Nano-objects are any materials that have at least one dimension (length, width, height and/or diameter) between 1 to 100 nanometers (nm). Nanoparticles refers to material in which at least two dimensions measure between 1-100 nm. Nanoparticles may be dry particles, suspended in a gas (as a nanoaerosol), suspended in a liquid (as a nanocolloid or nanohydrosol) or embedded in a matrix (as a nanocomposite).

EH&S has developed specific Guidance For Nanoparticles.