Satoyuki Kawano

Particles transport driven by a temperature gradient in a solution is known as thermophoresis or Soret effect. The drift velocity of a particle is expressed as , where is a thermophoretic mobility. Therefore, the thermophoretic mobility is a parameter to characterise the nature of thermophoresis, and the systematic measurement of for various combinations of particles and solvents is necessary for its potential application. In the present work, we develop the microfluidic system called microgap S

In this study, we have demonstrated the fabrication of a microbeam array (MBA) with various thicknesses and investigated the suitability it for an acoustic sensor with wide-range frequency selectivity. For this, an MBA composed of 64 beams, with thicknesses varying from 2.99–142 µm, was fabricated by using single gray-scale lithography and a thick negative photoresist. The vibration of the beams in air was measured using a laser Doppler vibrometer; the resonant frequencies of the beams were meas

We experimentally and theoretically characterize dielectric nano- and microparticle orbital motion induced by an optical vortex of the Laguerre-Gaussian beam. The key to stable orbiting of dielectric nanoparticles is hydrodynamic inter-particle interaction and microscale confinement of slit-like fluidic channels. As the number of particles in the orbit increases, the hydrodynamic inter-particle interaction accelerates orbital motion to overcome the inherent thermal fluctuation. The microscale co

Optical trapping and manipulation techniques have attracted significant attention in various research fields. Optical forces divided into two terms, such as a scattering force and gradient one, work to push forward and attract objects, respectively. This is a typical property of optical forces. In particular, a tool known as optical tweezers can be created when a laser beam is converged at a focal point, causing strong forces to be generated so as to trap and manipulate small objects. In this st

We report a novel vibration control technique of an artificial auditory cochlear epithelium that mimics the function of outer hair cells in the organ of Corti. The proposed piezoelectric and trapezoidal membrane not only has the acoustic/electric conversion and frequency selectivity of the previous device developed mainly by one of the authors and colleagues, but also has a function to control local vibration according to sound stimuli. Vibration control is achieved by applying local electrical

The diffusion of single‐stranded DNA (ssDNA) molecules near a glass surface by total internal reflection fluorescence microscopy has been observed. Substantially smaller diffusion coefficients compared to the bulk are caused by phenomenologically different types of surface effect that is not necessarily adsorptive. In particular, preliminary treatments of the glass substrate by low and high concentrations of KOH lead to highly and much less adsorptive effects on the ssDNA molecules, respectively

Thermophoretic forces acting on nanoparticles are investigated using molecular dynamics simulation. We assume the Lennard-Jones (LJ) potential for the interaction between fluid molecules. On the other hand, the interaction between the nanoparticle and the surrounding fluid molecules are assumed to be either LJ or Weeks-Chandler-Andersen (WCA) potential, where the latter is purely-repulsive. The effect of the interaction potential on the thermophoretic force is investigated for various situations

Total internal reflection fluorescence (TIRF) microscopy enables the single-molecule observation in liquid near substrate surface. However, the evaluation of the diffusion from their individually-tracked positions entails the difficulty in the treatment of molecular adsorption on the substrate. We propose a novel technique to evaluate them, and two types of near-surface Brownian motion were determined for DNA. One is the diffusion near glass surface, and the other is the adsorption-dominated mot

Particle flow separation is a useful technique in lab-on-a-chip applications to selectively transport dispersed phases to a desired branch in microfluidic devices. The present study aims to demonstrate both nano- and microparticle flow separation using microscale thermophoresis at a Y-shaped branch in microfluidic channels. Microscale thermophoresis is the transport of tiny particles induced by a temperature gradient in fluids where the temperature variation is localized in the region of microme

The discharge plasmas of electronegative gases such as chlorine are often used for etching poly-Si in the ultralarge-scale integrated (ULSI) manufacturing process. In the present work, systematic self-consistent particle-in-cell/Monte Carlo simulations are performed for a weakly ionized chlorine plasmas produced by a radio frequency discharge between parallel electrodes. Particle collisions are described using a set of cross section data and effective theoretical models. The effects on the plasm

In this mini-review, recent advances on the role of a focused laser in micro- and nanofluidic systems is widely introduced with special interest in thermo-fluid dynamical aspects and their importance in optical manipulation. As a brief introduction to microfluidic systems, we describe the advantages and challenges of the use of micro- and nanoscale confinement in optical trapping, as well as standard fabrication techniques for micro- and nanofluidic systems. From thermo-fluid dynamical viewpoint