Norihiro Umeda

Scanning attractive force microscope using photothermal vibration

An attractive force microscope using photothermal vibration is presented. A cantilever is vibrated by the optical absorption of a laser beam whose intensity modulation frequency is at resonance frequency, and the vibration is detected by an optical deflection method. The characteristics of the photothermal vibration and the attractive force gradient versus tip‐sample distance have been measured with a Ni foil cantilever. Topographic images of digital memory disks made from a polycarbonate and Mg–Al alloy were recorded.

Two-dimensional birefringence measurement using the phase shifting technique

The phase shifting technique for the measurement of a twodimensional birefringence distribution is described and discussed. The birefringent phase difference and azimuthal angle of a transparent material can be determined in the dependence of both measurements on the amplitude and phase of the polarization interferometry. A half-wave plate and a Babinet-Soleil compensator are used as phase shifters for the phase shifting technique. It can measure 256 x 256 values of the birefringent phase difference and azimuthal angle in a short time with sufficient accuracy. This method does not require moving the sample mechanically. The results and procedures for measuring such a birefringence distribution of optical components such as a calibrated Babinet-Soleil compensator, a lens, and a roof prism are discussed.

Bio rapid prototyping by extruding/aspirating/refilling thermoreversible hydrogel

This paper reports a method for rapid prototyping of cell tissues, which is based on a system that extrudes, aspirates and refills a mixture of cells and thermoreversible hydrogel as a scaffold. In the extruding mode, a cell-mixed scaffold solution in the sol state is extruded from a cooled micronozzle into a temperature-controlled substrate, which keeps the scaffold in the gel state. In the aspiration mode, the opposite process is performed by Bernoulli suction. In the refilling mode, the solution is extruded into a groove created in the aspiration mode. The minimum width of extruded hydrogel pattern is 114 +/- 15 microm by employing a nozzle of diameter 100 microm, and that of aspirated groove was 355 +/- 10 microm using a 500 microm-diameter nozzle. Gum arabic is mixed with the scaffold solution to avoid peeling-off of the gel pattern from the substrate. Patterning of Sf-9 cell tissue is demonstrated, and the stability of the patterned cell is investigated. This system offers a procedure for rapid prototyping and local modification of cell scaffolds for tissue engineering.

Scanning Wiener-fringe microscope with an optical fiber tip.

A scanning probe optical microscope using the Wiener fringe is presented. The Wiener fringe is formed by a standing wave between the incident and reflected waves on an optically reflective surface and is detected by inserting an optical fiber tip into the fringe-field region. The detected signal is used to maintain the tip-sample distance constant so that a topographic image of a sample can be obtained by a computer-assisted instrument. A spatial resolution of 200 nm has been achieved by observing a sample of known geometry.

Measurement of characteristics of magnetic fluid by the Mueller matrix imaging polarimeter

Optical characteristics of magnetic fluid are described and measured with the Mueller matrix. Furthermore, the optical activity of the magnetic fluid is discovered. A theory to determine the rotation ratio of two retarders of the Mueller matrix imaging polarimeter is also presented. To measure the entire Mueller matrix elements, due to the sampling theorem, the rate of 5 is chosen as the best and most unique for this polarimeter.

Significant correlation between refractive index and activity of mitochondria: single mitochondrion study.

Measurements of refractive indices (RIs) of intracellular components can provide useful information on the structure and function of cells. The present study reports, for the first time, determination of the RI of an isolated mitochondrion in isotonic solution using retardation-modulated differential interference contrast microscopy. The value was 1.41 ± 0.01, indicating that mitochondria are densely packed with molecules having high RIs. Further, the RIs of each mitochondrion were significantly correlated with the mitochondrial membrane potential, an index of mitochondrial activity. These results will provide useful information on the structures and functions of cells based on the intracellular distribution of RIs.

Single-shot birefringence measurement using radial polarizer fabricated by direct atomic force microscope stroking method

We describe a single-shot birefringence measurement using a radial polarizer fabricated by a direct atomic force microscope nano-stroking method. A radial polarizer, which converts linearly polarized light into radial polarized light, was prepared by radially aligning liquid crystal molecules in a 150 ? 150 ?m2 region. The birefringence of a calibrated sample is measured by performing image analysis of the sample illuminated by radial polarized light. The measured retardation and the azimuth angle of the calibrated sample almost agreed with the setting values. This method is effective for measuring a temporal change in birefringence.

Manipulation of metal nanoparticles using fiber-optic laser tweezers with a microspherical focusing lens

This paper describes the laser manipulation of metal nanoparticles and dielectric particles by fiber-optic laser tweezers with a microspherical focusing lens. In this manner, a small ball lens attached to the end of the core focuses light guided through a single-mode optical fiber. Numerical electromagnetic analysis of the microfocusing structure showed the possibility of metal nanoparticle trapping with this method. An effective focus allows metallic particles located in the path of the focused light to be attracted to the center of the beam path and to be two-dimensionally trapped on a substrate. In the experiment, manipulation of Au nanoparticles with diameters of 40, 100, and 200 nm was demonstrated. In addition to metallic samples, manipulation of dielectric particles with 1 and 3 µm diameters was also demonstrated using the same configuration, showing the extended capability of the fiber-optic laser manipulator.

Detection of swelling of single isolated mitochondrion with optical microscopy

Volume regulation under osmotic loading is one of the most fundamental functions in cells and organelles. However, the effective method to detect volume changes of a single organelle has not been developed. Here, we present a novel technique for detecting volume changes of a single isolated mitochondrion in aqueous solution based on the transmittance of the light through the mitochondrion. We found that 70% and 21% of mitochondria swelled upon addition of a hypotonic solution and Ca(2+), respectively. These results show the potential of the present technique to detect the physiological volume changes of individual small organelles such as mitochondria.

Optical Dew Sensor Using Surface Plasmon Resonance of Periodic Ag Nanostructure

The sensitivity of an optical dew sensor is enhanced by the use of the surface plasmon resonance (SPR) of a periodic Ag nanostructure. As the temperature of an SPR-excited Ag nanostructure decreases, vaporous water molecules condense and adsorb onto hydroxyl groups formed on the Ag surface. A redshift of 40 nm in absorption peak wavelength was observed owing to the amount of adsorbed water molecules due to the temperature. An SPR signal occurs at temperatures higher than the theoretical dew point and shows the sensitivity improvement of the optical dew sensor by the proposed SPR technique.