Factors that Determine the Protein Resistance of Oligoether Self-Assembled Monolayers − Internal Hydrophilicity, Terminal Hydrophilicity, and Lateral Packing Density

Abstract

Protein resistance of oligoether self-assembled monolayers (SAMs) on gold and silver surfaces has been investigated systematically to elucidate structural factors that determine whether a SAM will be able to resist protein adsorption. Oligo(ethylene glycol) (OEG)-, oligo(propylene glycol)-, and oligo(trimethylene glycol)-terminated alkanethiols with different chain lengths and alkyl termination were synthesized as monolayer constituents. The packing density and chemical composition of the SAMs were examined by XPS spectroscopy; the terminal hydrophilicity was characterized by contact angle measurements. IRRAS spectroscopy gave information about the chain conformation of specific monolayers; the amount of adsorbed protein as compared to alkanethiol monolayers was determined by ellipsometry. We found several factors that in combination or by themselves suppress the protein resistance of oligoether monolayers. Monolayers with a hydrophobic interior, such as those containing oligo(propylene glycol), show no protein resistance. The lateral compression of oligo(ethylene glycol) monolayers on silver generates more highly ordered monolayers and may cause decreased protein resistance, but does not necessarily lead to an all-trans chain conformation of the OEG moieties. Water contact angles higher than 70 degrees on gold or 65 degrees on silver reduce full protein resistance. We conclude that both internal and terminal hydrophilicity favor the protein resistance of an oligoether monolayer. It is suggested that the penetration of water molecules in the interior of the SAM is a necessary prerequisite for protein resistance. We discuss and summarize the various factors which are critical for the functionality of "inert" organic films.

Surface Sensing and Settlement Strategies of Marine Biofouling Organisms

“…A similar observation has been made by the Grunze group, who found that surfaces with similar wettability can show different settlement of zoospores [33,82]. In this study, ethylene glycols with different chain length and thus decreasing packing density were used [82,83]. Monte Carlo simulations revealed that such a decreased packing density facilitates penetration of water into the thin films, providing the necessary steric freedom for a stable binding of water [84,85].…”

“…Monte Carlo simulations revealed that such a decreased packing density facilitates penetration of water into the thin films, providing the necessary steric freedom for a stable binding of water [84,85]. Despite the different hydration, all of the tested surfaces have a similar water contact angle [82,83]. Ulva zoospore experiments show that spores adhere much weaker on well hydrated surfaces [33], an observation in line with the protein resistance of the surfaces [83].…”

“…Despite the different hydration, all of the tested surfaces have a similar water contact angle [82,83]. Ulva zoospore experiments show that spores adhere much weaker on well hydrated surfaces [33], an observation in line with the protein resistance of the surfaces [83]. The fact that changing hydration continuously alters the inertness of a surface was finally proven by Christophis et al [86] who used a microfluidic experiment to show that the adhesion strength of cells gradually decreases with increasing ethylene glycol chain length.…”

Progress of marine biofouling and antifouling technologies

“…(ZP=-46.9 mV) [140]. Microorganisms are negatively charged over a large pH range (Figure 10(a)), and in natural sea water (pH 7-8) will carry a negative charge [142]. As a result, electrostatic interaction between cells and metal cations promotes the adhesion process.…”

Surface functionalization of germanium ATR devices for use in FTIR-biosensors

“…When chemical grafting is concerned instead of coating, oligomers of ethylene oxide (chains containing 3 to 9 EO units) are also efficient [18][19][20]. Surface treatment of glass and metal oxides is generally performed with commercial silane derivatives, such as 3-[methoxy (polyethyleneoxy)] propyl trimethoxysilane or trichlorosilane ( Fig.…”