Comparative cytotoxicity of biogenic and chemical silver and gold nanoparticles on normal and tumoral lung cells

Silver (Ag) and gold (Au) nanoparticles (NPs) are largely employed in many different fields and are typically synthesized through chemical methods, involving reduction reactions, which can result in the production of hazardous compounds harmful to both human health and the environment. As a response to these concerns, there is an increasing interest in developing more environmentally friendly approaches for their synthesis. In this study, we analysed the cytotoxic response of human cells exposed to Ag and Au NPs, produced via alternative routes: the Lee-Meisel and the Turkevich chemical methods, and the biogenic method using tea extract. Ag and Au NPs were synthesized to achieve high NP concentrations and ensure the stability of the NP suspension over time. We assessed the effects of these NPs on two different lung cell lines, one normal (HBEC3-KT) and one tumoral (A549) since the cellular response to NPs may vary depending on the tumoral status of the cells. The results evidenced a higher cytotoxicity of Ag than Au NPs, irrespective of the synthesis method and consistent with silver's reported toxic properties. At 2 mu g/mL, both biogenic and chemical Ag NPs showed minimal toxicity but at 5 mu g/mL and above, biogenic Ag NPs exhibited greater cytotoxicity towards normal cells compared to cancer cells, distinguishing them from their chemical counterparts. Notably, long-term clonogenic assays revealed that biogenic Ag NPs affected the proliferation ability of cancer cells at lower concentrations than chemical Ag NPs. Biogenic Au NPs maintained minimal toxicity in both normal and cancer cells, similarly to chemically synthesized NPs, even at the highest concentration tested, highlighting the high biocompatibility of Au NPs. Our results show that biogenic synthesis using the tea extract is efficient to synthesize Ag NPs with potential anticancer or antimicrobial applications and Au NPs suitable for drug delivery.