Abstract:
A liquid storage apparatus provides a safe and easy to use device for efficiently managing liquid reagents used in a variety of laboratory equipment. The liquid storage apparatus helps reduce the likelihood of accidents, allows for flexibility of experimental design, and helps maximize the use of chemical regents to prevent waste. The apparatus includes a plurality of containers with a pierceable septum interface at each end. The apparatus also includes a lower array of needles with each of the lower needles in the lower array of needles arranged to penetrate the bottom pierceable septum of a different one of the containers. The apparatus further includes a piercing device arranged to penetrate the top pierceable septum of a different one of the containers. Each of the piercing devices include a passageway so gas can flow into the pierced container.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the storage and handling of liquid reagents in microfluidic systems. More particularly, the present invention relates to liquid containers and cartridges, piercing devices, mixing and administration systems, and methods of storing and handling liquid reagents for use in single molecule sequencing applications. 
       BACKGROUND INFORMATION 
       [0002]    Fluidic systems are used in a variety of areas including biochemical analysis, medical diagnostics, analytical chemistry, chemical synthesis, and environmental monitoring. Microfluidic systems provide certain advantages in acquiring chemical and biological information. For example, microfluidic systems permit complicated processes to be carried out using small amounts of reagents. 
         [0003]    In certain diagnostic equipment and systems, reagents are stored in containers with a needle pierceable septum at one end. Fluids can be extracted from these bottles in several ways. For example, the septum can be pierced with a short and a long needle. The long needle is designed to reach the bottom of the bottle to extract the liquid, and the short needle provides an air vent to replace the liquid with air as it is extracted from the bottle. A long needle causes safety concerns and requires complex mechanisms to protect and guide into the bottle. Another example of a method for extracting the liquid from these bottles is to provide a significant air volume above the liquid to only allow for low vacuum level buildup while extracting. This method has certain drawbacks as well because allowing even a small vacuum buildup in the bottle can introduce dispensing errors at selector valves in the liquid handling system. Furthermore, liquid storage systems and interfaces that use this method are difficult to manage. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides systems and methods for liquid reagent storage and handling. Systems and methods of the invention are useful in conjunction with any system in which reagent delivery is required, and are especially useful in apparatus for analyzing microfluidic volumes. Generally, the invention provides a safe and easy way to manage efficiently liquid reagents for use in a variety of laboratory equipment. The present invention helps reduce the likelihood of accidentals, allows for flexibility of experimental design, and helps maximize the use of chemical reagents to prevent waste. 
         [0005]    In a particular embodiment, the invention features an apparatus comprising a plurality of containers. Each of the containers includes, a top pierceable septum and a bottom pierceable septum. The apparatus also includes a lower array of needles. Each of the lower needles in the lower array of needles is arranged to penetrate the bottom pierceable septum of a different one of the containers and each of the needles include a passage so the liquid can flow out of the pierced container. The apparatus further includes a piercing device arranged to penetrate the top pierceable septum of each of the containers. The piercing device includes a passageway that allows gas to flow into the pierced container to occupy the space created as the liquid flows out of the container. 
         [0006]    In one aspect of the invention, the piercing device includes a housing that defines an internal region for receiving a container having a pierceable septum. The housing includes one or more slots to allow expansion of the housing when receiving a container. The housing also includes a septum piercing element affixed to the housing. The septum piercing element has a pointed tip and defines a passageway that allows gas to flow into the pierced container to occupy the space created as the liquid flows out of the container. One or more protrusions on the housing selectively engage an outer surface of the container to position and retain the container in the housing in an un-actuated position such that the septum piercing element does not pierce the septum prior to manipulation. 
         [0007]    In an alternative embodiment, a subset of two or more of the containers can be selectively secured together to form a cartridge assembly. One of more of these cartridge assemblies can be used to streamline or simplify the process of loading and unloading liquid reagents. A further aspect of this embodiment allows for customized cartridge assemblies designed for specific applications so that the liquid in each container of the cartridge is used up at approximately the same time. 
