http://www.cd-bioparticles.com/p/DiagNano™-Red-Coloured-Silica-Nanoparticles-100-nm_258_262_294_4002.html100 nm silica particles are available with covalently bound red dye in the silica matrix. These particles have a hydrophilic surface with terminal Si-OH bonds and are supplied in water without any surfactants.