Tuning the interactions of PEG-coated gold nanorods with BSA and model proteins through insertion of amino or carboxylate groups

• GNR–protein interactions can be modulated through functionalization with charged groups.
• GNR–protein interactions can be almost completely reversed by salt addition.
• Surface-induced protein structural changes are not completely reversed.
• Electrostatic forces lead GNR–protein interactions.
• Different GNR–protein interaction patterns provide useful hints for sensing applications.

Gold nanorods (GNRs) are important platforms for biosensing and drug delivery. As for most nanomaterials, appropriate coatings such as polyethylene glycol (PEG) are needed to stabilize GNRs within biological fluids. We show here that the interactions of GNRs with proteins can be finely modulated through surface modification using PEG-containing chains bearing charged headgroups. Interestingly, introduction of amino or carboxylate groups produces relevant and differential changes in GNR interactions with three representative proteins: lysozyme, cytochrome c, and bovine serum albumin. These effects were explored through the direct monitoring of plasmonic bands of the GNRs and are supported by independent dynamic light scattering (DLS) and circular dichroism (CD) determinations. Notably, GNR–protein interactions observed for these charged GNRs can be almost completely reversed by salt addition. These observations demonstrate the importance of electrostatic effects in governing GNR–protein interactions, and provide a basis for new sensing and delivery platforms.

Interaction of GNRs with proteins can be modulated through functionalization with cationic or anionic end-functionalized PEG-thiols. The direct monitoring of GNR's plasmonic bands shows differential changes in GNR interaction with proteins. Results demonstrate the importance of electrostatics in governing GNR–protein interactions, providing a basis for new sensing and delivery platforms.Figure optionsDownload as PowerPoint slide