The adsorption characteristics of three proteins [bovine serum albumin (BSA), myoglobin (
Mb), and cytochrome
c (CytC)] onto self-asse
mbled monolayers of mercaptoundecanoic acid (MUA) on both gold nanoparticles (AuNP)and gold surfaces (Au) are described. The co
mbination of quartz crystal microbalance measurements with dissipation(QCM-D) and pH titrations of the
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-potential provide information on layer structure, surface coverage, and potential.All three proteins formed adsorption layers consisting of an irreversibly adsorbed fraction and a reversibly adsorbedfraction. BSA showed the highest affinity for the MUA/Au, forming an irreversibly adsorbed rigid monolayer witha side-down orientation and packing close to that expected in the jamming limit. In addition, BSA showed a largechange in the adsorbed mass due to reversibly bound protein. The data indicate that the irreversibly adsorbed fractionof CytC is a monolayer structure, whereas the irreversibly adsorbed Mb is present in form of a bilayer. The observationof stable BSA complexes on MUA/AuNPs at the isoelectric point by
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-potential measurements demonstrates that BSAcan sterically stabilize MUA/AuNP. On the other hand, MUA/AuNP coated with either Mb or CytC formed a reversibleflocculated state at the isoelectric point. The colloidal stability differences may be correlated with weaker bindingin the reversibly bound overlayer in the case of Mb and CytC as compared to BSA.