Adsorption of lysozyme onto the silicon oxide surface chemically grafted with a monolayer of pentadecyl-1-ol

T. J. Su, R. J. Green, Y. Wang, E. F. Murphy, J. R. Lu, R. Ivkov, S. K. Satija

Research output: Contribution to journalArticlepeer-review

Abstract

The adsorption of chicken egg white lysozyme at the functionalized silicon oxide-solution interface has been studied using the combined measurement of spectroscopic ellipsometry and neutron reflection. The solid oxide surface was modified by coating a self-assembled monolayer of pentadecyltrichlorosilane with terminal hydroxyl groups (abbreviated to C15OH). Neutron reflection measurement at the solid-D2O interface showed that the C15OH layer was 16 ± 2 angstrom thick and the volume fraction was 0.94 ± 0.05, suggesting the formation of a close-packed monolayer. The adsorption of lysozyme was made at pH 4 and 7 with lysozyme concentration ranging from 0.03 to 4 g dm-3. The results were then compared with those from previous studies at the hydrophilic SiO2-water and the hydrophobed SiO2-water interfaces, with the latter formed by coating a monolayer of octadecyl trichlorosilane (abbreviated to OTS). At 0.03 g dm-3 and pH 7 the surface excess was found to be 0.6 ± 0.3 mg m-2 at the C15OH-water interface, as compared with 1.7 mg m-2 at the SiO2-water interface and 1.9 mg m-2 at the OTS-water interface. As lysozyme concentration is increased to 4 g dm-3, the surface excess at the C15OH-water interface reaches 2.1 mg m-2, as compared with 4.7 mg m-2 at the hydrophilic SiO2-water interface and 5.1 mg m-2 at the OTS-water interface. These values demonstrate the attainment of the minimum surface excess on the hydroxyl surface. Shifting solution pH from 7 to 4 reduces adsorption on all the surfaces studied, but the lowest level of adsorption is again obtained on the hydroxyl surface. The reversibility of the adsorption at the C15OH-water interface was examined by cycling the solution pH at different lysozyme concentrations. Adsorption was found to be completely reversible at the low lysozyme concentration of 1 g dm-3, while at the high concentration of 4 g dm-3 the adsorption was irreversible.

Original languageEnglish (US)
Pages (from-to)4999-5007
Number of pages9
JournalLangmuir
Volume16
Issue number11
DOIs
StatePublished - May 30 2000
Externally publishedYes

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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