Patent Publication Number: US-2023132614-A1

Title: Electromagnetic assemblies for processing fluids

Description:
CLAIM OF PRIORITY 
     This patent application is a national stage application of PCT/US2021/025587, filed Apr. 2, 2021, which claims the benefit of priority to U.S. Provisional Application Ser. No. 63/004,913, filed Apr. 3, 2020, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The preparation of samples is a critical phase of chemical and biological analytical studies. In order to achieve precise and reliable analyses, target compounds must be processed from complex, raw samples and delivered to analytical equipment. For example, proteomic studies generally focus on a single protein or a group of proteins. Accordingly, biological samples are processed to isolate a target protein from the other cellular material in the sample. Additional processing is often required, such as protein isolation (e.g., immunoprecipitation), matrix cleanup, digestion, desalting. Non-target substances such as salts, buffers, detergents, proteins, enzymes, and other compounds are typically found in chemical and biological samples. These non-target substances can interfere with an analysis, for example, by causing a reduction in the amount of target signal detected by analytical equipment. As such, complex, raw samples are typically subjected to one or more separation and/or extraction techniques to isolate compounds of interest from non-target substances. 
     Magnetic particles or beads are a technology that can be employed for sample preparation for chemical and biological assays and diagnostics. One key element in magnetic particle separation and handling technology is efficient mixing to enhance the reaction rate between the target substances and the particle surfaces, the mass transfer from one substrate to another or the transfer of an analyte from one medium to another. 
     One known technique for mixing fluids using magnetic particles, involves moving a magnet relative to a stationary container or moving the container relative to a stationary magnet using mechanical means to induce relative displacement of a magnetic field gradient within the container. Another technique involves the use of two electromagnets facing each other around a chamber having magnetic particles arranged therein. Sequentially energizing and de-energizing the two electromagnets (i.e., binary on/off control) at a sufficient frequency operates to suspend the magnetic particles within a fluid disposed in the chamber. Such techniques may require excessive power consumption and could cause magnetic particles to separate slowly. Or such techniques could require modified lens arrangements which could reduce mixing quality. But these and other techniques known in the art suffer from various drawbacks, including the aggregation of particles and inefficiency in mixing of the particles. Further, such techniques may require manual intervention between stages of the process. A technique to improve mixing solutions using magnetic beads is the use of electromagnets surrounding a sample container to create a changing magnetic field. 
     However, magnetic particles typically used for capture and isolation of biological molecules are paramagnetic. Paramagnetic beads are responsive to an applied external magnetic field but retain little or no residual magnetism when that field is removed. This low residual magnetism reduces or eliminates clumping of the beads, allowing the beads to remain dispersed and suspended in solution and to be easily transferred through a pipette tip. Paramagnetic beads, however, are generally less responsive to an external magnetic field and therefore are more difficult to effectively mix using an electromagnetic mixer, particularly in viscous solutions such as those used to selectively precipitate and isolate nucleic acids using magnetic beads. Accordingly, a need exists to provide an arrangement of electromagnetic elements that more effectively induces efficient mixing of such magnetic particles. 
     SUMMARY 
     Apparatus, systems, and methods are described herein allow for the processing of sampling devices and fluids using electromagnetic assemblies without the limitations of known techniques. For example, the apparatus, systems, and methods described herein allow for the processing of sampling devices and fluids using electromagnetic assemblies on sample volume without sample loss or magnetic particle loss. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       A description is provided herein below with reference, by way of example, to the following drawings. It will be understood that the drawings are provided as examples only and that all reference to the drawings is made for the purpose of illustration only and are not intended to limit the scope of the disclosure in any way. For convenience, reference numerals can also be repeated (with or without an offset) throughout the figures to indicate analogous components or features. 
         FIGS.  1 A- 1 D  are schematics of fluid processing systems according to various aspects described herein. 
         FIGS.  2 A and  2 B  are schematics illustrative open-well magnetic sample plate according to various aspects described herein. 
         FIG.  3    is a schematic illustrative fluid processing system according to various aspects described herein. 
         FIG.  4    is a schematic illustrative fluid processing structure and mixing pattern thereof according to various aspects described herein. 
         FIG.  5    is a schematic illustrative fluid processing structure and mixing patterns thereof according to various aspects described herein. 
         FIG.  6    is a schematic illustrative fluid processing and analysis system according to various aspects described herein. 
         FIGS.  7 A-B  is a schematic of another example of a fluid processing system according to various aspects described herein. 
         FIG.  8    is a representation of one example of the z-direction mixing resulting from the physical movement of the magnetic lenses described herein. 
         FIGS.  9 A-B  are representation fluid processing systems according to various aspects described herein. 
         FIG.  10 A-B  is a representation of a  4 -point lens shape. 
         FIG.  11    is a representation of an illustrative lens shape. 
         FIG.  12    is a picture of an example magnetic lens assembly where the lenses are fastened to the electromagnet core via a threaded nut. 
         FIG.  13 A-C  is a representation of a permanent magnet rails where such rail component moves in and out of the array of tubes for separation. 
         FIGS.  14 A-B  are representations of moving the sample tube  115  relative to magnetic lenses  730   b  ( FIG.  14 A ) created by a collection of lens members  730   c  and moving the entire magnetic assembly  900  relative to the sample tube  115  ( FIG.  14 B ). 
         FIG.  15    is a representation of one example of an assembly of vertically oriented permanent magnets which may be reversibly positioned adjacent to the fluid sample. 
     
    
    
     DESCRIPTION 
     Those skilled in the art will understand the methods, systems, and apparatus described herein are non-limiting examples and the scope of the applicant&#39;s disclosure is defined solely by the claims. While the applicant&#39;s teachings are described in conjunction with various aspects, it is not intended for the applicant&#39;s teachings be limited to such aspects. On the contrary, applicant&#39;s teachings encompass various alternatives, modifications, and equivalents, as will be appreciated by those of skill in the art. The features illustrated or described in connection with one example can be combined with the features of other aspects. Such modifications and variations are intended to be included within the scope of the applicant&#39;s disclosure. 
