Patent Grant
10913062
The present patent application claims priority of the co-pending patent application PCT/US2015/048141 filed on Sep. 2, 2015, the content of which is herein incorporated in its entirety for any purpose.
The present invention relates to the control and manipulation of liquids in a small volume, usually in the micro- or nanoscale format. In digital microfluidics, a defined voltage is applied to electrodes of an electrode array, so that individual droplets are addressed (electrowetting). For a general overview of the electrowetting method, please see Washizu, IEEE Transactions on Industry Applications, Volume 34, No. 4, 1998, and Pollack et al., Lab chip, 2002, Volume 2, 96-101. Briefly, electrowetting refers to a method to move liquid droplets using arrays of microelectrodes, preferably covered by a hydrophobic layer that is used as a working surface. By applying a defined voltage to electrodes of the electrode array, a change of the surface tension of the liquid droplet, which is present on the addressed electrodes, is induced. This results in a remarkable change of the contact angle of the droplet on the addressed electrode, hence in a movement of the droplet. For such electrowetting procedures, two principle ways to arrange the electrodes are known: using one single working surface with an electrode array for inducing the movement of droplets in a monoplanar setup or adding a second surface that is opposite a similar electrode array and that provides at least one ground electrode in a biplanar setup. A major advantage of the electrowetting technology is that only a small volume of liquid is required, e.g. a single droplet. Thus, liquid processing can be carried out within considerably shorter time. Furthermore, the control of the liquid movement can be completely under electronic control resulting in automated processing of samples.
In life science and diagnostic applications, extraction and purification of biomolecules often is done via functionalized magnetically responsive beads (or magnetic beads for short). During extraction, the targeted biomolecules bind specifically to the surface of the beads via chemical moieties. After immobilizing the magnetic beads with a magnetic force, undesirable biomolecules and fluids are removed, usually with a pipette or passing fluid flow. Optimal extractions are defined as ones with a maximum retention of desired biomolecules, and a maximum removal of un-wanted biomolecules; in practice, these requirements translate into maximizing bead retention while minimizing leftover fluid. Many parameters affect the efficiency of extraction and clean-up: the number of binding sites available as determined by the number of magnetic beads and the number of binding sites per bead, the speed with which the beads and binding molecules interact, the avidity with which the beads and captured biomolecules bind to each other, the strength of the magnetic field on the beads, the gradient of that magnetic field and the force with which the wash fluid moves past the magnetic beads.
Electrowetting with magnetic beads is an extremely attractive means by which to run heterogeneous assays that require serial binding and washing steps. Binding is extremely efficient in this microfluidic format as the beads can be mixed while the binding is taking place therefore effectively reducing diffusion distances. Washing is also efficient as most of the liquid can be removed when droplets are pulled away from the beads. A challenge with electrowetting systems that is similar to one with conventional systems is to hold the beads against the interfacial tension of the aqueous droplet and a filler-fluid (which e.g. is oil or air). In order to prevent the magnetic beads from being swept away, it is desirable to have a strong magnetic force that concentrates the beads in a small area to better enable a bead pellet to resist the tendency of the interface to sweep magnetic beads away.
In standard electrowetting devices, it is desirable to put magnets underneath the PCB (=printed circuit board) containing driving electrodes for electrowetting to pull magnetic beads out of a droplet. In film-based electrowetting in which the PCB is part of the instrument and not part of the consumable, one has the luxury of being able to incorporate many features directly into the PCB. This leads to increased PCB layers and therefore to a thicker PCB thickness. An example is an extra layer to accommodate embedded heaters. The amplitude of magnetic fields and gradients strongly depends on the distance between the magnet and the location of interest so a thick PCB reduces the effective magnetic force on the droplets and magnetic beads. A common way to generate strong magnetic fields into an electrowetting system is to use large magnets underneath the PCB.
