Ideal Diamagnetism in Brain Microtubules

With mounting evidences of superconductivity in brain microtubules, a key experiment to support its existence would be a nanometer-scale mapping of microtubule magnetic properties. Magnetic force microscopy is a convenient instrument to perform such mapping. Previously, it has been used qualitatively resulting in the detection of strong diamagnetic response coming from the in-plane bundles of microtubules. This was preliminary associated with the feature of ideal diamagnetism and therefore superconductivity in the microtubules. Numerical arguments, however, were absent and it was unclear in what substance superconductivity resides. In order to clarify this, magnetic force microscopy was extended to force spectroscopy, which records magnetic signal as function of distance from the surface. Moreover, the spectroscopy was performed on cross-sections of microtubules investigating them individually. In order to do this, a special technique of sample preparation has been developed allowing orienting microtubules perpendicular to the substrate. The magnetic mapping revealed strong diamagnetism coming from the inside of microtubules. The analysis of recorded force curves has been performed analytically separating magnetic and van der Waals contributions to the signal. Following this, estimation of the signal expected for ideal diamagnetism has been obtained and compared with the signal coming from the microtubules. It is concluded that microtubules display property of ideal diamagnetism. The substance, in which superconductivity develops, is likely to be structured water.