Ferritin is a family of iron-storage proteins that are found
in animals, plants, fungi and bacteria. As far as we know, ferritin
does not contribute to the magnetization of sediments, but it does
provide an excellent example of the biomimetic approach to
synthesizing small magnetic particles. Natural ferritin is produced
by a BOB process and consists of a spherical protein shell with a
external diameter of 12 nm surrounding a cavity with an internal
diameter of 9 nm containing an iron oxy-hydroxide core [
Lowenstam and Weiner, 1989; Mann et al. 1990b]. The iron
mineral cores can be removed from the protein shell and
``resynthesized'' under laboratory conditions as magnetite or
maghemite [ Meldrum et al., 1992]. The resulting magnetic
protein is called magnetoferritin and is a colloidal suspension (a
``bioferrofluid'') of uniformly sized SPM particles of magnetite or
maghemite. Magnetoferritin has potential uses in studies of
superparamagnetic relaxation effects, macroscopic quantum tunneling
of magnetic moments [ Awschalom et al., 1992], and magnetic
resonance imaging of biological tissue [ Bulte et al., 1994].
In one interesting study, natural ferritin was used to determine
the frequency factor (f
) in the Néel-Arhennius magnetic
relaxation equation for magnetization switching in SD and SPM
particles [ Dickson et al., 1993].