Such large magnets as positioned below the PCB have several disadvantages:
Automated liquid handling systems are generally well known in the art. An example is the Freedom EVO® robotic workstation from the present applicant (Tecan Schweiz AG, Seestrasse 103, CH-8708 Mannedorf, Switzerland). These automated systems are larger systems that are not designed to be portable and typically require larger volumes of liquids (microliter to milliliter) to process.
A device for liquid droplet manipulation by electrowetting using one single surface with an electrode array (a monoplanar arrangement of electrodes) is known from the U.S. Pat. No. 5,486,337. All electrodes are placed on a surface of a carrier substrate, lowered (embedded) into the substrate, or covered by a non-wettable (i.e. hydrophobic) surface. A voltage source is connected to the electrodes. Droplets are moved by applying a voltage to subsequent electrodes, thus guiding the movement of the liquid droplet above the electrodes according to the sequence of voltage application to the electrodes.
An electrowetting device for microscale control of liquid droplet movements, using an electrode array with an opposing surface with at least one ground electrode is known from U.S. Pat. No. 6,565,727 (a biplanar arrangement of electrodes). Each surface of this device may comprise a plurality of electrodes. The two opposing arrays form a gap. The surfaces of the electrode arrays directed towards the gap are preferably covered by an electrically insulating, hydrophobic layer. The liquid droplet is positioned in the gap and moved within a non-polar filler fluid by consecutively applying a plurality of electric fields to a plurality of electrodes positioned on the opposite sides of the gap.
The use of an electrowetting device for manipulating liquid droplets in the context of the processing of biological samples is known from the international patent application published as WO 2011/002957 A2. There, it is disclosed that a droplet actuator typically includes a bottom substrate with the control electrodes (electrowetting electrodes) insulated by a dielectric, a conductive top substrate, and a hydrophobic coating on the bottom and top substrates. The cartridge may include a ground electrode, which may be replaced or covered by a hydrophobic layer, and an opening for loading samples into the gap of the cartridge. Interface material (e.g. a liquid, glue or grease) may provide adhesion of the cartridge to the electrode array.
Disposable cartridges for microfluidic processing and analysis in an automated system for carrying out molecular diagnostic analysis are disclosed in WO 2006/125767 A1 (see US 2009/0298059 A1 for English translation). The cartridge is configured as a flat chamber device (with about the size of a check card) and can be inserted into the system. A sample can be pipetted into the cartridge through a port and into processing channels.
Droplet actuator structures are known from the international patent application WO 2008/106678. This document particularly refers to various wiring configurations for electrode arrays of droplet actuators, and additionally discloses a two-layered embodiment of such a droplet actuator which comprises a first substrate with a reference electrode array separated by a gap from a second substrate comprising control electrodes. The two substrates are arranged in parallel, thereby forming the gap. The height of the gap may be established by spacer. A hydrophobic coating is in each case disposed on the surfaces which face the gap. The first and second substrate may take the form of a cartridge, eventually comprising the electrode array.
From US 2013/0270114 A1, a digital microfluidics system for manipulating samples in liquid droplets within disposable cartridges is known. The disposable cartridge comprises a bottom layer, a top layer, and a gap between the bottom and top layers. The digital microfluidics system comprises a base unit with at least one cartridge accommodation site that is configured for taking up a disposable cartridge, at least one electrode array comprising a number of individual electrodes and being supported by a bottom substrate, and a central control unit for controlling selection of the individual electrodes of said at least one electrode array and for providing these electrodes with individual voltage pulses for manipulating liquid droplets within said cartridges by electrowetting.
