# Patent

## Title
Focusing chamber

## Abstract

Aspects of the invention relate to devices and methods of use thereof for concentrating, positioning and/or manipulating agents within a fluid, including but not limited to genomic DNA.

## Background
RELATED APPLICATION
This application claims priority to provisional patent application Ser. No. 61/102,578, filed Oct. 3, 2008 and entitled “FOCUSING CHAMBER”, the entire contents of which are incorporated by reference herein.


FEDERALLY SPONSORED RESEARCH
This invention was made with Government support under the Homeland Security Advanced Research Projects Agency. The Government has certain rights to this invention.


BACKGROUND
1. Field
Aspects of the invention relate to devices and methods of use thereof for harvesting, isolating, and/or manipulating agents, including but not limited to genomic DNA.
2. Discussion
Preparation and concomitant preservation of genomic DNA, according to many conventional techniques, is often time consuming, laborious and may require operators to have skills in handling DNA samples. Moreover such techniques are limited in the size of DNA that can be effectively handled. There exists a need to reduce the time, labor, and/or skills required to prepare essentially intact genomic DNA and other agents of similar length.
SUMMARY
The invention in its broadest sense provides devices and methods of use thereof for positioning or manipulating or concentrating agents within a fluid, including but not limited to polymers such as genomic DNA. Aspects of the invention allow the agents to be concentrated into relatively small portions of the fluid. This may provide a higher concentration of the agent within a portion of the fluid, which in turn may result in higher recovery of the agent from the fluid as the agent undergoes processing.
Certain aspects of the invention relate to using a chamber for positioning or manipulating an agent, such as genomic DNA. In some aspects, the chamber is minimally comprised of an inlet port, a porous substrate that allows fluid but not the agent of interest to pass through, and at least one side port. The chamber may be operated in a first mode where a fluid containing agents is introduced into the chamber through a first fluid port and flowed through a substrate in the chamber. A second flow of fluid may be introduced through one or more second fluid ports positioned about the substrate in the chamber. The second fluid flow at least partially surrounds the first fluid flow to direct the first fluid flow and any agents contained therein toward a portion of the substrate. The agents may then be positioned on the central portion of the substrate. Flow may be reversed through the first fluid port to move any agents positioned on the substrate out of the chamber in central streamlines that exit the chamber through the first fluid port. Flow may also be removed from about the central streamlines to separate fluid flow that lacks agents from the central streamlines that exit the chamber.
According to one aspect, a method is disclosed positioning agents in a fluid flow. The method includes providing a chamber having a substrate. A first fluid containing agents is flowed through a first fluid port and through the substrate in the chamber. A second fluid flow is flowed through one or more second fluid ports positioned about the substrate in the chamber. The second fluid flow at least partially surrounding the first fluid flow to direct the first fluid flow and any agents contained therein toward a central portion of the substrate. The agents are positioned on the central portion of the substrate. Flow through the first fluid port is reversed to move any agents positioned on the substrate out of the chamber in central streamlines that exit the chamber through the first fluid port. Flow from about the central streamlines is removed to separate fluid flow that lacks agents from the central streamlines that exit the chamber.
According to another aspect, a composition comprises isolated nucleic acids varying in length from 0.1 megabases to about 1 megabase in a fluid having a volume between about 30 uL to about 40 uL.
According to yet another aspect, a method is disclosed for positioning agents in a fluid flow. The method comprises providing a substrate; flowing a first fluid containing agents through the substrate, and flowing a second fluid flow through the substrate. The second fluid flow at least partially surrounds the first fluid flow to direct the first fluid flow and any agents contained therein toward a central portion of the substrate. The agents are positioned on the central portion of the substrate. Flow through substrate is reversed to move any agents positioned on the substrate away from the substrate in central streamlines of fluid moving away from the substrate.



BRIEF DESCRIPTION OF DRAWINGS
The accompanying figures are not intended to be drawn to scale. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the figures:
FIGS. 1a and 1b are views of a chamber, according to one embodiment of the invention;
FIG. 2 shows a cross sectional view of an embodiment of a chamber that illustrates the construction and placement of side ports, according to one embodiment;
FIG. 3 shows a velocity profile, according to one embodiment, near a side port of a chamber during a separation mode;
FIG. 4 shows an embodiment of a chamber that includes jets that may be used to agitate contents of the chamber;
FIGS. 5a-5f show, schematically, an embodiment of the chamber in various modes of operation;
FIGS. 6a-6h show, schematically, various stages of an operating protocol for DNA isolation and digestion in a chamber;
FIG. 7 shows pulse field gel of elution fractions obtained following an operating protocol like that of Example 2;
FIGS. 8-12 show visual representations of modeling results discussed with respect to Example 7;
FIG. 13 shows, schematically, one manner in which a reverse elution mode may be performed, with fluid introduced to the chamber through side ports;
FIG. 14 shows, schematically, a velocity provide of fluid exiting a chamber through a central port, according to one embodiment;
FIG. 15 shows, schematically, a reverse elution mode occurring within a chamber with fluid being removed through side ports;
FIG. 16 shows, schematically, a chamber having a second set of side ports and reverse elution being performed with fluid removed from the chamber through the second set of side ports and fluid introduced to the chamber through the first set of side ports; and
FIG. 17 shows another embodiment of a chamber that may be used to concentrate sample.



