Effect of 10-T magnetic fields on structural colors in guanine crystals of fish scales

Abstract

This work reports the magnetically modulated structural colors in the chromatophore of goldfish scales under static magnetic fields up to 10 T. A fiber optic system for spectroscopy measurements and a CCD microscope were set in the horizontal bore of a 10-T superconducting magnet. One leaf of a fish scale was set in a glass chamber, exposed to visible light from its side direction, and then static magnetic fields were applied perpendicular to the surface of the scale. In addition, an optical fiber for spectroscopy was directed perpendicular to the surface. During the magnetic field sweep-up, the aggregate of guanine thin plates partially showed a rapid light quenching under 0.26 to 2 T; however, most of the thin plates continued to scatter the side-light and showed changing iridescence, which was displayed individually by each guanine plate. For example, an aggregate in the chromatophore exhibited a dynamic change in structural color from white-green to dark blue when the magnetic fields changed from 2 to 10 T. The spectrum profile, which was obtained by the fiber optic system, confirmed the image color changes under magnetic field exposure. Also, a linearly polarized light transmission was measured on fish scales by utilizing an optical polarizer and analyzer. The transmitted polarized light intensities increased in the range of 500–550 nm compared to the intensity at 700 nm during the magnetic field sweep-up. These results indicate that the multi-lamella structure of nano-mirror plates in guanine hexagonal micro-plates exhibit diamagnetically modulated structure changes, and its light interference is affected by strong magnetic fields.