Effect of Surface Wettability on the Adsorption of Proteins and Detereents

This report describes the usc of surfacc plasmon spectroscopy to study the effect of surfacc wettability on the nonspecific adsorption of proteins and dctcrgcnts to self-assembled monolayers (SAMs) of alkanethiolatcs on gold. Thc adsorption of both proteins and detcrgcnts to uncharged SAMs showed a gencral depcndcncc on the wettability of the surface as determincd by thc contact anglc of watcr on the SAM undcr cyclooctane (9.n). The effect of the wettability of the SAMs on the adsorption of sodium dodecyl sulfatc (SDS) was dcpendcnt on whcther micelles were present. Abovc the critical miccllc conccntration (cmc), SDS adsorbed only on surfaces that gave contact angles with values of cos ?rn . 0 (i.c.. thc transfcr of the surfacc from watcr to cyclooctanc has a favorable lree energy). Below thc cmc. thc rcquircmcnt lor adsorption was much morc stringent: SDS adsorbed only on thc surlaces that gave valucs of cos 0rn . -0.9. Similarly, the effcct of thc wettability of the SAMs on the adsorption of protcins showed a dcpcndencc on thc size of thc protcins. Thc smallcr proteins tested (ribonuclease A and lysozyme) adsorbed only on thc least wettable surfaces testcd (cos 0,o . -0.83). Thc larger proteins tested (pyruvate kinase, fibrinogen. and y-globulin) also adsorbcd best to the least wettable surfaces, but adsorbed to some extent on almost all the surfaccs; the singlc exccption was a SAM prcscnting hexa(ethylenc glycol) groups at thc surfacc, to which no protein adsorbed. Films of adsorbed proteins were desorbed from thc SAMs by treatment with detergcnt.