DETAILED DESCRIPTION
The invention in based in part to methods and chambers (referred to herein interchangeably as a “focusing chamber” or a “reaction chamber” or a “fluidic chamber”) that may be used to concentrate a sample to a smaller volume of fluid. Concentrating samples may prove useful when relatively small volumes are available for analysis. Additionally or alternatively, concentrating a sample may prove useful in introducing a sample from a macro-scale environment, such as from where a sample may have been collected, to a micro-scale or nano-scale environment, such as where analysis may be performed on the sample.
Long DNA fragments (0.1-1 Mb) may used in some polymer physics studies, such as those that implement single-molecule approaches. Some methods and embodiments of chambers with membranes may be used to help reduce the labor and time associated with processing such DNA fragments. By way of example, some methods and chambers may be capable of extracting and purifying high quality genomic DNA and additionally perform various reactions such as restriction enzyme digestion, intercalation with fluorescent dyes, and labeling with sequence-specific tags. According to one embodiment, a 125 μl volume reactor performs preparations substantially faster than routine procedures. Additionally, the chamber may be completely automated.
Embodiments of chambers may also be capable of working with smaller bacterial loads (such as 106 cells vs. 108 cells). Such embodiments may use an axisymmetric flow focusing mode where flow fields are created within the chamber to focus the bacterial cells to a small area at the center of the membrane. This arrangement may help to limit the interaction of deformable DNA coils with membrane nanopores, which may lead to decreased sample losses. Such embodiments may also enable elution of the sample to a smaller volume, even up to 5 times higher concentrations, 10 times higher concentrations, and even greater than 10 times higher concentrations. As discussed herein, flow may be split during the elution process to further increase sample concentrations by removing, from the flow, fluid that does not contain sample. Such techniques may help increase concentrations by up to an order of magnitude or even greater.
According to some aspects, experimental and numerical characterization of the flow fields may be used to optimize performance of methods and/or chamber design. By way of example, experimental study have been performed with 160 kb DNA and 240 kDa proteins. Numerically, a semidilute DNA solution on the membrane has been modeled with deGennes' reptation model. Such models may be used to estimate flow fields capable of carrying out reactions and purification of genomic DNA on a membrane without shear degradation.
According to one embodiment of a chamber, DNA may be successfully extracted from E. coli cells, purified, specifically digested with NotI restriction enzyme, and intercalated with POPO-1. According to some embodiments DNA fragment up to or greater than 1 Mb-long may be eluted from the chamber.
Different types of chamber may be used to carry out methods of the invention. One embodiment of the chamber 10, as shown in FIGS. 1a and 1b, minimally comprises a central port 12, a porous substrate 14 that allows fluid but not the agents of interest to pass through, a reservoir 16 below the substrate, and at least one side port 18. FIGS. 1a and 1b show a schematic view and a cross-sectional view of a chamber, according to one embodiment of the invention. As illustrated, the chamber comprises a diffuser 20, a body section 22, and a porous substrate 14 that lies within the body section. A flow region 24 lies between the diffuser 20 and a first side of the substrate, and a reservoir lies on an opposite side of the substrate. A central port 12 (alternately referred to herein as a fluid introduction port, an inlet port, or injection port) is positioned substantially centrally in the diffuser 20 and may be used to move fluids into and/or out of the flow region of the chamber. One or more side ports 18 (alternately referred to herein as fluid exit ports) are positioned about the flow region, and near the first side of the substrate. The one or more side ports may be used to direct flow, typically introduced through the central port, in different directions. Waste ports 26 (alternately referred to herein as reservoir ports) provide fluid access to the reservoir 16 and may be used to introduce and/or remove fluids therefrom.
Embodiments of the chamber may be constructed with different configurations and dimensions, some examples of which are discussed herein. By way of example, the diffuser may provide a diffusive flow pathway between the central port and the flow region, which, in many embodiments, may laterally spread the flow of fluid introduced through the central port to promote even distribution of agents about the substrate. By way of another example, the chamber shown in FIG. 17, may be used to carry out various methods of the invention, as is described in greater detail herein.
The diffuser may be shaped differently according to various embodiments. The diffuser is typically designed to smoothly widen or diffuse flow that enters the flow region from the central port without subjecting agents to excessive shear forces. As shown in FIGS. 1a and 1b, the diffuser may be shaped like a symmetric, truncated cone with substantially linear sides that form an angle of about 60 degrees with a line that extends along a central axis of the central port. It is to be appreciated, however, that the diffuser may include walls that are angled differently, or that are gently curved instead of being linear, as aspects of the invention are not limited in this regard. According to some embodiments, the diffuser may include flat sides, appearing more like a truncated pyramid. Other embodiments may also include asymmetric diffusers.
Various fluidic modeling techniques, such as flow testing with dyes and/or computational fluidic modeling may be used to optimize the diffuser shape for various operating conditions and/or to promote the even distribution of agents about the substrate that have been introduced through the central port. Similar techniques may be used to optimize the diffuser for the minimization of shear forces that occur in the flow region or to accomplish other effects.
The central port is typically positioned in the central portion of the diffuser and, as shown in FIGS. 1a and 1b, is configured to direct a flow of fluid orthogonally toward the substrate of the chamber. According to other embodiments, however, the central port may be offset to one side of the diffuser, and in this respect, the term ‘central’ as used to describe the central port should not be found to be limiting. Additionally or alternatively, the central port may direct fluid flow toward the substrate at an angle, instead of orthogonally. It is also to be appreciated that embodiments of the chamber may include a plurality of central ports positioned about the diffuser, and in this respect, the term ‘central port’ should not be construed to refer solely a single fluid port.
The diffuser and/or central port, when described as being substantially opposed to the substrate, are understood to be positioned to direct fluid to impinge on a surface of the substrate. That is, at least a portion of the fluid flow is directed to intersect with the substrate.
The porous substrate (also referred to herein as a membrane or a filter) is typically positioned to receive flow that is introduced to the chamber from the central port, as shown in the embodiment of FIGS. 1a and 1b, such that agents in flow passing therethrough may be received on the substrate. The substrate typically has a threshold size that relates to the porosity of the substrate and that describes the size or molecular weight of agents or other constituents that are prevented from passing therethrough. According to some embodiments, the substrate has a threshold size that prevents the passage of cells, of genomic DNA, of proteins, and the like, although other threshold sizes are possible, as aspects of the invention are not limited in this respect. Some examples of membranes include ultrafiltration membranes. According to many embodiments, the membrane may be chosen such that it does not have an affinity for agents that may be processed in the chamber so that the membrane does not prevent the agent from being removed from the chamber.
The substrate may comprise circular shaped, removable filter material that is supported on a porous frit 28 in the chamber, as shown in FIGS. 1a and 1b. Some operating protocols may utilize substrates with different threshold sizes, or that are constructed differently, and may benefit from being removable from the chamber. The substrate of some embodiments may be sandwiched between a frit on the reservoir side and a supporting structure on the flow region side, such that the substrate is supported when/if flow is introduced from the reservoir to the flow region of the chamber, such as during elution. According to some embodiments, the substrate itself is relatively stiff, such that a frit or other supporting structure may not be required.
Embodiments of the chamber may include a body section that defines a wall of the chamber that lies between the substrate and the diffuser. As shown in FIGS. 1a and 1b, the diffuser is substantially cylindrical in shape and extends for a relatively short distance between the diffuser and the substrate. In other embodiments, the diffuser may be shaped differently, or the diffuser may extend directly to the substrate, such that there is no body section at all in the chamber.
One or more side ports are positioned about the flow region, generally adjacent to the substrate, as shown in FIGS. 1a and 1b, where the side ports are positioned about the circumference of the body section, or circumferentially. The one or more side ports, generally speaking, are positioned to allow fluid to flow in the flow region, above the substrate without also passing through the substrate.
Embodiments of the chamber may have multiple side ports, and in some embodiments have 2 side or 4 side ports positioned at even intervals about the chamber, such as on the body section. It is to be appreciated that embodiments of the chamber may have any number of side ports, such as 8 side ports, 11 side ports, or 16 side ports positioned evenly about the chamber, as illustrated in FIG. 2, or even a continuous slot or plenum that defines a substantially continuous side port extending partially or continuously about the flow region of the chamber. The one or more side ports are typically positioned so that fluid flow, initially directed toward the substrate, may change direction, such that at least a portion of the fluid flow moves toward a direction that is substantially parallel to the surface of the substrate facing the flow region. In many embodiments, side port(s) are positioned so that portions of fluid flow, initially directed toward the substrate, may move toward side ports positioned about the perimeter of the body section of the chamber, and thus move laterally over a surface of the substrate that faces into the chamber.
Construction and placement of the side ports may be guided by flow testing and/or computational analysis to minimize any low flow or dead zones in the flow region, reduce shear that might be imparted to agents, and/or to promote favorable velocity gradients through the flow region, such as during separation modes.
FIG. 2 shows a cross-sectional top view of one embodiment of a chamber taken laterally across and cutting through the side ports 18. As shown, each of the side ports has a smooth, curved opening to the flow region. Such a design may help minimize or eliminate any eddies, reduced flow, or dead regions that might otherwise be present in the flow region when operated in a separation mode. Reducing or eliminating such dead zones can promote more efficient separation of agents from non-agents, during separation modes, or may help to better accommodate more even distribution of agents during press down modes, among other benefits.
FIG. 2 also shows a cavity 30 that may be incorporated into embodiments of the chamber to promote more equal flow through each of the side ports. The cavity, as shown, is in fluid communication with four ports 32 that are connected to an external pump or valve that controls the proportion of flow that passes though the side ports. Any vacuum (or positive pressure) produced by the external pump, in turn, causes a vacuum (or pressure) in the flow equalization cavity. The cavity allows the vacuum (or pressure) to equalize across each of the side ports, and thus promotes even flow rates through each of the side ports. It is to be appreciated that the flow equalization zone may help accomplish a substantially symmetric fluid flow through the flow region (about an axis that lies along the central port), which may promote more efficient operation of the chamber. It is also to be appreciated that the cavity is but one example of features that may be used to equalize flow across multiple side ports, and that other methods and features for tuning flow may also be employed.
Embodiments of the chamber, and particularly those portions that are in contact with the flow region, like the central port, the diffuser, the side ports, the body section, and the substrate, may be designed to promote particular flow conditions. For instance, according to some embodiments, the chamber may be constructed to promote laminar flow so that shear forces acting on agents therein may be minimized. Additionally or alternately, the chamber may be constructed to promote flow through the side ports with a velocity profile, as shown in FIG. 3, where flow near the substrate is slower than flow that is further from the substrate. Such velocity profiles may prove advantageous during separation modes of the chamber, as discussed in greater detail herein.
As shown in FIG. 1a, the overall shape of the chamber may be cylindrical with a cone shaped diffuser. However, it is to be appreciated that embodiments of the chamber may be shaped differently as well, including oblong or ovalized shapes, or even shapes that include angular sides, like chambers that are square or rectangular in cross section.
Embodiments of the chamber may have features to promote mixing, such as microscale jets 34 that create a stirring motion to agitate reactants that are spread on or about the substrate. Microscale jets may be issued from small holes, such as micron sized holes, in the diffuser, according to one embodiment illustrated in FIG. 4. The jets may carry a relatively large momentum even at low flow rates and may agitate the agents spread on the substrate without substantial loss of the agents through side ports.
Embodiments of the chamber may also be equipped with features to regulate temperature in the flow region. According to one embodiment, a frit that lies below and supports the substrate is made of a thermally conductive material, like stainless steel, and may be heated or cooled by an external source, like a thermoelectric module, to regulate temperature. Additionally or alternately, fluid may pass through the reservoir to cool or heat the reservoir side of the substrate/frit to rapidly cool or heat the chamber. The chamber may also be equipped with other devices, like a radiant heater that heats fluid in the chamber through non-contact methods, or like an inline heater that heats fluids entering the chamber which, in turn, may help maintain uniform temperature conditions throughout the chamber volume.
As described herein, a reservoir may be positioned on a side of the substrate opposite to the flow region, as shown in FIGS. 1a and 1b. Broadly speaking, the reservoir receives fluid that has passed through the substrate from the flow region prior to the fluid being evacuated from the chamber through one or more waste ports. It is however to be appreciated that the reservoir may be used to accomplish other effects, such as heating and/or cooling of the flow region, as discussed herein. Additionally, some embodiments may not include a reservoir but, instead may directly pass fluids passing through the substrate to an outflow tube.
MODES OF OPERATION
The chamber may be operated in several different modes, including a press-down mode, a separation mode, an elution mode, a reacting mode, and a focusing mode, among others. Each of these modes is illustrated schematically in FIGS. 5a-5f, 13, 15, and 16.
The chamber may be operated in a press down mode (also referred to herein as an injection mode) to position agents or other constituents near the substrate or simply to introduce agents to the flow region where they may be acted upon. The agents or other constituents introduced during a press down mode may have been present in the flow region at the beginning of the mode, or may be introduced to the chamber through the central port during the press down mode. In a press down mode, as shown in FIG. 5a, fluid that may contain agents is introduced into the flow region from the central port. The fluid passes through the flow region, the substrate, the reservoir, and then exits the chamber through the waste ports. Any agents or other constituents present in the fluid that are larger than a threshold size of the substrate will be retained in flow region, and “pressed down” or held against the substrate. There is typically no flow through the side ports during a press down mode, to prevent the fluid and any agents therein from exiting the flow region although, according to some embodiments, some flow through the side ports may be acceptable.