     The disclosure generally relates to fluid processing methods and systems for mixing, separating, filtering, or otherwise processing a fluid sample by utilizing magnetic particles dispersed therein. In accordance with various aspects of the disclosure, the fluid sample can be disposed within a fluid chamber. In accordance with various aspects, the fluid could also be a viscous solution; however, the word fluid will be generally used to describe any material in which the sample can be suspended. A plurality of fluid chambers are held and dispersed throughout a fluid container. The fluid chamber can be an open tube or similar device (e.g., open to the atmosphere) such that the sample and/or reagents can be directly added to the open fluid chamber (e.g., via an auto-sampler or pipette inserted through the open end of the fluid chamber) and can likewise be directly removed therefrom (e.g., via a capture device) following the processing, for example. 
     The magnetic particles, disposed and dispersed within the fluid, can be configured to be agitated under the effect of magnetic fields (or gradients) generated by a magnetic assembly arranged adjacent to the fluid chambers (e.g., arranged about the periphery of the fluid container) so as to facilitate the movement of the magnetic particles within the fluid. The magnetic assembly can include a one or a plurality of magnetic structures arranged in horizontal or substantially horizontal layers. Each of the magnetic structures can be formed by one or more magnets, such as an electromagnet. The vertical position of one or more of the magnetic structures, relative to the fluid, can be movable or adjustable, for instance, before, during, or after facilitating the movement of the magnetic particles within the fluid. Adjustment of the vertical position of the one or more of the magnetic structures before facilitating movement of the magnetic particles can be used, for example, to process different sample volumes and/or to affect a characteristic of a magnetic field generated by the magnetic assembly. Vertical movement of the magnetic structures while facilitating the movement of the magnetic particles may add, for example, a vertical component of movement in the particles to provide a more effective or efficient mixing of the particles in the fluid. Additionally or alternatively, the electrodes of the various magnetic structures (e.g., of the different vertically-spaced layers) can be selectively energized so as to process different sample volumes and/or to affect a characteristic of a magnetic field generated by the magnetic assembly. 
     The magnetic assembly structures can be formed from a plurality of electromagnets disposed around the fluid chamber at one or more different vertical heights, with each electromagnet being individually controlled to generate a desired magnetic field within the fluid chamber effective to influence the magnetic particles disposed therein. Based on the selective application of electrical signals to the plurality of electromagnets surrounding the fluid chamber, the magnetic particles can be influenced to rotate, spin, move horizontally side-to-side, and/or vertically up-and-down, or any combination of such movements, within the fluid sample by the combined effect of the magnetic field gradients generated by the various electromagnets. By way of example, the signals applied to the electromagnets of each magnetic structure (e.g., in a single horizontal layer) can be configured to generate magnetic field gradients substantially in the x-y plane, while the signals applied to the electromagnets of the different magnetic structures, if present (e.g., the electromagnets in different horizontal layers) can result in magnetic field gradients exhibiting a z-direction or vertical component. In this manner, the combined effect of the plurality of electromagnets can produce a magnetic field within a sample container with different characteristics, such as different strengths and/or directionality so as to rapidly and efficiently mix the fluid and/or capture target analytes within the fluid, by way of non-limiting example. 
     Making reference to  FIG.  8   , an assembly  900  comprising a pin  901  made of a magnetically permeable metal is placed through the center of a coil  730 , the pin  901  extending above the coil  730 . When the coil  730  is actuated, it creates a magnetic field that is transmitted to pin  901  and, in turn, to lens assembly  730   a,  which is also made of a magnetically permeable metal. Lens assembly  730   a  comprises a plurality of magnetic lenses  730   b  (see  FIG.  10 A ) created by a collection of lens members  730   c,  each focusing and shaping the magnetic field in a desired area, in this example within sample tube  115  comprising magnetic particles (not shown). The lens members  730   c  comprised in assembly  730   a  can have any suitable shape. In various examples, the lens member  730   c  can have a circular shape. In various examples, the lens member  730   c  has a  4 -point shape, such as the one shown in  FIG.  10 B . By further example, the lens member could be formed in any shape most efficient to the assembly such as those show in  FIG.  11   . In various aspects, the magnetic lens is brought into contact (or very close to) the samples described herein, such as a sample tube  115 . 
     In various examples, the lenses are 0.25 mm thick to 20 mm thick. In another example, the lenses are 2 mm thick to 12 mm thick. 
     Although the lens assemblies shown in  FIG.  10 A and  10 B  are substantially unitary because each lens member  730   c  is joined by linking members  730   d,  in various examples, one or more of the plurality of lens members  730   c  can be individual. See for example  FIG.  12   , where each individual lens member  730   c  comprises threads configured to accept and thread on to threaded pin  901 . In various aspects, the magnetic lenses are formed of a single lens member  730   c  and a plurality of the lens members  730   c  would make up lens assembly  730   a.    
     In various examples, the coils used to induce the magnetic field are encased in aluminum or copper. In various examples, the array of electromagnetic coils is completely encased in a block of aluminum, or other highly thermally conductive material with low magnetic permeability. In addition, a small amount of thermal potting compound (not shown) can be placed between the block and the coil to create full contact between the coils and block. In various aspects, the coils  730  and lens assembly  730   a  are encased in a solid potting material (not shown). 
     In various examples, the heat from the coils is isolated from the samples and removed from the device in order to maintain a suitable temperature of the sample. 
     In various examples, the samples can be heated or cooled such that they are maintained or thermocycled at a different temperature than ambient. The heating or cooling can be accomplished using any suitable heating or cooling element. In one example, the samples can be heated using the heat generated by the coils used to induce the magnetic fields. 
