Aggregation of Human Serum Albumin on Graphite and Single-Walled Carbon Nanotubes as Studied by Scanning Probe Microscopies
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.
Keywords: ATOMIC FORCE MICROSCOPY; GRAPHITE; HUMAN SERUM ALBUMIN; SCANNING; SINGLE-WALLED CARBON NANOTUBES; TUNNELING MICROSCOPY
Document Type: Research Article
Publication date: 01 June 2011
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