Magnetic motion of biogenic guanine crystal plate combined with Fe2O3 nanoparticles

To reduce the magnetic field amplitude required to orient guanine crystal plates, we have attached magnetic nanoparticles to these guanine crystal plates. Fe2O3 nanoparticles are mixed with the guanine crystal plates, which are dispersed in water. Observation by optical microscopy confirmed that the large particles, which are nanoparticle aggregates, attach preferentially to the side edges of the guanine crystal plates. The individual crystal plate surfaces show clear, undisturbed light interference patterns, which mean that each plate’s optical properties have been maintained. The magnetic orientation experiments of these guanine crystal plates with different numbers of optically observed particles are conducted under both in-plane and vertical magnetic fields. The positions of the attached particles do not change, even when the magnetic field is applied. In these experiment, it was difficult to align the crystal direction with the magnetic field direction because the magnetic orientation characteristics are strongly affected by the positions and numbers of the attached particles. However, in-plane rotation and an increased tilt angle are achieved for the guanine crystal plates using magnetic fields of several millitesla.