     The lens assembly can be moved relative to the sample tube, while one or more of the coils are actuated, in order to move the beads up and down through the sample liquid. The lens assembly can be physically moved while the sample tube remains stationary. The sample tube can be physically moved while the lens assembly remains stationary. Both the lens assembly and the sample tube can be physically moved. In various examples, the lens magnetic assemblies and/or structures cause particles (e.g., ferrimagnetic particles) to spin, or travel back and forth in x-, y-, and z-directions as confined by the presence of the magnetic fields. By way of example, the signals applied to the electromagnets  110   a - d  of each magnetic structure  110  (e.g., in a single horizontal layer) can be configured to generate changing magnetic fields substantially in the x-y plane, while the movement of the lens assembly relative to the sample tube creates a changing field in a z-direction or vertical component of mixing. In this manner, the combined effect of the plurality of electromagnets can produce a magnetic field within the container  115  with different characteristics, such as different strengths and/or directionality so as to rapidly and efficiently mix the sample and/or capture target analytes within the sample, by way of non-limiting example. The vertical movement of the lens assembly or sample tube can be a single motion upward or downward or may include any combination of upward and downward movements in succession. The vertical movement can begin at any vertical position of the lens assembly relative to the sample tube. In some aspects, upward vertical movement can begin when the lens assembly is positioned near the bottom of the sample tube in order to induce vertical resuspension of magnetic particles that may have settled toward the bottom of the tube. In some examples, vertical movement of the lens assembly or sample tube can begin when the lens assembly is positioned near a sedimentation or boundary layer between liquids or components that can be separating in the sample fluid. In this way, the vertical movement of the lens assembly or sample tube, while the coils are actuated, can help disrupt this sedimentation or boundary layer to provide more effective mixing of the entire sample fluid. The rate of vertical movement can be any suitable rate that maintains effective mixing in the x-y plane while providing sufficient distribution of mixing along the z-direction. The range of the vertical motion can be any suitable range required to maintain sufficient mixing along the z-direction. 
     In various examples, the controller can be configured to differentially actuate the electromagnets via the application of one or more of radio frequency (RF) signals, direct current (DC) signals, alternating current (AC) signals, electro frequency (EF), or the like, and also including any combination thereof. In various examples, the RF signals applied to the plurality of electromagnets can exhibit different phase delays relative to one another so as to effect the desired movement of the electromagnets within the sample fluid. In some aspects, the DC signals can be effective to isolate the particles (e.g., draw magnetic particles to one side and/or vertical level of the fluid chamber) such that fluid can be withdrawn from the chamber without aspiration of the magnetic particles, by way of non-limiting example. In some examples, a constant-voltage DC signal can be interspersed between alternating or changing actuating signals in order to provide more effective mixing of the sample fluid. The alternating or changing actuating signals surrounding the constant-voltage DC signal can be any suitable RF, AC, DC, or EF signal, or the like. 
     In various examples, the tube is to remain nonrotatable during the mixing process. For example, the tube can be mechanically fixed in place with an interference fit mechanism. The tube can also be screwed or similarly rotated into a locked position within the rack. The tube can also be held in a nonrotatable manner by use of lid or similar feature associated with the rack. 
     Fluid processing systems described according to various examples can be configured to process fluids at the micro-scale or macro-scale (including large-volume formats). In general, the macro-scale involves fluid volumes in the milliliter range, while micro-scale fluid processing involves fluid volumes below the milliliter range, such as microliters, picoliters, or nanoliters. Large-volume formats can involve the processing of fluid volumes greater than 1 mL. For example, fluid processing systems in accordance with various aspects of the present teaching can be capable of processing a fluid volume of about 1 μL. to about 15 mL and even greater, including for example, about 1.5 mL, about 2 mL, about 5 mL, about 10 mL, or greater. In some aspects, the fluid chamber is configured to hold a volume in a range of about 20-200 μL. 
     In some examples, the fluid chamber is configured to extend from a lower, closed end to an upper, open end that is configured to be open to the atmosphere to receive the fluid to be processed therethrough. In some examples, the fluid chamber comprises a lid. 
     However, it will be appreciated in light of the disclosure that the fluid processing systems can process any fluid volume capable of operating as described herein. 
     The use of magnetic assemblies to influence magnetic particles according to various examples, for instance, as compared to conventional magnetic particle processing systems, can provide multiple technological advantages. One non-limiting example of such an advantage includes significantly improved rates of diffusion for increased sample contact rate in various volumes of the sample fluid, for example, to improve analyte capture efficiency in a magnetic immunoassay. Another non-limiting example of a technological advantage includes increased sample mixing efficiency as the magnetic structures of a magnetic assembly can influence the magnetic particles to provide for faster and more effective sample mixing due to, for example, more robust magnetic particle movement and movement in multiple dimensions. This can, for example, lead to increased mass transfer between components. 
     Processing samples using the fluid processing structures configured according to applicant&#39;s teachings generates fast reaction kinetics. For instance, protein processing (including immunological affinity pull-down, washing, elution/denaturation, reduction, alkylation, and digestion steps) can be completed in about 10-12 minutes, compared with a one- or two-day processing time for manual, in-tube processing. The increased processing speed can be achieved, for example, due to overcoming diffusion as a rate-limiting step of fluid processing (e.g., a rate-limiting step of LC) and the necessity of utilizing small, fixed volumes in known microfluidic platforms. In addition, such fast, efficient sample processing can be achieved across a large array of sample reaction containers simultaneously as the fluid processing structures configured according to applicant&#39;s teachings can be integrated into large arrays of sample reaction wells, thereby increasing sample processing and enabling automation via an autosampler, for example. It will be appreciated in light of the disclosure that the fluid processing systems described herein provide multiple other technological advantages in addition to the aforementioned non-limiting examples. 
