Motion of submicrometer particles in micrometer-size channel measured by defocusing nano-particle image velocimetry

Abstract

Understanding the motion of colloidal particles flowing in small spaces is a general issue in various fields such as thermal engineering and micro/nanofluidics. In the present study, we investigated the motion of fluorescent submicrometer particles in a 3- μm microchannel by defocusing nanoparticle image velocimetry. An optical measurement system with controlled spherical aberration and an algorithm for processing defocused particle images with multiple diffraction rings were developed. By detecting the centroid position and the diameter of the outermost diffraction ring, which is proportional to the distance between the focal plane and the particle, the position of particles was determined with the spatial resolutions of 154–204 nm in the streamwise direction and 76–311 nm in the depthwise direction, which are comparable to or smaller than the optical diffraction limit. A reusable microfluidic device containing a size-regulated microchannel made of glass was developed, which is suitable for optical measurements and precise flow control. By controlling the strength of low-temperature glass bonding, detachment of the bonded glass substrates, washing, and reuse were achieved. Based on this method and technology, the velocity of particles with diameters of 199, 457, and 1114 nm was successfully measured in pressure-driven laminar flow. Results suggested that for larger particles comparable to the channel size, the particle velocity is slowed from the flow velocity by particle–wall hydrodynamic interactions. Therefore, the motion of colloidal particles in 100- μm spaces is considered to be affected by particle–wall hydrodynamic interactions, as well as 102- μm spaces reported previously.

Past and current components-based detailing of particle image velocimetry: A comprehensive review

“…One of the latest works considers nano scale defocusing particle image velocimetry. With the use of nano scale defocusing particle image velocimetry, motion of submicrometer particles are studied [ 191 ].…”

Effect of finite spatial and temporal resolutions on super-resolution particle tracking velocimetry for pressure-driven flow in a nanochannel

“…A nano uidic device containing nanochannels interfaced with microchannels (width: 500 µm, depth: 10 µm) for sample injection was prepared based on a top-down fabrication process (Shoda et al 2020;Kuwano et al 2022). After the pattern of nanochannels was formed on a fused-silica substrate by photolithography using a photoresist (THB-111N, JSR Corp., Tokyo, Japan), the channels were fabricated by dry etching using a mixture of gaseous CHF 3 and SF 6 .…”

“…The evanescent wave generated by the total internal re ection of light was used to determine the position of nanoparticles owing in a nanochannel from the uorescent intensity related to the exponential decay of the evanescent wave from the wall (Kazoe et al 2013;Kazoe et al 2015). In the other method, defocused nanoparticle images with spherical aberration were used to determine the position of nanoparticles from the diameter of the defocused image in proportion to the distance between the focal plane and the particle (Kazoe et al 2021;Kuwano et al 2022). Despite different principles, the velocity distribution of nanoparticles in the nanochannel obtained by these two methods suggested a pro le with a large slip velocity even at the hydrophilic channel wall, which is inconsistent with that obtained by previous studies on near-wall ow measurements suggesting almost non-slip boundary (Voronov & Papavassiliou 2008;Li & Yoda 2010).…”

“…To examine whether the nanoparticle velocity distribution statistically indicates the original ow pro le of the pressure-driven ow, the average velocity and depthwise position of the nanoparticles were estimated by dividing the nanochannel region of a < z < (H − a) into ve regions. As reported previously(Li & Yoda 2010;Kuwano et al 2022), the average depthwise position for each of the ve regions was calculated considering the centroid as follows:…”