A separation mode may be used to separate agents and other constituents that reside within the flow-region. As shown in FIG. 5b, fluid is introduced to the chamber from the central port, and a first portion of the fluid flows through the flow region and the substrate, and then exits the chamber through the reservoir/waste ports. A second portion of the fluid flow enters the flow region from the central port and then exits the flow region through the plurality of side ports that are positioned on opposed sides of the chamber. Broadly speaking, the first portion of the fluid flow urges agents and/or other constituents hydro dynamically toward the substrate. The other constituents or agents that migrate away from the substrate and into the flow region, such as through diffusion, are urged through the side ports and out of the chamber by the second portion of the fluid flow. The combination of the first and second portions of fluid flow allow the other constituents to be separated from agents within the chamber.
Embodiments of the chamber allow separation of agents from other constituents primarily as a result of two factors. First, flow through the substrate may create a concentration of agents and other constituents at the substrate. For larger components, typically the agents, the concentration gradient may decrease more rapidly at points further from the substrate. Second, diffusion of components (agents or other constituents) away from the substrate occurs and may be driven by the concentration gradient within the chamber. Smaller components (often the other constituents) typically have concentration gradients that decrease less rapidly, meaning essentially that portions further from the substrate will be more greatly populated by other constituents than agents (taken as percentages of the total amounts of other constituents and agents, respectively), since the other constituents typically have greater diffusion rates than the agents. These factors, as illustrated in FIG. 3, allow the chamber to be used in a separation mode to remove other constituents from the chamber that have concentration distributions extending away from the substrate. Due to their faster diffusion rates, smaller components (typically the other constituents) tend to quickly reestablish the concentration gradient and repopulate the layers of liquid further from the substrate that have exited the chamber through side ports. Thus, allowing the other constituents to be efficiently removed from the chamber, while slowly diffusing larger components (typically the agents) may be retained on or about the substrate. Similarly, the buffer in the chamber can be exchanged efficiently using the separation mode (also referred to herein as selective retention).
The flow of fluid toward the side ports may have greater velocity at points that are further from the substrate, as shown in FIG. 3, due to boundary layer effects of the fluid flow near the substrate. The flow may be linearly approximated in the region above the substrate, as is also represented in FIG. 3. As discussed herein, this phenomenon may aid with the removal of smaller components from the reaction chamber, whose distribution about the membrane extends further from the membrane than the distribution of large particles, and thus into the flow that is moving radially toward the side ports, or at least that is moving radially toward the side ports with a greater velocity.
Embodiments of the chamber utilize other devices to urge agents and/or constituents about a chamber. By way of example, electric fields, and/or magnetic fields may be used in combination with or in place of the flow fields and diffusion mechanisms discussed herein.
During an elution mode, the contents of the flow region, including any agents therein, exit the chamber through one or more of the central port and/or side ports. According to one embodiment, as shown in FIG. 5c, fluid is introduced to the chamber through each of the waste ports and urges any agents or non-agents in the flow region out of the chamber through the central port. In this embodiment, the side ports may be closed to prevent fluid from passing there. It is to be appreciated, however, that elution may take place through other approaches, such as by introducing fluid to the flow region through a first portion of the side ports and out of the flow region through a second portion of side ports, or through other schemes. Additionally or alternatively, elution may be performed electrokinetically by creating an electric field that directs agents out of the flow region through the central and/or side ports.
Reactions are allowed to occur in the flow region of the chamber during a reaction mode. According to some embodiments, reaction modes may occur while fluid is flowing into the flow region from the central port and out of the flow region through the substrate, as shown in FIG. 5d. Here, the fluid flow may concentrate reactants about the substrate within the chamber to effectively create a localized, reaction zone within the chamber for agents and other constituents, like reagents that are introduced to the flow region. Such reagents may be introduced while agents, previously introduced to the chamber, are being held at the substrate. Alternately, reagents may be introduced to the chamber with agents in a common fluid flow. Alternately, fluid flow through the reaction may be halted altogether during a reaction mode, which may allow greater diffusion of reactants throughout the flow region.
Reaction modes may also involve controlling the environment of the flow region to promote reactions, such as by controlling the temperature, light conditions, and the like.
The chamber may be operated in a focusing mode to position agents on a select portion of the substrate, such as a central portion. As shown in FIG. 5e, a first fluid that includes agents is introduced to the flow region through the central port while a second fluid is also introduced to the flow region through the side ports. The second fluid flow may at least partially or completely circumferentially surround the first fluid as both the first and second fluids pass through the substrate into the reservoir. Agents in the first fluid are held at a central portion of the substrate through which the first fluid passes and in this regard are focused to the central portion of the substrate. It is to be appreciated that similar methods may be used to position agents on portions of the substrate other than the central portion, as aspects of the invention are not limited in this respect.
The ratio of fluid that passes through the central port versus the side ports may be altered to change the degree of focusing. Increasing the proportion of flow that enters the chamber through the side ports, relative to the proportion entering through the central port may reduce the size of the central portion of the membrane onto which agents are focused. All else constant, however, it may take longer to pass a similar volume of fluid containing agents from the central port and through the membrane when flow though the central port occurs at a lower flow rate.
The chamber may also be used, in a focusing mode, to position agents in particular streamlines of fluid that exit the chamber, such as central streamlines. This mode may also be referred to as reverse elution. Fluid may be moved from the reservoir and through the substrate to lift agents off of the substrate and out of the chamber through the central port, as shown in FIG. 5f. When agents are only present on central portions of the substrate, the flow that exits the central port will only include agents in its central streamlines 13. Flow through the side ports may be prevented during such reverse elution modes. Alternatively, some flow may be introduced through the side ports to further direct the fluid that enters the flow region from through the substrate toward central portions of the flow exiting the chamber through the central port, as shown in FIG. 13. A reverse elution mode like that of FIG. 13, may serve to further direct agents toward central streamlines 13 of fluid that exit the chamber through the central port.
Operating the chamber in a focusing mode may also help concentrate sample within a fluid in the direction of flow. That is, agents introduced to the chamber in a fluid may be spread apart from one another such that they contact the membrane at different points in time. Operating the chamber in focusing mode, however, causes them to be grouped or concentrated closer to one another, such that when eluted the agents are closer to one another in the direction of flow as well as being grouped in central streamlines of flow exiting the chamber. This may help the chamber achieve higher peak concentrations of agents.
A reverse elution mode performed on agents located in a central portion 15 of the membrane may result in the agents being grouped close to one another, in the direction of flow, as the agents exit the chamber. FIG. 8 shows how, generally speaking, streamlines that pass through central portions of the membrane may be required to travel a shorter distance than streamlines passing through peripheral regions of a membrane. This may be true whether the chamber is operated in a press down mode, a focusing mode, or a reverse elution mode. Given this, streamlines that pass through or emanate from peripheral portions of the membrane, including any agents carried by these streamlines, may reach the central port later than those emanating or passing through central portions of the membrane. The different times that it takes fluid emanating from the different portions of the membrane to reach the central port can cause agents that are moved from different portions of the membrane to reach the central port at different time, and thus be spread apart from one another in the direction of flow. Having the agents focused to a central portion 15 of the membrane, however, tends to equalize the distance that each of the agents travels during reverse elution, thereby helping to concentrate the agents in the direction of flow during reverse elution.
Focusing agents toward a central portion 15 of the membrane prior to performing reverse elution may also help position agents in streamlines that have a velocities that are more consistent with one another. Internal flow through tubes and the like may often be characterized with a parabolic velocity profile 17, as shown in FIG. 14 where the length of the arrows is proportional to flow velocity, or at least with slower flow velocities near the internal walls of the tube or other flow conveying structure. Streamlines toward the center of flow 19 generally have velocities that are greater and that are more consistent with one another than flow near the internal walls. In this respect, agents positioned in the central streamlines 19 may be moved from the chamber at velocities that are more consistent with one another. This may help further concentrate agents as the exit the chamber through the central port. Positioning agents within streamlines having velocities more consistent with one another may also help keep the agents closer together in a smaller plug or bolus as the agents travel from the chamber and toward other devices in the system. Importantly, the bolus or plug may be 10 times smaller, 100 times smaller, or even 1000 times smaller when compared to a bolus of agents that travels across all streamlines of a similarly sized tube and over a similar distance. As will be recognizable to those of ordinary skill in the art, given the range of velocities in various streamlines of a laminar flow, if agents were located throughout the flow cross-section, then once the fluid has traveled these distances (after leaving a chamber), the agents would be dispersed across a greater volume. If on the other hand, the agents are present in only the central streamlines, then the agents are expected to travel at significantly the same velocity, thereby preventing substantial dispersion through the post chamber distance.
Concentrating agents closer together in the direction of flow and/or in central streamlines may provide several benefits. Sample eluted from the chamber may include higher peak agent concentration, including higher peak DNA concentration (when the agent includes DNA). Additionally or alternatively, improved agent recovery may be achieved from sample provided to the chamber. Other benefits may also be realized. For instance, agents may be kept closer together in streamlines of more consistent velocities, as described above, as aspects of the invention are not limited in this respect.
Positioning agents in the central streamlines may prevent dispersion of sample that is conveyed from the chamber in a tube. As mentioned above and shown in FIG. 14 central streamlines move through tubes at more consistent velocities. As such, agents positioned in these central streamlines may move through tubing at more consistent velocities, and may remain concentrated closer together. By way of example, Applicants have found that without focusing, a sample eluted from a reaction chamber like that of FIGS. 1a and 1b, may disperse 3.6 cm in the direction of flow when conveyed through a tube that is 20 cm long and that has a 1 mm inner diameter. This equate to the sample dispersing over 282 uL as it is conveyed. However, when a similar sample is eluted from the chamber after having been focusing with flow rates through the side ports that are four times flow rates through the central port, dispersion is limited to 1.23 cm (dispersion through a volume of 10 uL). When flow rates through side ports are increased to twenty times the flow through the central ports, dispersion may be limited to 0.0735 centimeters in the direction of flow through the tube, or equivalently, a volume of 0.577 uL.
Reverse elution modes may also occur with fluid removed from the side ports of the chamber, as shown in FIG. 15. This may result in a further concentration of agents within the fluid exiting the chamber and/or a reduced volume of fluid that contains agents. As with focusing mode, the ratio of fluid exiting the chamber through the side ports and the central port may be adjusted to achieve different results. A greater proportion of fluid exiting through the side ports will result in a lower volume of central streamlines, and potentially a higher concentration of agents, exiting the chamber through the central port.
According to some embodiments, the chamber may include a second set of side ports from which fluid that surround, or that at least partially surrounds the central streamlines is removed during reverse elution. FIG. 16 shows one such embodiment. Here, a second set of side ports is positioned between the central port and the first set 23 of side ports. The second set 21 of side ports may be opened and fluid drawn from them during reverse elution to further concentrate sample removed from the chamber. Reverse elution, performed in this manner or like that described above, may also promote a reduction in the overall plug or bolus size of agents that is removed from the chamber. As shown, fluid may be introduced through the first set of side ports during reverse elution. This may move agents further toward central streamlines that exit the chamber through the central ports, as discussed herein. Alternately, flow through the first set of side ports may be blocked or flow may also be removed through the first set of side ports.
According to other embodiments, fluid that surrounds central streamlines that pass through the central port may be removed at points further away from the chamber. As discussed herein, positioning the sample in central streamlines may prevent dispersion of the sample. In this respect, it may be beneficial, according to some embodiments, to remove fluid, other than the central streamlines just prior to another apparatus, such as a detector that may analysis the sample, or before sample is collected for storage or delivery to another apparatus.
It is to be appreciated that the above described modes of operation, and others, may be performed in chambers other than that shown in FIGS. 1a and 1b. By way of example, the above described modes may be performed in the chamber shown in FIG. 17, according to some embodiments.
The chamber of FIG. 17 comprises a vial like structure having an open top 29 and a membrane 14 that extends across the internal, cross-sectional area of the vial. By way of example a chamber like that shown in FIG. 17 is sold under the name Centricon and may be acquired from Millipore. As shown, a tube or needle may be positioned into the vial, and may perform functions similar to the central port described with respect to FIGS. 1a and 1b. 
The chamber of FIG. 17, may be operated a focusing mode to position agents on a select portion of the substrate. Flow may be introduced to the chamber and urged through the membrane, either by a vacuum force below the membrane or a pressure force above the membrane. Concurrently, sample may be introduced to the chamber through the tube 27 and directed to a particular portion of the membrane, such as the central portion. The degree of focusing may be altered by changing the size of the tube, relative to the size of the membrane in chamber. Additionally or alternatively, altering the amount of flow that passes through the tube, relative to the total amount of fluid that passes through the membrane, may alter the degree of focusing that occurs.
