Are Silver and Gold Nanoparticles Obtained by 'Green' Synthesis Biocompatible?

In scientific literature, the biosynthesis of gold and silver nanoparticles and synthesis of these nanoparticles using small organic molecules such as citrate have been called 'green' processes. In abstracts of scientific publications, gold or silver nanoparticles obtained by 'green' synthesis have rather frequently been characterized as biocompatible. Biocompatible means having no negative impact on exposed organisms. Two reasons have been used to underpin this characterization. The first is the biocompatibility of the substances used in 'green' synthesis and coating nanoparticles. This reason lacks a solid empirical basis. The second reason given for biocompatibility is limited testing of the nanoparticles obtained by 'green' synthesis (mainly in vitro testing). Such limited testing is inconclusive. Use-specific comprehensive in vitro and in vivo testing, including clinical studies, and control of hazardous substances such as lipopolysaccharide and flagellins are needed to provide a solid basis for their characterization as biocompatible for humans.