Yuri Mizukawa

Light Reflection Control in Biogenic Micro-Mirror by Diamagnetic Orientation

As has become known, most materials, such as proteins and DNA, show orientation under strong magnetic fields. However, the critical threshold for the magnetic field of the magnetomechanical phenomena is still unknown. We demonstrate that a thin micro-mirror from a fish scale with high reflectivity exhibits a distinct magnetic response at 100 mT. A dramatic event under a magnetic field is the decrease of light scattering from guanine crystals as well as rapid rotation against the applied magnetic field. Enhancement of light scattering intensity is also observed when the three vectors of light incidence, magnetic field, and observation are orthogonally directed. The results indicate that biogenic guanine crystals have a large diamagnetic anisotropy along the surface parallel and normal directions. The micrometer to submicrometer scale of thin biogenic plates can act as a noninvasively, magnetically controlled micro-mirror for light irradiation control in the micrometer-scale region.

Light intensity modulation by coccoliths of Emiliania huxleyi as a micro-photo-regulator

In this study, we present experimental evidence showing that coccoliths have light-scattering anisotropy that contributes to a possible control of solar light exposure in the ocean. Changing the angle between the incident light and an applied magnetic field causes differences in the light-scattering intensities of a suspension of coccoliths isolated from Emiliania huxleyi. The magnetic field effect is induced by the diamagnetic torque force directing the coccolith radial plane perpendicular to the applied magnetic fields at 400 to 500 mT. The developed technique reveals the light-scattering anisotropies in the 3-μm-diameter floating coccoliths by orienting themselves in response to the magnetic fields. The detached coccolith scatters radially the light incident to its radial plane. The experimental results on magnetically oriented coccoliths show that an individual coccolith has a specific direction of light scattering, although the possible physiological effect of the coccolith remains for further study, focusing on the light-scattering anisotropies of coccoliths on living cells.

Magnetic Control of the Light Reflection Anisotropy in a Biogenic Guanine Microcrystal Platelet

Bioinspired but static optical devices such as lenses, retarders, and reflectors have had a significant impact on the designs of many man-made optical technologies. However, while numerous adaptive and flexible optical mechanisms are found throughout the animal kingdom, highly desirable biomimetic copies of these remarkable smart systems remain, in many cases, a distant dream. Many aquatic animals have evolved highly efficient reflectors based on multilayer stacks of the crystallized nucleic acid base guanine. With exceptional levels of spectral and intensity control, these reflectors represent an interesting design pathway towards controllable micromirror structures. Here we show that individual guanine crystals, with dimensions of 5 μm × 20 μm × 70 nm, can be magnetically controlled to act as individual micromirrors. By applying magnetic fields of 500 mT, the reflectivity of these crystals can be switched off and on for the change in reflectivity. Overall, the use of guanine represents a novel design scheme for a highly efficient and controllable synthetic organic micromirror array.

Magnetic control of the inclination of biogenic guanine crystals fixed on a substrate

In the present study, we describe the fabrication and manipulation of a micro-mirror system similar to the iridophores of neon tetra that allow microstructural light control. Biogenic guanine crystals as micro-mirrors were adhered to a glass substrate with flexible DNA joints under a vertical magnetic field of 480 mT. We then observed the movement of the micro-mirrors under sub-Tesla horizontal magnetic fields. Under ambient fields, the orientation of the guanine micro-mirrors did not change. Appling a horizontal magnetic field of approximately 400 mT generated by an electromagnet induced motion and width changes of the guanine micro-mirrors, which were observed by an optical microscope. However, the inclination of the micro-mirrors recovered upon removal of the magnetic field. The developed guanine micro-mirrors on a glass substrate demonstrate the remote control of microstructural diamagnetic materials, and may show promise for use as an underwater microactuator for microfluidic systems.

Magnetic light cloaking control in the marine planktonic copepod Sapphirina

We investigated the light cloaking behavior of the marine planktonic copepod Sapphirina under a magnetic field. Optical interferences in the multi-laminated guanine crystal layer beneath the dorsal body surface create a brilliant structural color, which can be almost entirely removed by changing the light reflection. In the investigation, we immersed segments of Sapphirina in seawater contained in an optical chamber. When the derived Sapphirina segments were attached to the container surface, they were inert to magnetic fields up to 300 mT. However, when the back plate segments were attached to the substrate at a point, with most of the plate floating in the seawater, the plate rotated oppositely to the applied magnetic field. In addition, the brilliant parts of the Sapphirina back plate rotated backward and forward by changing the magnetic field directions. Our experiment suggests a new model of an optical micro-electro-mechanical system that is controllable by magnetic fields.