The chamber of FIG. 17 may also be used in a reverse elution mode by drawing fluid from the chamber through the tube 27. In a reverse elution mode, fluid may be drawn from the chamber by introducing a vacuum above the membrane, by introducing a pressure source below the membrane, or solely by drawing fluid from the chamber through the tube.
Fluid flow may be controlled through the chamber during the various modes of operation with different configurations of pumps and valves. According to some embodiments, flow is controlled by a first variable flow rate pump in fluid communication with the central port and by a second variable flow rate pump that is in fluid communication with the side ports, and with a valve that is configured to control flow through the waste ports. It is to be appreciated, however, that other arrangements of pumps (either pressure or vacuum) and valves may be used to control flow through the chamber in various modes of operation, as aspects of the invention are not limited in this respect. Additionally, aspects of the invention are not limited to any one type of pump or valve.
Embodiments of the chamber may be operated by a controller that receives information for a particular operating protocol and, in turn, controls pumps and/or valves to run the system automatically to complete the protocol. The term ‘automatically’, as used herein, refers to a system that is capable of switching between modes of operation without the intervention of an operator, such as between a press down mode, a separation mode, a reaction mode, and/or an elution mode, among others, or to a system that is otherwise capable of altering operating condition, such as flow rates or temperatures without manual operator intervention, such as by following an predefined operating protocol or by controlling the system to predetermined set points. The controller and operating protocol combination may be implemented in any of numerous ways. For example, in one embodiment the controller and operating protocol combination may be implemented using hardware, software or a combination thereof. When implemented in software, the software code can be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers. It should be appreciated that any component or collection of components that perform the functions described herein can be generically considered as one or more controllers that control the functions discussed herein. The one or more controllers can be implemented in numerous ways, such as with dedicated hardware, or with general purpose hardware (e.g., one or more processors) that is programmed using microcode or software to perform the functions recited above. The one or more controllers may be included in one or more host computers, one or more storage systems, or any other type of computer that may include one or more storage devices coupled to the one or more controllers.
In this respect, it should be appreciated that one implementation of the embodiments of the present invention comprises at least one computer-readable medium (e.g., a computer memory, a floppy disk, a compact disk, a tape, etc.) encoded with an operating protocol in the form of a computer program (i.e., a plurality of instructions), which, when executed by the controller, performs the herein-discussed functions of the embodiments of the present invention. The computer-readable medium can be transportable such that the treatment protocol stored thereon can be loaded onto any computer system resource to implement the aspects of the present invention discussed herein. In addition, it should be appreciated that the reference to an operating protocol or controller which, when executed, performs the herein-discussed functions, is not limited to an application program running on a host computer. Rather, the term operating protocol is used herein in a generic sense to reference any type of computer code (e.g., software or microcode) that can be employed to program a processor to implement the herein-discussed aspects of the present invention.
The system may also comprise one or more sensors that receive information from the chamber or fluidic conduits used to connect the chamber to other portions of the system. Such sensors may receive information regarding pressure, temperature, flow rates, and the like, in any portion of the chamber or system. The system may also receive information for detectors that are used to analyze or detect the presence of an agent in a portion of the system.
The processing steps of the invention generally comprise the use of one or more reagents (i.e., at least one reagent) that acts on or reacts with and thereby modifies an agent. At least one reagent however is less than an infinite number of reagents as used herein and more commonly represents less than 1000, less than 100, less than 50, less than 20, less than 10, or less than 5 reagents. The nature of the reagents will vary depending on the processing step being performed with such reagent. The reagent may be a lysing agent (e.g., a detergent such as but not limited to deoxycholate), a labeling agent or probe (e.g., an intercalator or a sequence-specific probe), an enzyme (e.g., a lytic enzyme, an exonuclease, or an endonuclease such as a restriction endonuclease), an enzyme co-factor (e.g., cations such as Mg2+, a stabilizer (e.g., an anti-oxidant), and the like. One of ordinary skill in the art can envision other reagents to be used in the invention. Although the agent can be modified through those techniques mentioned above, it is to be appreciated that other techniques can also be used to modify the agent.
Additionally, the fluids used in the invention may contain other components (or constituents) such as buffering compounds (e.g., TRIS), chelating compounds (e.g., EDTA), ions (e.g., monovalent, divalent or trivalent cations or anions), salts, preservatives, and the like.
By way of example, a fluid may contain a lysing agent that lyses agents (e.g., eukaryotic cells or pathogens such as bacteria, viruses and the like) in the chamber, thereby releasing cellular contents, such as nucleic acids, into the chamber.
The invention in based in part on the discovery of a chamber (referred to herein interchangeably as a “focusing chamber” or a “reaction chamber”) that is able to isolate and/or manipulate and/or concentrate large agents without loss of structural integrity. In the case of high molecular weight agents such as genomic DNA, the chamber is able to isolate and/or manipulate genomic DNA without shearing, thereby yielding genomic fragments that are at least tens or hundreds of kilobases in length, and in some instances are megabases in length. These manipulations can be carried out on the order of hours rather than days (as is commonplace in the prior art). Moreover, the invention contemplates automated handling of the chamber and the device comprising it. These features alone and in combination define and apparatus and method of use thereof that greatly enhances and facilitates analysis of large agents such but not limited to genomic DNA. The ability to manipulate long stretches of DNA facilitates various analyses including but not limited to identification of the source of the genomic material (e.g., in pathogen analysis and screening).
The invention provides a fluidic chamber that is minimally comprised of an inlet port, a porous substrate that allows fluid but not the agents of interest to pass through, and at least one side port. Fluid flow is used to introduce, manipulate, separate, remove and/or harvest agents and/or other constituents from the chamber. The invention further provides devices and systems that comprise the fluidic chamber. The invention further provides methods for using the fluidic chamber, device and/or system to handle, isolate, purify, and/or manipulate large molecular weight agents such as but not limited to naturally and non-naturally occurring agents such as naturally or non-naturally occurring polymers including but not limited to nucleic acids, proteins, polysaccharides, and the like. Possible uses of the chamber include but are not limited to agent (e.g., polymer) harvest, isolation, purification, manipulation, and concentration such as nucleic acid hybridization, restriction endonuclease digestion of nucleic acids, amplification of nucleic acids (including whole genome amplification), labeling of nucleic acids using intercalators and/or sequence specific and/or sequence non specific probes, covalent or non-covalent modification of nucleic acids including but not limited to biotinylation of nucleic acids and optionally subsequent conjugation to streptavidin coated beads, and the like. One or more or all of these manipulations may be carried out in the chamber according to the invention. Those of ordinary skill in the art will readily envision a variety of other uses of the fluidic chamber (and devices) provided herein.
The chamber may also be used for concentration of agents, mixing of reactants, buffer exchange, and/or removal of waste products and excess reagents. In the process of carrying out any of the manipulations described herein, therefore, the chamber may function by concentrating an agent (e.g., genomic DNA) in a particular region, by distributing agents evenly across the substrate or other porous surface of the chamber, by promoting a reaction between the agent(s) and one or more other substrates or reagents, by separating agent(s) from other components present in the chamber including for example reaction catalysts, substrates and/or by products. The device is able to perform these various functions primarily by modulating the fluid flow and path into and out of the chamber as described in greater detail herein.
Fluid flow that is introduced through a central port and diffuser of the chamber may be substantially opposed to the substrate, according to some embodiments, such that the fluid flow is directed toward or perpendicular to the substrate, unlike in field flow fractionation devices, where the flow is directed along or parallel to a membrane. Any agents or other constituents in the fluid flow may be retained, at least temporarily, for manipulation on the substrate.
As used herein, the term ‘agent’ is used to refer to the entity, molecule or compound being harvested, isolated, purified and/or manipulated within the chamber. As stated above, the agent may be naturally occurring or non-naturally occurring. It may be a cell that is lysed in the chamber in order to release cellular components such as but not limited genomic DNA. It may be another vehicle that carries genetic material such as but not limited to a phage or virus. It may be a polymer such as but not limited to nucleic acids (including DNA, RNA, and the like), proteins (including peptides and polypeptides), polysaccharides, and the like. These agents may be introduced into the chamber directly or they may be provided to the chamber following manipulation of another agent such as but not limited to the cells that are lysed within the chamber to release nucleic acids.
In some embodiments, the chamber functions to separate agents from ‘other constituents’ (or other components) within the chamber. As used herein, the term ‘other constituents’ is used to refer to any component being physically separated from agents in the chamber. Other constituents may include reagents, waste material, and/or any material introduced to the chamber to act upon an agent and/or to alter the environment of the chamber. By way of example, other constituents may comprise lytic enzymes that are introduced into the chamber to lyse cells, cellular debris that is created following cell lysis, excess unbound probes, excess unbound intercalator, excess unincorporated nucleotides, restriction endonucleases, and the like.
Use of the chamber of the invention allows the structural integrity of agents to be maintained. This is particularly useful if the agent is otherwise fragile and subject to shearing or cleavage using conventional manipulation techniques, or where it is important to keep the agent intact, such as in analysis of nucleic acids that requires kilobase or megabase lengths of nucleic acids. In one example, the reaction chamber may obviate the need to manually handle strands of DNA, and this too can reduce probability and extent of fragmentation of the DNA. In another manner, shear forces associated with velocity gradients in moving fluids of the reaction chamber may be controlled, such that longer strands of polymers, like genomic DNA, may remain intact within the reaction chamber. According to some embodiments, nucleic acids that are at least 30 kilobases, at least 40 kilobases, at least 50 kilobases, at least 100 kilobases, at least 150 kilobases, at least 500 kilobases, at least 1 megabase, or at least 5 megabases may be retained in the chamber intact for subsequent analysis.
The chamber may allow the processes described herein, and others, to be performed without or with minimal manual intervention by an operator, such as is typically required in other processes, like in those that involve agarose plugs. An automated process is one that requires initial input from an operator but thereafter occurs independent of operator intervention. Examples of automated processes or methods include the harvest of agents upon manual loading of a sample into the chamber or an apparatus comprising the chamber. It would preferably not require manual loading of fluid and/or reagents. It would also not preferably require manual elution of the agent from the chamber. The degree of automation desired and implemented will depend on the particular application and can be modified accordingly by one of ordinary skill in the art.
Accordingly, embodiments of the chamber may also be used with automated operating protocols, such that systems using the chamber may be operated with minimal or no operator involvement and/or oversight. One or more reaction chambers may be incorporated into a system that receives a sample, either manually or automatically, and then initiates an automated operating protocol for processing the sample that is carried out by a controller of the system. By way of example, one automated operating protocol may involve nucleic acid harvest, isolation and restriction digestion, as discussed herein. It will be understood by those of ordinary skill in the art that other protocols may also be automated and the invention is not to be limited in this regard.
The chamber is able to prepare samples for analysis in less time than is required by conventional techniques. Most if not all manipulations may be performed on the order of hours including less than 12 hours, preferably less than 9 hours, more preferably less than 6 hours and even more preferably less than 3 hours, depending on the embodiment. In still other embodiments, the manipulations may be carried out in less than 1 hour. As non-limited examples of the speed of manipulation and analysis according to the invention, cell lysis and labeling of released nucleic acids (e.g., by sequence specific probes and/or intercalators) may be performed in 6 hours or less (including 5.5 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, or 1.5 hours or less), cell lysis and digestion of released nucleic acids may be performed in 4 hours or less (including 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, or 1 hour or less).
As used herein, “harvesting” refers to the process of extracting an agent from a sample or from a component within a sample such as but not limited to a cell or phage. Harvesting may also refer to the extraction of a smaller nucleic acid from a larger nucleic acid, including for example extracting a nucleic acid from a chromosome whether the chromosome is naturally or non-naturally occurring.
As used herein, “isolating” refers to the process of separating the agent from other components or constituents in the sample and/or chamber. An example of an isolated agent is a nucleic acid that has been separated from the cell from which it was originally presented. As used herein, “purification” refers to the degree to which the agent is separated from other components or constituents in the sample and/or chamber. The more purified the agent, the fewer components or constituents it is still present with. As used herein, “manipulating” or “modifying” an agent are used interchangeably to refer to making a change to the agent including but not limited binding a probe to the agent, deliberating cleaving the agent, and the like.
In some aspects of the invention, a number of processes are performed in the chamber. In the case of agents that are nucleic acids (including but not limited to genomic DNA), these processes may be harvest, isolation and/or purification of the nucleic acid (e.g., from a cell or from a sample including for example release of nucleic acids after chemical or enzymatic lysis (e.g., lysozyme and/or proteinase K digestion) of cells), digestion of the nucleic acid (e.g., using exonucleases or endonucleases), hybridization of sequence specific probes to the nucleic acids, and optionally binding of an intercalator to the nucleic acids.
