Prof.Nikolai

I have observed the presence of Gold NPs in cells by TEM analysis. The nanoparticles enter into the cells, but many are located on the outside of the cells membrane. Analysis by confocal microscopy (scattering 633nm) show the presence of nanoparticles around the nucleus but the same cells analyzed by TEM do not present NPs around the nucleus. The increased number of particles scattering around the nucleus of cells treated with Gold NPs is due to some biological effect, probably they are microvesicles. By ICP-MS analysis of cells treated with Gold NPs is impossible to understand if the amount of gold detected derives from NPs adhering to the cell membrane (external side) or not. Furthermore, it is difficult to assess the presence of gold ions in the solutions, in fact analyzing solutions after centrifugation or filtration by TEM can be observed NPs. Centrifugation and filtration are not able to completely eliminate the NPs from a solution. Finally, gold is unaffected by air, moisture and most corrosive reagents, and is therefore well suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert. Gold is almost insoluble, but can be dissolved in aqua regia. Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate. Gold first ionization energy 1st: 890.1 kJ·mol−1

I repeated the experiments to study the ionization of gold nanoparticles. The presence of gold ions in the solution of nanoparticles is due to the presence of metal gold. I have experimentally confirmed by TEM analysis that the gold nanoparticles do not ionize in lysosomes. The toxicity of this nanomaterial is very complex and it is due to multiple factors. Only in the case of metal oxides the ionization of nanomaterials explains the cause of their toxicity as demonstrated by Zhang, H. in their recent work "Use of metal oxide nanoparticle band gap to develop a predictive paradigm for oxidative stress and acute pulmonary inflammation" ACS Nano, 2012 May 22;6(5):4349-68

I would like your opinion on a biological issue. I am analyzing the toxicity of gold nanoparticles (AuNPs) and I'm almost sure that the mechanism of toxicity of these nanoparticles is due to multiple effects very different from the effects observed by other types of nanoparticles (silver, titanium oxide, etc.). Indeed all other types of nanoparticles can release ions while AuNPs can not ionize. To definitively demonstrate this effect I want to understand whether the metal ions can cross biological membranes. In addition, I would like to understand whether gold ions can enter and/or exit from the different cellular vesicles. Thank you very much for your help, Nikolai

I also believe that the gold nanoparticles can not release ions. But the question is that I can not explain to myself the toxic effects. Some authors have demonstrated that the toxicity of the gold nanoparticles is due to their interaction with the proteins of lysosomes. So cell death is given by the blockade of vesicular trafficking (Quantitative Evaluation of Cellular Uptake and Trafficking of Plain and Polyethylene Glycol-Coated Gold Nanoparticles, Small 2010) The lysosome has an internal pH of 4.0-4.5, can allow the ionization of gold? Yet another question concerns the output of gold ions from the lysosome. The biological membrane is permeable to gold ions? Thank you all for your help.

Several authors in various papers attribute the toxic effects of nanomaterials to the release of ions from the main nanostructure (nanoparticles, nanorods, etc.). This is easy to perceive in the case of metal oxides and in the case of metals such as silver (1st Ionization energy of silver: 731.0 kJ·mol−1). About gold? Why gold nanoparticles induces toxic effects in living cells? It is possible that gold ions are released by gold nanoparticles (1st Ionization energy of gold: 890.1 kJ·mol−1)?