Biomedical Engineering Reference
In-Depth Information
Magnetic flux lines
(a)
(c)
Permanent
magnet
Permanent
magnet
A
M
M
Microchannel
B
Fenomegnetic microstructure
Ni structure
Slide Glass
(b)
M
microscope
B
A
Figure 3.2
(a, b) Schematic view of the
relationship between a permanent magnet
and a ferromagnetic microstructure
positioned near a permanent magnet.
According to the magnetization direction of
the magnet, magnetic-fi eld generation appears
in different shapes. Because of the
ferromagnetic structure located around the
edge of the magnet, a magnetic fl ux - density
gradient is generated in a slanted direction,
rather than horizontal to the sidewall of the
ferromagnetic structure. In order to effectively
exploit the enhanced magnetic fl ux - density
gradient, microchannels must be located in
area A rather than area B, in (a) and (b),
respectively; (c) Experimental set-up of a
microfl uidic device and a permanent magnet
and an inverted microscope. The dark-circled
edges of ferromagnetic structures in (a-c)
depict highly converged points of magnetic
fl ux lines; while the open circles represent a
depletion of the fl ux lines. Reproduced with
permission from Ref. [41]; © 2007, Wiley-
VCH Verlag GmbH & Co. KGaA.
3.3.2
Experimental Set - Up
Measurements for magnetophoretic biosensing and separation in microfl uidic
devices are carried out using a charge - coupled device ( CCD ) - mounted microscopic
system. If the materials used to create the device are transparent (e.g., glass or
PDMS), it is possible to use an inverted microscope; however, if the materials are
opaque (e.g., Si wafers or metal layers), then a refl ecting microscope should be
used. As shown in Figure 3.6, the inverted microscopic system is generally
employed for PDMS- based microfl uidic devices, with the images being captured
simultaneously by a CCD camera linked to a computer. Aqueous solutions injected
into the microfl uidic devices are manipulated precisely with syringe pumps, with
the syringes and devices being connected by silicone tubes. When a permanent
magnet which is several tens of millimeters in size is used, care must be taken to