     While the systems, devices, and methods described herein can be used in conjunction with many different fluid processing systems, an example of a suitable fluid processing system  100  is illustrated schematically in  FIG.  1 A . It should be understood that the fluid processing system  100  represents only one possible fluid processing system for use in accordance with systems, devices, and methods described herein, and fluid processing systems and/or components thereof having other configurations and operational characteristics can all be used in accordance with the systems, devices, and methods described herein as well. 
     In various aspects, in solutions where a sample has been added to a more viscous bead-containing solution, the two liquids may partially separate, forming at least one boundary between partially-separated liquid layers. Vertical movement of a magnetic assembly near or across such a boundary, while actuating one or more electromagnets of the assembly to mix the combined sample and bead solution, may provide more effective or thorough mixing of the combined sample and bead solution. In some examples, the vertical position of the boundary can be pre-estimated based on known volumes of the bead-containing solution and the added sample. In other examples, the vertical movement of the magnetic assembly is programmed to encompass a majority or a totality of the range of the sample fluid or sample tube in order to facilitate effective mixing regardless of the initial vertical position of the boundary. 
       FIG.  1 A  schematically depicts an example of a fluid processing system  100 . As shown in  FIG.  1 A , the fluid processing system  100  includes a fluid processing structure or container  130  having a fluid chamber  115  and a magnetic structure  105  configured to generate a magnetic field gradient or magnetic force within the fluid chamber, as discussed in detail below. The fluid chamber  115  can generally comprise any type of vessel configured to hold a sample fluid, such as a sample well, a vial, a fluid reservoir, or the like, defining a fluid-containing chamber therein. As best shown in  FIG.  1 B , the fluid chamber  115  extends from an open, upper end  115   a  (open to the ambient atmosphere) to a lower, closed end  115   b  such that the fluid within the fluid chamber  115  can be loaded and/or removed therefrom by one or more liquid loading/collection devices  135  that can be inserted into the open, upper end  115   a.  It will be appreciated by those skilled in the art that the chamber  115  can include a removable cap that can be coupled to the open, upper end  115   a  (e.g., an Eppendorf tube) during various processing steps, for example, to prevent the escape of fluid during mixing, contamination, and/or evaporation. Illustrative liquid loading/collection devices  135  can include, without limitation, manual sample loading devices (e.g., pipette), multi-channel pipette devices, acoustic liquid handling devices, and/or an auto-sampler, all by way of non-limiting example. 
     With reference again to  FIG.  1 A , the sample fluid can have a plurality of magnetic particles  120  disposed therein and that can be added to the sample fluid before transferring the sample fluid to the fluid chamber  115 , or can be added to the fluid chamber  115  before or after the sample fluid has been transferred thereto. 
     Suitable magnetic particles  120  for use in the systems and methods described herein include, but are not limited to paramagnetic particles, such as AMPure XP beads available from Beckman Coulter, Inc., Brea, CA. Suitable magnetic particles also include those described in U.S. Pat. Nos. 5,705,628; 5,898,071; and 6,534,262, and in Published PCT Appl. No. WO 2020/018919, published Jan. 23, 2020, all of which are incorporated by reference as if fully set forth herein. 
     As used herein, “ferrimagnetic particles” refers to particles comprising a ferrimagnetic material. Ferrimagnetic particles can respond to an external magnetic field (e.g., a changing magnetic field), but can demagnetize when the external magnetic field is removed. Thus, the ferrimagnetic particles are efficiently mixed through a sample by external magnetic fields as well as efficiently separated from a sample using a magnet or electromagnet but can remain suspended without magnetically induced aggregation occurring. 
     The magnetic particles  120  described herein are sufficiently responsive to magnetic fields such that they can be efficiently moved through a sample. In general, the range of the field intensity could be the same range as any electromagnet as long as it is able to move the particles. For example, the magnetic field has an intensity of between about 10 mT and about 250 mT, between about 20 mT and about 80 mT, and between about 30 mT and about 50 mT. In some examples, more powerful electromagnets can be used to mix less responsive microparticles. In some examples, the magnetic field can be focused into the sample as much as possible. Also, the electromagnets can be as close to the sample as possible since the strength of the magnetic field decreases as the square of the distance. 
     The magnetic particles  120  can be a variety of shapes, which can be regular or irregular. In some examples, the shape maximizes the surface areas of the particles. For example, the magnetic particles  120  can be spherical, bar shaped, elliptical, or any other suitable shape. The magnetic particles  120  can be a variety of densities, which can be determined by the composition of the core. In some examples, the density of the magnetic particles can be adjusted with a coating. 
     The magnetic structure  105  can include a plurality of electromagnets  110   a - d . Although four electromagnets  110   a - d  are depicted in  FIG.  1 A , the number and kind of magnets are not so limited as any number of electromagnets capable of operating according to various aspects of the applicant&#39;s teachings can be used. The four electromagnets  110   a - d  can operate the same as or substantially similar to a quadrupole magnet structure. For example, a magnetic structure  105  can include two electromagnets, three electromagnets, or four electromagnets  110   a - d , as depicted in  FIG.  1 A ; however, there can be more electromagnets as necessary. The electromagnets  110   a - d  can include any electromagnet known to those having skill in the art, including, for example, a ferromagnetic-core electromagnet. The electromagnets  110   a - d  may have various shapes, including square, rectangular, round, elliptical, or any other shape capable of operating according to various aspects of the applicant&#39;s teachings. 
