@article{kaufman_belyea_johnson_nicholson_ricks_shah_bayless_pettersson_feldoto_blomberg_et al._2007, title={Probing protein adsorption onto mercaptoundecanoic acid stabilized gold nanoparticles and surfaces by quartz crystal microbalance and zeta-potential measurements}, volume={23}, ISSN={["0743-7463"]}, DOI={10.1021/la063725a}, abstractNote={The adsorption characteristics of three proteins [bovine serum albumin (BSA), myoglobin (Mb), and cytochrome c (CytC)] onto self-assembled monolayers of mercaptoundecanoic acid (MUA) on both gold nanoparticles (AuNP) and gold surfaces (Au) are described. The combination of quartz crystal microbalance measurements with dissipation (QCM-D) and pH titrations of the zeta-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 adsorbed fraction. BSA showed the highest affinity for the MUA/Au, forming an irreversibly adsorbed rigid monolayer with a side-down orientation and packing close to that expected in the jamming limit. In addition, BSA showed a large change in the adsorbed mass due to reversibly bound protein. The data indicate that the irreversibly adsorbed fraction of CytC is a monolayer structure, whereas the irreversibly adsorbed Mb is present in form of a bilayer. The observation of stable BSA complexes on MUA/AuNPs at the isoelectric point by zeta-potential measurements demonstrates that BSA can sterically stabilize MUA/AuNP. On the other hand, MUA/AuNP coated with either Mb or CytC formed a reversible flocculated state at the isoelectric point. The colloidal stability differences may be correlated with weaker binding in the reversibly bound overlayer in the case of Mb and CytC as compared to BSA.}, number={11}, journal={LANGMUIR}, author={Kaufman, Eric D. and Belyea, Jennifer and Johnson, Marcus C. and Nicholson, Zach M. and Ricks, Jennifer L. and Shah, Pavak K. and Bayless, Michael and Pettersson, Torbjorn and Feldoto, Zsombor and Blomberg, Eva and et al.}, year={2007}, month={May}, pages={6053–6062} }
 @article{liu_shipton_ryan_kaufman_franzen_feldheim_2007, title={Synthesis, stability, and cellular internalization of gold nanoparticles containing mixed peptide-poly(ethylene glycol) monolayers}, volume={79}, ISSN={["0003-2700"]}, DOI={10.1021/ac061578f}, abstractNote={Gold nanoparticles have shown great promise as therapeutics, therapeutic delivery vectors, and intracellular imaging agents. For many biomedical applications, selective cell and nuclear targeting are desirable, and these remain a significant practical challenge in the use of nanoparticles in vivo. This challenge is being addressed by the incorporation of cell-targeting peptides or antibodies onto the nanoparticle surface, modifications that frequently compromise nanoparticle stability in high ionic strength biological media. We describe herein the assembly of poly(ethylene glycol) (PEG) and mixed peptide/PEG monolayers on gold nanoparticle surfaces. The stability of the resulting bioconjugates in high ionic strength media was characterized as a function of nanoparticle size, PEG length, and monolayer composition. In total, three different thiol-modified PEGs (average molecular weight (MW), 900, 1500, and 5000 g mol-1), four particle diameters (10, 20, 30, and 60 nm), and two cell-targeting peptides were explored. We found that nanoparticle stability increased with increasing PEG length, decreasing nanoparticle diameter, and increasing PEG mole fraction. The order of assembly also played a role in nanoparticle stability. Mixed monolayers prepared via the sequential addition of PEG followed by peptide were more stable than particles prepared via simultaneous co-adsorption. Finally, the ability of nanoparticles modified with mixed PEG/RME (RME = receptor-mediated endocytosis) peptide monolayers to target the cytoplasm of HeLa cells was quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Although it was anticipated that the MW 5000 g mol-1 PEG would sterically block peptides from access to the cell membrane compared to the MW 900 PEG, nanoparticles modified with mixed peptide/PEG 5000 monolayers were internalized as efficiently as nanoparticles containing mixed peptide/PEG 900 monolayers. These studies can provide useful cues in the assembly of stable peptide/gold nanoparticle bioconjugates capable of being internalized into cells.}, number={6}, journal={ANALYTICAL CHEMISTRY}, author={Liu, Yanli and Shipton, Mathew K. and Ryan, Joseph and Kaufman, Eric D. and Franzen, Stefan and Feldheim, Daniel L.}, year={2007}, month={Mar}, pages={2221–2229} }