Mitsuhisa Ichiyanagi

Combined Laser-Based Measurements for Micro- and Nanoscale Transport Phenomena

The present paper summarizes our recent research in combined laser-based measurement techniques for investigating micro- and nanoscale transport phenomena. Micrometer-resolution particle image velocimetry has been combined with the laser-induced fluorescence (LIF) technique in order to simultaneously analyze velocity and scalar fields. The measurement system is based on confocal microscopy to realize a depth resolution of approximately 2 m, and we have applied this technique to liquid–liquid mixing flows, gas–liquid two-phase flows, gas permeation phenomena through membranes, and surface-modified microchannel flow. Furthermore, in order to evaluate the electrostatic potential at a solid–liquid interface (i.e., zeta potential), the LIF technique was extended by evanescent wave illumination, and only the fluorescent dye within approximately 100 nm of the microchannel wall was irradiated. The extended LIF technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. The proposed techniques will contribute to novel applications related to microscale multiphase flows or electrokinetics.

Two-dimensional manipulation of microbubbles using primary Bjerknes force

In this paper, two-dimensional (2D) microbubble manipulation is demonstrated using the primary Bjerknes force resulting from an ultrasound pressure gradient. This technique is expected to be useful in a variety of medical applications such as drug delivery systems, gene transfer mechanisms, and so on. Should this technique become established, it could allow microbubbles to be applied selectively to target cells and allow the positional relation between cells and microbubbles to be investigated quantitatively. However, in previous works, the acoustic manipulation of microbubbles has not been applied to precise spatial control in more than one dimension. Accordingly, as proposed microbubble manipulation tools, we prepared two devices, one utilizing four flat transducers and another using a six-channel (6-ch) ring transducer, both of which could create 2D acoustic pressure fields. Using these devices, it was found to be possible to trap and manipulate microbubbles as desired.

Laser-based measurement techniques for interfacial transport phenomena in microchannels

This paper summarized our recent works of the laser-based measurement techniques for investigating micro- and nano-scale transport phenomena. Micron-resolution particle image velocimetry combined with the laser induced fluorescence (LIF) technique was developed for analyzing velocity and ion concentration distributions simultaneously. The measurement system was based upon a confocal microscopy to realize the depth-resolution of approximately 2 μm, and this technique was applied to liquid-liquid mixing flows, gas-liquid two-phase flows and gas permeation phenomena through membranes. To evaluate the electrostatic potential at solid-liquid interface (i.e., zeta-potential), the LIF technique was advanced with the evanescent wave illumination. Fluorescent dye within approximately 100 nm from a microchannel wall was irradiated. This technique was applied to microdevices with a surface modification pattern, and the zeta-potential distribution was successfully visualized. Two proposed techniques will contribute to novel applications related to microscale multiphase flows or electrokinetics.Copyright