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Published May 22, 2018 | Published + Supplemental Material
Journal Article Open

Magnetic control of heterogeneous ice nucleation with nanophase magnetite: Biophysical and agricultural implications


In supercooled water, ice nucleation is a stochastic process that requires ∼250–300 molecules to transiently achieve structural ordering before an embryonic seed crystal can nucleate. This happens most easily on crystalline surfaces, in a process termed heterogeneous nucleation; without such surfaces, water droplets will supercool to below −30 °C before eventually freezing homogeneously. A variety of fundamental processes depends on heterogeneous ice nucleation, ranging from desert-blown dust inducing precipitation in clouds to frost resistance in plants. Recent experiments have shown that crystals of nanophase magnetite (Fe_3O_4) are powerful nucleation sites for this heterogeneous crystallization of ice, comparable to other materials like silver iodide and some cryobacterial peptides. In natural materials containing magnetite, its ferromagnetism offers the possibility that magneto-mechanical motion induced by external oscillating magnetic fields could act to disrupt the water–crystal interface, inhibiting the heterogeneous nucleation process in subfreezing water and promoting supercooling. For this to act, the magneto-mechanical rotation of the particles should be higher than the magnitude of Brownian motions. We report here that 10-Hz precessing magnetic fields, at strengths of 1 mT and above, on ∼50-nm magnetite crystals dispersed in ultrapure water, meet these criteria and do indeed produce highly significant supercooling. Using these rotating magnetic fields, we were able to elicit supercooling in two representative plant and animal tissues (celery and bovine muscle), both of which have detectable, natural levels of ferromagnetic material. Tailoring magnetic oscillations for the magnetite particle size distribution in different tissues could maximize this supercooling effect.

Additional Information

© 2018 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND). Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved March 26, 2018 (received for review January 7, 2018). Published ahead of print May 7, 2018. We thank two anonymous referees for useful suggestions on the manuscript. Mr. Hiroshi Nirasawa of the Yatsugatake Chuo Agriculture Training College in Hara Village provided Nagano Japan celery samples. This study was supported by Japan Society for the Promotion of Science KAKENHI Grants JP26630062 and JP16H04276 (to A.K.). Author contributions: A.K. designed research; A.K. and M.H. performed research; A.K., M.H., J.L.K., and H.N.G. contributed new reagents/analytic tools; A.K. and J.L.K. analyzed data; and A.K., J.L.K., and H.N.G. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1800294115/-/DCSupplemental.

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Published - 5383.full.pdf

Supplemental Material - pnas.1800294115.sm01.avi

Supplemental Material - pnas.201800294SI.pdf


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August 21, 2023
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