title: Aggregation of human serum albumin on graphite and single-walled carbon nanotubes as studied by scanning probe microscopies.
abstract: Human serum albumin (HSA) is the most abundant protein in blood plasma showing a remarkable ability to bind a broad range of hydrophobic substrates. We employed scanning tunneling microscopy and atomic force microscopy to characterize the morphology of HSA aggregates on highly-ordered pyrolytic graphite (HOPG) and single-walled carbon nanotubes (SWNTs). The morphologies found for albumin aggregates on HOPG are quite different from the ones observed on SWNTs. On HOPG, HSA forms aggregates of roughly 10-20 molecules; single protein molecules were observed as well. In the case of SWNTs, nanotubes were partially or totally covered with HSA, exhibiting four general types of aggregation: (i) SWNT sidewalls contain single molecules of albumin which are away from each other at distances longer than the HSA molecular size; (ii) SWNTs are completely covered with HSA, which forms a thin and relatively homogeneous layer; (iii) SWNTs have a complete layer of HSA with additional accumulation of protein at separate sites; and (iv) several SWNTs totally covered with albumin assemble into a bundle-like structure common for bare nanotubes. These observations are interpreted in terms of stronger interactions of HSA with nanotube sidewalls than with flat graphite surface.
authors.affiliation: Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria 04510, México DF, México.
authors.forename: Andrés
authors.initials: A
authors.lastname: Rodríguez-Galván
authors.forename: Flavio F
authors.initials: FF
authors.lastname: Contreras-Torres
authors.forename: Elena V
authors.initials: EV
authors.lastname: Basiuk
authors.forename: Edgar
authors.initials: E
authors.lastname: Alvarez-Zauco
authors.forename: Alejandro
authors.initials: A
authors.lastname: Heredia
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Basiuk
mesh_terms: D006108:Graphite / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D018625:Microscopy, Atomic Force; D020527:Microscopy, Scanning Probe; D037742:Nanotubes, Carbon / Q000737:chemistry* / Q000648:ultrastructure; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D013059:Spectrum Analysis, Raman
chemical_list: D037742:Nanotubes, Carbon; D012709:Serum Albumin; D006108:Graphite