         [0008]    In another aspect of the invention, the lower array of needles includes non-coring needles with a closed sharpened end. These needles include an aperture in the side of the needle, which can be positioned slightly inside the bottom pierceable septum to maximize the utilization of the liquid reagents. 
         [0009]    In a further aspect of the invention, the upper array of needles is fluidly coupled to a filter, ventilation system, check valve or an inert gas system. For a variety of reasons it may be important to regulate the flow of gas into, or out of the containers as the liquids are being withdrawn. Some reagents may give off toxic fumes or unpleasant odors while others may degrade in the presence of oxygen. Providing a partially or completely sealed system can help provide a safer work environment and prevent the liquid reagents from breaking down or altering their composition. 
         [0010]    In yet another aspect of the invention, the liquid storage apparatus further includes a liquid level sensor. Analytical equipment utilizing the liquid reagents stored in the apparatus can be damaged if gasses are allowed to enter the other systems. One way of preventing this damage is to provide liquid level sensors for each individual container or for the entire apparatus that either notifies the user when the liquid level is getting low or shuts down the equipment. Various types of sensors can be used with the apparatus including, for example, ultrasonic, optical, capacitance level sensing. 
         [0011]    The invention is especially useful in automated systems, as for example when robotics are desired to deliver reagents. Thus, a cartridge system comprising a plurality of reservoirs is loaded into an instrument comprising robotics for accessing and dispensing reagents as described above. Robotic systems can include a separate module of needles that can be replaced at intervals determined by a user. 
         [0012]    The invention is also useful to effect on-time delivery of reagents, either under manual control or under the control of a computer or other electronic processor. Reagents can be accessed as needed and are isolated from environmental contaminants. In that regard, reagent dispensing bottles may be opaque, depending upon their contents. 
         [0013]    Pierceable reagent containers of the invention may be used in various applications known to the skilled artisan, examples of which are described below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a fuller understanding of the nature and operation of various embodiments according to the present invention, reference is made to the following description taken in conjunction with the accompanying drawing figures which are not necessarily to scale and wherein like reference characters denote corresponding or related parts throughout the several views and wherein: 
           [0015]      FIG. 1  is a schematic perspective view of an exemplary embodiment of a needle and container arrangement showing the containers in the process of being loaded; 
           [0016]      FIG. 2A  is a schematic perspective view of the needle and container arrangement of  FIG. 1  showing the containers in the loaded position; 
           [0017]      FIG. 2B  is an enlarged schematic perspective view of the needle and container arrangement of  FIG. 2A  showing the lower needles pierced through the bottom pierceable septum of two of the containers; 
           [0018]      FIG. 3A  is a schematic perspective view of a Trocar needle for use in the lower array of needles of the needle and container arrangement of  FIG. 1 ; 
           [0019]      FIG. 3B  is a schematic front view of the Trocar needle shown in  FIG. 3A ; 
           [0020]      FIG. 4A  is a schematic top view of a deflected tip needle for use in the upper array of needles of the needle and container arrangement of  FIG. 1 ; 
           [0021]      FIG. 4B  is a schematic front view of the deflected tip needle shown in  FIG. 4A ; 
           [0022]      FIG. 4C  is a schematic side view of the deflected tip needles shown in  FIG. 4A ; 
           [0023]      FIG. 5  is a schematic perspective view of a piercing device according to one exemplary embodiment of the present invention; 
           [0024]      FIG. 6A  is a schematic perspective view of a piercing device according to a second exemplary embodiment of the present invention; 
           [0025]      FIG. 6B  is a cross section view of the piercing device shown in  FIG. 6A ; 
           [0026]      FIG. 6C  is a an enlarged schematic perspective view of the piercing element shown in  FIG. 6B ; 
