Thermophoretic Manipulation of Micro- and Nanoparticle Flow through a Sudden Contraction in a Microchannel with Near-Infrared Laser Irradiation

Abstract

A temperature gradient in a continuous fluid induces the motion of dispersed micro-and nanoparticles even when the fluid is motionless. This phenomenon is known as thermophoresis, and it is expected to be the basis for techniques to control particle motion. In this study, we use the thermophoresis of microand nanoparticles in a microchannel filled with an aqueous solution to control the particle motion near the inlet of a sudden contraction, which is a narrower channel connecting two wider channels. Microfluidic devices with sudden contractions are widely used to develop various devices with micro-and nanometer dimensions, such as nanopore sensors. A near-infrared laser is used to create a strong temperature gradient of O(10 6) K m −1 and induce thermophoresis of micro-and nanoparticles. Because the heating by the laser irradiation is localized near the inlet of the contraction, this configuration is useful for controlling particle translocation into and through the contraction. We characterize our experimental setup by quantifying flow and temperature fields near the contraction channel using particle image velocimetry and laser-induced fluorescence, respectively. Then, we observe the obstruction of the particle translocation into the contraction channel induced by the laser-induced thermophoresis for various parameters such as channel dimensions, flow speeds, particle sizes, and laser powers. Near the inlet of the contraction channel, the counterbalance of thermophoretic force and flow drag leads to the ringlike pattern formation of the particle distribution. Moreover, we carry out some demonstrations using the proposed system to selectively translocate particles and enhance the sensing performance due to increased particle density. Thanks to the noncontact nature of laser-induced thermophoresis, the integration of our method into existing microfluidic devices is feasible and expected to improve technologies for manipulating particles in fluids.

Microparticle manipulation using laser-induced thermophoresis and thermal convection flow

“…1c,d), achieving 'optical-thermophoretic tweezing' . Although similar phenomena have been reported by other research groups [46][47][48][49][50][51][52] , in many cases the substrates of their devices needed to be pre-treated by a thin layer of high optical absorber, and in no cases have biological cells been used. Our method of using SWNTs clusters instead of an absorbing substrate is important as it will allow cells to be concentrated within standard glass/plastic-ware such as slides, well plates and Petri dishes without modification, which significantly reduces the device fabrication time and cost and so is truly suitable for single-use applications.…”

Separation of Nano- and Microparticle Flows Using Thermophoresis in Branched Microfluidic Channels

“…Thermophoresis is a rather weak effect, that is, it can be hindered by the fast flow of continuous phase. Therefore, to observe the effect of thermophoresis effectively, we should induce a creeping flow of O(1)–O(10) μm0.166667em·0.166667ems−1 in the microfluidic channel [53,54]. However, in general, the creeping flow is difficult to control since a finer pressure control resolution is required.…”

“…Then, the reservoir for the inlet is lifted by ΔH, as shown in Figure 1b, to induce the fluid flow of a sample solution with a required flow rate. As discussed in [54], the generated pressure difference ΔP in Figure 1 is estimated as ΔP=ρgΔH, where ρ is the mass density of the sample solution and g=9.8 m0.166667em·0.166667ems−2 is the acceleration of gravity. In this research, an aqueous solution is used and thus ρ=1.0×103 kg0.166667em·0.166667emm−3.…”

“…Given such a growing interest in thermophoretic manipulation, the previous study by the authors tried to apply microscale thermophoresis to particle flow control in LOC devices [53,54]. More specifically, using micro-electro-mechanical-systems (MEMS) technologies, a micro heater was installed in a straight microfluidic channel, and the on-chip thermophoretic separation device was developed [53].…”

Thermophoretic Micron-Scale Devices: Practical Approach and Review

“…Application examples. Several researchers have already utilized the fluorescence intensity method with various dyes (RhB [ 43 , 45 , 59 ], BCECF [ 27 , 70 , 93 ], Ruthenium [ 94 , 95 ]) to observe the temperature field in a thermophoresis experiment. To our best knowledge, despite the experimental robustness, fluorescence lifetime imaging measurements have not been used in thermophoretic studies.…”