U.S. Pat. No. 7,816,121 B2 and U.S. Pat. No. 7,851,184 B2 disclose a droplet actuation system and corresponding method of its use. The system comprises a substrate with electrowetting electrodes (or PCB), temperature control means for carrying out PCR-based nucleic acid amplification in droplets, means for effecting a magnetic field in proximity to electrowetting electrodes for immobilizing magnetically responsive beads in droplets that are located in a gap on the PCB. The processor, the electrowetting electrodes, and the magnetic field are configured to cause splitting of a droplet comprising magnetically responsive beads. Using the system for splitting droplets yields two daughter droplets, one with magnetically responsive beads and one with substantially reduced amount of beads. Means for effecting a magnetic field may comprise on a side of the gap opposite to the PCB a magnet and means for moving the magnet into and out of proximity with electrowetting electrodes.
U.S. Pat. No. 8,927,296 B2 discloses a method of reducing liquid volume surrounding beads. The method encompasses the steps of providing, in an operations gap of a digital microfluidics system, a droplet that comprises one or more magnetically responsive beads. The method further encompasses exposing these beads in the droplet to a magnetic field of the digital microfluidics system, and separating the droplet from the magnet field by electrowetting. As a result of the method, the magnetically responsive beads remain in the magnetic field and in a sub-droplet atop an electrowetting electrode of the digital microfluidics system.
When working with magnetically responsive beads, another common problem is settling of the beads or clumping of beads that have already been in the presence of a strong magnet field. On the bench, such clumping is typically remedied by vortexing the bead solution. However, with electrowetting based systems it is a challenge to find methods to sufficiently stir up the magnetic beads via electrowetting manipulations, especially since fluid flow in most microfluidic systems can be characterized as laminar. Suspension and re-suspension of beads is important for efficient bead washing, increasing binding-site surface area, and promoting uniformity of bead concentrations in daughter droplets formed via electrowetting from a larger bulk of magnetic beads.
It is an object of the present invention to suggest alternative devices for and/or alternative methods of substantially removing magnetically responsive beads from droplets on a working surface in digital microfluidics. It is another object of the present invention to suggest alternative devices for and/or alternative methods of substantially re-suspending magnetically responsive beads in droplets on a working surface in digital microfluidics.
According to a first aspect and in particular for re-suspension of magnetically responsive beads, these objects are achieved by the arrangement of at least one barrier element positioned at least partially on an operating electrode located at a cartridge accommodation site of a PCB of a digital microfluidics system. The barrier element narrows the working gap between a flexible working film and hydrophobic cover surface of a disposable cartridge that situated on a surface of this cartridge accommodation site. Preferably, the flexible working film of the cartridge is pressed to the surface of the cartridge accommodation site by underpressure between the cartridge and its accommodation site or by internal overpressure inside of the working gap of the cartridge.
According to a second aspect and in particular for substantially removing magnetically responsive beads from droplets, these objects are achieved by the additional integration of a magnetic conduit into the PCB of a digital microfluidics system that is equipped with at least one backing magnet for magnetic bead separation during electrowetting operations in the gap of a disposable cartridge. Preferably, the magnetic conduit is located on top of such a backing magnet and below a path of a droplet that is manipulated by electrowetting.
According to a third aspect, these objects are achieved by the arrangement of two barrier elements and a magnetic conduit/backing magnet combination for magnetic bead separation and re-suspension, the barrier elements being positioned upstream and downstream of the magnetic conduit/backing magnet combination that is located at an electrowetting droplet path.
Additional and inventive features, preferred embodiments, and variants of the present invention derive from the respective dependent claims.
Advantages of the present invention comprise:
Integration of barrier elements that narrow the working gap of a disposable cartridge as well as integration of magnetic conduits into the PCB or first substrate and/or second substrate according to the present invention is described with the help of the attached schematic drawings that show selected and exemplary embodiments of the present invention without narrowing the scope and gist of this invention. It is shown in:
The inventive barrier elements, their combination with magnetic conduits with backing magnets and their use is now described in detail.
In the context of the present invention, an electrode array is a regular arrangement of electrodes, e.g. in an orthogonal lattice or in any other regular arrangement such as a linear or hexagonal array.