     As shown in  FIG.  1 A , the fluid processing system  100  additionally includes a controller  125  operatively coupled to the magnetic structure  105  and configured to control the magnetic fields produced by the electromagnets  110   a - d . In various aspects, the controller  125  can be configured to control one or more power sources (not shown) configured to supply an electrical signal to the plurality of electromagnets  110   a - d . The electrical signal can be in the form of radio frequency (RF) waveforms, DC current, AC current, or the like. Although RF waveforms are generally used herein as an example of waveforms that can be applied to the electromagnets  110   a - d  to promote mixing of the fluid sample, the types of electrical signals are not so limited, as any type of electrical current capable of operating according to various aspects of applicant&#39;s teachings are contemplated herein. By way of example, a DC signal can additionally or alternatively be applied to one or more of the electromagnets so as to draw magnetic particles to one side of the fluid chamber. A further example may include a DC signal that can be supplied between RF and/or AC signals to facilitate mixing of the sample, or be supplied after RF and/or AC signals so as to aid in fluid transfer from the chamber after the mixing step and/or prevent the aspiration of the magnetic particles. In various examples, the controller  125  can be any type of device and/or electrical component capable of actuating an electromagnet. The controller  125  can operate to regulate the magnetic field produced by each of the electromagnets  110   a - d  by controlling the electrical current passing through a solenoid or coil of each of the electromagnets. The controller  125  can include or be coupled to a logic device (not shown) and/or a memory, such as a computing device configured to execute an application configured to provide instructions for controlling the electromagnets  110   a - d . The application can provide instructions based on operator input and/or feedback from the fluid processing system  100 . The application can include and/or the memory can be configured to store one or more sample processing protocols for execution by the controller  125 . 
     In various aspects, each electromagnet  110   a - d  can be individually addressed and actuated by the controller  125 . For example, the controller  125  can supply RF electrical signals of different phases to each of the one or more of the electromagnets  110   a - d  such that one or more of the electromagnets generate a different magnetic field. In this manner, the magnetic field gradient generated by the magnetic structure  105  within the fluid chamber  115  can be rapidly and effectively controlled to manipulate the movement of magnetic particles  120  within the sample fluid. The RF waveforms and the characteristics thereof (e.g., phase shifts) can be applied to the electromagnets  110   a - d  according to the sample processing protocol. It will be appreciated in light of the disclosure that the magnetic structures  105  can be utilized to manipulate the magnetic particles  120  within the sample fluid in various processes including, without limitation, protein assays, sample derivatization (e.g., steroid derivatization, sample derivatization for gas chromatography, etc.), and/or sample purification and desalting. Following this processing, processed fluid can be delivered to various analytical equipment  140 , such as a mass spectrometer (MS) for analysis. A single layer of electromagnets  110   a - d  (e.g., arranged at a height above the bottom  115   b  of the fluid chamber about the periphery of the fluid container) can be actuated to generate a magnetic field within the fluid chamber  115  that captures and/or suspends the magnetic particles  120  in a particular plane within the fluid chamber. For example, the magnetic particles  120  can be suspended in a particular plane to move the magnetic particles away from the bottom of the fluid chamber during a fluid collection process and/or for processing fluids (e.g., reagents) in a plane above material (e.g., cells adhering to the lower surface of the fluid chamber), where contact with the material on the lower surface of the fluid chamber is to be avoided. 
     In accordance with various examples of the disclosure, the magnetic structures  105  can be incorporated into various fluid processing systems and fluid handling devices. With reference now to  FIG.  1 B , an example of a magnetic structure  105  is depicted as a standalone mixing device. For instance, a magnetic structure  105  can be used as the mixing element of a magnetic mixer or as a mixing element of a vortex-type mixer (i.e., replacing the motor-driven mixing element). The fluid chamber  115  (e.g., a single vial and/or a sample well of a sample plate) can be pressed against an actuator  150  to initiate the controller  125  to actuate the electromagnets  110   a - d  according to applicant&#39;s teachings. In other examples, magnetic structures  105  can be used for mixing magnetic particles  120  within the sample wells of a sample plate, such as a conventional 4, 8, 12, or 96 well sample plate. Magnetic structures  105  can be configured to mix magnetic particles  120  within the sample wells of open-well sample plate (i.e., open-to-atmosphere, sealed with a removable covering or cap, and/or partially enclosed). As shown in  FIG.  1 C , the fluid chamber  115  (i.e., sample well) of a sample plate  160  may fit down within a cavity formed between the electromagnets  110   a - d . In another example, as shown in  FIG.  1 D , a sample plate  160  can be placed on a portion of the fluid processing system  100 , such as on a planar surface  170  thereof, such that the sample well  115  can be arranged adjacent to the electromagnets  110   a - d.    
       FIG.  2 A  depicts an example of an open-well magnetic sample plate. As shown in  FIG.  2 A , a 96-well sample plate  205  can include a plurality of sample wells  215 . Although diamond-shaped sample wells  215  are depicted in  FIG.  2 A , it will be appreciated that the fluid chambers in accordance with the disclosure are not so limited. For instance, the sample wells  215  can have various shapes, including square, rectangular, round, elliptical, or any other shape capable of operating according to various examples of the applicant&#39;s teachings. Each sample well  215  can be surrounded about its periphery by a magnetic structure  210  that includes a plurality of electromagnets  220   a - d . The magnetic structures  210  and the methods of mixing magnetic particles using RF-driven oscillating magnetic fields according to various aspects of the applicant&#39;s teachings can be incorporated into existing sample plate devices, including sample plate devices configured as large, open arrays of sample wells  215 . For example, the magnetic structures  210  can be configured to receive standard sample plate devices, such as industry standard 96-sample well arrays  205 . This can be achieved, for instance, by using electromagnets  220   a - d  and magnetic structure  210  formations having a geometry that corresponds with standard sample well plates. In this manner, fluidic channels and pumps are not required, reducing and even eliminating fluid processing issues relating with these elements, including, without limitation, non-specific binding and carryover (i.e., use of disposable sample plate). In addition, the use of open-well sample systems provides for more efficient methods for sample loading and collection, such as integration with an auto-sampler and other automated fluid-handling systems. In this manner, fluid processing systems according to various examples of the applicant&#39;s teachings may allow for the simultaneous processing of large arrays of samples that is simple and efficient from a fluid manipulation and a mechanical complexity perspective. 
