J. Koc, L. Schardt, K. Nolte, C. Beyer, T. Eckhard, P. Schwiderowski, J. L. Clarke, J. A. Finlay, A. S. Clare, M. Muhler, A. Laschewsky, A. Rosenhahn
Effect of the dipole orientation in mixed, charge-equilibrated self-assembled monolayers on protein adsorption and marine biofouling
ACS Appl. Mater. Interfaces 2020, 12, 50953-50961
DOI: 10.1021/acsami.0c11580
Zwitterionic interfaces exhibit excellent low-fouling properties. Still, the underlying molecular principles are not clear. In particular, the role of the zwitterion orientation at the interface has been discussed recently. To clarify the importance of this parameter, densely packed self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate group. By varying the alkyl chain length of the anionic thiols, different charged groups were preferentially exposed at the interface, although overall, the SAMs maintain full charge neutrality. In model biofouling studies, protein adsorption, diatom accumulation and the settlement of zoospores were all sensitive to the interfacial charge distribution of the SAMs. Overall biofouling was the lowest when the anionic and cationic groups were placed at the same distance from the substrate. This demonstrates the importance of the zwitterion dipole orientation in mixed charged SAMs for their inertness to fouling.
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