The chamber and system of the invention allow these processes to occur rapidly, particularly as compared to prior art methods. For example, lysis of cells through to the digestion of nucleic acid can occur in about 2.5 hours or less, lysis of cells through to hybridization with probes can occur in about 3.5 hours or less, and lysis of cells through to intercalation can occur in about 4 hours or less.
The rapid harvest and/or manipulation of agents such as nucleic acids is due at least in part to the ability of the chamber and the system to sufficiently expose agents (including cells and nucleic acids) to the various reagents (including enzymes, co-factors, buffers, probes, intercalators, quenchers, the like) introduced into the chamber. The fluid flow through the chamber facilitates in some embodiment relatively uniform distribution of agents and reagents onto the substrate (e.g., the membrane). This ensures better mixing of reaction components within the chamber and less shearing forces than are provided by prior art methods.
The following is an exemplary and non-limiting example of the use and operation of the chamber. A test sample (e.g., a sample suspected of containing a biowarfare agent such as an anthrax spore) is introduced into the chamber through the introduction port. The reservoir port is open while the side port(s) is closed. Temperature of the chamber may be room temperature (e.g., about 25 degrees C. Leaving the configuration of the chamber as is, a solution of lysozyme and proteinase K is introduced into the chamber followed by an incubation at about 60 degrees C. This is followed by removal of cell debris by flowing (wash) fluid into the introduction port and out through the side port(s). The side port(s) is again closed and a solution comprising restriction enzyme is introduced into the chamber through the introduction port followed by incubation at about 40 degrees C. Restriction enzyme is then removed, along with other small molecular weight debris and reagents through the side port(s), and then the digested DNA fragments are eluted from the chamber through the side port(s). The fragments may then be analyzed in any number of ways including but not limited to gel electrophoresis to determine the distribution of fragments resulting from digestion with that particular enzyme. Unique and thus identifying fragment distributions may be used to identify the presence of particular agents such as anthrax spores. These patterns in most instances will be known a priori and the analysis will require a comparison with that known pattern and distribution.
Using the methods of the invention, it has been possible to extract restriction fragments corresponding to 340 microns in length, as well as fragments corresponding to more than 291 kilobases, about 210 kilobases, about 194 kilobases, about 145 kilobases, and about 60 kilobases from Bacillus spores using the chamber of the invention. These were prepared by the chamber in about 4 hours, using an automated process. This is to be compared to the prior art methodology that takes about 6 days and results in less clearly discernable restriction fragments. In this way, the chamber and system can be used to rapidly identify pathogens, leading to more rapid response times by emergency personnel.
The chamber and method of the invention has also been used to successfully harvest nucleic acids on the order of 1700 microns in length. It is to be understood that the quality of the nucleic acids prepared using the chamber and methods of the invention is similar if not superior to the quality achieved using gel plug methods of the prior art. Moreover, the methods of the invention are far faster than those prior art methods. Another advantage of the methods of the invention are that the nucleic acids prepared according to the methods provided herein are not random fragments. This is so at least because of the ability of the invention to maintain the nucleic acid in an intact form (i.e., without substantial shearing or unintentional fragmentation or cleavage). Nucleic acid recoveries range from at least 50% of input to greater than 75% of input. In some embodiments, greater than 80%, greater than 85%, greater than 90%, and in some embodiments about 100% of input is recovered.
Still other applications contemplated by the invention are hybridization of genomic DNA with fluorescently labeled probes (e.g., to characterize sequence specificity and site occupancy of DNA binding ligands), fluorescently labeled restriction enzyme labeling of genomic DNA (e.g., for rapid mapping of large DNA), detection and optionally quantification of nucleic acids and/or proteins utilizing DNA as a capture unit carrier, plasmid preparations from bacterial cells and/or cultures, combined DNA isolation and amplification, and the like.
It is to be understood that similar methods can be employed to identify and analyze nucleic acids from subjects (e.g., for genomic sequencing, for forensic analysis, for paternity testing, etc.). Many of these analyses can be accomplished using restriction enzymes akin to the analysis performed with respect to pathogen detection and identification (as described above). As an example, restriction fragment length polymorphism analysis (wherein differences in length of restriction fragments can be used to determine source of a nucleic acid) can be facilitated by harvesting and manipulating nucleic acids in the chamber.
Similarly, samples can be analyzed for the presence (or absence) of proteins as may be applicable to diagnostic, prognostic or therapeutic monitoring. In some embodiments, proteins may be detected and/or identified by binding to them to binding partners (or probes) such as antibodies or antibody fragments. Following labeling within the chamber, the proteins may be eluted (as described herein) and analyzed by any number of systems and instruments including but not limited to FACS or other single molecule detection systems. The chamber and system may also be used to simply harvest and separate proteins in a sample away from debris in the sample, thereby allowing the protein profile of a sample to be analyzed using for example standard techniques such as Western blots, HPLC, mass spectrometry, and the like.
The invention is not limited in the nature of the agent being harvested, manipulated, detected or analyzed (i.e., the target agent). These agents include but are not limited to cells and cell components (e.g., proteins and nucleic acids), chemicals and the like. These agents may be biohazardous agents as described in greater detail herein. Target agents may be naturally occurring or non-naturally occurring, including agents synthesized ex vivo but released into a natural environment. As described herein, the methods and systems of the invention can be used to modify one or more agents concurrently, simultaneously or consecutively. A plurality of agents is more than one and less than an infinite number. It includes less than 1010, less than 109, less than 108, less than 109, less than 107, less than 106, less than 105, less than 104, less than 5000, less than 1000, less than 500, less 100, less than 50, less than 25, less than 10, or less than 5 agents, or as little as one agent, as well as every integer therebetween as if explicitly recited herein.
The conditions, temperature, buffers and reagents of the chamber will vary depending on the particular type of modification being performed and will be known to those of ordinary skill in the art. See for example Sambrook et al, “Molecular Cloning: A Laboratory Manual” (2nd. Ed.), Vols. 1-3, Cold Spring Harbor Laboratory Press (1989); F. Ausubel et al, eds., “Current protocols in molecular biology”, Green Publishing and Wiley Interscience, New York (1987); Lewin, “Genes II”, John Wiley & Sons, New York, N.Y., (1985); Old et al., “Principles of Gene Manipulation: An Introduction to Genetic Engineering”, 2nd edition, University of California Press, Berkeley, Calif. (1981).
The invention can be applied to the detection and optionally identification and/or quantification of any agent, including rare agents or agents that would be costly to detect given the reagents necessary therefor. One example of such agents is biohazardous or biowarfare agents. These agents can be biological or chemical in nature. Biological biowarfare agents can be classified broadly as pathogens (including spores thereof) or toxins. As used herein, a pathogen (including a spore thereof) is an agent capable of entering a subject such as a human and infecting that subject. Examples of pathogens include infectious agents such as bacteria, viruses, fungi, parasites, mycobacteria and the like. Prions may also be considered pathogens to the extent they are thought to be the transmitting agent for CJD and like diseases. As used herein, a toxin is a pathogen-derived agent that causes disease and often death in a subject without also causing an infection. It derives from pathogens and so may be harvested therefrom. Alternatively, it may be synthesized separately from its naturally occurring source. Biological warfare agents may be weaponized (i.e., aerosolized) for maximum spread. Examples of pathogens are provided below.
CDC Category A agents include Bacillus anthracis (otherwise known as anthrax), Clostridium botulinum and its toxin (causative agent for botulism), Yersinia pestis (causative agent for the plague), variola major (causative agent for small pox), Francisella tularensis (causative agent for tularemia), and viral hemorrhagic fever causing agents such as filoviruses Ebola and Marburg and arenaviruses such as Lassa, Machupo and Junin.
CDC Category B agents include Brucellosis (Brucella species), epsilon toxin of Clostridium perfringens, food safety threats such as Salmonella species, E. coli and Shigella, Glanders (Burkholderia mallei), Melioidosis (Burkholderia pseudomallei), Psittacosis (Chlamydia psittaci), Q fever (Coxiella burnetii), ricin toxin (from Ricinus communis castor beans), Staphylococcal enterotoxin B, Typhus fever (Rickettsia prowazekii), viral encephalitis (alphaviruses, e.g., Venezuelan equine encephalitis, eastern equine encephalitis, western equine encephalitis), and water safety threats such as e.g., Vibrio cholerae, Cryptosporidium parvum. 
CDC Category C agents include emerging infectious diseases such as Nipah virus and hantavirus.
Further examples of bacteria that can be harvested and/or manipulated according to the invention include Gonorrhea, Staphylococcus spp., Streptococcus spp. such as Streptococcus pneumoniae, Syphilis, Pseudomonas spp., Clostridium difficile, Legionella spp., Pneumococcus spp., Haemophilus spp. (e.g., Haemophilus influenzae), Klebsiella spp., Enterobacter spp., Citrobacter spp., Neisseria spp. (e.g., N. meningitidis, N. gonorrhoeae), Shigella spp., Salmonella spp., Listeria spp. (e.g., L. monocytogenes), Pasteurella spp. (e.g., Pasteurella multocida), Streptobacillus spp., Spirillum spp., Treponema spp. (e.g., Treponema pallidum), Actinomyces spp. (e.g., Actinomyces israelli), Borrelia spp., Corynebacterium spp., Nocardia spp., Gardnerella spp. (e.g., Gardnerella vaginalis), Campylobacter spp., Spirochaeta spp., Proteus spp., and Bacteriodes spp.
Further examples of viruses that can be harvested and/or manipulated according to the invention include Hepatitis virus A, B and C, West Nile virus, poliovirus, rhinovirus, HIV, Herpes simplex virus 1 and 2 (including encephalitis, neonatal and genital forms), human papilloma virus, cytomegalovirus, Epstein Barr virus, Hepatitis virus A, B and C, rotavirus, norovirus, adenovirus, influenza virus including influenza A virus, respiratory syncytial virus, varicella-zoster virus, small pox, monkey pox and SARS virus.
Further examples of fungi that can be harvested and/or manipulated according to the invention include candidiasis, ringworm, histoplasmosis, blastomycosis, paracoccidioidomycosis, crytococcosis, aspergillosis, chromomycosis, mycetoma, pseudallescheriasis, and tinea versicolor.
Further examples of parasites that can be harvested and/or manipulated according to the invention include both protozoa and nematodes such as amebiasis, Trypanosoma cruzi, Fascioliasis (e.g., Facioloa hepatica), Leishmaniasis, Plasmodium (e.g., P. falciparum, P. knowlesi, P. malariae,) Onchocerciasis, Paragonimiasis, Trypanosoma brucei, Pneumocystis (e.g., Pneumocystis carinii), Trichomonas vaginalis, Taenia, Hymenolepsis (e.g., Hymenolepsis nana), Echinococcus, Schistosomiasis (e.g., Schistosoma mansoni), neurocysticercosis, Necator americanus, and Trichuris trichuria, Giardia. 
Further examples of mycobacteria that can be harvested and/or manipulated according to the invention include M. tuberculosis or M. leprae. 
Examples of toxins include abrin, ricin and strychnine. Further examples of toxins include toxins produced by Corynebacterium diphtheriae (diphtheria), Bordetella pertussis (whooping cough), Vibrio cholerae (cholera), Bacillus anthracis (anthrax), Clostridium botulinum (botulism), Clostridium tetani (tetanus), and enterohemorrhagic Escherichia coli (bloody diarrhea and hemolytic uremic syndrome), Staphylococcus aureus alpha toxin, Shiga toxin (ST), cytotoxic necrotizing factor type 1 (CNF1), E. coli heat-stable toxin (ST), botulinum, tetanus neurotoxins, S. aureus toxic shock syndrome toxin (TSST), Aeromonas hydrophila aerolysin, Clostridium perfringens perfringolysin O, E. coli hemolysin, Listeria monocytogenes listeriolysin O, Streptococcus pneumoniae pneumolysin, Streptococcus pyogenes streptolysine O, Pseudomonas aeruginosa exotoxin A, E. coli DNF, E. coli LT, E. coli CLDT, E. coli EAST, Bacillus anthracis edema factor, Bordetella pertussis dermonecrotic toxin, Clostridium botulinum C2 toxin, C. botulinum C3 toxin, Clostridium difficile toxin A, and C. difficile toxin B.
The foregoing lists of infections are not intended to be exhaustive but rather exemplary.
It may be necessary, in some embodiments, to disrupt pathogen cell walls, cell membranes or viral envelopes. The invention contemplates performing such lysis within the chamber optionally followed by isolation and/or manipulation of cellular contents released after lysis. Disruption can be accomplished by any number of means including chemical, enzymatic, or osmotic lysis.
In other embodiments, the agent being harvested and/or manipulated is a naturally occurring or non-naturally occurring polymer. A polymer as used herein is a compound comprised of monomers linked together by linkages. An monomer as used herein is the smallest building block that can be linked directly or indirectly to other building blocks (or monomers) to form the particular polymer. At a minimum, the polymer contains at least two linked monomers. The particular type of monomer will depend upon the type of polymer being analyzed. The polymer may be a nucleic acid, a protein, a peptide, a carbohydrate, an oligo- or polysaccharide, a lipid, etc. The polymer may be branched or unbranched. In some embodiments, the polymer is unbranched as is the case with naturally occurring nucleic acids such as genomic DNA.
In some embodiments, the polymer is capable of being bound to or by sequence- or structure-specific probes. Where the polymer and the probes are both nucleic acids and the binding is sequence specific, the probes are hybridized to the nucleic acid polymer. The probes may bind to the polymer at a sequence or structure that is unique to that polymer or to a region of that and other polymers. Polymers may also be labeled with non-sequence specific probes or labels including intercalators or non-specific dyes.
In some instances the polymers may be manipulated without prior isolation and/or purification, while in other instances the polymers may be manipulated following isolation and/or purification.
In some embodiments, the method can be used to harvest and/or manipulate a plurality of identical polymers in a sample or a plurality of different polymers in a sample.
In some important embodiments, the agents are naturally occurring or non-naturally occurring nucleic acids. Non-naturally occurring nucleic acids include but are not limited to bacterial artificial chromosomes (BACs) and yeast artificial chromosomes (YACs). The term “nucleic acid” refers to multiple linked nucleotides (i.e., molecules comprising a sugar (e.g., ribose or deoxyribose) linked to an exchangeable organic base, which is either a pyrimidine (e.g., cytosine (C), thymidine (T) or uracil (U)) or a purine (e.g., adenine (A) or guanine (G)). “Nucleic acid” and “nucleic acid molecule” are used interchangeably and refer to oligoribonucleotides as well as oligodeoxyribonucleotides. The terms shall also include polynucleosides (i.e., a polynucleotide minus a phosphate) and any other organic base containing nucleic acid. The organic bases include adenine, uracil, guanine, thymine, cytosine and inosine.
In important embodiments, the nucleic acid is DNA or RNA. DNA includes genomic DNA (such as nuclear DNA and mitochondrial DNA), as well as in some instances complementary DNA (cDNA). RNA includes messenger RNA (mRNA), ribosomal RNA (rRNA), microRNA (miRNA), and the like. Harvest and isolation of nucleic acids are routinely performed in the art and suitable methods can be found in standard molecular biology textbooks. (See, for example, Sambrook et al, “Molecular Cloning: A Laboratory Manual” (2nd. Ed.), Vols. 1-3, Cold Spring Harbor Laboratory Press (1989); F. Ausubel et al, eds., “Current protocols in molecular biology”, Green Publishing and Wiley Interscience, New York (1987); Lewin, “Genes II”, John Wiley & Sons, New York, N.Y., (1985); Old et al., “Principles of Gene Manipulation: An Introduction to Genetic Engineering”, 2nd edition, University of California Press, Berkeley, Calif. (1981)).
