A sheathless inertial focusing technique for optofluidic devices
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Here, we demonstrate single-position, three-dimensional (3D) focusing of cells or micron-sized particles in the range 0.175 < a/w < 0.9 (a, cell or particle diameter; w, width of the microchannel), on a single-layer, single-channel microfluidic chip, which totally alleviates the need of using any sheath flow or external force, making the microfluidic chip standalone operational. The focusing is a result of inertial microfluidic hydrodynamic forces such as inertial lift forces and Dean drag forces, which are determined by the geometry of microchannel. With the microfluidic channel comprising a series of radially increasing, uniform semi-arcs interleaved by linear sections, sheathless focusing at flow rates up to 700 μL/min is achieved in our study. The result can be well explained by a developed empirical model relating the ratio of inertial lift forces and Dean drag forces, and the geometrical parameters of the microchannel. Following this approach, we illustrate experimental characterization of micron-sized sample focusing using fluorescent microparticles, pancreatic cancer cells, and macrophages under Reynolds number flows ranging between 20 and 153. We foresee the single-position focusing outcome of the proposed sheathless chip design in developing portable microfluidic and optofluidic devices for in vitro theranostics.
KeywordsInertial focusing Hydrodynamics Optofluidic Sheathless
The authors acknowledge the support of the School of Electrical and Electronic Engineering, Nanyang Technological University, NTU-NHG Innovation Collaboration (M4061202.040) Grant, NTU–A*STAR Silicon Technologies, Centre of Excellence (11235100003) grant, NEWRI EDB Funding, MOE Tier 2 Funding (MOE2017-T2-2-002), the Scientific Research Foundation for Newly Introduced Teachers of Shenzhen University (2019136), Guangdong Medical Science and Technology Research Fund Project (A2019359), and the School of Electrical and Electronic Engineering, NTU, Singapore.