Engineered nanoparticles (ENPs) are now ubiquitous in a host of consumer products and applications, with more nano-enabled products poised to enter the marketplace in the next ten years. In biomedicine, nanotherapeutics and nanotheranostic agents are enabling new imaging and drug-delivery applications. Understanding and controlling the formation of the protein corona around ENPs is essential for ensuring successful targeting in vivo. In particular, the formation of protein coronas around small ENPs (dcore &lt; 10 nm) requires more systematic investigation, because small ENPs are generally more efficiently taken up and retained by target cells and tissues in vivo. This makes smaller ENPs superior choices for a host of theranostics applications. This study investigated the protein adsorption of bovine serum albumin (BSA) with 5 nm gold nanoparticles (AuNPs) displaying different ω-functionalized thiols. AuNPs were synthesized using three different functionalized thiols to display five different surface chemistries: a neutral ω-functionalized thiol ligand (mercapto-ethoxy-ethoxy-ethanol, MEEE), a thiol ligand that is negatively charged at pH 7.4 (mercaptohexanoic acid, MHA), a thiol ligand that is positively-charged at all pH values (mercaptopentyltrimethyl ammonium chloride, MPTMA) and two mixed-monolayer surface chemistries (mixed-ligand AuNPs, MPTMA:MEEE and MHA:MEEE). The binding constants (Ka) of the different AuNP surface chemistries with bovine serum albumin were determined using absorbance spectroscopy, fluorescence quenching titrations, and dynamic light scattering (DLS). Fluorescence titrations indicated that the binding affinity of BSA was on the order of 0.50 ± 0.02 nM-1, but that the functional group displayed by the thiol led to significantly different Ka values among the surface chemistries tested. Hill plot analysis of the fluorescence titration data indicated that for all five AuNP surface chemistries, BSA exhibited cooperative binding behavior. Absorbance spectroscopy titration and measurement of the hydrodynamic diameter (Dh) by DLS suggests that 1 to 2 BSA molecules adsorb to each AuNP, regardless of surface chemistry. Differences observed between the binding constants determined using the different spectroscopic methods will be discussed, with reference to MD simulations of BSA interacting with the nanoparticle surface.

Comparing spectroscopically-determined binding constants in the binding of bovine serum albumin to small thiol-stabilized ω-functionalized gold nanoparticles

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