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.

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 field effects on mitochondrion-activity-related optical properties in slime mold and bone forming cells.

In the present study, a cellular level response of Cyto-aa3 oxidation was investigated in real time under both time-varying and strong static magnetic fields of 5 T. Two kinds of cells, a slime mold, Physarum polycephalum, and bone forming cells, MC-3T3-E1, were used for the experiments. The oxidation level of the Cyto-aa3 was calculated by optical absorptions at 690 nm, 780 nm and 830 nm. The sample, fiber-optics and an additional optical fiber for light stimulation were set in a solenoidal coil or the bore of a 5-T superconducting magnet. The solenoidal coil for time-varying magnetic fields produced sinusoidal magnetic fields of 6 mT. The slime mold showed a periodic change in Cyto-aa3 oxidation, and the oxidation-reduction cycle of Cyto-aa3 was apparently changed when visible-light irradiated the slime mold. Similarly to the case with light, time-varying magnetic stimulations changed the oxidation-reduction cycle during and after the stimulation for 10 minutes. The same phenomena were observed in the MC-3T3-E1 cell assembly, although their cycle rhythm was comparatively random. Finally, magnetic field exposure of up to 5 T exhibited a distinct suppression of Cyto-aa3 oscillation in the bone forming cells. Exposure up to 5 T was repeated five times, and the change in Cyto-aa3 oxidation reproducibly occurred.

Magnetic rotations of uric acid crystals and uratic crystals by static magnetic fields of up to 500 mT.

In recent years, the disease concerning ureteral calculus is increasing possibly due to the changing lifestyles. For example, it is well known that the urinary calculi have a large impact to gout. As eating habitual diseases, gout and the hyper-uricemia are related to the formation of urinary calculus. In the previous studies, therapeutic agents were developed to enhance the uric acid excretion. From the viewpoint of side effects induction by the chemical agents, we are motivated to explore an alternative method to control the formation of ureteral crystals stimulator by physical stimulations. Therefore in the present study, we focused on the behaviors of uric acid crystals under magnetic fields of several hundreds of mT (Tesla). The uric acid crystals were re-crystallized from a suspension of uric acid powder, and the micro-crystals were prepared to be floating in the solution. We generated horizontal magnetic fields of maximum 500 mT by an electromagnet which contained a CCD microscope. A permanent magnet with magnetic fields of 200∼400 mT was also utilized. During the magnetic fields were applied to the uric acid crystals, we observed that the uric acid crystals were oriented by the magnetic fields down to 200 mT at the room temperature. It was speculated that the dimagnetic anisotropy in the uric acid crystals exhibited the rotational responses. The results indicate the possible remote control of the uric acid crystals in living body by the magnetic fields of 200 mT to 500 mT.