title: A first test of the hypothesis of biogenic magnetite-based heterogeneous ice-crystal nucleation in cryopreservation.
abstract: An outstanding biophysical puzzle is focused on the apparent ability of weak, extremely low-frequency oscillating magnetic fields to enhance cryopreservation of many biological tissues. A recent theory holds that these weak magnetic fields could be inhibiting ice-crystal nucleation on the nanocrystals of biological magnetite (Fe3O4, an inverse cubic spinel) that are present in many plant and animal tissues by causing them to oscillate. In this theory, magnetically-induced mechanical oscillations disrupt the ability of water molecules to nucleate on the surface of the magnetite nanocrystals. However, the ability of the magnetite crystal lattice to serve as a template for heterogeneous ice crystal nucleation is as yet unknown, particularly for particles in the 10-100 nm size range. Here we report that the addition of trace-amounts of finely-dispersed magnetite into ultrapure water samples reduces strongly the incidence of supercooling, as measured in experiments conducted using a controlled freezing apparatus with multiple thermocouples. SQUID magnetometry was used to quantify nanogram levels of magnetite in the water samples. We also report a relationship between the volume change of ice, and the degree of supercooling, that may indicate lower degassing during the crystallization of supercooled water. In addition to supporting the role of ice-crystal nucleation by biogenic magnetite in many tissues, magnetite nanocrystals could provide inexpensive, non-toxic, and non-pathogenic ice nucleating agents needed in a variety of industrial processes, as well as influencing the dynamics of ice crystal nucleation in many natural environments.
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan. Electronic address: kobayashi.a.an@m.titech.ac.jp.
authors.forename: Atsuko
authors.initials: A
authors.lastname: Kobayashi
authors.affiliation: Division of Mechanical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Harry N
authors.initials: HN
authors.lastname: Golash
authors.affiliation: Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan; Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Kirschvink
mesh_terms: D000818:Animals; D001703:Biophysics; D015925:Cryopreservation; D003460:Crystallization; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D005615:Freezing; D007053:Ice; D053758:Nanoparticles / Q000737:chemistry*
chemical_list: D007053:Ice; D052203:Ferrosoferric Oxide
keywords: Biogenic magnetite; Ice crystal nucleation; SQUID magnetometry; Supercooling