In the context of the present invention, a liquid droplet 8-1,8-1′ has a size that covers on the hydrophobic surface 5 an area that is larger than a single individual electrode 2. Thus, a liquid droplet 8-1,8-1′ is the smallest liquid volume that may be manipulated (i.e. transported) by electrowetting. In the context of the present invention, a liquid portion 8-2,8-2′ has a size that covers on the hydrophobic surface 5 an area that is larger than two adjacent individual electrodes 2. Thus, a liquid portion 8-2,8-2′ is larger than the smallest liquid volume that may be manipulated (i.e. transported) by electrowetting.
According to the present invention, in the first substrate 3 of the microfluidics system 1 and below said individual electrodes 2 there may be located at least one magnetic conduit 9 that is configured to be backed by a backing magnet 10. The term “below” is to be understood in the context of the present invention as “on the backside of the PCB to which's front-side the electrodes 2 are attached, no matter what spatial orientation the PCB may have. Further according to the present invention, said at least one magnetic conduit 9 is located in close proximity to individual electrodes 2 (see
A preferred and inventive method of keeping suspended or re-suspending magnetically responsive beads in liquid portions or droplets in digital microfluidics takes advantage of this setup and comprises the steps of
Carrying out the step b) produces a narrowed gap height 46 that is reduced with respect to the normal gap height 28, which is defined by a gasket 27 that preferably belongs to the disposable cartridge 17 or to the cartridge accommodation site 18 of the microfluidics system 1.
When carrying out the above preferred method of keeping suspended or re-suspending magnetically responsive beads in liquid portions or droplets in digital microfluidics, it is preferred that for spreading of the flexible working film 19 of the disposable cartridge 17 on the uppermost surface 22 of the cartridge accommodation site 18 of the digital microfluidics system 1 and over said at least one barrier element 40:
For applying such underpressure, there are vacuum lines 23′ preferably arranged in the microfluidics device 1, the vacuum lines 23′ connecting an evacuation space 24 with the vacuum source 23 of the digital microfluidics system 1. According to the present invention, such evacuation space 24 is defined by the flexible working film 19 of the cartridge 17, a gasket 27, and the uppermost surface 22 of the cartridge accommodation site 18. This vacuum source 23 of the digital microfluidics system 1 is configured for establishing an underpressure in an evacuation space 24 between the uppermost surface 22 of the cartridge accommodation site 18 and the backside 21 of the working film 19 of a disposable cartridge 17 that is accommodated at the cartridge accommodation site 18 (see e.g. US 2013/0134040 A1).
When working with underpressure or overpressure as described, it is further preferred that the cover plate 20 of the disposable cartridge 17 is configured as a rigid cover plate, evenly defining a top of said working gap 4. For applying such overpressure inside the working gap 4, a filler fluid (e.g. silicone oil) or another fluid that preferably is not miscible with the droplets or liquid portions that are to be manipulated within the working gap 4 is pressed into the working gap 4.
On this first hydrophobic surface 5, magnetically responsive beads 11 in the liquid droplet 8-1 are attracted by the magnetic field produced by the activated electromagnet 10′″ and directed by the magnetic conduit 9″.
On this first hydrophobic surface 5, magnetically responsive beads 11 in the liquid droplet 8-1 are attracted by the magnetic field produced by the switchable permanent magnet 10″ and directed by the magnetic conduit 9″. Because the magnetic field of the permanent magnet of the PE-magnet is not compensated by the electromagnet of the PE-magnet. Such PE-magnets 32 (e.g. ITS-PE 1212-24 VDC-TEC of M RED MAGNETICS® (Intertec Components GmbH, 85356 Freising, Germany) may have a diameter of 12 mm, a height of 12 mm, and work with 24 V DC. A great advantage of using such PE-magnets 32 is the fact that absolutely no moving parts are involved or necessary for switching on and off the switchable permanent magnets 10″. Preferably, the microfluidics system 1 comprises a cartridge accommodation site 18 that is configured for taking up a disposable cartridge 17 (see for example US 2013/0134040, herein incorporated by reference in its entirety).
