A silica-gold core-shell structure to mimic the large size of gold particles for promoting cell growth: A comparative study of the silica core size and the nanogold amount in the shell

Recently, the biosafety of gold nanomaterials has attracted more attention. Some consider them as an adverse factor for cell growth, whereas others regard them as biocompatible. In this work, we reported a type of silica-gold core-shell structure (SiO 2 @AuNPs) with the diameter more than 70   nm that could promote cell growth. The synthesis of SiO 2 @AuNPs adopted a step-by-step protocol involving the fabrication of silica substrate followed by their amination, the attachment of fine (about 4   nm) gold seeds, and the formation of a gold shell by reducing HAuCl 4 on seeds. The cell viability experiment indicated that AuNPs attached to silica substrate could promote the growth of HeLa cell. With increasing concentration of SiO 2 @AuNPs or the content of gold shell, the viability of co-cultured HeLa cells also increased; on the contrary, acute cytotoxicity was observed when pure 4   nm AuNPs were added. Moreover, we found that the proliferative effect could be enhanced by enlarging the size of silica substrate. Due to large SiO 2 @AuNPs not entering the cell, their nano-size concavo-convex surface was facilitated to cell adhesion, probably leading to the proliferation of HeLa cells. However, detailed mechanism responsible for cell growth is still unclear and it requires more studies. Although the mechanism remains enigmatic, the findings may have practical significance for cell proliferation, which is in great demand in numerous fields such as tissue engineering. In addition, the core-shell materials were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray spectrum (EDX), and the cell viability was measured by Cell Counting Kit-8 (CCK-8).