Magnetite biomineralization in the human brain.

Although the mineral magnetite (Fe3O4) is precipitated biochemically by bacteria, protists, and a variety of animals, it has not been documented previously in human tissue. Using an ultrasensitive superconducting magnetometer in a clean-lab environment, we have detected the presence of ferromagnetic material in a variety of tissues from the human brain. Magnetic particle extracts from solubilized brain tissues examined with high-resolution transmission electron microscopy, electron diffraction, and elemental analyses identify minerals in the magnetite-maghemite family, with many of the crystal morphologies and structures resembling strongly those precipitated by magnetotactic bacteria and fish. These magnetic and high-resolution transmission electron microscopy measurements imply the presence of a minimum of 5 million single-domain crystals per gram for most tissues in the brain and greater than 100 million crystals per gram for pia and dura. Magnetic property data indicate the crystals are in clumps of between 50 and 100 particles. Biogenic magnetite in the human brain may account for high-field saturation effects observed in the T1 and T2 values of magnetic resonance imaging and, perhaps, for a variety of biological effects of low-frequency magnetic fields. IMAGES:

尽管矿物磁铁矿（Magnetite，Fe₃O₄）可通过细菌、原生生物及多种动物的生物化学途径沉淀生成，但此前尚未在人体组织中见诸报道。
本研究在洁净实验室环境中，采用超灵敏超导磁力计（Ultrasensitive Superconducting Magnetometer），在多组人体脑组织样本中检测到了铁磁性物质（Ferromagnetic Material）的存在。
通过对经溶解处理的脑组织进行磁颗粒提取，并结合高分辨透射电子显微镜(High-resolution Transmission Electron Microscopy)、电子衍射（Electron Diffraction）与元素分析（Elemental Analysis）开展检测，我们鉴定出样本中存在磁铁矿-磁赤铁矿（Maghemite）族矿物，且多数晶体的形貌与结构与趋磁细菌（Magnetotactic Bacteria）及鱼类所沉淀的矿物高度相似。
上述磁力检测与高分辨透射电子显微镜结果显示，脑内多数组织中每克至少含有500万个单畴晶体（Single-domain Crystal），而软脑膜（Pia）与硬脑膜（Dura）组织中的单畴晶体数量则超过每克1亿个。
磁特性数据表明，这些晶体以50至100个颗粒为一簇的聚集体形式存在。
人脑内的生物成因磁铁矿可能是磁共振成像（Magnetic Resonance Imaging, MRI）中T1、T2值出现的高场饱和效应的成因，同时也可能与低频磁场引发的多种生物学效应存在关联。
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