Nanosphere Size Standards are uniform polystyrene spheres calibrated in nm with NIST traceable methodology. 1nm is one billionth of a meter, 0.001 µm, micron or 10 Angstrom units. They are packaged as aqueous suspensions in 15 mL dropper-tipped bottles. The concentrations are optimized for ease of dispersion and colloidal stability. The spheres have a density of 1.05g/cm3 and an index of refraction of 1.59 @ 589 nm. Methods used by Thermo Scientific to calibrate the diameters of the Nanospheres include dynamic light scattering (DLS) and transmission electron microscopy (TEM). Nanosphere Size Standards are ideal for the calibration of electron and atomic force microscopes. They are also used in laser light scattering studies, and colloidal systems research. The 20 to 900nm range of diameters is also convenient for checking the sizes of bacteria, viruses, ribosomes and sub-cellular components in biology laboratories.