A preferred and inventive method of substantially removing magnetically responsive beads from liquid portions or droplets in digital microfluidics takes advantage of this setup and comprises the steps of:
When carrying out the above removing method, on the one hand it is preferred for spreading the flexible working film 19 of the disposable cartridge 17 on the uppermost surface 22 of the cartridge accommodation site 18 of the digital microfluidics system 1 and over said at least one barrier element 40 to using a vacuum source 23 of the digital microfluidics system 1 for establishing an underpressure in an evacuation space 24 between the uppermost surface 22 of the cartridge accommodation site 18 and the backside 21 of the flexible working film 19 of the disposable cartridge 17.
When carrying out the above removing method, on the other hand it is preferred for spreading the flexible working film 19 of the disposable cartridge 17 on the uppermost surface 22 of the cartridge accommodation site 18 of the digital microfluidics system 1 and over said at least one barrier element 40 to using a filler-fluid or other fluid for establishing an overpressure within the working gap 4 of the disposable cartridge 17.
Preferably for carrying out the above removing method in one way or the other, the cover plate 20 of the disposable cartridge 17 is configured as a rigid cover plate, evenly defining a top of said working gap 4.
It is preferred that said at least one magnetic conduit 9 consists of a single solid ferromagnetic element, or of a multitude of randomly orientated ferromagnetic elements, or of an amorphous paste filled with ferromagnetic material. It is further preferred that said at least one magnetic conduit 9 is located under and is covered by an individual electrode 2 or that said at least one magnetic conduit 9 is located beside of and is not covered by at least one individual electrode 2.
The backing magnet 10 that is used to operatively back at least one magnetic conduit 9, preferably is configured as a movable permanent magnet 10′ (see
In consequence, actuating said backing magnet (10) is achieved by:
Preferably, said at least one magnetic conduit 9 is a cylindrical, cuboid, pyramidal, frustoconical, conical, or magnetic conduit 9′,9″ located in a blind hole 15 or in a through hole 16 in the first substrate 3 of the digital microfluidics system 1.
Independent from the method of working, it is preferred that the cartridge accommodation site 18 of the digital microfluidics system 1 or the disposable cartridge 17 comprise a gasket 27, using which said evacuation space 24 (if present) is sealingly enclosed and always, a height 28 of the working gap 4 between said hydrophobic surfaces 5,6 of the disposable cartridge 17 is defined.
When working with overpressure in the gap 4, it is preferred that the cartridge accommodation site 18 of the digital microfluidics system 1 comprises at least one check valve 42, using which said working gap 4 is sealingly closed and an overpressure produced by a filler fluid or other fluid inside said working gap 4 is enabled (see
Using barrier elements 40 with rectangular cross section is preferred when working with “low” underpressure in the range of about −2 psi (which is equal to 875 mbar). The low underpressure does not attract the entire flexible working film 19, which thus forms ramp-like transitions between the normal gap height 28 and the narrowed gap height 46.
Using barrier elements 40 with trapezoid cross section is preferred when working with “high” underpressure in the range of about −6 psi (which is equal to 600 mbar). The high underpressure does attract the entire flexible working film 19. The preferred ramp-like transitions between the normal gap height 28 and the narrowed gap height 46 are defined by the trapezoid flanks of the barrier elements 40.
When using such high underpressure, avoidance of bubbles inside the gap 4 has been observed. This effect is most likely supported or due by a semi-permeable constitution or property of the flexible working film 19.
The liquid droplet 8-1′ has been moved over and/or around the barrier element 40 and comprises practically no magnetically responsive beads 11. A small liquid portion 8″ with substantially all beads is left behind on top of the magnetic conduit 9″.