Preferably, prior amplification of nucleic acids using techniques such as polymerase chain reaction (PCR) are not necessary. Accordingly, the polymer may be a non in vitro amplified nucleic acid. As used herein, a “non in vitro amplified nucleic acid” refers to a nucleic acid that has not been amplified in vitro using techniques such as polymerase chain reaction or recombinant DNA methods prior to manipulation, detection and/or analysis by the methods contemplated by the invention. A non in vitro amplified nucleic acid may however be a nucleic acid that is amplified in vivo (in the biological sample from which it was harvested) as a natural consequence of the development of the cells in vivo. This means that the non in vitro nucleic acid may be one which is amplified in vivo as part of for example locus amplification, which is commonly observed in some cell types as a result of mutation or cancer development.
As used herein, “linked” or “linkage” means two entities bound to one another by any physicochemical means. Any linkage known to those of ordinary skill in the art, covalent or non-covalent, is embraced. Natural linkages are those ordinarily found in nature connecting for example naturally occurring entities. Natural linkages include, for instance, amide, ester and thioester linkages. Nucleic acid targets or probes of the invention may comprise synthetic or modified linkages.
Nucleic acids commonly have a phosphodiester backbone because this backbone is most common in vivo. However, they are not so limited. Backbone modifications are known in the art. One of ordinary skill in the art is capable of preparing such nucleic acids without undue experimentation. The probes, if nucleic acid in nature, can also have backbone modifications such as those described herein.
Thus the nucleic acids may be heterogeneous in backbone composition thereby containing any possible combination of nucleic acid units linked together such as peptide nucleic acids (which have amino acid linkages with nucleic acid bases, and which are discussed in greater detail herein). In some embodiments, the nucleic acids are homogeneous in backbone composition.
The nucleic acids may be double-stranded, although in some embodiments the nucleic acid targets are denatured and presented in a single-stranded form. This can be accomplished by modulating the environment of a double-stranded nucleic acid including singly or in combination increasing temperature, decreasing salt concentration, and the like. Methods of denaturing nucleic acids are known in the art.
The methods of the invention in part may be used to analyze agents using probes that recognize and specifically bind to an agent. Binding of a probe to an agent may indicate the presence and location of a target site in the target agent, or it may simply indicate the presence of the agent, depending on user requirements. As used herein, a target agent that is bound by a probe is “labeled” with the probe and/or its detectable label.
As used herein, a probe is a molecule or compound that binds preferentially to the agent of interest (i.e., it has a greater affinity for the agent of interest than for other compounds). Its affinity for the agent of interest may be at least 2-fold, at least 5-fold, at least 10-fold, or more than its affinity for another compound. Probes with the greatest differential affinity are preferred in most embodiments.
The probes can be of any nature including but not limited to nucleic acid (e.g., aptamers), peptide, carbohydrate, lipid, and the like. A nucleic acid based probe such as an oligonucleotide can be used to recognize and bind DNA or RNA. The nucleic acid based probe can be DNA, RNA, LNA or PNA, although it is not so limited. It can also be a combination of one or more of these elements and/or can comprise other nucleic acid mimics. With the advent of aptamer technology, it is possible to use nucleic acid based probes in order to recognize and bind a variety of non-nucleic acid agents, including peptides and carbohydrates, in a structurally specific manner. Other probes for nucleic acid agents include but are not limited to sequence-specific major and minor groove binders and intercalators, nucleic acid binding peptides or proteins, etc.
As used herein a “peptide” is a polymer of amino acids connected preferably but not solely with peptide bonds. The probe may be an antibody or an antigen-binding antibody fragment. Antibodies include IgG, IgA, IgM, IgE, IgD as well as antibody variants such as single chain antibodies. Antigen-binding antibody fragments include but are not limited to Fab, F(ab)2, and Fv fragments.
The methods provided herein involve the use of probes that bind to the target polymer in a sequence-specific manner. “Sequence-specific” when used in the context of a nucleic acid means that the probe recognizes a particular linear (or in some instances quasi-linear) arrangement of nucleotides or derivatives thereof. In some embodiments, the probes are “polymer-specific” meaning that they bind specifically to a particular polymer, possibly by virtue of a particular sequence or structure unique to that polymer. The degree of specificity with which the probes bind to target agents will depend on the conditions in which the binding (or hybridization) occurs. For example, salt concentration and temperature can be modulated in order to vary the range of sequences recognized by the nucleic acid probes. Generally speaking the more stringent the conditions, the more specific the binding and the less likely will be the occurrence of non-specific binding events. Those of ordinary skill in the art will be able to determine optimum conditions for a desired specificity.
In some instances, nucleic acid probes will form at least a Watson-Crick bond with a target nucleic acid. In other instances, the nucleic acid probe can form a Hoogsteen bond with the target nucleic acid, thereby forming a triplex. A nucleic acid probe that binds by Hoogsteen binding enters the major groove of a nucleic acid polymer and hybridizes with the bases located there. Examples of these latter probes include molecules that recognize and bind to the minor and major grooves of nucleic acids (e.g., some forms of antibiotics). In some embodiments, the nucleic acid probes can form both Watson-Crick and Hoogsteen bonds with the nucleic acid polymer. BisPNA probes, for instance, are capable of both Watson-Crick and Hoogsteen binding to a nucleic acid.
The length of probe can also determine the specificity of binding. The energetic cost of a single mismatch between the probe and the nucleic acid polymer is relatively higher for shorter sequences than for longer ones. Therefore, hybridization of smaller nucleic acid probes is more specific than is hybridization of longer nucleic acid probes because the longer probes can embrace mismatches and still continue to bind to the polymer depending on the conditions. One potential limitation to the use of shorter probes however is their inherently lower stability at a given temperature and salt concentration. In order to avoid this latter limitation, bisPNA probes can be used to bind shorter sequences with sufficient hybrid stability. Longer probes are desirable when unique gene-specific sequences are being detected.
Notwithstanding these provisos, the nucleic acid probes of the invention can be any length ranging from at least 4 nucleotides to in excess of 1000 nucleotides. The length of the probe can be any length of nucleotides between and including the ranges listed herein, as if each and every length was explicitly recited herein. Thus, the length may be at least 5 nucleotides, at least 10 nucleotides, at least 15 nucleotides, at least 20 nucleotides, or at least 25 nucleotides, or more, in length. The length may range from at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 12, at least 15, at least 20, at least 25, at least 50, at least 75, at least 100, at least 150, at least 200, at least 250, at least 500, or more nucleotides (including every integer therebetween as if explicitly recited herein). In preferred embodiments, the probes are 5-100 nucleotides in length, more preferably between 5-25 nucleotides in length, and even more preferably 5-12 nucleotides in length.
The probes are preferably single-stranded, but they are not so limited. For example, when the probe is a bisPNA it can adopt a secondary structure with the nucleic acid polymer resulting in a triple helix conformation, with one region of the bisPNA clamp forming Hoogsteen bonds with the backbone of the polymer and another region of the bisPNA clamp forming Watson-Crick bonds with the nucleotide bases of the polymer.
In some embodiments, the probes may be molecular beacons. When not bound to their targets, the molecular beacon probes form a hairpin structure and do not emit fluorescence since one end of the molecular beacon is a quencher molecule. However, when bound to their targets, the fluorescent and quenching ends of the probe are sufficiently separated so that the fluorescent end can now emit.
In some embodiments, the probe is a nucleic acid that is a peptide nucleic acid (PNA), a bisPNA clamp, a pseudocomplementary PNA, a locked nucleic acid (LNA), DNA, RNA, or co-nucleic acids of the above such as DNA-LNA co-nucleic acids. siRNA or miRNA or RNAi molecules can be similarly used.
In some embodiments, the probe is a peptide nucleic acid (PNA), a bisPNA clamp, a locked nucleic acid (LNA), a ssPNA, a pseudocomplementary PNA (pcPNA), a two-armed PNA (as described in co-pending U.S. patent application having Ser. No. 10/421,644 and publication number US 2003-0215864 A1 and published Nov. 20, 2003, and PCT application having serial number PCT/US03/12480 and publication number WO 03/091455 A1 and published Nov. 6, 2003, filed on Apr. 23, 2003), or co-polymers thereof (e.g., a DNA-LNA co-polymer).
PNAs are DNA analogs having their phosphate backbone replaced with 2-aminoethyl glycine residues linked to nucleotide bases through glycine amino nitrogen and methylenecarbonyl linkers. PNAs can bind to both DNA and RNA targets by Watson-Crick base pairing, and in so doing form stronger hybrids than would be possible with DNA or RNA based probes. BisPNA includes two strands connected with a flexible linker. One strand is designed to hybridize with DNA by a classic Watson-Crick pairing, and the second is designed to hybridize with a Hoogsteen pairing. Pseudocomplementary PNA (pcPNA) (Izvolsky, K. I. et al., Biochemistry 10908-10913 (2000)) involves two single stranded PNAs added to dsDNA. Locked nucleic acid (LNA) molecules form hybrids with DNA, which are at least as stable as PNA/DNA hybrids (Braasch, D. A. et al., Chem & Biol. 8(1):1-7 (2001)).
As stated herein, the agent may be labeled. As an example, if the agent is a nucleic acid, it may be labeled through the use of sequence-specific probes that bind to the polymer in a sequence-specific manner. The sequence-specific probes are labeled with a detectable label (e.g., a fluorophore or a radioisotope). The nucleic acid however can also be synthesized in a manner that incorporates detectable labels such as fluorophores directly into the growing nucleic acid. Nucleic acids can be synthesized de novo (e.g., using automated nucleic acid synthesizers) using fluorescently labeled nucleotides. Such nucleotides are commercially available from suppliers such as Amersham Biosciences, Invitrogen, and New England Nuclear/Perkin Elmer.
Alternatively, nucleic acids may be synthesized or modified post synthesis to include active amino or thiol groups. (Proudnikov and Mirabekov, Nucleic Acid Research, 24:4535-4532, 1996.) An extensive description of modification procedures that can be performed on a nucleic acid polymer can be found in Hermanson, G. T., Bioconjugate Techniques, Academic Press, Inc., San Diego, 1996, which is incorporated by reference herein. There are several known methods of direct chemical labeling of DNA (Hermanson, 1996; Roget et al., 1989; Proudnikov and Mirabekov, 1996). One of the methods is based on the introduction of aldehyde groups by partial depurination of DNA. Fluorescent labels with an attached hydrazine group are efficiently coupled with the aldehyde groups and the hydrazine bonds are stabilized by reduction with sodium labeling efficiencies around 60%. The reaction of cytosine with bisulfite in the presence of an excess of an amine fluorophore leads to transamination at the N4 position (Hermanson, 1996). Reaction conditions such as pH, amine fluorophore concentration, incubation time, and temperature affect the yield of products formed.
Probes are generally labeled with a detectable label. A detectable label is a moiety, the presence of which can be ascertained directly or indirectly. Generally, detection of the label involves the creation of a detectable signal such as for example an emission of energy. The label may be of a chemical, peptide or nucleic acid nature although it is not so limited. The nature of the label used will depend on a variety of factors, including the nature of the analysis being conducted, the type of energy source and detector used, and the type of polymer and probe. The label should be sterically and chemically compatible with the entities to which it is bound.
The label can be detected directly for example by its ability to emit and/or absorb electromagnetic radiation of a particular wavelength. A label can be detected indirectly for example by its ability to bind, recruit and, in some cases, cleave another moiety which itself may emit or absorb light of a particular wavelength (e.g., an epitope tag such as the FLAG epitope, an enzyme tag such as horseradish peroxidase, etc.). Generally the detectable label can be selected from the group consisting of directly detectable labels such as a fluorescent molecule (e.g., fluorescein, rhodamine, tetramethylrhodamine, R-phycoerythrin, CY-3TM, CY-5TM, CY-7TM, TEXAS RED®, PHAR-REDTM, allophycocyanin (APC), fluorescein amine, eosin, dansyl, umbelliferone, 5-carboxyfluorescein (FAM), 2′7′-dimethoxy-4′5′-dichloro-6-carboxyfluorescein (JOE), 6 carboxyrhodamine (R6G), N,N,N′,N′-tetramethyl-6-carboxyrhodamine (TAMRA), 6-carboxy-X-rhodamine (ROX), 4-(4′-dimethylaminophenylazo) benzoic acid (DABCYL), 5-(2′-aminoethyl)aminonaphthalene-1-sulfonic acid (EDANS), 4-acetamido-4′-isothiocyanatostilbene-2,2′-disulfonic acid, acridine, acridine isothiocyanate, r-amino-N-(3-vinylsulfonyl)phenylnaphthalimide-3,5, disulfonate (Lucifer Yellow VS), N-(4-anilino-1-naphthyl)maleimide, anthranilamide, Brilliant Yellow, coumarin, 7-amino-4-methylcoumarin, 7-amino-4-trifluoromethylcouluarin (Coumarin 151), cyanosine, 4′,6-diaminidino-2-phenylindole (DAPI), 5′,5′′-diaminidino-2-phenylindole (DAPI), 5′,5′′-dibromopyrogallol-sulfonephthalein (Bromopyrogallol Red), 7-diethylamino-3-(4′-isothiocyanatophenyl)-4-methylcoumarin diethylenetriamine pentaacetate, 4,4′-diisothiocyanatodihydro-stilbene-2,2′-disulfonic acid, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid, 4-dimethylaminophenylazophenyl-4′-isothiocyanate (DABITC), eosin isothiocyanate, erythrosin B, erythrosin isothiocyanate, ethidium, 5-(4,6-dichlorotriazin-2-yl)aminofluorescein (DTAF), QFITC (XRITC), fluorescamine, IR144, IR1446, Malachite Green isothiocyanate, 4-methylumbelliferone, ortho cresolphthalein, nitrotyrosine, pararosaniline, Phenol Red, B-phycoerythrin, o-phthaldialdehyde, pyrene, pyrene butyrate, succinimidyl 1-pyrene butyrate, Reactive Red 4 (Cibacron® Brilliant Red 3B-A), lissamine rhodamine B sulfonyl chloride, rhodamine B, rhodamine 123, rhodamine X, sulforhodamine B, sulforhodamine 101, sulfonyl chloride derivative of sulforhodamine 101, tetramethyl rhodamine, riboflavin, rosolic acid, and terbium chelate derivatives), a chemiluminescent molecule, a bioluminescent molecule, a chromogenic molecule, a radioisotope (e.g., P.sup.32 or H.sup.3, .sup.14C, .sup.125I and .sup.131I), an electron spin resonance molecule (such as for example nitroxyl radicals), an optical or electron density molecule, an electrical charge transducing or transferring molecule, an electromagnetic molecule such as a magnetic or paramagnetic bead or particle, a semiconductor nanocrystal or nanoparticle (such as quantum dots described for example in U.S. Pat. No. 6,207,392 and commercially available from Quantum Dot Corporation and Evident Technologies), a colloidal metal, a colloid gold nanocrystal, a nuclear magnetic resonance molecule, and the like.
The detectable label can also be selected from the group consisting of indirectly detectable labels such as an enzyme (e.g., alkaline phosphatase, horseradish peroxidase, β-galactosidase, glucoamylase, lysozyme, luciferases such as firefly luciferase and bacterial luciferase (U.S. Pat. No. 4,737,456); saccharide oxidases such as glucose oxidase, galactose oxidase, and glucose-6-phosphate dehydrogenase; heterocyclic oxidases such as uricase and xanthine oxidase coupled to an enzyme that uses hydrogen peroxide to oxidize a dye precursor such as HRP, lactoperoxidase, or microperoxidase), an enzyme substrate, an affinity molecule, a ligand, a receptor, a biotin molecule, an avidin molecule, a streptavidin molecule, an antigen (e.g., epitope tags such as the FLAG or HA epitope), a hapten (e.g., biotin, pyridoxal, digoxigenin fluorescein and dinitrophenol), an antibody, an antibody fragment, a microbead, and the like. Antibody fragments include Fab, F(ab)2, Fd and antibody fragments which include a CDR3 region.
