The effect of gold nanosphere physiochemical properties on corona formation and cellular uptake

Gold nanosphere (GNS) application in nanomedicine as a drug delivery platform has been increased recently due to their unique physicochemical properties and biocompatibility to human cells. Immediately after GNS exposure to the physiological environment, blood plasma’s protein will adsorb to GNS surface. These adsorbed proteins called protein corona, determine GNS ability to deliver drugs selectively and efficiently to the diseased site. Therefore, the study of GNS behavior in the physiological environment is crucial in advancing GNS therapeutic application. Size and surface modification of GNS are crucial factors in corona formation. In this study, the effect of different sizes and surface modification in adsorption of the most abundant proteins in blood plasma (HSA, fibrinogen, & γ-globulin) was studied. Further, GNS cellular uptake in different sizes and surface modification was studied on SKBR3 and Hep2 cell lines

Gold nanospheres in different sizes (15 & 50 nm) was synthesized following the method devised by Turkevich et al. [2]. Then half of the stock solution was modified with thiolated polyethylene glycol (PEG). Corona formation on different size and surface modified (citrate-capped & PEG capped) GNS was qualified and quantified after incubation with HSA, fibrinogen, & γ-globulin by UV-Vis spectrophotometer, dynamic light scattering (DLS, scanning transmission electron microscope (STEM), and BCA protein assay. Then gold nanoparticles cellular uptake on different cell lines was quantified and qualified by inductively coupled plasma optical emission spectrometer (ICP-OES), and confocal microscope.

GNS characterization after one-hour incubation with proteins shows that by increasing GNS size, protein adsorption is increasing due to higher negative surface charge on bigger particles. Surface modification of GNS with PEG decrease protein adsorption significantly in compare to citrate-capped GNS, since PEG strands decrease the interaction between GNS surface and proteins. Also PEG will increase the surface charge of particles. To quantify GNS cellular uptake ICP-OES method was used and results represent that GNS in 50nm has more cellular uptake than 15nm (Fig 1 a). Since anionic particle uptake by cells through caveolae-mediated endocytosis and caveolar invagination is about 50-100nm, this size of particles will uptake in a higher extent in compare to 15 nm. For 15 nm, a cluster of particles should be uptake by cells. Although coating gold nanospheres with PEG decrease protein adsorption, it decreases cellular uptake. PEGylation reduces uptake due to the formation of hydrophilic stealth on the particle and PEG strands limit the GNS-cell interaction. Previous literature proved that anionic and cationic particles have more cellular uptake in compared to neutral particles. Coating GNS and PEGylated GNS with proteins, increase particles surface charge and it will make surface charge close to zero. Therefore, protein corona decreases cellular uptake in both cell lines. Also, confocal microscopy images prove the presence of nanoparticles in the cytoplasm of both cell line.