Preliminary Quality Criteria of Citrate-Protected Gold Nanoparticles for Medicinal Applications

Gold nanoparticles (GNPs) are one of the most widely studied and utilized materials in nanomedicine, but there is no business or national quality standard for their medicinal applications. This has become the bottleneck in the translation of clinical applications of gold-based nanomaterials. To solve this issue, the most frequently used citrate-reduced GNPs were selected as demonstration in this study to conduct quality standard research. The different molar ratios of chloroauric acid to trisodium citrate in preparation were changed, from 1:1 to 1:5, to adjust the particle size and main ingredients in gold colloids. The compositions of reduced Au0 and residual Au3+ were determined by X-ray photoelectron spectroscopy (XPS), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and photodynamic catalysis, while the residual citrate and its oxidation products in supernatants were detected by nuclear magnetic resonance (1H NMR) spectroscopy and nonaqueous titration. Cell viability of human normal liver (L02) and hepatoblastoma (HepG2) cells was detected to evaluate the cytotoxicity of main ingredients (Au0) and impurities (Au3+ and citrate salt) in gold colloids. The results showed that the main impurities in gold colloids did not show significant effect on the cell viability, and the cytotoxicity was mainly caused by GNPs. Furthermore, in the experiments of the cell apoptosis, cycle, autophagy, and hemolysis assays, GNPs were not completely inert when the gold concentration exceeded 1.5 mg/L. The smallest GNPs showed the greatest degree of apoptosis, autophagy, and G2/M phases retention against L02 and HepG2 cells when compared with the other two larger gold colloids. Based on the above results, a preliminary quality criterion was drafted to ensure the safety of GNPs for their medicinal application.