           [0027]      FIG. 6D  is a side elevation view of the piercing device shown in  FIG. 6A ; 
           [0028]      FIG. 7A  is a schematic perspective view of the piercing element shown in  FIG. 6A  attached to the top end of a container in an un-actuated position; 
           [0029]      FIG. 7B  is a schematic perspective view of the piercing element shown in  FIG. 6A  attached to the top end of a container in an actuated position; 
           [0030]      FIG. 8  is a schematic perspective view of the needle and container arrangement of  FIG. 1  showing the cover in a closed position; 
           [0031]      FIG. 9  is a schematic perspective view of a syringe pump system according to one exemplary embodiment of the present invention; 
           [0032]      FIG. 10A  is a cross-section front view of an individual container of the needle and container arrangement of  FIG. 1  showing a lower needle pierced through the bottom pierceable septum; 
           [0033]      FIG. 10B  is a top view of an individual container of the needle and container arrangement of  FIG. 1 ; 
           [0034]      FIG. 11  is a schematic perspective view of an alternative exemplary embodiment of a needle and container arrangement with different sized containers; 
           [0035]      FIG. 12A  is a schematic view of an apparatus that can be used to perform analytical experimentation with an exemplary embodiment of needle and container arrangement shown in  FIG. 1 ; 
           [0036]      FIG. 12B  is a schematic view of an apparatus that can be used to perform analytical experimentation with an exemplary embodiment of needle and container arrangement shown in  FIG. 1  with its liquids compartment drawer in the open position; 
           [0037]      FIG. 12C  is a schematic view of a needle and container assembly of  FIG. 1  integrated into a liquids compartment of the apparatus used to perform analytical experimentation shown in  FIGS. 12A and 12B ; 
           [0038]      FIG. 12D  is an enlarged schematic view of the needle and container assembly of  FIG. 12C ; and 
           [0039]      FIG. 12E  is a schematic view of the needle and container assembly of  FIG. 12C  showing the cover in an opened position. 
       
    
    
     DESCRIPTION 
       [0040]    Embodiments of the present invention are described below. It is, however, expressly noted that the present invention is not limited just to these disclosed embodiments. Various modifications not specifically detailed are within the scope of this disclosure. All relative descriptions herein such as top, bottom, left, right, up, and down are with reference to the figures, and thus should not be construed in a limiting sense. The present invention can be applied to liquid storage and handling systems for many types of analytical equipment such as, for example, flow cytometers and chemical analyzers. Further, the disclosed liquid storage and handling system can be used as part of a system for detecting single molecules by, for example, optical detection of single nucleotides. 
         [0041]    As indicated above, the present invention relates to the storage and handling of liquid reagents in microfluidic systems. Embodiments of a fluidic system and apparatus according to the present invention generally streamline the analysis of biochemical assays. The system, devices, and methods enable simple and safe loading and unloading of reagent containers or cartridges, allow for more accurate discharge and mixing of reagent volumes, and maximizes the utilization of the liquid volume in each individual container or cartridge. 
         [0042]    Referring now to  FIG. 1 , a liquid storage apparatus  10  includes a plurality of containers  20  filled with liquid reagents being loaded into a frame  40 . The containers  20  are selectively secured to a tray carrier  22  thereby forming a cartridge assembly  24 . Other means for arranging the plurality of containers  20  into a unitary cartridge assembly  24  will be apparent to one skilled in the art. In alternative embodiments, the containers  20  can be loaded into the frame  40  individually or in multiple cartridge assemblies. The containers  20  can be glass or a suitable plastic material such as acrylic, polycarbonate, or polypropylene. In some embodiments, the materials used in each container  20  can be the same or different from the other containers  20  depending on the liquid being stored, such that the liquid is not reactive with the container  20  material. Also, individual liquids may need to be stored in different thermal or atmospheric conditions and therefore thermal expansion characteristics may be an important consideration when selecting the container material. 
