8
1. INTRODUCTION
(a) (b)
Cell
Channel
Reagent
Channel
Sorting
Channel
Cell Trapping
Area
To Waste
CCD
Sample Flow
Buer Flow
ROI
Trap Direction
Bright Field
Objective Lens
IR
CCD
F
lourescence
: Non-target Cell
: Target Cell
: Optical Trap
Inlet
Inlet
Optical Tweezers
Outlet
(Collection)
Outlet
(Waste)
(c) (d)
Figure 1.4: Optical trap methods: (a) ber tweezers for 3D capture of single cells [77]; (b) array-type
capture of single cells [78], based on and used with permission from the Royal Society of Chemistry;
(c) passive sorting of microuidic chips [79]; and (d) active sorting microuidic chip [80]. Image (c)
and (d) based on and used with permission from the Royal Society of Chemistry.
Although optical tweezers can accurately manipulate single cells, the laser beam is easy to
damage cells, and require expensive optical system.
1.2.3 MAGNETIC METHODS
Generally, cells have very weak magnetic properties. Selectively modifying the surface of a cell to
change its magnetic properties such that the cell can be micro-operated by an external magnetic
eld [81, 82]. e typical magnetic activated cell sorting methods can be used to separate cells. It is
based on the combination of cell surface antigens and specic antibodies linked to magnetic beads.
e external magnetic eld can hold the cells modied with magnetic beads in the magnetic eld,
thereby realizing cell separation [83, 84]. Magnetic activated cell sorting methods are low cost,
easy to operate, and highly sensitive. Huang et al. developed a ferromagnetic microuidic system
for enhanced CTC detection (Figure 1.5) [85]. Because the ferromagnetic micro-magnet is mag-
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