Silver nanoparticles were grown in aqueous solution, without the presence of typical surfactant molecules, but under the presence of different proteins. The shape of the resulting silver nanoparticles could be tuned by the selection of the types of proteins. The amount of accessible lysine groups was found to be mainly responsible for the anisotropy in nanoparticle formation. Viability measurements of cells exposed to protein capped spherical or prism-shaped NPs did not reveal differences between both geometries. Thus, in the case of protein-only coated Ag NPs, no shape-induced toxicity was found under the investigated exposure conditions.