Optical Behavior of Guanine Microcrystals from Aquatic Species upon Exposure to a Magnetic Field

Various aquatic animals have evolved their own particular systems for manipulating light to effect rapid color change, light concentration, optical cloaking, etc. utilizing a multilayered guanine crystal structure. This study focuses on the optical and magnetic properties of microscopic (approximately 1 μm) guanine crystals isolated from Sapphirina and scallop eyes. Crystals were suspended in an aqueous solution, and light reflecting properties and structural color were evaluated by real-time microscopic and spectroscopic analysis, with and without exposure to a 500 millitesla horizontal magnetic field. Diamagnetic anisotropic energy was also calculated. Results show that guanine crystals display significant light-reflection switching properties upon application of a magnetic field, regardless of the origin or size and shape of the crystals. Furthermore, it may be possible to devise a means for remote control of highly efficient microscopic light reflection and optical coloring utilizing the diamagnetic anisotropy of guanine crystals.