Patent Application: US-201214342198-A

Abstract:
in a centrifugal microfluidic device for conducting capture assays , a microfluidic platform rotates in a plane of rotation and has at least one capture surface for immobilizing a target particle of interest in the device . the capture surface oriented so that it is not parallel to the plane of rotation of the device and is positionally fixed in the device during operation of the device . the centrifugal force arising from rotation of the device forces the target particles against the capture surface . capture efficiency is independent of the rate of flow of the fluid and independent of the rate of rotation of the microfluidic platform .

Description:
referring to fig1 and fig2 , a centrifugal microfluidic device for centrifugally enhanced capture of a pathogen comprises holding blade 11 that rotates around rotation axis 12 . top surface 13 of the holding blade is perpendicular to the rotation axis and therefore parallel to the rotation plane and parallel to direction of centrifugal acceleration a cf . mounted rigidly on the top surface of the holding blade are capture chip 14 , sample reservoir 20 and waste reservoir 21 . capture chip 14 comprises capture surface 15 located in capture chamber 16 . under the influence of centrifugal force generated by rotation of the blade , a biological fluid containing the pathogen flows from sample reservoir 20 via a channel to capture chip 14 , enters capture chamber 16 through inlet 17 , flows through capture chamber 16 where the fluid encounters capture surface 15 , and then flows out of capture chamber 16 through outlet 18 to be carried by a channel into waste reservoir 21 . because capture chip 14 is oriented perpendicularly to holding blade 11 , capture surface 15 , which is the bottom wall of the capture chip , is oriented orthogonally to the plane of rotation . when the biological fluid flows into the capture chamber it is forced to flow up the chip in a direction orthogonal to the plane of rotation . however , since centrifugal acceleration a cf is still parallel to the plane of rotation , pathogen particle 19 in capture chamber 16 experiences centrifugal force f cf parallel to the plane of rotation that pushes the pathogen particle toward capture surface 15 , even though the fluid is flowing with velocity u and exerting a force f η on the pathogen particle in a direction perpendicular to the plane of rotation . as a consequence of the two opposed forces f cf and f η , pathogen particle 19 follows a curved path before encountering capture surface 15 . f cf is a long range force field that acts identically on all objects entering the capture chip and will force the objects in the flow ( e . g . pathogen particles , cells , debris , etc .) to cross fluid streamlines and curve their trajectories towards the capture surface . the centrifugal force f cf and fluid flow rate q ( the scalar component of fluid flow velocity u ) are responsible for distance l capture traveled by pathogen particles from inlet 17 to capture point 25 on capture surface 15 . these two important quantities ( centrifugal force f cf and flow rate q ) can easily be tuned by the positions of sample reservoir 20 and capture chip 14 on holding blade 11 ( r 0 and r c , respectively ) and the hydrodynamic resistance r hyd of the microfluidic circuit between the sample reservoir and the capture chip . capture length l capture is given by the analytical expression : in the two equations above η is the dynamic viscosity of the fluid , h the thickness of the capture chip , r b and ρ b the radius and density of the pathogen particle respectively , ρ the density of the fluid , s chip the cross - sectional area of the capture chip and ω the angular velocity of the microfluidic device . the condition for a 100 % probability of capture is that l capture ≦ l , where l is the length of the capture chip in the direction of the fluid flow . it can be seen from eq . ( 1 ) that l capture is independent of ω whereas q is not . this means that the l capture depends only on the device &# 39 ; s geometrical setup ( i . e . position of reservoirs , position of the capture chip , geometry and hydrodynamic resistance of the microfluidic circuits , etc .) and it is the same regardless of rotational speed . in contrast , the fluid flow rate q , as shown in eq . ( 2 ), can be tuned by adjusting the rotational speed . consequently , the capture efficiency is decoupled from the rate of fluid flow , and for a specific geometry of the device , there is the same capture probability regardless of the rotational speed and the fluid flow rate of the biological fluid above the capture surface . further , it is evident from eq . 1 that l capture is a function of the radius and density of the particle . thus , in complex sample with multiple species , particles , debris of different sizes and densities , the capture of these different objects will occur at different points along the capture surface , providing a spatially distributed or tuned immobilization and separation ( fig3 ) providing the ability to separate along the flow trajectory the capture position of known target particles in the fluid . this is especially advantageous in applications such as the capture of target particles ( e . g . bacteria or other cells ) from complex food / water samples or the simultaneous detection of multiple pathogens . referring to fig4 , the capture surface in a device of the present invention may be unfunctionalized ( fig4 b ) or functionalized with antibodies ( fig4 a and fig4 c ) that bind to the pathogen particles . further , the capture surface may be unstructured ( fig4 a ) or structured with micro - scale features ( fig4 b and fig4 c ). fig4 a depicts an unstructured capture surface functionalized with antibodies that interact with antigens on the surface of the pathogen particle . the pathogen particle experiences centrifugal force f cf pushing the pathogen particle toward the capture surface , even though the fluid is flowing with velocity u and exerting a force f η on the pathogen particle in a direction perpendicular to the centrifugal force . further , the “ wall effect ” exerts a force f h in an opposite direction as the centrifugal force pushing the pathogen particle away from the capture surface . provided f cf is greater than f h , the pathogen particle will eventually encounter the functionalized capture surface and be captured . in fig4 b , the unfunctionalized capture surface has micro - scale grooves angled against the fluid flow so that pathogen particles can be captured physically in the grooves . in fig4 c , the capture surface is both functionalized with antibodies and has a micro - scale grating . the grating captures pathogen particles physically while the antibodies bind to antigens on the surface of the pathogen particle thereby increasing capture efficiency . references : the contents of the entirety of each of which are incorporated by this reference . amagliani g , brandi g , et al . 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