Magnetic Orientational Properties of Monosodium Urate Crystals

Monosodium urate (MSU) crystals are the cause of gout and are formed from uric acid and sodium. Because they can be rotated by the torque induced by an applied magnetic field, we have characterized their detailed magnetic orientational properties to improve the detection sensitivity from outside the body using the magnetic orientation. The MSU crystals were precipitated by dissolving uric acid powder in aqueous sodium hydroxide. In serum, the MSU crystals were small and uniformly sized, similar to those obtained from gout patients. The MSU crystals were not completely oriented perpendicular to the magnetic-field direction, but rather the c-axis of the crystal was inclined with respect to the field direction. Specifically, they were inclined at a mean of 69.3 degrees under a magnetic field of 500 mT. The MSU crystals were not perfectly oriented in magnetic fields <200 mT. The inclination results from the molecular structure of the MSU crystal.