The effect of size and surface chemistry on the exocytosis of gold nanoparticles in macrophages

Abstract

Gold nanoparticles (AuNPs) have become prevalent as a novel biosafe and biocompatible tool for various applications, including biological imaging, clinical diagnostics and therapeutics, because of their surface plasmon resonance. Understanding the interactions of functional nanoparticles with cells is of great importance, not only for development of new therapeutic tools, but also for realizing the fundamental cellular mechanisms and cytotoxicity of nanomaterials. In particular, the synthesis of non-aggregated nanoparticles and exocytosis studies are of tremendous importance, as it relates directly to chronic cytotoxicity and clearance from the body. To overcome these problems, we firstly made a nanoparticle-protein complex before the experiment and investigated the endocytosis and exocytosis of functionalized AuNPs in macrophages according to their size and surface chemistry. The amount of AuNPs entering and leaving macrophages was evaluated in vitro by ICP-MS, and the phenomena of endocytosis and exocytosis were recorded by two photon excitation microscope, dark field microscope and differential interference contrast (DIC). To prevent aggregation, AuNPs were coated by serum proteins for 1h. This indicates that proteins coated on the surface prevent AuNP aggregation and allow each particle to interact with cells individually. The average hydrodynamic diameter of AuNPs generally increases from 10nm to 15nm after protein coating. Positively-charged and PEGylated AuNPs bind fewer serum proteins on the surface of nanoparticles than negatively and neutrally-charged AuNPs. Unusually, the surface charges of protein-coated AuNPs changed to negative after protein coating, regardless of the initial value. The changes of hydrodynamic diameter and surface charges deeply related to compositions of serum proteins. In endocytosis, positively-charged AuNPs displayed the highest uptake efficiency in macrophages and monocytes whereas PEGylated AuNPs displayed the lowest regard...