In some embodiments, the detectable label is a member of a FRET fluorophore pair. FRET fluorophore pairs are two fluorophores that are capable of undergoing FRET to produce or eliminate a detectable signal when positioned in proximity to one another. Examples of donors include ALEXA® 488, ALEXA® 546, BODIPY® 493, OYSTER® 556, FLUOR® (FAM), CY3TM and TMRTM (Tamra). Examples of acceptors include CY5TM, ALEXA® 594, ALEXA® 647 and OYSTER® 656. CY5TM can work as a donor with CY3TM, TMRTM or ALEXA® 546, as an example. FRET should be possible with any fluorophore pair having fluorescence maxima spaced at 50-100 nm from each other.
The polymer may be labeled in a non-sequence-specific manner. For example, if the polymer is a nucleic acid such as DNA, then its backbone may be stained with a backbone label. Examples of backbone stains that label nucleic acids in a sequence non-specific manner include intercalating dyes (or intercalators) such as phenanthridines and acridines (e.g., ethidium bromide, propidium iodide, hexidium iodide, dihydroethidium, ethidium homodimer-1 and -2, ethidium monoazide, and ACMA); minor grove binders such as indoles and imidazoles (e.g., Hoechst 33258, Hoechst 33342, Hoechst 34580 and DAPI); and miscellaneous nucleic acid stains such as acridine orange (also capable of intercalating), 7-AAD, actinomycin D, LDS751, and hydroxystilbamidine. All of the aforementioned nucleic acid stains are commercially available from suppliers such as Invitrogen.
Still other examples of nucleic acid stains include the following dyes from INVITROGENTM: cyanine dyes such as SYTOX® Blue, SYTOX® Green, SYTOX® Orange, POPOTM-1, POPOTM-3, YOYO®-1, YOYO®-3, TOTO®-1, TOTO®-3, JOJOTM-1, LOLOTM-1, BOBOTM-1, BOBOTM-3, PO-PROTM-1, PO-PROTM-3, BO-PROTM-1, BO-PROTM-3, TO-PRO®-1, TO-PRO®-3, TO-PRO®-5, JO-PROTM-1, LO-PROTM-1, YO-PRO®-1, YO-PRO®-3, PICOGREEN®, OLIGREEN®, RIBOGREEN®, SYBR® Gold, SYBR® Green I, SYBR® Green II, SYBR® DX, SYTO®-40, -41, -42, -43, -44, -45 (blue), SYTO®-13, -16, -24, -21, -23, -12, -11, -20, -22, -15, -14, -25 (green), SYTO®-81, -80, -82, -83, -84, -85 (orange), SYTO®-64, -17, -59, -61, -62, -60, -63 (red).
The foregoing written specification is considered to be sufficient to enable one skilled in the art to practice the invention. The present invention is not to be limited in scope by examples provided, since the examples are intended as a single illustration of one aspect of the invention and other functionally equivalent embodiments are within the scope of the invention. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and fall within the scope of the invention. The advantages and objects of the invention are not necessarily encompassed by each embodiment of the invention.
The present invention is further illustrated by the following Examples, which in no way should be construed as further limiting.
EXAMPLES
Example 1
Chamber Construction
One chamber embodiment includes a circular substrate that has an exposed surface area of about 95 mm2, and a flow region volume of 115 mL. The chamber is configured generally as shown in FIGS. 1a and 1b, except that the chamber includes only sixteen side ports, positioned on opposed sides of the flow region. The chamber operates during a separation mode with a flow rate of about 0.63 mL/min through the central port, roughly 0.05 mL/min passes through the substrate while the remaining flow (0.58 mL/min) is diverted through the side ports. This configuration has been found to effectively hold 15 kilobase to 5 Megabase DNA on or about the substrate, under these operating conditions.
Example 2
Operating Protocol for DNA Isolation and Digestion in a Chamber, as Shown in FIG. 6, Using the Chamber of Example 1
1. Injection of cells. A sample of E. coli cells is introduced directly into the chamber in a press down mode, as shown in FIG. 6a. The chamber waste ports are open while the side ports are closed. The solvent can pass through the substrate while the E. coli cells are retained inside the chamber substantially uniformly distributed on the substrate. The chamber is maintained at the appropriate temperature for lysis. Flow through the central port is 0.1 mL/min and the temperature of the flow region is maintained at 37° C.
2. Washing. The buffer of the sample can be exchanged with lysis buffer, in a separation mode, by introducing lysis buffer containing detergents such as laurylsarcosine and Triton. The buffer is injected through the central port. The excess liquid is removed through the waste ports and the side ports in a separation mode. An appropriate ratio of the waste and side port flow rates is maintained that allows the cells to be held at the substrate inside the chamber without disturbing their distribution. Flow through the central port is 0.8 mL/min, flow through the side ports is 0.75 mL/min, flow through the substrate is 0.05 mL/min, and the temperature is maintained at 37° C.
3. Injection of lytic enzymes. Lysis buffer containing lysozyme is introduced through the central port, in a press down mode, as shown in FIG. 6b. The excess liquid passes through the substrate and is removed through the waste ports. The side ports remain closed. The E. coli cells remain immobilized on the substrate. The enzymes accumulate at the substrate with a concentration gradient extending within tens of microns into the flow region from the substrate. Flow through the central port is 0.05 mL/min and the temperature is maintained at 37° C.
4. Lysis. Lysis is allowed to proceed in a substantially quiescent chamber, in a reaction mode, as shown in FIG. 6c. The result is the release of genomic DNA and waste materials (e.g., cellular debris). The temperature is maintained at 37° C.
5. Injection of Proteinase K. Buffer containing proteinase K is introduced through the central port, in a press down mode, as shown in FIG. 6b. The excess liquid passes through the substrate and is removed through the waste ports. The side ports remain closed. The E. coli cells remain immobilized on the substrate. The enzymes accumulate at the substrate with a concentration gradient extending within tens of microns into the flow region from the substrate. Flow through the central port is 0.05 mL/min and the temperature is maintained at 37° C.
6. Proteinase K Digestion. Proeteinase K digestion is allowed to proceed in a substantially quiescent chamber, in a reaction mode, as shown in FIG. 6c. The temperature is maintained at 55° C.
7. Washing. Buffer is introduced through the central port to remove unwanted materials from the flow region in a separation mode, as shown in FIG. 6d. Again, the excess liquid carrying the waste is removed through the waste ports and the side ports maintaining an appropriate ratio of the two flows. The Megabase genomic DNA, which is larger than the threshold size of the substrate, is held by the flow through the substrate. Several buffers can be used consecutively in this step to achieve the desired purification level. The last buffer introduced is the buffer required for restriction enzyme digestion. The flow rate through the central port is 0.8 mL/min, the flow rate though the side ports is 0.75 mL/min, and the flow through the substrate is 0.05 mL/min. The temperature is maintained at 37° C.
8. Introduction of restriction enzyme. Restriction enzyme is introduced the chamber through the central port in a press down mode, as shown in FIG. 6e. The flow rate through the central port is 0.05 mL/min and the flow through the substrate is 0.05 mL/min. The temperature is maintained at 37° C.
9. Restriction. Digestion is allowed to proceed in an enclosed system, in a reaction mode, as shown in FIG. 6f. The result is digestion of genomic DNA into smaller fragments. There is no flow through the chamber and the temperature is maintained at an appropriate temperature for the chosen restriction enzyme.
10. Washing. Buffer is introduced through the central port to remove the restriction enzyme and exchange the restriction enzyme buffer with elution buffer, in a separation mode, as shown in FIG. 6g. Several buffers can be used consecutively in this step to achieve the desired purification level. The last buffer introduced is the buffer for elution. The flow rate through the central port is 0.8 mL/min, the flow rate though the side ports is 0.75 mL/min, and the flow through the substrate is 0.05 mL/min. The temperature is maintained at 37° C.
11. Elution. Buffer is added to the chamber through one of the side ports and genomic DNA is eluted from the chamber through the central port, in an elution mode, as shown in FIG. 6h. The side ports remain closed. The elution flow rate is 0.1 mL/min. The temperature is room temperature.
12. The reaction chamber is now ready to isolate DNA from another sample.
Example 3
Results from Using an Operating Protocol Like that Described in Example 2
FIG. 7 shows representations of genomic DNA from Bacillus spores and E. coli cells isolated and digested in the reaction chamber following a protocol similar to the example protocol described above with respect to Example 2, and illustrates pulsed field gel of elution fractions from the reaction chamber. Lane 1 shows lambda ladder used as a size marker, lane 2-4 show the first three elution fractions. Slide A shows DNA fragments from decoated Bacillus spores that were introduced into the reaction chamber and DNA was isolated, purified, digested with NotI and eluted by reverse flow elution through the central port. All expected fragments are present. Slide B shows DNA fragments from E. coli cells which were introduced into the reaction chamber and subjected to spore decoating, lysis, purification, and NotI digestion. Genomic DNA was recovered by reverse flow elution through the central port. All expected fragments are present. Slide C shows DNA fragments from a mixture of Bacillus spores and E. coli cells that were introduced into the chamber and subjected to spore decoating, lysis, DNA purification and NotI digestion. Digested genomic DNA from both organisms was recovered by reverse flow elution through the central port. The digestion pattern is clearly a sum of Bacillus and E. coli fragments.
Example 4
Operating Protocol for Circular Plasmid/BAC Isolation and Purification in a Chamber, Using the Chamber of Example 1
Injection of cells. A sample of E. coli cells is introduced into the chamber in a press down mode. The chamber waste ports are open while the side ports are closed. The solvent can pass through the substrate while the E. coli cells are retained inside the chamber uniformly distributed on the substrate. The chamber is maintained at the appropriate temperature for lysis.
Washing. The buffer of the sample can be exchanged with lysis buffer by introducing lysis buffer containing detergents such as laurylsarcosine and Triton. The buffer is introduced through the central port. The excess liquid is removed through the waste ports and the side ports. An appropriate ratio of the waste and side port flow rates is maintained in a separation mode to allow the cells to be held at the substrate inside the chamber without disturbing their distribution.
Injection of lytic enzymes. Lysis buffer containing lysozyme is introduced through the central port, in a press down mode. The excess liquid passes through the substrate and is removed through the waste ports. The side ports remain closed. The E. coli cells remain immobilized on the substrate. The enzymes accumulate at the substrate with a concentration gradient extending within tens of microns into the flow region from the substrate. Flow through the central port is 0.05 mL/min and the temperature is maintained at 37° C.
Lysis. Lysis is allowed to proceed in a substantially quiescent chamber, in a reaction mode. The result is the release of genomic DNA and waste materials (e.g., cellular debris). The temperature is maintained at 37° C.
Injection of Proteinase K. Buffer containing proteinase K is introduced through the central port, in a press down mode. The excess liquid passes through the substrate and is removed through the waste ports. The side ports remain closed. The E. coli cells remain immobilized on the substrate. The enzymes accumulate at the substrate with a concentration gradient extending within tens of microns into the flow region from the substrate. Flow through the central port is 0.05 mL/min and the temperature is maintained at 37° C.
Proeteinase K Digestion. Proeteinase K digestion is allowed to proceed in a substantially quiescent chamber, in a reaction mode. The temperature is maintained at 55° C.
Washing. Buffer is introduced through the central port to remove all unwanted materials in a separation mode. The excess liquid carrying the waste is removed through the waste ports and the side ports maintaining an appropriate ratio of the two flows. The DNA is held by the substrate. Several buffers can be used consecutively in this step to achieve the desired purification level. The last buffer introduced is the buffer required for exonuclease digestion.
Injection of restriction enzyme and exonuclease. A DNA exonuclease and a DNA endonuclease are introduced into the chamber in a press down mode. The endonuclease is selected such that it will have recognition site(s) only on the genomic DNA.
Digestion of genomic DNA. Digestion is allowed to proceed in a substantially quiescent system in a reaction mode. At the end of this step, the temperature of the chamber is raised for the appropriate time to inactivate the exconuclease.
Washing. Buffer is introduced through the central port to remove all unwanted materials in a separation mode. Again, the excess liquid carrying the waste is removed through the waste ports and the side ports maintaining an appropriate ratio of the two flows. To keep the plasmid/BAC DNA inside the chamber. Several buffers can be used consecutively in this step to achieve the desired purification level. The last buffer introduced is the buffer required for elution.
Elution. Plasmid/BAC DNA is eluted from the chamber.
Example 5
Operating Protocol for DNA Tagging in a Chamber Like that of Example 1
Injection of DNA. A sample of DNA is introduced directly into the chamber in a press down mode. The chamber waste ports are open while the side ports are closed. The solvent can pass through the substrate while the DNA molecules are retained inside the chamber uniformly distributed on the substrate.
Washing. The buffer of the sample can be exchanged with tagging buffer in a separation mode. The buffer is introduced through the central port. The excess liquid is removed through the waste ports and the side ports. An appropriate ratio of the waste and side port flow rates is maintained that allows the DNA to be held at the substrate inside the chamber without disturbing its distribution.
Injection of tags. Sequence specific DNA tags (e.g. fluorescently labeled bis-PNA or fluorescently modified restriction enzymes) are introduced through the central port in a press down mode. The excess liquid passes through the substrate and is removed through the waste ports. The side ports remain closed. The DNA molecules remain immobilized on the substrate.
Tagging. Tagging is allowed to proceed in a substantially quiescent system, in a reaction mode. Alternatively, tagging may be performed using slow injection flow through the central port and the waste ports only. The chamber temperature is maintained at the appropriate value for the tagging reaction.
Washing. Buffer is introduced through the central port to remove excess free tags in a separation mode. Again, the excess liquid carrying the waste is removed through the waste ports and the side ports maintaining an appropriate ratio of the two flows. Several buffers can be used consecutively in this step to achieve the desired purification level. In the case of bis-PNA tagging the buffer may contain high salt concentration to assist the removal of non-specifically bound tags. In the case of restriction enzyme tags the tagging buffer can be used in this step.
Removal of non-specifically bound tags. The removal of non-specifically bound tags can be carried out in a reaction mode in a substantially quiescent system. The chamber temperature is maintained at the appropriate value which will allow fast disassociation of non-specifically bound tags.
Washing. Buffer is introduced through the central port in a separation mode to remove any residual excess free tags and to introduce the desired elution buffer in an elution mode.
Elution. Tagged DNA eluted from the chamber.
Example 6
Modeling of Flow in a Chamber
Models and simulations were used to optimize the design and function of an embodiment of the chamber. The models focused on flow fields for manipulating genomic sized DNA with minimal or no shear degradation. Microbes and free flowing DNA were modeled as rigid particles whereas semi-dilute DNA solution immobilized on the substrate was modeled according to the reptation model of Doi and Edwards. The nomenclature used in reporting the modeling results of Example 7 is shown below in Table 1.