It is to be noted that here, a movable permanent magnet 10′ is depicted. The permanent magnet 10′ is supported by a movable support 35. In this case, the support 35 is turnable around an axis (see dashed double arrow and chain dotted line). In order to move the permanent magnet away from and again to the magnetic conduit 9, also other sorts of movement, such as sliding or lifting are possible too.
The check valve 42 on the left is closed by pushing the valve ball 43 up by the valve spring 44. This pushing up lifts the flexible working film 19 and presses it against an opening of the pipetting guide 41 of the disposable cartridge 17 that is inserted in or attached to the ridge accommodation site 18 of a PCB 3 of a digital microfluidics system 1. In consequence, establishing an overpressure in the filler fluid inside of the working gap 4 is enabled.
The check valve 42 on the right is open by pressing a liquid (here a sample portion) via the sealing pipetting guide 41 into the working gap 4 of the disposable cartridge 17. The pipette tip 47 used (preferably a disposable polypropylene pipette tip) is pushed into the pipetting guide 41 such that its circumference is sealingly pressed against the pipetting guide 41. When doing this, the pipette tip 47 pushes about halfway down the working gap height 28 the valve ball 43 against the force of the valve spring 44. Liquid injection additionally moves the valve ball 43 against the force of the valve spring 44 and opens the check valve more. Such injecting of liquid portions gradually enhances the internal pressure inside of the working gap 4, whereupon the flexible working film 19 of the disposable cartridge 17 more evenly spreads on the uppermost surface 22 of the cartridge accommodation site 18 of the digital microfluidics system 1 and over said at least one barrier element 40.
The pipetting guides 41 may be sealed and blocked by pushing-in cones 48 of appropriate size and shape. However, these cones 48 shall not reach to the inside of the working gap 4. Alternatively, the pipetting guides 41 may be sealed with portions of liquid wax poured-in, which portions then solidify. For removing and disposing a disposable cartridge 17 equipped with pipetting guides 41 and with an overpressure inside the working gap 4, such blocking of all pipetting guides 41 is advisable for safety reasons. It is feasible that, when removing such a sealed disposable cartridge 17 from the cartridge accommodation site 18 of a digital microfluidics system 1, the overpressure previously applied to the working gap is balanced by the flexibility of the working film 19. This is even more so, if a number of barrier elements 40 have been placed on the uppermost surface 22 of that cartridge accommodation site 18.
It may be required to add underpressure to the working film 19 from the outside. For this purpose, it is preferred to additionally equip the digital microfluidics system 1 with a vacuum source 23 that is linked to the uppermost surface 22 of the that cartridge accommodation site 18 by vacuum lines 23′.
In this case on the left side, an angled barrier element 40 has been deposited to the uppermost surface 22 of the cartridge accommodation site 18; the broader, angled central part having a rectangular cross section and the smaller, angled extension parts having a square cross section.
In this case on the right side, two broad, angled barrier elements 40 have been deposited to the uppermost surface 22 of the cartridge accommodation site 18. Both broad, angled barrier elements 40 have a rectangular cross section and are not touching each other; thus, an open passage is left between them.
While the droplet 8-1 may be moved over the barrier element 40 on the left, it may be moved around (i.e. through the open passage between) the barrier elements 40 on the right.
In this case on the left side, an broad, angled barrier element 40 has been deposited to the uppermost surface 22 of the cartridge accommodation site 18; the broad, angled barrier element 40 having a trapezoid cross section over its entire length.
In this case on the right side, an angled barrier element 40 has been deposited to the uppermost surface 22 of the cartridge accommodation site 18. Two broad, angled parts of the barrier element 40 have a rectangular cross section and are connected to each other by a small, straight part of the barrier element 40 with a square cross section.
While the droplet 8-1 may be moved over the barrier element 40 on the left, it may partly be moved around and partly moved over the barrier element 40 on the right.
