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Moiré fringes are created by superimposing two periodic or quasi-periodic networks of lines. This established technique is an important metrological tool for methods such as super-resolution microscopy. Biogenic guanine crystals show light and dark striped patterns on the broadest surface of their crystal plates when optical interference occurs because of the flatness and transparency of the crystal. In this work, using the optical interference pattern of a goldfish guanine crystal plate, we successfully observe the appearance of moiré fringes on a guanine crystal plate floating in water above herringbone patterns with micron and sub-micron periods. It is demonstrated experimentally that a variety of moiré fringes can be obtained by varying the long-axis direction of the guanine crystal plate using an in-plane magnetic field, which corresponds to a change in the direction of the structured illumination, because of the diamagnetic anisotropy of the crystal. The results of observation of the moiré fringes formed when the tilt angle of the guanine crystal's (102) plane relative to the substrate is varied using a vertical magnetic field are also presented. [ABSTRACT FROM AUTHOR]

This paper focuses on the light interference in biogenic guanine crystals that have interesting optical properties such as high reflectivity and optical biaxiality. In this paper, we find that a Moiré effect pattern is generated on a single guanine crystal of goldfish combining with the mirror surface substrate. An observation system, in this paper, is consisted with telecentric lens and coaxial vertical illumination using blue LED light source. It is clearly seen that homogeneous light and shade stripe patterns are observed on the broadest surface of the single guanine crystal plate floating in water. By contrast, when the guanine crystals are set on the substrates having the diffused reflection surface, this light and shade stripe pattern is not observed on the single guanine crystal but observed on two cross-stacked crystals as reported before. These results show that the light and shade stripe pattern on the single guanine crystal is produced by the optical interference, so-called Moiré effect, between guanine crystal and the mirror substrate surface. The angle dependence of reflection brightness and the magnetic orientation of guanine crystal are investigated by using Moiré patterns. Furthermore, we demonstrate that small curvatures and steps can be optically detected and estimated by the pattern change of Moiré stripes. It is confirmed that the direction of curvature is detected by controlling the guanine crystal orientation with magnetic fields and the curvature shape is reproduced from the Moiré pattern. [ABSTRACT FROM AUTHOR]

Lanternfish, a family Myctophidae, use ventro-lateral body photophores for camouflage of the ventral silhouette, a strategy called counterillumination. While other deep-sea fishes possess pigmented filters and silver reflectors to match sunlight filtering down through the depths, myctophids developed a blue-green reflector for this purpose. In this study, we showed in a lanternfish Diaphus watasei that the reflector comprised monolayered iridophores containing multilayered guanine crystals which enable high reflection with light interference colouration. Platelets shape in body photophores is an unique near-regular hexagonal, probably to allow the homogeneity of reflection angle of the luminescence from photocytes. Focus point of the parabola-like reflector is positioned on the photocytes that ensures the light produced from the photocytes is redirected to the ventral direction. In vitro luminescence reaction using purified luciferase and the substrate coelenterazine showed the light emission at λ max 454 nm, while reflection spectra of the iridophores exhibit peaks at longer wavelength, which accomplish to alter the luminescence emitted from photocytes to longer wavelength to fit the mesopelagic light environment. Taken together, we revealed multiple mechanistic elaborations in myctophid body photophores to achieve effective control of biochemical luminescence for counterillumination. • Reflector of lanternfish's photophore is parabola-like/the focus point is on the photocytes. • Platelet of the reflector is anhydrous guanine crystal/unique regular hexagonal. • Luciferin-luciferase reaction showed deep-blue luminescence at 454 nm in maximum. • Coloured reflector alters the spectrum of light from photocytes to longer wavelength. • The reflector is bio-mechanically/-chemically elaborated for effective counterillumination. [ABSTRACT FROM AUTHOR]

The light reflection intensity from a biogenic guanine crystal that shows strong light scattering on the broadest surface of the crystal can be modulated by the magnetic field switching due to the dynamic motion of magnetic orientation caused by the diamagnetic anisotropy. Magnetic field amplitudes required for magnetic orientation are drastically decreased by hybridizing the guanine crystal with a ferromagnetic thin film, which is one of the important factors for device application from the viewpoint of power consumption and field generation method. In this paper, we present the 3-D magnetic orientation control of the guanine crystal hybridized with the 5 nm thick permalloy film by applying the magnetic field with a three-axis Helmholtz coil. Vertical magnetic field dependences of the tilt angle of (102) plane of the guanine crystal from the substrate for various in-plane magnetic fields are investigated. It is clarified that the hybrid plate can be controlled three-dimensionally with the magnetic field less than several milliteslas by applying the suitable in-plane field. It is shown that the hybrid plate floating under water is transported by the magnetic field gradient using the permanent magnet, which is effective for carrying it to the target position. The 3-D magnetic orientation characteristics of the hybrid plate that shows the similar behavior to the biogenic guanine crystal for the vertical magnetic field are also mentioned. [ABSTRACT FROM AUTHOR]

Synthetic guanine crystals, with the same magnetic controllable reflection property as a biogenic guanine crystal from fish scales, were prepared using a classical Ostwald ripening method for crude crystals, from the aqueous sodium hydroxide solution of a commercially available synthesized guanine powder. The resulting synthetic guanine crystals with an average size of several tens of micrometers were in the same crystal system as the biogenic guanine crystals under measurement by X-ray diffraction (XRD). However, XRD patterns of water-floating crystals showed that the correlation between the growing direction and reflecting surface in the synthetic crystals is different from that in the biogenic crystals. Therefore, the synthetic crystals were ground by an agate mortar for refinement of its optical and magnetic-orientation characters. As a result, we realized a fast-magnetic orientation against the vertical field, which is related to the magnetic control of light reflection, the same as the biogenic guanine crystal behavior. [ABSTRACT FROM AUTHOR]

In micro-optical device and micro-electromechanical systems applications, the driving power and response time are the important factors for their performance. In this paper, a diamagnetic guanine crystal/ferromagnetic film hybrid plate is fabricated by the sputtering method in order to decrease the magnetic field amplitude required for the guanine crystal orientation. The behavior of the hybrid plate having a 5 nm-thick permalloy film in water under magnetic fields is investigated by using a three-axis Helmholtz coil. The hybrid plate rotates according to the horizontal magnetic field so that the length of (102) plane of guanine crystal is parallel to the field direction. For the vertical magnetic field, the hybrid plate easily stands up. These behaviors are attributed to the large shape anisotropy of ferromagnetic film of hybrid plate. Magnetic field amplitudes required for magnetic orientation drastically decrease compared to those for diamagnetic orientation of the pure guanine crystal. It has been demonstrated that LED lights which are simultaneously irradiated from different directions can be selectively introduced into the microscope by using the reflection of hybrid plate which is controlled with external magnetic fields. [ABSTRACT FROM AUTHOR]