       FIG.  2 B  depicts an example of a partial view of container comprising a layout of a plurality of sample wells  215   a - d  and associated magnetic structures that comprise electromagnets  220   a - f  that demonstrates the sharing of electromagnets  220   a - f  between multiple sample wells  215   a - d . In this example, sample well  215   d  is surrounding by magnetic structure comprising electromagnets  220   a,    220   b,    220   c,  and  220   d.  Electromagnets  220   a  and  220   c  also surround sample well  215   c  that is itself also surrounded by electromagnets  220   e  and  220   f.  Electromagnets  220   a  and  220   c  can generate a magnetic field that penetrates into both sample wells  215   c  and  215   d . Similarly, sample wells  215   b  and  215   d  share electromagnets  220   a  and  220   b  and sample wells  215   a  and  215   c  share electromagnets  220   e  and  220   f.  Electromagnet  220   a  is shared by sample wells  215   a - d  and can generate a magnetic field in all four sample wells. As should be appreciated, this structure can similarly repeat throughout the sample well plate  205  to all sample wells. 
       FIG.  3    schematically depicts an illustrative fluid processing system according to various aspects. As shown in  FIG.  3   , the fluid processing system  300  includes a plurality of magnetic structures  305   a - f  configured to generate a magnetic field gradient within associated fluid chambers  315   a - f . Each magnetic structure  305   a - f  can include a plurality of electromagnets  310   a - l , with certain of the electromagnets  310   a - l  being shared among the magnetic structures  305   a - f . The electromagnets  310   a - l  can be controlled via the application thereto of RF signals having any suitable phase delays. 
     As shown in  FIG.  3   , the electromagnets  310   a - l  are labeled A-D. The phase delay of the electromagnets  310   a - l  of the magnetic structures  305   a - f  can produce a 90° phase shift for adjacent electromagnets. However, the disclosure is not so limited, as other phase shift values can be used according to various aspects of the applicant&#39;s teachings, such as a 180° phase delay, a 270° phase delay, or the like. In various aspects, the actuation of the electromagnets  310   a - l  according to the phase delay equations  320  causes the magnetic particles (not shown) in sample wells  315   a ,  315   e,  and  315   c  to mix in a clockwise motion and the magnetic particles in sample wells  315   b,    315   d,  and  315   f  to mix in a counter-clockwise motion. 
     Mixing fluids using magnetic particles agitated according to various examples of the applicant&#39;s teachings causes the magnetic particles to be dispersed homogeneously within each fluid chamber, providing for optimal exposure and enhanced mixing with the fluid. 
       FIG.  4    depicts an illustrative fluid processing structure and mixing pattern thereof according to various examples of the applicant&#39;s teachings. The graph  405  depicts the magnetic fields  410   a,    410   b  resulting from the application of electric current to the electromagnets  420   a - d  of a fluid processing structure  400  at time intervals T 1 -T 5  according to various aspects of applicant&#39;s teachings. In various examples, the waveforms of the magnetic fields  410   a,    410   b  represent sine waves which generate the exemplary, schematic movement  425  of the magnetic particles within the container to facilitate continuous magnetic particle mixing and improved mixing efficiency. The magnetic fields  410   a,    410   b  have a 90° phase shift relative to one another, with the magnetic field  410   a  corresponding to electromagnets  420   a  and  420   d  and magnetic field  410   b  corresponding to electromagnets  420   b  and  420   c.  In the illustrative depiction of  FIG.  4   , it will be appreciated that the electromagnets  420   a - d  are arranged at different locations relative to the fluid sample such that the orientation of the magnetic field generated by each electromagnet generally differs when the same electrical signal is applied thereto. Likewise, because the electromagnetic pairs (i.e.,  420   a  and  420   d,  and  420   b  and  420   c ) are arranged on opposed sides of the fluid sample, the magnetic field generated by the electrode in each pair is in the same direction  430  when an electrical signal of the same magnitude and of opposite phase are applied to the electromagnet in each pair. Thus, when the exemplary sinusoidal electrical signals of eq. (1)-(4) are applied to electromagnets  420   a - d , respectively, the resulting magnetic field in the sample fluid will vary overtime as schematically depicted in  FIG.  4   , with the pair of electromagnets  420   a  and  420   d  together generating the magnetic field  410   a  and the pair of electromagnets  420   b  and  420   c  together generating the magnetic field  410   b  (magnetic field  410   b  is delayed 90° relative to magnetic field  410   a ), thereby causing the fluid to experience mixing due to the generally counter-clockwise movement  425  and alignment  435  of the particles at the various time points as schematically depicted. 
     It will thus be appreciated in light of the disclosure that different mixing patterns can be effectuated by controlling the RF waveforms applied to the electromagnets of a magnetic structure. For example, with reference to  FIG.  5   , another illustrative mixing pattern for the fluid processing structure of  FIG.  4    is depicted according to various aspects of the applicant&#39;s teachings. As shown, the fluid mixing pattern differs from that shown in  FIG.  4    in that, for example, the controller is configured to apply RF signals of different phase delays to the electromagnets  420   a - d.    
     As shown in  FIG.  5   , when sinusoidal electrical signals are applied to electromagnets  420   a - d , respectively, the resulting magnetic field in the sample fluid will vary over time as schematically depicted, with the pair of electromagnets  420   a  and  420   d  together generating the magnetic field  410   a  and the pair of electromagnets  420   b  and  420   c  together generating the magnetic field  410   b.  In this case, the magnetic field  410   a  is instead delayed 90° relative to magnetic field  410   b,  thereby causing the fluid to be mixed in a general clockwise manner due to the movement  425  of the particles at the various time points as schematically depicted. 
