Electrospraying and in-flight heating of ferritin, the iron-storage protein, was used to produce controlled size, monodisperse aerosol particles which can be used as size standards for instrument calibration. As aerosol particles can be collected in liquids or on a substrate, standard size aerosol nanoparticles can be used for the calibration and development of not only aerosol instrumentation, but also colloid instrumentation and electron microscopes. Differences in the sizes of apoferritin and ferritin were detectable using scanning mobility particle spectrometry. Apoferritin has a mobility diameter of 11.8 nm, while iron-rich ferritin had a mobility diameter of 13.1 nm and the size distribution function of both apoferritin and ferritin had geometric standard deviations of 1.05. In-flight heating in a furnace aerosol reactor was used to remove the ferritin protein coat and produce monodisperse iron oxide particles 7.9 nm in diameter and a size distribution function geometric standard deviation of 1.07. Ferritin dimers and higher order n-mers, produced from multiple ferritin complexes being present in a single electrospray droplet, remained bound to each other after in-flight heating. Monte Carlo simulations of the electrospray process showed that as long as the electrospray droplets are sufficiently monodisperse, monodisperse standard size nanoparticles can also be produced from ferritin n-mers. (C) 2008 Published by Elsevier Ltd.