Table 1.

Microfluidic options for label-free cell analysis and sorting based on a variety of characteristics

Criterion	Technology	Type	Description	References
Size	Inertial focusing	Sort	Inertial forces cause cells of a predetermined size to migrate to specific positions within a channel	(Di Carlo et al., 2007; Ozkumur et al., 2013)
Size	Vortex high throughput	Sort	Larger cells are trapped in microvortices that form in periodic wide sections of a microfluidic channel	(Che et al., 2016; Renier et al., 2017; Vortex Biosciences, 2018)
Size	Deterministic lateral displacement	Sort	Slightly offset rows of pillars deflect cells variably based on size	(Beech et al., 2012; Huang et al., 2004; Karabacak et al., 2014; Loutherback et al., 2012)
Size	Weir-type filter	Sort	Larger cells are captured in segments of a channel with a shallower depth	(Tu et al., 2016; Yeo et al., 2016; L. Zhu et al., 2004)
Size	Pillar-type filter	Sort	Larger cells or cell clusters are captured by narrowly-spaced pillars	(Au et al., 2017; Sarioglu et al., 2015)
Size	Resistive-pulse sensing	Measure	As cells pass through a channel, they cause a current drop that indicates cell size	(Becker et al., 1995; Satake et al., 2002)
Size	Electrical impedance cytometry / spectroscopy (EIC/EIS)	Measure	At low frequencies, measured impedance is dominated by cell size	(Cheung & Berardino, 2010; S Gawad et al., 2001)
Size	Standing surface acoustic waves	Sort	Cell velocity toward pressure node is proportional to the square of the cell radius	(Nam et al., 2011; Shi et al., 2009)
Size	Deformability cytometry	Measure	Size of deformed cells is measured with high-speed brightfield microscopy (100,000 FPS)	(Cytovale, 2018; Gossett et al., 2012)
Size	Real-time deformability cytometry	Measure	Size of deformed cells is measured with high-speed brightfield microscopy (1,000 FPS)	(Mietke et al., 2015; Otto et al., 2015; Xavier et al., 2016)
Size	Optofluidic rotation	Measure	Cells are continuously imaged with brightfield microscopy during trapping and rotation	(Kolb et al., 2015)
Size	Optical stretcher	Measure	Cells are imaged with brightfield microscopy before and after stretching	(Guck et al., 2005; Lincoln et al., 2004)
Size	Optical chromatography	Measure	Cells are imaged with brightfield microscopy before and after stretching	(Hebert et al., 2017; Imasaka et al., 1995; Kaneta et al., 2001; Lumacyte, 2018)
Deformability	Deterministic Lateral Displacement	Sort	Slightly offset rows of pillars in conjunction with a constrictive channel height sorts cells based on deformability	(Beech et al., 2012)
Deformability	Optical stretcher	Measure	Cells are stretched into an ellipsoid by optical traps; deformability is measured by the aspect ratio of this ellipsoid, imaged in a 2D plane	(Guck et al., 2005; Lincoln et al., 2004)
Deformability	Optical chromatography	Measure	Cells are stretched into an ellipsoid by opposing optical trap and flow force; deformability is measured by the aspect ratio of this ellipsoid, imaged in a 2D plane	Hebert et al., 2017; Imasaka et al., 1995; Kaneta et al., 2001; Lumacyte, 2018)
Deformability	Deformability cytometry	Measure	Two high-velocity fluid streams collide and deform a cell into an ellipse between them; deformability is measured by the aspect ratio of this ellipsoid, imaged in a 2D plane	(Cytovale, 2018; Gossett et al., 2012)
Deformability	Real-time deformability cytometry	Measure	Cells transiting a narrow channel are deformed into a bullet-like shape due to high shear; deformability is measured by the aspect ratio of this shape, imaged in a 2D plane	(Mietke et al., 2015; Otto et al., 2015; Xavier et al., 2016)
Deformability	Mechano-node-pore sensing	Measure	Cell volume and transit time through a constriction channel are measured using node-pore sensing to characterize deformability, resistance to deformation, and recovery	(J. Kim et al., 2018)
Compressibility	Standing surface acoustic waves	Sort	Lower cell compressibility results in faster cell velocity toward pressure node	(Ding et al., 2014)
Electrical properties	EIC/EIS (impedance, permittivity, membrane capacitance, cytoplasm conductivity)	Measure	AC signal is applied across the cell; the measured current response yields information about impedance, permittivity, membrane capacitance, and cytoplasm conductivity	(Cheung & Berardino, 2010; S. Gawad et al., 2004; Holmes et al., 2009; Sohn et al., 2000)
Surface markers	Node-pore sensing	Measure	Channel segments are coated in antibodies which react with cell surface markers. Cells expressing the corresponding marker traverse the channel segment more slowly	(Balakrishnan et al., 2015)
3D tomography	Optofluidic rotation	Measure	Cells are immobilized with an optical trap, rotated with fluidic flow, and imaged with brightfield microscopy	(Kolb et al., 2015)