Preventing Protein Adsorption and Macrophage Uptake of Gold Nanoparticlesviaa Hydrophobic Shield

Abstract

Polyethylene glycol (PEG) surface coatings are widely used to render stealth properties to nanoparticles in biological applications. There is abundant literature on benefits of PEG coatings and their ability to reduce protein adsorption, to diminish non-specific interactions with cells, and to improve pharmacokinetics, but very little discussion of the limitations of PEG coatings. Here, we show that physiological concentrations of cysteine and cystine can displace methoxy-PEG-thiol molecules from the gold nanoparticle (GNP) surface that leads to protein adsorption and cell uptake in macrophages within 24 hours. Furthermore, we address this problem by incorporating an alkyl linker between the PEG and the thiol moieties that provides a hydrophobic shield layer between the gold surface and the hydrophilic outer PEG layer. The mPEG-alkyl-thiol coating greatly reduces protein adsorption on GNPs and their macrophage uptake. This has important implications for the design of GNP for biological systems.

A tetraethylene glycol coat gives gold nanoparticles long in vivo half-lives with minimal increase in size

“…Spleen tissue had significantly increased TUNEL positive cells (predominantly localized to the red pulp) relative to control tissue with an average of 88±15 positive cells for experimental samples versus an average of 19±3 positive cells for control samples (P,0.001) (Figure 6). While TEG gold nanoparticles are collected promiscuously through the spleen, likely by macrophages per Larson et al's 13 work characterizing ligand-exchanged PEG-coated particles ( Figure 4D and E), these results suggest that the nanoparticles taken up in the spleen red pulp, by perhaps reticular meshwork macrophages as previously described, are toxic. 19 Thus, both TEG-and PEG-coated nanoparticles are toxic, albeit to different organs.…”

“…To determine whether intracellular concentrations of glutathione are sufficient to induce ligand exchange reactions with TEG nanoparticles, 13 a TEG nanoparticle preparation was mixed 1:1 with glutathione dissolved in water to yield aliquots with a final glutathione concentration of 0.1 mM (low concentration), 1 mM (low cellular concentration), 5 mM (medium cellular concentration), and 10 mM (high cellular concentration).…”

“…19 The particles were perhaps collected by the spleen due to exposure to serum compounds that could trigger aggregation and phagocytosis following ligand exchange, which is known to preferentially lead to splenic clearance with PEG-coated nanoparticles. 3,5,13,21 A minority of particles would aggregate as splenectomized animal half-life results and column work …”

“…[7][8][9][10] The change in charge is thus likely due to interaction with small molecules, such as glutathione, that more readily penetrate the particles' TEG shield and trigger ligand exchange reactions. 13 PEG-coated particles have been shown to undergo ligand exchange reactions, which also increase protein adsorption and their uptake by macrophages. 13 The change is unlikely due to cations as gel electrophoresis illustrated that neither concentrated salts (0.1 M potassium, sodium, and calcium) (data not shown) nor physiological hydrogen or hydroxide ion concentrations elicited the observed change ( Figure S3).…”

Plasmonic nanoparticles and their characterization in physiological fluids

“…Several studies have shown that physiological concentrations of thiolcontaining molecules such as cysteine easily displace, for example, thiolated Polyethylene-glycol (PEG) from the surface of Au NPs [50,51]. The (partial) loss of the ligand, however, has far-reaching consequences as it impacts colloidal stability of the core NP, changes the adsorbed protein profile, and may lead to the complete loss of any functional grafted ligands such as fluorescent dyes, antibodies, or drug molecules.…”