SERS-based nanotoxicology assessment of gold nanoparticles

In the last few years, gold nanoparticles (AuNPs) have been widely used in biomedical applications; unfortunately, in some cases, they induce toxic effects on biological systems. Among these, the activation of the innate immune system (inflammatory response) is considered a central issue for assessing health risks. Although the origin of nanotoxicity is not well known, the cause could be associated with the presence of contaminants on nanoparticles surface, such as bacterial endotoxin. The bacterial endotoxin, also known as Lipopolysaccharide (LPS), is the main component of gram-negative bacteria cell walls and is considered one of the major contaminants in the environment. Therefore, AuNPs can be easily contaminated during the synthesis process or their manipulation, and nanotoxicological assessment has to be performed before using AuNPs for biomedical purposes. Traditional assays for LPS detection are not always effective because AuNPs could interfere with other components and alter the final readout. Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for the analysis of molecules on metallic NPs, allowing to detect low concentration LPS with excellent sensitivity and reproducibility. In this work, we demonstrate that SERS technique can detect low amount of LPS (fg) on AuNPs (50 nm); moreover, we studied the internalization of bare and LPS-coated AuNPs in human monocyte-derived macrophages, by Raman Imaging, and their inflammatory effect by in vitro evaluation of pro and anti-inflammatory cytokine production.