Hydrodynamic particle focusing enhanced by femtosecond laser deep grooving at low Reynolds numbers

Tianlong Zhang,Yansheng Hao,Eri Akita,David Inglis,Norihiro Teranishi,Misuzu Namoto,Yo Tanaka,Yaxiaer Yalikun,Dian Anggraini,Tao Tang,Ming Li,Kazunori Okano,Yoichiroh Hosokawa

doi:10.1038/s41598-021-81190-y

Abstract

Microfluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. In this study, we propose a novel hydrodynamic focusing method by taking advantage of open v-shaped microstructures on a glass substrate engraved by femtosecond pulse (fs) laser. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). Numerical simulations were performed to explain the mechanisms of particle focusing and experiments were carried out to investigate the effects of groove depth, groove number and flow rate on the performance of the groove-embedded microchannel for particle focusing. We found out that 10-µm polystyrene particles are directed toward the channel center under the effects of the groove-induced secondary flows in low-Re flows, e.g. Re < 1. Moreover, we achieved continuous focusing of live cells with different sizes ranging from 10 to 15 µm, i.e. human T-cell lymphoma Jurkat cells, rat adrenal pheochromocytoma PC12 cells and dog kidney MDCK cells. The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable.

Highlights

Microfluidic focusing of particles, which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation
Arrays of open v-shaped microstructures were patterned on glass substrates (Borosilicate, 76 × 26 × 1t, Matsunami Glass ind., Ltd., Video S1) by a near infrared (NIR) fs laser for particle focusing (Fig. 1a, b)
The SEM analysis revealed that the grooves with similar width were formed when the energy of fs laser increases from 0.7 to 2.8 μJ/pulse, while the depth of the grooves is strongly dependent on the laser energy

Summary

Introduction

Microfluidic focusing of particles (both synthetic and biological), which enables precise control over the positions of particles in a tightly focused stream, is a prerequisite step for the downstream processing, such as detection, trapping and separation. The fs laser engraved microstructures were capable of focusing polystyrene particles and live cells in rectangular microchannels at relatively low Reynolds numbers (Re). The glass grooves fabricated by fs laser are expected to be integrated with on-chip detection components, such as contact imaging and fluorescence lifetime-resolved imaging, for various biological and biomedical applications, where particle focusing at a relatively low flow rate is desirable. Active techniques, such as thermophoresis[14], dielectrophoresis (DEP)[15], optical trapping[16] and a coustophoresis[17], apply external forces to achieve particle focusing in microchannels These techniques require complicated fabrication processes or bulky external setup, and the external actuation may cause negative effects (e.g. cell damage by heating or cavitation)[18]. The fs laser micromachining shows advantages over other methods such as wet e tching[40] and deep reactive ion etching (DRIE)[41] for rapid and direct deep writing in glasses[42,43,44], enabling the fabrication of different types of glass-based microfluidic devices, such as a 12-μm ultra-flexible c hip[45] and a high-throughput microparticle filter[46]

Methods

Results

Discussion

Conclusion