Magnetically Controlled Biogenic Crystals as Photo-Bioreactors for Algae

Biogenic guanine crystal (GC) is abundantly contained in fish scales. This crystal has thin plate form and high light reflectance with the largest plane of it. Effects of magnetic fields on GC, which shows diamagnetic orientation were investigated in our previous studies. In this paper, we tried to apply the biogenic crystals to micro algae culture for the purpose of acceleration of the micro algaes photonic synthesis. Recently, micro algae were focused on the view of producing bio-ethanol or bio-fuel. In particular, crystals, which have high refractive index and contain nitrogen in their molecule, seem be to available for one of fertilizer for plants. In addition, crystals, which have high refractive index, reflect light well, so we expect that these properties help algaes photonic synthesis. Additionally, some algae have the photo-tactic characteristics, phototaxis. Therefore, we also aim to utilize these crystals for efficient culturing of algae. In this paper, microscopic observations of behaviors of the micro algae in the cell culture chamber with a buffer containing the crystals were carried out. We tried controlling of alga motions with directive light stimulation from magnetically aligned biogenic GCs.

Effect of intense magnetic fields on the convection of biogenic guanine crystals in aqueous solution

In this study, the basic magneto-optic properties of biogenic microcrystals in aqueous media were investigated. Microcrystals, mica plates, silica, and microcrystals from a diatom cell and biogenic guanine crystals from goldfish showed light scattering inhibition when the crystals were observed in water under a 5 T magnetic field and dark-field illumination. In particular, in 50% ethanol/water medium, convection of the biogenic guanine particle aggregates was reversibly inhibited when the microcrystal suspension was exposed to a 5 T magnetic field. Microscopic observation comparing the biogenic guanine crystals in water with 95% ethanol or 99% acetone revealed that light flickering on the surface of the crystals was affected by the surface interaction of the crystal with the surrounding medium. By considering both the magnetic orientation of the microcrystals and the possible interactions of crystals with the surrounding medium, a magnetically controllable fluidic tracer was suggested.

Magnetic Manipulation of Nucleic Acid Base Microcrystals for DNA Sensing

This paper develops a magneto-DNA sensing device composed of a crystalline nucleic acid base, which is a component of DNA on the basis of the dynamic rotation due to its diamagnetic anisotropy under a magnetic field of the mT order. As a basic study, recrystallized nucleic acid bases, such as cytosine, adenine, and guanine, were used for the measurement. We focused on the induced dynamic orientation effect on the nucleic acid base crystals by exposure of the magnetic field at 0.5 T. The morphologically long axis of a cytosine crystal oriented parallel to the applied magnetic fields, while those of adenine and guanine oriented perpendicular to the magnetic field. As a next stage, we traced the angular difference of the magnetic rotation of DNA adhered to guanine crystals comparing the rotation angles of the pre-exposure sample and the during exposure sample with and without DNA. It was revealed that the degree of the magnetic rotation of guanine crystals with DNA was seemingly less than that of guanine crystals without DNA. The difference in angle of the magnetic rotation of the guanine crystal may allow to detect the adhesion of DNA. The method obtained by detecting precise magnetic rotation of nucleic acid base crystals can be applied to the manipulation and sensing of macromolecules in dispersion containing nucleic acid bases, such as DNA and RNA.

Synchrotron Microscopic Fourier Transform Infrared Spectroscopy Analyses of Biogenic Guanine Crystals Along Axes of Easy Magnetization

Our previous study remained a question why biogenic guanine crystals that cause magnetic orientation under magnetic fields scattered light so intensively. In addition, the magnetic orientation analyses indicated that the crystal plate has primal and second axes of easy magnetization by diamagnetism, by which two-stage orientation of the crystal is caused. This paper aims to reveal the molecule arrangement inside the guanine crystal, which is related to optical and magnetic anisotropy. A transient light scattering increase from the guanine crystals that occurs with increasing and decreasing magnetic fields between 0 and 0.5 T was measured. The results indicate that the biogenic guanine crystal plates have a specific direction to scatter the light incidence. In the next, molecular vibrations in a single-crystal plate were investigated by utilizing the synchrotron microscopic Fourier transform infrared (FTIR) spectroscopy, and the obtained spectrum compared with that in magnetically oriented guanine crystal. The FTIR and attenuated total reflectance measurements reproducibly observed the IR absorbance spectrum peak appearance and disappearance when the polarization direction was set parallel and perpendicular to the morphological length of a biogenic guanine crystal. It is speculated that spectrum peak appearance and disappearance were caused by vibration of C = O bonds and N-H bonds in guanine crystal for polarization direction. In conclusion, we revealed that the surface and inside of biogenic guanine crystal possessed the anisotropy for molecule orientation related to optical and magnetic property.