Kensuke Kanda

Measurement of Particle Distribution in Microchannel Flow Using a 3D-TIRFM Technique

The presence of bio-substances in the near-wall region in micro bio-chemical analysis chips is an important topic but one which is difficult to investigate directly. In this paper we developed an accurate 3D-TIRFM technique, which was used to investigate the three-dimensional positions of nano-particles. The depth was calibrated using a piezo stage. As an example of an application of this technique, the concentration profile of nano-particles near a wall surface was investigated. The results showed that the concentration profile was non-uniform and lower than that in the bulk. In addition the ionic strength of the solvent strongly influenced the concentration profile. It was concluded that the non-uniform concentration profile is due to the influence of the electric double layer around the particles and the surface. This demonstrates the importance of selecting suitable electric characteristics, since a non-uniform and low concentration profile near the wall will affect the reaction efficiency and the sensitivity in micro bio-chemical analysis.

Near-wall nanoparticles perpendicular distribution measured using evanescent illumination

Nanoparticle imaging using evanescent illumination is a very useful technique for elucidating physical phenomena near the walls of microchannels in microfluidic systems. Since the intensity of evanescent illumination decays exponentially with distance from the wall surface, particles closer to the wall appear brighter than those further from the wall. This enables the three-dimensional positions of nanoparticles in near-wall regions to be measured. In this study, the behavior of nanoparticles in a microfluid was observed experimentally. 20-nm-diameter fluorescent nanoparticles were employed rather than biological molecules for single-particle imaging. To overcome the poor measurement accuracy due to the small diameter of the nanoparticles used for imaging and the low fluorescence intensity of a single nanoparticle far from the wall, the image settings were optimized and a novel image processing algorithm was proposed. The experimental results reveal that the nanoparticle concentration varies in the direction normal to the wall. The nanoparticle concentration decreased with proximity to the wall surface; in particular, the concentration in the region from 0 to 170 nm, was much lower than that in more distant regions from the wall. Moreover, the nanoparticle concentration in the near-wall region decreased as the diffusion coefficient of the nanoparticles decreased.

Measurement and control of motion of nanoparticles in microchannel

In microbiochemical analysis, the concentration of biomaterials near a wall greatly affects the detection and reaction efficiency. In this paper, we evaluate the interaction between nanoparticles and a microchannel wall. We measured the concentration distribution of 100-nm-diameter particles, which are equivalent in size to viruses, and attempted to cause nanoparticles to accumulate near the wall by applying an electric field with the aim of improving the reaction efficiency. We used total internal reflection fluorescence microscopy to measure the 3D particle distribution. This technique employs evanescent light (the intensity of which decays exponentially with distance) as illumination. By exploiting the characteristics of evanescent light, we were able to determine the 3D-position of a particle from its luminescence. The results reveal that there are very low concentrations of particles near a channel wall due to the potential barrier between the particles and the wall. This implies that immune reactions will not occur effectively near walls. Subsequently, we tried to concentrate nanoparticles near the wall by applying an electric field to the suspension. The particles moved toward the wall and became attached to it, overcoming the potential barrier. We anticipate that applying this method to biochemical analysis will greatly increase reaction efficiencies.

Velocity Field Measurements in a Near-Wall Flow of Drag Reducing Solution in Microchannel

The velocity profile of a dilute polymer solution and a surfactant solution near the wall surface in a microchannel was clarified using evanescent wave illumination and a particle tracking velocimetry system. Fluorescent particles with a diameter of 100 nm were used as tracer particles. The test fluids were polyethylene-oxide (Peo15) solution at 5 ppm, oleyl-bihydroxyethyl methyl ammonium chloride (Ethoquad O/12) solution at 200 ppm and distilled water. The results obtained for the velocity profiles for distilled water and surfactant solution were found to agree well with the two-dimensional Poiseuille velocity profile. On the other hand, the velocity profile of the dilute polymer solution decreases significantly compared with that of water within 200 nm of the wall surface. These data provide the first velocity profile measurements of a dilute polymer solution and a surfactant solution in the near-wall region.Copyright

Measurement of the Velocity Profile Near the Wall in Bio-Fluid Flow Using Evanescent Light Source

For the investigation of near surface phenomena, a novel method, which is to measure velocity profile in the direction of depth, are suggested. By changing the angle of induce light, illuminated penetration depth is changed. The velocities of fluorescent tracers are successfully measured using PTV technique. The fluid including bio-molecules is employed for velocity measurement. The velocity profile of bio-fluid is measured by eliminating the influence of the Brownian motion of tracers. The velocity profile of the flow agrees well with the plane Poiseruille flow equation except for the results at large distance from the wall. It is assumed that the difference in the velocity at the large distance results from the inhomogeneous concentration profile due to surface potential. In our knowledge, the method suggested in this study is the first one in terms of measuring flow velocity profile in direction of depth near wall surface.Copyright

Measurements of Surface Effects on Bio-Fluids Flow in Micro-Channel by Using SPM

For the establishment of the design methodologies of micro fluidic chips, the essential analysis of the flow behavior on the micro-meter scale and surface interactions on the nano-scale has been investigated. The understanding of bio-fluid flow behavior in the micro-systems includes both the basic fluid dynamic problems and driving forces from the fields of application. Attention has been focused on the clarification of the surface effects on the solution of bio-molecular flow at micro-scale dimensions. Investigations of pressure drop measurements in bio-molecular flow together with measurements of biomolecular absorption and the lateral forces on various surfaces were carried out on both micro and nano scale. The results demonstrated a clear correlation between flow drag and bio molecular interaction with the surface. The validity is demonstrated of the evaluation method suggested in this paper.© 2004 ASME