     Although the sinusoidal RF waveforms applied to each of four electromagnets surrounding the containers of  FIGS.  3 - 5    exhibit a ±90° shift relative to the adjacent electromagnets, the disclosure is not so limited. Indeed, it will be appreciated that any type of waveform can be supplied to electromagnets capable of operating according to applicant&#39;s teachings. By way of non-limiting example, the number of electromagnets surrounding each fluid chamber, the phase shifts between adjacent electromagnets (e.g., a 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300°, and 330° phase shifts), and the waveform shape can be varied in accordance with variance aspects of the disclosure. Non-limiting examples of electrical current waveforms can include square, rectangular, triangular, asymmetrical, saw-tooth, or any combination thereof. The type of current supplied to the electromagnets can be modified during operation of a fluid processing system configured according to some embodiments. For instance, at least a portion of the electromagnets may receive an RF waveform with a 90° phase shift, while another portion may receive an RF waveform with a 180° phase shift. In such an embodiment, the phase shift of each portion can be modified during operation of the fluid processing system (e.g., the phase shifts can be switched, synchronized, or the like). At least a portion of the electromagnets can be operated in parallel, sequence, pulsed, or the like. In various aspects, the current supplied to the electromagnets can be controlled according to a processing protocol. The processing protocol can be dynamically altered during operation of the fluid processing system based on various factors, such as feedback, operator input, detection of mixing efficiency, analysis results, or the like. 
     In various examples, the waveform can include different segments with differing amplitudes. For example, the waveform can include an initial segment of relatively short duration with a higher amplitude (boost), followed by a lower-amplitude sustained segment. In various aspects, the amplitude of the sustained segment is below that which would excessively heat the sample. In various embodiments, the boost amplitude is higher but can be tolerated at the beginning of actuation. In various aspects, the sustained segment can be followed by a constant segment. The constant section can comprise a DC signal of constant voltage, including a voltage of zero. The combination of boost, sustained, and constant segments, or any sub-combination thereof, can be sequentially repeated. In various examples, the boost amplitude can be 1-50% higher than the sustained amplitude. In various aspects, the boost amplitude can be 10-30% higher than the sustained amplitude. In various aspects, the boost amplitude can be 20% higher than the sustained amplitude. 
     In another example, as shown in  FIG.  15   , vertically oriented neodymium magnets  330  are an example of a separate, permanent magnet used to draw or pull down the beads within a chamber. The magnets  330  can be used within a tray  340  or other holding mechanism. When neodymium magnets are utilized, by example, such magnets are arranged in a single row on opposing sides of at least one chamber or row of chambers. In such an example, one row of magnets  330  would be arranged such that a north pole oriented upward and in the opposing row the south pole would be oriented upward. A plate  350 , by example made of steel, can be placed below the magnets  330  to connect the magnets  330  to a magnetic circuit. Further, a motor  360  can be coupled with one or both of the tray  340  and plate  350  such that when the one or both of the tray  340  and plate  350  are inserted in the guide bracket  370 , the motor  360  can cause movement of the tray  340 . Such movement is to a position adjacent to the chambers to pull down the beads. During mixing, the tray  340  moves the magnets  330  away from the chambers to allow the beads to remain in suspension. 
       FIG.  13    is another example of the separate, permanent magnet used to pull-down beads. It is shown here in the pull-down position. The permanent magnet is the bar closest to the bottom of the tube, (the tapered, conical part, shown upside down in the current figure). In the retracted position, the tray pulls the magnetic bar away from the sample tubes. With  FIG.  13 B  being a view from the top,  FIG.  13 A  a view from the right, and  FIG.  13 C  a view from the front. 
     Additionally, as noted herein, the electromagnets  420   a - d  can alternatively have a DC signal applied so as to generate a static magnetic field so as to draw magnetic particles to one side of the fluid chamber (and out of the bulk fluid) so as aid in fluid transfer from the chamber after the mixing step and/or prevent the aspiration of the magnetic particles, by way of non-limiting example. In various aspects, a separate magnet is used to draw the particles to one side of the chamber. In some examples, the separate magnet is a permanent magnet. In another example, the separate magnet is movable to be positioned immediately adjacent the container, at a desired height relative to the bottom of the container, to draw the particles. In some examples, the separate magnet can be configured to slide horizontally to the position immediately adjacent the container. In some examples, the separate magnet may have its magnetic axis aligned perpendicular to the vertical axis of the container. In another example, the separate magnet may have its magnetic axis aligned parallel with the vertical axis of the container. 
     With reference now to  FIGS.  7 A-B , these figures provide examples of a fluid processing system  700  in accordance with various examples of the disclosure. With reference first to  FIG.  7 A , the fluid processing system  700 , depicted in exploded view, comprises a base plate  710 , a printed circuit board (PCB)  720 , an plurality of electromagnetic structures  730 , and an upper plate  740  defining a plurality of sample wells  740  extending from a substantially planar upper surface  740   a  thereof. It will be appreciated by a person skilled in the art that that though the upper plate  740  is depicted in  FIG.  7 A  as a 96-well format in which the sample wells have a substantially circular cross-sectional shape, the upper plate  740  can include any number of sample wells  742  exhibiting a variety of cross-sectional shapes and maximum volumes as discussed above. For example, in accordance with the disclosure, each of the open sample wells  742  can be filled or partially-filled with various volumes of the fluid sample, thereby allowing for the reduction or expansion of the sample volume to be processed, depending, for example, on the availability or expense of the sample and/or on the requirements of a particular assay. It will further be appreciated that the upper plate  740  can be manufactured of any material known in the art or hereafter developed in accordance with the disclosure such as a polymeric material (e.g., polystyrene or polypropylene), all by way of non-limiting example. Additionally, as known in the art, the surfaces can be coated with a variety of surface coatings to provide increased hydrophilicty, hydrophobicity, passivation, or increased binding to cells or other analytes. In some examples, the bottom surface  740   b  of the upper plate  740  can be configured to engage (permanently or removably) with the lower portions of the fluid processing system, as discussed below. For example, in some aspects, the bottom surface  740   b  can include depressions formed therein for engaging the upper end  730   a  of the electromagnetic structures  730  or bores through which a portion of the electromagnetic structures can extend to be disposed around and about each of the sample wells  742 . 