         [0043]    Each container  20  includes a top pierceable septum  26  and a bottom pierceable septum  28 . These septa  26 ,  28  can be made from any pliable material that allows penetration by a needle or piercing device and then seals the outside periphery of the needle or piercing device to prevent leakage. Examples of such materials are polytetrafluoroethylene (PTFE), fluorinated ethylene-propylene (FEP) and perfluoroalkoxy polymer resin (PFA), which are known generally by DuPont&#39;s brand name Teflon®. The septa  26 ,  28  can be the same or different depending on the desired application and/or the liquid being stored in each container. The septa  26 ,  28  can be secured to the container  20  in any of a number of ways including, for example, snap on, screw cap, mechanically fastened, heat welding, vibration welding, ultrasonically welding, or bonding with an adhesive. 
         [0044]    The liquid storage apparatus  10  also includes a lower array of needles  60 . Each of the needles  60  are disposed in a cavity  42  recessed into the bottom surface  44  of the frame  40 . As the cartridge assembly  24  is being lowered into the frame  40  in the direction indicated by line A, the bottom pierceable septa  28  are received into the cavities  42 . The cavities  42  can be slightly tapered with the widest part at the bottom surface  44  of the frame  40  to help guide the containers  20  into the cavities  42 . The needles  60  are disposed in the cavities  42  such that the points  62  of the needles  60  are below the bottom surface  44  of the frame  40  to help prevent accidental sticks. The cavities  42  also help ensure proper alignment of the needles  60  in the center of each septum  28  prior to penetration. 
         [0045]    Referring now to  FIGS. 2A and 2B , the containers  20  are shown partially loaded into the frame  40 . Each of the needles  60  have pierced the bottom pierceable septum  28  of each of the containers  20  and is penetrating into the liquid reagent. Each of the needles  60  has a passageway allowing the liquid reagent in the pierced container  20  to flow out of the container  20  to a liquids mixing and handling system. 
         [0046]    Liquid reagents used in certain analytical procedures are very expensive and therefore it is desirable to utilize as much of the liquid volume as possible to prevent waste. Referring now to  FIGS. 3A and 3B , a Trocar needle for use in the lower array of needles  60  is shown. As shown, the needle  60  has a closed sharpened point  62  and an aperture  64  in the side of the needle  60  to allow the point  62  of the needle  60  to protrude into the container  20  a sufficient distance to pierce the septum  28 , while also providing the outlet for the liquid in close proximity to the septum  28 . Such an arrangement allows for maximum utilization of the liquid volume in each container  20 . In alternative embodiments, the needles in the lower array of needles  60  can be any type of needle including, for example, a thoracentesis needles, Veress needles, or Huber needles. The needles  60  can be fabricated from stainless steel, titanium or other similarly rigid material in a range of sizes and lengths depending on the requirements of a particular application. 
         [0047]    Referring now back to  FIGS. 2A and 2B , the liquid storage apparatus  10  further includes an upper array of needles  80 . Each of the needles  80  are disposed in a cavity  52  recessed into the bottom surface  54  of a cover  50  pivotally attached to the frame  40 . The cavities  52  can be slightly tapered with the widest part at the bottom surface  54  of the cover  50  to help guide the containers  20  into the cavities  52 . The needles  80  are disposed in the cavities  52  such that the points  82  of the needles  80  are below the bottom surface  54  of the cover  50 . These cavities  52  are similar to the cavities  42  described above in relation to the frame  40  and perform substantially the same function, such as prevention of accidental sticks and ensuring proper alignment of the needles  80  in the center of each upper septum  26 . 
         [0048]    As described above, when liquids are removed from sealed containers, it is sometimes desirable to replace the liquid with air as it is being extracted to prevent formation of a vacuum in the container. To accomplish this goal, a needle, or other piercing device can be uses to puncture the top pierceable septa  26  to vent of each of the containers  20  to the atmosphere. For example, as shown in  FIG. 2A , after the containers  20  have been loaded in to the frame  40 , the cover  50  can be closed and needles  80  disposed in the cavities  52  penetrate the top pierceable septa  26 . When an array of needles  80  such as this are used to pierce the septa  26 , it can be difficult to puncture the septa  26  at the same time because of the hinging action of the cover  50 . In addition to utilizing relatively short needles  80  to prevent accidental sticks, shorter needles  80  also help ensure that all of the needles  80  make contact with the septa  26  at approximately the same time. However, the needles  80  still need to be long enough to adequately puncture the septa  26  so a vacuum doesn&#39;t form in the container  20  as the liquid is withdrawn. 
