image: This is a TEM image of cells of magnetotactic bacteria aligned in a magnetic field at 140 millitesla. The dark crystals are made of biological magnetite. view more
Credit: PNAS
Researchers report that nanophase magnetite is a powerful nucleation material for ice crystals, and that magnetically driven motions of magnetite can disrupt ice formation. Without a nucleation surface on which water molecules can organize, water does not freeze until it supercools to around -30 degrees Celsius. Atsuko Kobayashi and colleagues measured cooling rates and volume expansion, which are indicators of freezing, in balloons containing either purified water or water spiked with nanophase magnetite crystals. The magnetite-spiked balloons froze at a higher temperature and expanded to a greater extent than purified water, which supercooled. Magnetite-spiked balloons in a magnetic field at a strength of 1-1.5 millitesla supercooled, suggesting that the magnet-driven motion of magnetite disrupted normal ice nucleation. Further tests in both celery and beef, representing plant and animal food products known to contain detectable levels of biogenic magnetite, showed that the magnetic field promoted supercooling. Because ice crystals that form after supercooling are smaller and less damaging to tissues than those that form near 0 degrees Celsius, the results suggest a potential method for reducing frost and ice damage in agricultural products and other applications that require cryopreservation, according to the authors.
Article #18-00294: "Magnetic control of heterogeneous ice nucleation with nanophase magnetite: Biophysical and agricultural implications," by Atsuko Kobayashi, Masamoto Horikawa, Joseph Kirschvink, and Harry Golash.
MEDIA CONTACT: Atsuko Kobayashi, Tokyo Institute of Technology; tel: +81-3-5734-2708; e-mail: <kobayashi.a.an@m.titech.ac.jp>
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