Preferably, an inventive digital microfluidics system 1 configured for substantially removing or suspending magnetically responsive beads from or in liquid portions or droplets comprises,
wherein the digital microfluidics system 1 further comprises at least one barrier element 40 positioned at least partially on an individual operating electrode 2 located at the cartridge accommodation site 18 of the PCB 3, the barrier element 40 narrowing the working gap 4 of a disposable cartridge 17 situated on a surface of said cartridge accommodation site 18.
Preferably, said least one barrier element 40 comprises a material chosen of a group of materials, said group comprising Kapton® tape, Teflon® sheets, solder mask and silk screen printing, and paper strips.
Preferably, said least one barrier element 40 has a thickness of 0.02 to 0.25 mm, a width of 0.4 to 1.0 mm, and a length of 3 to 5 mm.
Preferably, said least one barrier element 40 has a cross section in a trapezoid, rectangular, or square shape. Combinations of these shapes are possible and preferred too.
Preferably, in combination with a mixing zone of the electrode path 2′, one, two, or four barrier elements 40 are provided.
Preferably, in the first substrate or PCB 3 of the microfluidics system 1 and below said individual electrodes 2 there is located at least one magnetic conduit 9 that is backed by a backing magnet 10, said at least one magnetic conduit 9 being located in close proximity to individual electrodes 2.
Preferably, said at least one magnetic conduit 9 is located under and is covered by an individual electrode 2.
Preferably, said at least one magnetic conduit 9 is located beside of and is not covered by at least one individual electrode 2.
Preferably, said backing magnet 10 is configured as a moving permanent magnet 10′, a switchable permanent magnet 10″, or as an electromagnet 10″.
Preferably, in combination with a magnetic conduit 9 and a backing magnet 10, one or two barrier elements 40 are provided.
Preferably, the digital microfluidics system 1 comprises a vacuum source 23 for establishing an underpressure in an evacuation space 24 between the uppermost surface 22 of the cartridge accommodation site 18 and the backside 21 of the flexible working film 19 of the disposable cartridge 17.
Preferably, the cartridge accommodation site 18 of the digital microfluidics system 1 comprises at least one check valve 42 configured to sealingly close the working gap 4 and to enable an overpressure in a filler fluid or other fluid inside said working gap 4.
Preferably, the cartridge accommodation site 18 of the digital microfluidics system 1 comprises a pressure sensor for measuring the actual underpressure between the uppermost surface 22 of the cartridge accommodation site 18 and the flexible working film 19 of the disposable cartridge 17. If an underpressure is to be established, a pressure of −2 psi to −6 psi i.e. 875 to 600 mbar is preferred.
Preferably, the cartridge accommodation site 18 of the digital microfluidics system 1 comprises a pressure sensor for measuring the actual overpressure between the uppermost surface 22 of the cartridge accommodation site 18 and the flexible working film 19 of the disposable cartridge 17.
It is evident from this description that the liquid droplets 8-1,8-1′ or liquid portions 8-2,8-2′ with or without magnetically responsive beads 11 in each case may also be moved from the right to the left of the shown electrode paths 2′. It is further evident from this description that such movements can also be directed in any other direction of an electrode array. Moreover, inverse movements and inverse actions on the removal of magnetically responsive beads 11 from liquid droplets 8-1 or liquid portions 8-2 as well as on the suspension of magnetically responsive beads 11 within liquid droplets 8-1′ or liquid portions 8-2′ are disclosed and evident from the present description and drawings.
In general, the magnetic conduits 9,9′,9″ according to the present invention preferably consist of or comprises material with the potential for a high degree of magnetization. The type of material that can be a ferromagnetic element (iron, nickel, cobalt) or an alloy (permalloy, Kovar, mu-metal, stainless-steel 410). The magnetic conduits 9 according to the present invention may comprise a single solid ferromagnetic element, or of a multitude of randomly orientated ferromagnetic elements (e.g. metallic shavings, preferably iron shavings), or of an amorphous paste filled with ferromagnetic material (e.g. magnetic epoxy). Preferably, the ferromagnetic material is kept inside a magnetic conduit 9 with epoxy or with a tape at the bottom of the magnetic conduit 9 or of the PCB 3.