TABLE 1





Nomenclature
















Vz
Axial downward direction velocity (m/s)


z
Distance perpendicular from the substrate in um (axial direction)


Q
Flow rate (mL/min)


Vr
Radial direction velocity (m/s)


r
Radial distance from the central axis of the chamber (m)


rho
Particle density (g/cm3)


z90
Axial distance from the substrate that includes 90% of reactants









FIG. 7 shows a simulation of injection flow in the chamber. This particular geometry that is illustrated was optimized for injection flow rates ≦0.7 mL/min. Bending of the flow stream lines, as shown, is attributed to a change from a parabolic velocity profile in the diffuser section to a more uniform velocity profile at the substrate surface. This bending can disturb reactants that are distributed on or about the substrate surface. To prevent this disturbance, the ratio of the radial (r) velocity component to the normal (z) velocity component may be minimized so that the fluidic drag force in the downward (z) direction is larger as compared to the drag force in the radial direction. FIGS. 9 and 10 show that this criterion is met in the chamber for a range of flow rates through the central port that are typically used. Meeting this requirement allows reagents to be introduced through the central port sequentially without disturbing a layer of agents that are already spread about the substrate. In FIG. 9, the ratio Vr/Vz versus radial distance is shown for Q=0.05 ml/min. FIG. 10 shows the variation of Vr/Vz ratio with flow rates through the central port.
Modeling shows that there may be an upper limit on the size and density of particles that will follow the flow within the chamber to spread uniformly about the substrate in a press down mode. FIG. 11 shows the spreading of particles as a function of particle diameter, particle density (rho) and flow rate (Q) through the central port. The modeling calculations are based on the assumption that the particles are in the dilute regime i.e. the inter-particle distance is larger than particle radius, such that particle-particle interactions may be neglected.
Modeling confirmed that downward flow fields exert a downward force on particles in the chamber, which can be used to hold agents on or about the substrate, even against the upward diffusion of agents, which may also be occurring within the chamber. FIG. 11 shows the variation of spreading coefficient versus particle diameter. Spreading coefficient was estimated by releasing a particle at r=0.9 mm at the central port and tracking the final radial distance of that particle on the substrate. a measure of the confinement region of reagents about the substrate. FIG. 11 illustrates the axial distance ‘z’ from the substrate below which 90% of the reagents are confined. The model assumes no passage of reagents through the substrate. FIG. 12 shows that the chamber may be used to create a micro-reaction zone within the chamber (FIG. 12 is representative for Q=0.05 mL/min. This micro-reaction zone may be used to enhance reaction rates.
Example 7
Operating Times for an Operating Protocol that Involves Isolation of Bacterial Genomic DNA
Table 2 shows times associated with isolation of bacterial genomic DNA performed in a chamber, like that described herein with respect to Example 1, and compares processing times for portions of the operating protocol with a conventional test tube protocol.










TABLE 2







Operating Protocol for



Test tube protocol
Time
Chamber
Time




















Pellet 1 × 108 cells
10
minutes
Inject 1 × 108 cells in a
5
minutes





press down mode


Wash cells and pellet
20
minutes
Wash cells in a separation
0
minutes


again


mode


Resuspend in lysozyme
4-16
hours
Introduce lysozyme in a
25
minutes


containing buffer and


press down mode and


incubate


incubate


Add proteinase K and
6-48
hours
Intorduce proteinase K in
26
minutes


buffer and incubate


a press down mode and





incubate


Dialyse
20-48
hours
Wash in a separation
25
minutes





mode


Add restriction enzyme
4-16
hour
Introduce restriction
26
minutes


and incubate


enzyme in a press down





mode and incubate


Dialyse
16
hours
wash in a separation mode
18
minutes











Total Time
>50
hours
Total Time
2 hours, 5






minutes









Example 8
Operating Times for an Operating Protocol that Involves Tagging of DNA with Bis-PNA
Table 3 shows times associated with the tagging of DNA with bis-PNA performed in a chamber, like that described herein with respect to Example 1, and compares processing times for portions of the operating protocol with a conventional test tube protocol.










TABLE 3







Operating Protocol for



Test tube protocol
Time
Chamber
Time




















Mix DNA and bis-PNA
1.2
hours
Introduce DNA and bis-
37
minutes


and incubate


PNA to chamber in a press





down mode and incubate


Dialyze excess bis-PNA
17
hours
Wash excess bis-PNA in a
14
minutes





separation mode


After-heating
0.2-1
hour
After heating in chamber
12
minutes





Wash in a separation
27
minutes





mode



Total Time
>18
hours
Total Time
1.5
hours









Example 9
Proof of Principle
Focusing Mode Performed with Digital DNA
A chamber like that described with respect to Example 1 was provided with 100 ng of digital DNA introduced to the chamber through the central port with the chamber operating in a focusing mode, as discussed with respect to FIG. 5e. The DNA was successfully focused to a central portion of the membrane. A tagging protocol, like that described with respect to Example 5, was performed on the DNA while held at the central portion of the membrane without the position occupied by the DNA increasing substantially. An intercalating protocol was performed on the DNA while held at the central portion of the membrane without the position occupied by the DNA increasing substantially. The chamber was then operated in a reverse elution mode, as discussed with respect to FIG. 13. As reflected in Table 4 below, the plug size retrieved after elution was 34 uL and had a peak concentration of 3.5 ng/uL. Also shown in Table 4 are DNA plug sizes and peak concentrations for tests run with digital DNA without focusing, with focusing (sample eluted after focusing), with focusing and a wash mode, and with focusing and intercalation.









TABLE 4







Peak Concen-


Experiment
DNA Plug Size (uL)
tration (ng/uL)

















Without Focusing
98
0.7


With Focusing
38
2.4


With Focusing and Wash
59
2


With Focusing and Intercalation
41
1.6


With Focusing, Tagging, and
34
3.5


Intercalation









Example 10
Evaluation of Various Flow Focusing Modes
A chamber like that described with respect to Example 1 was provided with 2×10^7 E. coli/Notl/YOTO-1. Lysis, digestion, and intercalation were performed on the cells at the different ratios of injection flow rates to side flow rates reflected in Table 5. DNA recovery and peak concentration were measured. An increase in the focusing flow was found to result in an improved recovery and DNA peak concentrations.







TABLE 5







Lysis, Digestion, and Intercalation


with Various Flow Focusing Ratios









Injection flow/Focusing




flow ratio
DNA Recovery
Peak Concentration





1:4 
63%
1.4


1:12
92%
1.7


1:19
>100% 
5.3









Example 11
Various Lysis, Digestion, Tagging, and Intercalation Tests
Lysis, digestion, tagging, and intercalation tests were run with 20 ng of sample and 100 ng of sample. Resulting elution profiles, peak concentrations and recovery percentages comet plots are shown below in Table 6.







TABLE 6







Test Results










Peak Concentration
Recovery %


Input
(from elution profile)
(from elution profile)





 143 ng
0.1 ng/uL
 4%


83.3 ng
0.17 ng/uL 
16%


N/A
0.3 ng/uL
24%









Example 12
Intercalation Protocol Optimization
Experiments were run to optimize parameters used during intercalation. DNA recovery and intercalation backbone intensity were measured for the different parameters listed in Table 6. All experiments were run with 2×107 cell injection (100 ng), 1:19 ratio of flow focusing to injection flow of cells and lytic enzymes. Standard reagent concentrations were used. Intercalator concentration was found to have minimal effect on DNA recovery. Injection volume and concentration were found to strongly effect backbone intensity. Decreased incubation time was found to cause in increase in recovery. Plug size and injection volume were found to show similar effects on recovery. Optimized parameters that were identified during the experiment are shown in Table 7.







TABLE 7







Optimization Parameters











Optimized



Parameter Values used
Parameter


Parameter to be Tested
During Experiments
Values













Intercalator
0.3 uM, 1 uM, 3 uM
3
uM


concentration


POPO-1 Plug Size
10 uL, 25 uL, 50 uL, 75 uL,
60
uL



100 uL


Injection Volume
145 uL, 290 uL, 350 uL,
500
uL



435 uL, 500 uL


Temperature
4 c., 25 C.
25
C.


Wash Time
10 minutes, 5 minutes
5
mL


Incubation
10 minutes, 7.5 minutes, 5
0
minutes



minutes, 0 minutes









Example 13
Reverse Elution Mode Performed in Focusing Chambers of Different Constructions
Agents were introduced to the chamber, in a first experiment, in a press down mode without focusing. Reverse elution was performed without removing fluid through the chamber side ports. 60% of a 125 uL of a 100 uL DNA plug was recovered from the chamber (margin of error +/−25%) without removing fluid through the side ports.
The experiment was repeated, except that the sample was introduced to the chamber in a flow focusing mode (with a 1:30 ratio of injection flow to side flow), like that shown in FIG. 5e, and 19% of a 100 uL DNA plug was recovered during a reverse elution performed without removing fluid through the side ports.
The experiment was repeated, again, except in a chamber with a second set of side ports like that shown in FIG. 16. The sample was introduced to the chamber in a flow focusing mode (with a 1:30 ratio of injection flow to side flow), like that shown in FIG. 5e. 7% of a 100 uL DNA plug was recovered during a reverse elution performed with fluid removed through second set of side ports. A 1:30 ratio of fluid removed through the central ports versus fluid removed from the side ports was used during reverse elution.
Removal of fluid through side ports during reverse elution was found to reduce the plug or bolus size of fluid that contains agents removed from the chamber. A lower recovery percentage may result, however, from low ratios of fluid removed through the central ports versus fluid removed from the side ports
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

## Claims

1. A method of positioning agents in a fluid flow, the method comprising:
providing a chamber having a porous substrate;
flowing a first fluid flow through a first fluid port and through the porous substrate in the chamber, wherein the first fluid flow contains agents;
flowing a second fluid flow through the chamber, the second fluid flow at least partially surrounding the first fluid flow to direct the first fluid flow and any agents contained therein toward a central portion of the porous substrate;
positioning the agents on the central portion of the porous substrate; and
reversing flow through the first fluid port to move any agents positioned on the porous substrate out of the chamber in central streamlines that exit the chamber through the first fluid port.

2. The method of claim 1, wherein flowing the second fluid flow comprises flowing the second fluid flow through one or more second fluid ports positioned about the porous substrate in the chamber, the second fluid flow completely surrounding the first fluid flow to direct the first fluid flow and any agents contained therein toward the central portion of the porous substrate.

3. The method of claim 1, wherein providing the chamber comprises providing a chamber that includes an open top.

4. The method of claim 1, wherein a flow rate of the second fluid flow is five times or greater than a flow rate of the first fluid flow.

5. The method of claim 1, wherein a flow rate of the second fluid flow is fifteen times or greater than a flow rate of the first fluid flow.

6. The method of claim 1, wherein a flow rate of the second fluid flow is twenty times or greater than a flow rate of the first fluid flow.

7. The method of claim 1, wherein agents removed from the chamber are concentrated ten times greater than prior to entering the chamber.

8. The method of claim 1, wherein agents removed from the chamber are concentrated one hundred times greater than prior to entering the chamber.

9. The method of claim 1, wherein the agents are nucleic acids.

10. The method of claim 9, wherein the agents are DNA.

11. The method of claim 9, wherein the nucleic acids maintain 75% to 100% of original length after exiting the chamber.

12. The method of claim 9, wherein the nucleic acids maintain 90% to 100% of original length after exiting the chamber.

13. The method of claim 9, wherein the nucleic acids include DNA having lengths of about 1 megabase in length after exiting the chamber.

14. The method of claim 1, further comprising:
conveying flow with agents positioned in central streamlines from the chamber prior to removing flow from about the central streamlines.

15. The method of claim 14, wherein conveying comprises conveying a fluid a distance greater than 10 cm.

16. The method of claim 14, wherein conveying comprises conveying a fluid a distance greater than 20 cm.

17. The method of claim 16, wherein agents are conveyed without dispersing more than 2 cm in a direction of flow.

18. The method of claim 17, wherein agents are conveyed without dispersing more than 2 cm in a direction of flow.

19. The method of claim 1, wherein flowing the second fluid flow comprises flowing the second fluid flow through one or more second fluid ports positioned about the porous substrate in the chamber.

20. The method of claim 1, further comprising:
removing flow from about the central streamlines to separate fluid flow that lacks agents from the central streamlines that exit the chamber.

21. The method of claim 1, wherein flowing the second fluid flow comprises the second fluid flow completely surrounding the first fluid flow to direct the first fluid flow and any agents contained therein toward the central portion of the porous substrate.

22. The method of claim 3, wherein flowing the first fluid flow comprises flowing the first fluid flow containing agents through a tube that is positioned at the open top on the chamber.

23. The method of claim 1, wherein reversing flow through the first fluid port includes flowing a fluid through a port positioned on a side of the porous substrate opposite the first fluid port such that the fluid flows toward the first fluid port.

24. The method of claim 20, wherein removing flow from about the central streamlines to separate fluid flow that lacks agents from the central streamlines that exit the chamber comprises removing flow through one or more second fluid ports.

25. The method of claim 20, wherein removing flow from about the central streamlines to separate fluid flow that lacks agents from the central streamlines that exit the chamber comprises removing flow through one or more third fluid ports that are positioned between the first fluid port and one or more second fluid ports.

26. The method of claim 25, wherein flow through the one or more second fluid ports is prevented when reversing flow through the first fluid port.

27. The method of claim 25, wherein flow is introduced through the one or more second fluid ports when reversing flow through the first fluid port.