     With reference now to the lower portions of the fluid processing system  700 ,  FIG.  7 A  depicts a PCB  720 , a base plate  710 , and a plurality of electromagnetic structures  730 . As shown, the PCB  720  comprises a plurality of electrical contacts  722  to which an electrical signal can be applied by a power source (not shown) and to which the electromagnetic structures  730  can be electrically coupled. As otherwise discussed herein, the PCB  720  can be wired such that each electromagnetic structure can be individually addressed and actuated by a controller through the selective application of electrical signals thereto. Additionally, the PCB  720  includes a plurality of holes  724  through which a portion of the electromagnetic structures can extend to make electrical contact with the base plate  710 . For example, as shown in  FIG.  7 A , the electromagnetic structures  730  can include a mounting post  732  that extends through the holes  724  when the electromagnetic structures  730  are seated on the electrical contacts  722 , and such that conductive leads associated with the mounting posts  732  can be electrically coupled to the base plate  710 . As shown, the base plate  710  can include bores corresponding to the mounting posts  732  so as to ensure that the mounting posts  732  are in secure engagement therewith. The base plate  710  can also be coupled to a power supply (or grounded) to complete the circuit(s) such that one or more electrical signals can be applied to the plurality of electrical contacts  722  of the PCB  720  to allow an electrical current to flow through the electromagnetic structures  730  in accordance with the disclosure. As shown in  FIG.  7 A , the electromagnetic structures  730  can include an upper post around which is coiled a conductive wire  734  that is electrically coupled to the contacts  722 , and which terminates in an upper end  730   a.  It will thus be appreciated that as current flows between the electrical contacts  722 , the wire coil  734 , upper end  730   a,  and the metal base plate  710  (current direction depends on the voltage of the signal applied to the particular contacts  722  of the PCB  720 ), the wire coil  734  acts as a solenoid to thereby generate a magnetic field through and about the wire coil  734 , the directionality of which is dependent on the direction of the current. The upper end  730   a  of the electromagnetic structures  730  can have a variety of shapes (e.g., substantially the same cross-section shape as the post around which the wire is coiled), though it has been found that the upper end  730   a  can be preferentially formed from a conductive material and shaped to correspond to the peripheral surfaces of the sample wells, so as to act as a lens that concentrates the magnetic field and/or increases its uniformity within the sample wells. As should be appreciated, the examples embodied by  FIGS.  1 - 5  and  7    are directed to apparatuses and methods wherein the magnetic structures are arranged about a fluid container in only a single horizontal layer. In this configuration, the generation of magnetic fields causes mixing of particles in substantially the x-y plane which describes just one aspect of the disclosure. As will be detailed further in this disclosure, such systems and methods can be modified in a manner in which additional magnetic fields are generated to cause mixing of particles in the z direction as well. 
     It will thus be appreciated in light of the disclosure that different mixing patterns can be effectuated by controlling the RF waveforms applied to the electromagnets of a magnetic structure. 
     While cylindrical members have been described above in describing the tube  115 , it should be appreciated that other shapes with varying cross-sectional shapes can also be utilized include triangular, square, rectangular or any other multi-sided shape. 
     The magnetic assemblies and/or magnetic structures that comprise electromagnets can be placed outside of the metal tube or can be part of the metal tube itself and directly integral to metal at or near the tip. 
     It should be appreciated that teachings described herein can be modified and adapted to meet specified needs as can be determined by ordinary skilled persons. 
     The magnetic structures and fluid processing systems described in accordance with the applicant&#39;s disclosure can be used in combination with various analysis equipment known in the art and hereafter developed and modified in accordance with the disclosure, such as an LC, CE, or MS device. With reference now to  FIG.  6   , one illustrative fluid processing and analysis system according to various aspects of the applicant&#39;s teachings is schematically depicted. As shown in  FIG.  6   , a fluid processing system  610  can be configured to process fluid samples using magnetic structures and an open-well sample plate in accordance with some embodiments. The processed fluid can be collected from the fluid processing system  610  using any of a manual sample loading device (e.g., pipette, a multi-channel pipette) or various automated systems such as a liquid handling robot, an auto-sampler, or an acoustic liquid handling device (e.g., Echo® 525 liquid handler manufactured by LabCyte, Inc. of Sunnyvale, Calif.), all by way of non-limiting example. The processed fluid can be transferred using various fluid transfer devices, such as a vortex-driven sample transfer device. As noted above, the sample removed from one sample well can be added to a different sample well on the plate for further processing steps or can be delivered to the downstream analyzer. For example, in some aspects, the processed sample can be delivered to an LC column  615  for in-line LC separation, with the eluate being delivered to the ion source  620  for ionization of the processed analytes, which can be subsequently analyzed by a DMS  625  that analyzes the ions based on their mobility through a carrier gas and/or a mass spectrometer  630  that analyzes the ions based on their m/z ratio. In some aspects, processed samples can be transferred directly to an ion source  615 , with separation being provided by a differential mobility spectrometer (DMS) assembly, for example, in-line with a MS as described in U.S. Pat. No. 8,217,344. Fluid processing systems described in accordance with the applicant&#39;s disclosure in combination with a DMS assembly for chemical separation may eliminate the need for a LC (or HPLC) column for processing samples for MS analysis. In various aspects, processed samples can be introduced into analytical equipment, such as an MS, using a surface acoustic wave nebulization (SAWN) apparatus, an electrospray ionization (ESI) device, and a matrix assisted inlet ionization (MAII) source. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, can be desirably combined into many other different systems or applications. It will also be appreciated that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein can be subsequently made by those skilled in the art which alternatives, variations and improvements are also intended to be encompassed by the following claims.