon nanotube conjugates, but also as a cleaning agent for the purification of biofouled carbon nanotubes. The dissociation concentrations of Gdn·HCl were higher than the midpoint of protein denaturation, suggesting that protein adsorption on carbon nanotubes is more stable than protein folding toward Gdn·HCl.
authors.affiliation: Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hirano
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Maeda
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Yuan
authors.forename: Ryuuichi
authors.initials: R
authors.lastname: Ueki
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Miyazawa
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Fujita
authors.forename: Takeshi
authors.initials: T
authors.lastname: Akasaka
authors.forename: Kentaro
authors.initials: K
authors.lastname: Shiraki
mesh_terms: D015374:Biosensing Techniques / Q000379:methods; D004337:Drug Carriers / Q000737:chemistry*; D019791:Guanidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D037742:Nanotubes, Carbon / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding
chemical_list: D004337:Drug Carriers; D037742:Nanotubes, Carbon; D019791:Guanidine