The inflammatory properties of carbon nanoparticles are regarded as a major roadblock in their use for biomedical applications. On page 4194, S. Giordani, E. C. Lavelle and co-workers describe a simple and reproducible strategy to address this issue using a novel purification process combined with surface chemical functionalization. The carbon nano-onions are also shown to promote less inflammation than carbon nanotubes and this can be further reduced by surface functionalization. This is the first report that single walled carbon nanotubes and carbon nano-onions have the ability to activate the NLRP3 inflammasome.