Abstract
Massive growth of the microfluidics field has triggered numerous advances in focusing, separating, ordering, concentrating, and mixing of microparticles. Microfluidic systems capable of performing these functions are rapidly finding applications in industrial, environmental, and biomedical fields. Passive and label-free methods are one of the major categories of such systems that have received enormous attention owing to device operational simplicity and low costs. With new platforms continuously being proposed, our aim here is to provide an updated overview of the state of the art for passive label-free microparticle separation, with emphasis on performance and operational conditions. In addition to the now common separation approaches using Newtonian flows, such as deterministic lateral displacement, pinched flow fractionation, cross-flow filtration, hydrodynamic filtration, and inertial microfluidics, we also discuss separation approaches using non-Newtonian, viscoelastic flow. We then highlight the newly emerging approach based on shear-induced diffusion, which enables direct processing of complex samples such as untreated whole blood. Finally, we hope that an improved understanding of label-free passive sorting approaches can lead to sophisticated and useful platforms toward automation in industrial, environmental, and biomedical fields.
Highlights
Particle sorting is a critical step in numerous industrial, research, and biomedical applications.[1,2,3,4] For instance, in mining and petroleum industries, microparticle separation is strongly associated with the economic value of end products.[4,5] Separation of microparticles from cosmetics is important for quality control and regulation enforcement.[6]
The purpose of this review is to provide an updated discussion of the state-of-the-art microfluidic devices developed for passive labelfree particle separation
In 2003, laminar vortices in a microchannel were reported by Lim et al.[113] when they observed recirculation of 1 lm microbeads in diamond shaped microcavities attached to channel sidewalls
Summary
Particle sorting is a critical step in numerous industrial, research, and biomedical applications.[1,2,3,4] For instance, in mining and petroleum industries, microparticle separation is strongly associated with the economic value of end products.[4,5] Separation of microparticles from cosmetics is important for quality control and regulation enforcement.[6]. Magnetic,[26,27,28] electrical,[29,30,31] acoustic,[32,33,34] and optical[35,36,37,38,39,40,41,42] forces are commonly used for differentiating particles flowing in a microfluidic channel Such microfluidic devices typically offer precise, on-demand control of particle spatial distribution and are generally viewed as active methods of particle separation. Performance and applications of microfluidic devices of the same method are generally provided in these reviews, but crosscomparison among different methods is less detailed and the newly emerged approaches such as particle separation using shear-induced diffusion (SID)[57,58] or viscoelastic flow are either not included or discussed only briefly. Include the newly emerged SID method, which is capable of direct processing complex samples such as untreated whole blood.[57,58] In the concluding section, comparison and discussion of the reviewed methods will be presented along with perspectives on future developments
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