Table 1.

CTCs Isolation Comparison Chart.

Technology	Isolation Factors	Benefits	Drawbacks	Description	Reference
CROSS Chip (Microfluidic Cell Filter)	Size and deformability	70% efficiency, high purity, cost-effective, easily applicable (low set-up), and higher sensitivity than CellSearch	To increase throughput, multiple screenings might be necessary; smaller CTCs are more difficult to obtain	A syringe pumps the blood sample into a microfluidic chip with filters that separates it into four sections for analysis	[18]
Labyrinth (Inertial Microfluidic Cell Filter)	Size (inertia)	High throughput, high yield, and high purity	Difficulty with focusing and separating smaller cells	The labyrinth design functions in separating CTCs from blood cells by filtering them through straight and curved channels	[14]
Optofluidic Cell Technology Chip	Size and the refractive index	High purity, high recovery, and no foreign material introduction	Time and cost unspecified	Uses molecules to bind CTCs to RBCs and then uses laser illumination to separate them on a chip, based on the refractive index	[24]
Dual-Immunopatterned microfluidic device	Surface antigen expression	High efficiency and captures mesenchymal cells	More time, possibly experiment-dependent, and less general applicability	Microfluidic device with two layers. Each layer is coated with a different antibody (anti-EpCAM or anti-63B6) to isolate and separate the types of CTCs	[9]
Acoustic Separation Device	Cell size/velocity (response to sound waves)	High throughput and cost-effective	Prior processes required for RBC removal and more time	The device uses the acoustic-wave field that is amplified by a PDMS barrier to send cells at different trajectories for separation	[25]
Wavy-Herringbone Microfluidic Device	Immunoaffinity (+EpCAM) and magnetic force	High efficiency, high purity, and high viability	Dependent on the dispersion of MPs (hard to control) and may be unable to capture non-EpCAM-expressing CTCs	A herringbone pattern was made on silicon wafers which were injected with bonded magnetic particles and anti-EpCAM. As the sample travels through, the CTCs are separated by the magnetic EpCAM	[10]
Vortex HT Chip	Size (movement)	Extremely high throughput, high viability, high purity, and no pre-processing steps	Certain CTCs not captured effectively, possible difficulties with cell recovery, and low capture efficiency	Laminar microvortices are created on this microdevice to separate CTCs from blood cells and other bodily fluids based on flow	[15]
Lateral filter array with immunoaffinity	Size and immunoaffinity (+EpCAM)	High efficiency, high purity, and high viability	May be unable to capture certain non-EpCAM-expressing CTCs	Embedded lateral filters in a serpentine channel on a microfluidic device. The blood sample flows through the main channel and the CTCs are caught in the filter. Immunoaffinity works in the lateral filters by testing for a bond force between certain antibodies and the cells as compared to the hydrodynamic force	[21]
Spiral Shape Microfluidic Channel	Magnetic force and immunoaffinity (+EpCAM)	High efficiency and high flow rate	May be unable to capture non-EpCAM-expressing CTCs; more tests with actual samples necessary	Magnetic nanoparticles bond with the EpCAM antibody. These are circulated through a spiral chamber with a decreasing radius and a permanent magnet. The magnetic force causes the bonded particles to be attracted and filter into specific regions for isolation	[11]
LFFF-DEP microfluidic device	Dielectrophoresis	No statistical results; however, based on the provided image, it seems to be efficient in separation	Further analysis necessary and time and throughput may be an issue	Oppositely charged electrodes are positioned on a glass wafer. Cancer cells are attracted to the positive DEP electrode, while normal blood cells are attracted to the negative DEP electrode	[23]
Cluster-isolating microfluidic device	Size and asymmetry	Able to isolate clusters, high recovery, and high viability	The flow rate has to be slowed to ensure viability (very low throughput) and less adept to isolating small clusters and single CTCs	Deterministic lateral displacement is used to isolate large clusters based on size (using micropillars with different sized gaps in between). During stage two, the clusters that were unable to be filtered by size are put through shaped micropillars that result in rotation if they are asymmetrical for separation	[16]
Magnetic Micropore CaTCh FISH Chip	Magnetic force (immunoaffinity of -CD45 on WBC) and size	Higher throughput compared to other magnetic chips, High recovery rate and the ability to conduct RNA analysis on the chip	WBC with low CD45 expression not filtered and cost unclear	Two-part system. The first section of the chip has magnetic traps at edges of the pores to attract WBCs labeled with MNPs. The RBCs and platelets are then filtered by size leaving the CTCs, which undergo RNA analysis on the chip	[22]
rVAR2 using IsoFlux system	Immunoaffinity (+ofCS)	High recovery, captures mesenchymal cells, and high sensitivity	May be unable to capture non-ofCS-expressing CTCs and may be expensive	Uses the IsoFlux system model (Dynabeads) but altered so the immunomagnetic capture is used with the rVAR2 protein to bond to the ofCS in the CTCs	[13]
PLT-WBC Immunomagnetic Beads	Immunoaffinity (+EpCAM) and magnetic force	High Efficiency, increased binding ability, and avoidance of WBC collection	May be unable to capture non-EpCAM-expressing CTCs and requires additional preparation process for magnetic beads	A hybrid membrane of platelets and WBCs is formed and coated onto magnetic particles. The particles are then treated with EpCAM-binding antibodies. The resulting magnetic beads target the CTCs while specifically avoiding homologus WBCs	[12]
Photosensitive Polymer-Based Microfilter	Size and deformability	High efficiency, relatively high viability, and simple set-up	Smaller CTCs are difficult to capture	The photosensitive polymer which is removed with UV exposure coats a microfilter with many densely dispersed slits. The slits have a larger inlet which decreases in diameter towards the outlet, trapping larger CTCs	[17]
SDI Chip	Immunoaffinity (+EpCAM) and size	High efficiency, high purity, and greater sensitivity as compared to CellSearch	Lower-expression EpCAM was more frequently not recovered and shear stress caused the dislodgement of many cells	Microchip on which triangular micropillars are coated with anti-EpCAM antibodies. The pillars are spaced and rotated to create a decreasing hydrodynamic gradient and gaps. Due to gradient cells migrating downstream and at certain locations due to their size and immunoaffinity, the CTCs become lodged at pillars	[20]
Monolithic CTC iChip	Immunoaffinity (-CD45, -CD16, and -CD66B) and size	High throughput and high recovery	Smaller cells had difficulty being caught, WBCs with low antigen expression levels and difficulty being caught, and average purity	The microfluidic chip first holds a size-based array with micropillars with a waste channel for RBCs and plasma. The next portion has magnets on either side. The magnetic-tagged WBCs are filtered to the sides, while the CTCs are caught in the middle (non-magnetic) portion.	[19]