Review of micro/nanofluidic particle separation mechanisms: Toward combined multiple physical fields for nanoparticles

Micro-/nanofluidic particle separation mechanisms depend on various physical fields that are applied to the fluid flow and/or particles. These external fields have been widely used for microparticle separation on a chip, mostly in a single physical field (SPF) mechanism. The relevant mechanisms have been elucidated, and the resulting performance of the devices has been clearly demonstrated. However, the SPF-based micro-/nanofluidic separation techniques (MNSTs) have not been highly successful for nanoparticle separation on a chip, as an additional understanding of the underlying physicochemical mechanisms is required. Recently, methods based on a combination of multiple physical fields (MPFs) have attracted more attention than SPFs because they can provide novel working principles for micro-/nanofluidics, thereby offering new opportunities for nanoparticle separation. This review briefly discusses SPF-based MNSTs and then focuses on those based on MPFs. We discuss the MNSTs as categorized by the applied physical fields, and their separation performance is evaluated considering their resolution, throughput, and efficiency. In addition, we discuss the practical and potential applications of the state-of-the-art MPF-based MNSTs for various biological and biomedical analysis tools, and industrial and environmental applications. Therefore, it is expected that, MPF-based MNSTs can provide unprecedented working principles for various micro-/nanofluidic devices.