3.6.1. Particle focusing
Particle/cell focusing inside a microchannel is a crucial pre-step for
downstream particle/cell counting, detection and sorting (Kung, Huang,
Chong, & Chiou, 2016; X. Wang, Zandi, Ho, Kaval, & Papautsky, 2015).
Jia et al. (Y. Jia, Ren, & Jiang, 2015), for the first time,
demonstrated particle focusing in generated MVs under the AC electric
field around the planar floating electrode placed at the bottom of a
microchannel (Fig. 5A ). Chen et al. (Xiaoming Chen et al.,
2017) employed this focusing method for the pre-focusing of particles in
different solutions prior to their dielectrophoretic separation. Song et
al. (Song, Wang, Li, Pan, & Li, 2016) demonstrated particle focusing
under DC electric field at the desired location in the microchannel by
the induced MVs around a polarizable plate located near the microchannel
walls (Fig. 5B ). Ren et al. (Ren et al., 2016) developed a
continuous-flow microfluidic device in which the desired number of
focused particles were isolated at the target outlets using the
generated MVs around asymmetric electrodes placed at the bottom of the
microchannel (Fig. 5C ). Liu et al. (W. Liu et al., 2016)
presented a flow-focusing device in which a suspension of particles was
forcused within a cylindrical volume with a diameter range of 1-8 µm
(nominal diameter of 4 µm) and conducted toward the desired outlet by
the induced MVs around a floating electrode (Fig. 5D ).