Percoll consists of colloidal silica particles of 15-30 nm diameter (23% w/w in water) which have been coated with polyvinylpyrrolidone (PVP). It is used to establish non-toxic low viscosity, low osmolarity density gradients that can be used to isolate cells, organelles and viruses. It has been used to separate inner and outer membrane vesicles from E. coli. Percoll is isosmotic throughout the gradient, non-toxic, and is easily removed from the purified materials.
