Zwitterionic SAMs that resist nonspecific adsorption of protein from aqueous buffer

This paper describes the use of surface plasmon resonance spectroscopy and self-assembled monolayers (SAMs) of alkanethiols on gold to evaluate the ab ility of surfaces terminating in different combinations of charged groups t o resist the nonspecific adsorption of proteins from aqueous buffer. Mixed SAMs formed from a 1:1 combination of a thiol terminated in a trimethylammo nium 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 grou ps combining a positively charged moiety and a negatively charged moiety we re also capable of resisting the adsorption of proteins. Single-component S AMs presenting single charges adsorbed nearly a full monolayer of protein. The amount of protein that adsorbed to mixed zwitterionic SAMs did not depe nd on the ionic strength or the pH of the buffer in which the protein was d issolved. The amount of protein that adsorbed to single-component zwitterio nic SAMs increased as the ionic strength of the buffer decreased; it also d ecreased as the pH of the buffer increased (at constant ionic strength). Si ngle-component zwitterionic SAMs composed of thiols terminating in N,N-dime thyl-amino-propane-1-sulfonic acid (-N+(CH3)(2)CH2CH2CH2SO3-) groups were s ubstantially more effective at resisting adsorption of fibrinogen and lysoz yme from buffer at physiological ionic strength and pH than single-componen t zwitterionic SAMs composed of thiols terminating in phosphoric acid 2-tri methylamino-ethyl ester (-OP(O)(2)-OCH2CH2N+(CH3)(3)). Several of these zwi tterionic SAMs were comparable to the best known systems for resisting nons pecific adsorption of protein.