A sheathless inertial focusing technique for optofluidic devices

Abstract

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.