In general, the magnetic conduits 9 according to the present invention can be located in a through hole or in a blind hole. Blind holes provide less magnetic coupling than the through holes. Both allow the use of vertical electrical vias in the PCB 3. The blind holes allow better electrical insulation and pressure difference between the uppermost surface 22 of the cartridge accommodation site 18 or PCB 3 and the bottom surface of the PCB or first substrate 3. Typically but not exclusively, the voltage in a digital microfluidics system 1 is applied in pulses to one or more selected electrodes 2′ that define one or more paths for one or more liquid portions 8-2 or liquid droplets 8-1 (see for example US 2013/0134040 A1 and US 2013/0175169 A1, herein incorporated by reference in their entirety).
Preferably and in general, the backing magnet 10 is configured as a permanent magnet 10′, or as a switchable permanent magnet 10″, or as an electromagnet 10′″. Most preferred are permanent magnets 10′ or switchable permanent magnets 10″. Such backing magnets 10 may be activated by a selection of the following alternatives:
It is noted expressly that all features in the shown and described embodiments that appear reasonable to a person of skill may be combined with each and every one of these features. Especially preferred materials and dimensions are disclosed in Table 1 below: Cytop is an amorphous fluoropolymer with high optical transparency (AGC Chemicals Europe). Mylar®, Neoprene®, Teflon®, and Viton® are Trademarks of DuPont, Wilmington, USA.
Preferably, the magnetic conduits 9 are in physical contact or in close proximity to the backing magnet 10 when the magnetic force is enabled. Preferred distances (if there are some) range from 1 μm to 1 mm, more preferably from 1 μm to 100 μm.
In some embodiments, the permanent magnet height is 5 mm-20 mm, preferably 10 mm-15 mm with a diameter of preferably 3 mm-7 mm. If a single, large permanent magnet is used, the magnet length can be 30-100 mm, preferably 50 mm-70 mm. The magnetic force generated on a single 1-μm-diameter magnetic bead is 100 fN-10 pN, preferably 500 fN-2 pN.
Even if not particularly described in each case, the reference numbers refer to similar elements of the digital microfluidics system 1 and in particular of the disposable cartridge 17 of the present invention. All drawings are schematic and not to scale.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/049952 | 9/1/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/040818 | 3/9/2017 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5486337 | Ohkawa | Jan 1996 | A |
| 6565727 | Shenderov | May 2003 | B1 |
| 7816121 | Pollack et al. | Oct 2010 | B2 |
| 7851184 | Pollack et al. | Dec 2010 | B2 |
| 8927296 | Sista et al. | Jan 2015 | B2 |
| 20090298059 | Gumbrecht | Dec 2009 | A1 |
| 20100270156 | Srinivasan | Oct 2010 | A1 |
| 20100279374 | Sista et al. | Nov 2010 | A1 |
| 20130126358 | Lee et al. | May 2013 | A1 |
| 20130134040 | Lee et al. | May 2013 | A1 |
| 20130175169 | Feiglin et al. | Jul 2013 | A1 |
| 20130270114 | Feiglin | Oct 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2006125767 | Nov 2006 | WO |
| 2008106678 | Sep 2008 | WO |
| 2010069977 | Jun 2010 | WO |
| 2011002957 | Jan 2011 | WO |
| Entry |
|---|
| International Search Report for corresponding PCT application No. PCT/US2016/049952, dated Nov. 23, 2016. |
| Written Opinion for orresponding PCT application No. PCT/US2016/049952, dated Mar. 9, 2017. |
| Number | Date | Country | |
|---|---|---|---|
| 20180339923 A1 | Nov 2018 | US |
