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Simultaneous and Sequential Protein and Organothiol Interactions with Gold Nanoparticles

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journal contribution
posted on 24.01.2013, 00:00 by Karthikeshwar Vangala, Kumudu Siriwardana, Erick S. Vasquez, Yan, Xin, Charles U. Pittman, Keisha B. Walters, Dongmao Zhang
Proteins and organothiols (OTs) are known to have high affinity for gold nanoparticles (AuNPs). Systematic investigation of protein and OT coadsorption onto AuNPs is, however, mostly an unexplored area. Presented here is a comparison of simultaneous and sequential protein and OT interactions with AuNPs in which a protein and an OT are either simultaneously or sequentially added to colloidal AuNPs. Using bovine serum albumin (BSA) as the model protein and eight model organothiols, both the protein and the OT were coadsorbed onto AuNPs in samples formed by sequential or simultaneous addition. AuNP stability against OT-adsorption-induced AuNP aggregation differed significantly among the AuNP/OT and AuNP/BSA/OT mixtures. The stability of AuNPs in the AuNP/BSA/OT mixtures with the same compositions increased from (AuNP/OT)/BSA to AuNP/(BSA/OT) and finally (AuNP/BSA)/OT (where the two components inside the parentheses are mixed first followed by the addition of the third component). Aging the (AuNP/BSA) mixtures before OT addition also increased the AuNP stability in (AuNP/BSA)/OT samples. This sequence and aging dependence of AuNP stability indicates that protein and OT coadsorption onto AuNPs is kinetically controlled. It also offers a plausible explanation to the large discrepancy in the binding constants reported for the BSA interaction with AuNPs (from 105 to 1011 M–1). The work is important for AuNP biological/biomedical applications because AuNPs encounter a mixture of proteins and OTs in addition to other molecular species in biofluids.