A Comparative AFM Study of the Compressibility and Friction of Unmodified and Oligo(ethylene oxide)-Modified Alkane Thiol SAMs on Au(111) Using Nanografting

Published

October 12, 2021

Author(s)

Ying Hu, David J. Vanderah, Guangyao Liu, William J. Price, Milan Mrksich, G Scoles

Abstract

Self-assembled monolayers (SAMs) terminated with oligo(ethylene glycol) (OEG) segments are known to resist non-specific protein adsorption and are used in biomaterial and biosensor applications. In this report we use an atomic force microscopy (AFM) nanografting technique to see if the mechanical response properties of these SAMs may be related to possible OEG conformational changes induced during protein-surface interactions (compressions) and, therefore, provide insight into their protein-resistant properties. The well-characterized octadecanethiol (ODT) SAM is used as a reference film to accurately characterize the compressibility and friction of the OEG SAMs. We show that SAMs of HS(CH2CH2O)6C18H37 and HS(CH2)11O(CH2CH2O)3H, self-assembled from ethanol solutions onto gold (111) surfaces, can be reversibly compressed to half of their height with imagining forces that do not affect the ODT SAMs ( 50 nN). At compression forces > 50 nN the HS(CH2CH2O)6C18H37 SAMs adopt a second, stable conformational structure that resists further compression. In addition, the height of the HS(CH2CH2O)6C18H37 SAMs is found to decrease significantly by simply changing the contact solution from ethanol to ethanol/water (1/1). A structural model for these compression- and water-induced changes for the HS(CH2CH2O)6C18H37 SAMs, which may be similar, is proposed and discussed in the context of its potential relevance to the protein resistant properties of OEG coated surfaces.

Citation

Langmuir

Pub Type

Journals

Keywords

atomic force microscope, nanografting, protein resistance, self-assembled monolayers (SAMs)

Citation

Hu, Y. , Vanderah, D. , Liu, G. , Price, W. , Mrksich, M. and Scoles, G. (2021), A Comparative AFM Study of the Compressibility and Friction of Unmodified and Oligo(ethylene oxide)-Modified Alkane Thiol SAMs on Au(111) Using Nanografting, Langmuir (Accessed October 10, 2025)