Sheathless Focusing and Separation of Diverse Nanoparticles in Viscoelastic Solutions with Minimized Shear Thinning

Abstract

Viscoelastic microfluidics becomes an efficient and label-free hydrodynamic technology to enrich and separate micrometer-scale particles, including blood cells, circulating tumor cells, and bacteria. However, the manipulation of nanoscale particles by viscoelastic microfluidics remains a major challenge, because the viscoelastic force acting on the smaller particle decreases dramatically. In contrast to the commonly used polymer solutions of high molecular weight, herein we utilize the aqueous solutions of poly­(ethylene oxide) (PEO) of low molecular weight with minimized shear thinning but sufficient elastic force for high-quality focusing and separation of various nanoparticles. The focusing efficiencies of 100 nm polystyrene (PS) nanoparticles and λ-DNA molecules are 84% and 85%, respectively, in a double spiral microchannel, without the aid of sheath flows. Furthermore, we demonstrate the size-based viscoelastic separation of two sets of binary mixtures100/2000 nm PS particles and λ-DNA molecules/blood plateletsall achieving separation efficiencies of >95% in the same device. Our proposal technique would be a promising approach for enrichment/separation of the nanoparticles encountered in applications of analytical chemistry and nanotechnology.

Particle manipulations in non-Newtonian microfluidics: A review

“…7d) and k-DNA molecules in the flow of PEO solution with a molecular weight of 0.6 MDa through a double-spiral microchannel. They observed a decreasing focusing efficiency with the increase of PEO molecular weight (up to 4 MDa) [28].…”

“…They also proposed a six-stage process model to explain the observed particle focusing process in Deancoupled elasto-inertial flows. In a recent study Liu et al [28] demonstrated a high-quality focusing of various nanoparticles in PEO solutions of low molecular weight that can offer sufficient elastic forces while at minimized shear thinning effects. They achieved an over 80% focusing efficiency for both 100 nm diameter PS particles (Fig.…”

“…10d). Recently Liu et al [28] has demonstrated a viscoelastic separation of 100 nm/2 mm PS particles and k-DNA molecules/platelets in 0.6 wt.% low-molecular-weight PEO solution through a 30 mm wide/4 mm high double spiral microchannel. The flow-induced elastic lift and Dean drag acts together to focus the nanoparticles and microparticles toward the channel center and sidewalls, respectively.…”

“…This inertial lift-based approach in Newtonian fluids, however, becomes ineffective and even fails for small particles and/or at low flow rates where the particle Reynolds number becomes much smaller than 1 [25]. Recent studies have demonstrated the potential of elastic lift in non-Newtonian fluids for manipulating particles with a much smaller size [26][27][28] and over a much wider range of flow rates [29] than in Newtonian fluids. Moreover, the combination of elastic lift with inertial lift can greatly enhance the particle control in microchannels at increasing flow rates [30,31].…”

Field-Free Isolation of Exosomes from Extracellular Vesicles by Microfluidic Viscoelastic Flows

“…For PEO solutions of low concentrations (c < 0.19 wt %, the overlapping concentration for PEO of 600 kDa 13 ), η p and λ can be expressed as 0. U, indicating that the particle trajectory is predominately dependent on the particle size, PEO concentration, and flow speed.…”