Patent Application: US-71118807-A

Abstract:
in an arrangement for the transport of at least one magnetic particle fraction through a microfluidic system including a structure with micro - channels and means for generating a back and forth flow of fluid in the channels in which the magnetic particle fraction is contained for movement of the magnetic particles through the micro channels , means are provided for generating a magnetic field to be switched on while the fluid flows in one direction for fixing the magnetic particles and to be switched off while the fluid flows in the opposite direction so that the magnetic particles are carried along with the fluid when flowing in that direction .

Description:
fig1 a to 1 c show in cross - sectional views , the essential elements and the operating principle of a fluidic ratchet . it includes an actuator 1 for generating a fluid flow 8 in the fluid channels 6 . the fluid flow 8 moves the beads 4 . it also includes a mixing chamber volume 3 and a micro - structured soft iron magnet core 2 for generating a magnetic blocking force . the arrangement is closed up by a housing wall 5 . depending on the direction of operation of the actuator 1 , the fluid 8 moves through the passages 6 in a particular direction 7 and the beads 4 are moved by the fluid . when the blocking force is switched on , the beads are retained in contact with the wall 5 by the magnetic forces 9 . fig2 is a schematic cross - sectional view showing the field lines 10 of a switched on inhomogeneous magnetic field as generated by a soft iron micro - structured magnetic core 2 , which is embedded in plastic 11 . the magnetic beads 4 are moved in the fluid filled channel 6 toward the magnet core 2 in the direction 12 and retained thereby . fig3 shows schematically an example for the manufacture of the soft magnetic microstructure wherein , on the substrate 13 ( for example of silicon or glass ), a galvanic starter layer 16 is deposited , then a resist 15 is applied and is structured by openings 17 and then galvanically treated for example by permalloy ( nife ) at a ratio of 80 / 20 ) and then a sealing layer 14 is applied . fig4 shows schematically an exemplary manufacture of a microfluidic channel structure 18 . the substrate 13 is provided with openings 19 for the introduction of fluid . the openings can be formed mechanically ( for example , by boring or laser cutting ) by wet chemical procedures or by reactive ion etching . the groove structures are prepared by structuring ( stripping ) of the resist deposited on the substrate ( for example , su8 , pmma , polyimide ). fig5 shows the procedure for bonding the structures provided in fig3 and fig4 , by application of pressure forces and heat ( arrows 20 ), whereby microfluidic channel structures 21 are provided . fig6 shows an exemplary embodiment of an apparatus according to the invention consisting of a micro - structured magnet , a microfluidic channel structure , an actuator and fluidic connections . the top view of this system shows the fluidic structures . the periodic fluid movement 7 needed for the transport of the beads 8 is generated by an actuator 1 , which is disposed at the beginning of the fluid system . the beads are introduced into the system via an opening 28 and are moved through the microfluidic channel in accordance with the ratchet principle [ fig1 ]. a compensation chamber 24 at the end of the fluid structure with a certain fluid level so as to provide resiliency makes the periodic movement possible . in the mixing chamber , volume 25 , the residence time of the beads 4 can be controlled by the geometric shape as column structures guide the beads 4 in that area . in the last mixing chamber volume 23 of the system , the beads are collected and flushed out when desired . in the mixing chamber volume 25 , the reaction compounds are added in a direction normal to the bead movement direction 27 via the microfluidic fluid supply . via the inlet 26 and the junction 22 , the filling of the chambers is facilitated and a continuous control of the material concentration is made possible . 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