Resistance of Galactoside-Terminated Alkanethiol Self-Assembled Monolayers to Marine Fouling Organisms

Abstract

Self-assembled monolayers (SAMs) of galactoside-terminated alkanethiols have protein-resistance properties which can be tuned via the degree of methylation [Langmuir 2005, 21, 2971-2980]. Specifically, a partially methylated compound was more resistant to nonspecific protein adsorption than the hydroxylated or fully methylated counterparts. We investigate whether this also holds true for resistance to the attachment and adhesion of a range of marine species, in order to clarify to what extent resistance to protein adsorption correlates with the more complex adhesion of fouling organisms. The partially methylated galactoside-terminated SAM was further compared to a mixed monolayer of ω-substituted methyl- and hydroxyl-terminated alkanethiols with wetting properties and surface ratio of hydroxyl to methyl groups matching that of the galactoside. The settlement (initial attachment) and adhesion strength of four model marine fouling organisms were investigated, representing both micro- and macrofoulers; two bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), barnacle cypris larvae (Balanus amphitrite), and algal zoospores (Ulva linza). The minimum in protein adsorption onto the partially methylated galactoside surface was partly reproduced in the marine fouling assays, providing some support for a relationship between protein resistance and adhesion of marine fouling organisms. The mixed alkanethiol SAM, which was matched in wettability to the partially methylated galactoside SAM, consistently showed higher settlement (initial attachment) of test organisms than the galactoside, implying that both wettability and surface chemistry are insufficient to explain differences in fouling resistance. We suggest that differences in the structure of interfacial water may explain the variation in adhesion to these SAMs.

Synthesis of oligo(lactose)-based thiols and their self-assembly onto gold surfaces

“…[26,27] All three spectra also have a shoulder around 3230-3240 cm -1 , indicating the presence also of tetrahedrally coordinated (ice-like) water, but to a lesser extent, [26,27] which is in agreement with the hydration structure of fully hydroxylated monosaccharide-terminated SAMs. [21] The absorptions area very strong in this region, indicating that a considerable amount of water is retained in the film, even after drying the samples under a stream of N 2 gas, and after purging the spectrometer for 30 min before the measurement commences. …”

“…[20][21][22] The ellipsometric thicknesses (Table 1) vary in a non-intuitive manner, since the thickness difference between 1 and 2 is smaller than that between 2 to 3 (5.2 Å and 8.9 Å, respectively), although the nominal length differences between the molecules are identical. This observation is discussed further down, in conjunction with the IRAS results.…”

“…We have earlier reported that carbohydrate-based SAMs both have proteinresistant properties comparable to those of OEGs, and that they also are highly resistant to fouling by several marine fouling species. [20][21][22] In this study we present the synthesis of three oligosaccharides 1-3 (di-, tetra-, and hexa-) ( Figure 1), all functionalized with a thiopropanoylic residue, starting from the corresponding fully protected oligosaccharides (di-, tetra-, and hexa-). [23] These thiols have successfully been used to form SAMs on gold surfaces and nanoparticles.…”

Enhanced Antifouling Properties of Carbohydrate Coated Poly(ether sulfone) Membranes

“…20,21 Surface coatings consisting of high molecular weight polysaccharides such as dextran have been shown to reduce protein or cell adhesion to surfaces, 22,23 while modifications with short oligosaccharides or monosaccharides have also been demonstrated to have a pronounced effect on minimizing unspecific protein adsorption and biomass accumulation. [24][25][26][27] Previous work from our group showed that Galactose-modified carbon surfaces obtained via spontaneous grafting of aryldiazonium salts display an increased resistance to Bovine Serum Albumin (BSA) adsorption, compared to bare carbon surfaces. 18 Such an effect was achieved, remarkably, via immobilization of only 1-3 ML of the monosaccharide.…”

Protein adsorption and cell adhesion controlled by the surface chemistry of binary perfluoroalkyl/oligo(ethylene glycol) self-assembled monolayers

“…In most cases of investigating protein and cell adsorption, surface modification is used to generate highly hydrophilic or hydrophobic surfaces, and both of which have proven to be resistant to protein adsorption and cell adhesion. For examples, surface modification by tethering highly hydrophilic small molecular surfactants or polymers, such as oligo(ethylene glycol) (OEG) [12], polysaccharides [13], zwitterionic compounds [14], or alternatively, highly hydrophobic perfluoroalkyl (PFA) compounds [15], etc., can achieve this function. On the other hand, moderate water wettable surfaces, obtained by altering the surface composition and surface roughness, have shown appreciable protein adsorption and cell adhesion [16].…”