Zwitterionic SAMs that Resist Nonspecific Adsorption of Protein from Aqueous Buffer

TLDR

The study aims to evaluate how surfaces with different charged groups resist nonspecific protein adsorption from aqueous buffer. The authors use surface plasmon resonance spectroscopy and alkanethiol self‑assembled monolayers on gold to perform this assessment. Mixed zwitterionic SAMs of trimethylammonium and sulfonate adsorbed less than 1 % of fibrinogen and lysozyme, while single‑component zwitterionic SAMs also resisted adsorption but single‑charge SAMs adsorbed nearly a full monolayer; protein adsorption on mixed SAMs was independent of ionic strength or pH, whereas on single‑component zwitterionic SAMs it increased with decreasing ionic strength and decreased with increasing pH, and N,N‑dimethyl‑amino‑propane‑1‑sulfonic acid SAMs outperformed phosphoric‑acid‑based zwitterions and several zwitterionic SAMs matched the best known protein‑resistant systems.

Abstract

This paper describes the use of surface plasmon resonance spectroscopy and self-assembled monolayers (SAMs) of alkanethiols on gold to evaluate the ability of surfaces terminating in different combinations of charged groups to resist the nonspecific adsorption of proteins from aqueous buffer. Mixed SAMs formed from a 1:1 combination of a thiol terminated in a trimethylammonium group and a thiol terminated in a sulfonate group adsorbed less than 1% of a monolayer of two proteins with different characteristics: fibrinogen and lysozyme. Single-component SAMs formed from thiols terminating in groups combining a positively charged moiety and a negatively charged moiety were also capable of resisting the adsorption of proteins. Single-component SAMs presenting single charges adsorbed nearly a full monolayer of protein. The amount of protein that adsorbed to mixed zwitterionic SAMs did not depend on the ionic strength or the pH of the buffer in which the protein was dissolved. The amount of protein that adsorbed to single-component zwitterionic SAMs increased as the ionic strength of the buffer decreased; it also decreased as the pH of the buffer increased (at constant ionic strength). Single-component zwitterionic SAMs composed of thiols terminating in N,N-dimethyl-amino-propane-1-sulfonic acid (−N+(CH3)2CH2CH2CH2SO3-) groups were substantially more effective at resisting adsorption of fibrinogen and lysozyme from buffer at physiological ionic strength and pH than single-component zwitterionic SAMs composed of thiols terminating in phosphoric acid 2-trimethylamino-ethyl ester (−OP(O)2-OCH2CH2N+(CH3)3). Several of these zwitterionic SAMs were comparable to the best known systems for resisting nonspecific adsorption of protein.