         [0049]    One example of a needle that can be used in the upper array of needles  80  is shown in  FIGS. 4A-4C . The deflected tip needle  80  has a sharpened point  82  that is slightly bent or offset from the longitudinal axis  84  of the needle  80 . This deflected tip design provides a “non-coring” needle such that as the septum  26  is pierced, none of the septum  26  material is removed, which could potentially cause an obstruction. Each needle  80  has a passageway  81  allowing gas to flow into the container  20  to occupy the space created by withdrawal of liquid reagent volumes. Alternatively, the upper needles  80  can be any type of needle including, for example, a thoracentesis needles, Veress needles, Huber needles, or Trocar needles. The needles  80  can be fabricated from stainless steel, titanium or other similarly rigid material in a range of sizes and lengths depending on the requirements of a particular application. 
         [0050]    Even though the needles  80  are disposed in the cavities  52  such that their points  82  are below the bottom surface  54  of the cover  50 , these “semi-exposed” needles can still inadvertently poke or stick the finger of a user. Also, since the needles  80  are integral with the cover  50 , it may be necessary to clean the needles  80  periodically to ensure that the containers are vented with an uncontaminated venting mechanism. As an alternative to an upper array of needles  80 , an individual piercing device can be affixed to the top end of each bottle to vent the containers. 
         [0051]    Referring now to  FIG. 5 , a piercing device  280  for use with a fluidic system and apparatus of the present invention is shown. The piercing device  280  performs substantially the same function as the needles  80  described above, and therefore like reference numerals preceded by the numeral “2” are used to indicate like elements. 
         [0052]      FIG. 5  illustrates a piercing device  280  that can be used to puncture the septum  26  of a container allowing gas to flow into the container to occupy the space created by withdrawal of the liquid reagent. As shown, the piercing device  280  includes a housing  283  that defines an internal region  286  configured for receiving a container. One or more slots  288  extend longitudinally from the receiving end of the housing  283  to allow slight expansion of the housing. The receiving end of the housing  283  can have in internal diameter equal to or slightly smaller than the diameter of the container prior to insertion of the container. The slots  288  allow for slight expansion of the housing  283  sufficient to allow insertion of the container, while maintaining a secure fit of the device  280  on the container. 
         [0053]    The housing  283  also includes one or more protrusions  285  extending into the interior region  286  of the housing  283 . The protrusions  285  assist in positioning and retaining the container within the housing. Additionally, the protrusions  286  provide support and assist in positioning as the device  280  is actuated to pierce the septum of a container. 
         [0054]    The housing  283  can also include one or more fingers  287  to assist in positioning and/or selectively retaining the container within the housing  283 . As shown, the fingers  287  extend longitudinally away from the receiving end and are positioned within an aperture of the housing  283 . The fingers  287  can be used independently from, or in conjunction with the slots  288  to assist in positioning and retaining the container within the housing  283 . For example, in an alternative embodiment, the housing does not include any slots and the receiving end of the housing has an internal diameter that is slightly larger than the diameter of the container. In this embodiment, the fingers  287  position and securely retain the container within the housing  283 . 
         [0055]    The piercing device  280  also includes a base surface  289  opposite from the receiving end. A piercing element  295  extends away from the base surface  289  into the interior region  286  of the housing  283  and defines a passageway  281 . As shown, the piercing element  295  tapers to a closed pointed tip  282  and the opening  297  to the passageway  281  is positioned on the side of the piercing element  295 . In order to properly vent the container to the atmosphere, the pointed tip  282  has to pierce the septum and protrude into the container a sufficient distance such that the opening  297  to the passageway  281  is passes through the septum and remains inside the container. 
         [0056]    Referring now to  FIGS. 6A-6D , an alternative embodiment of a piercing device  380  for use with a fluidic system and apparatus of the present invention is shown. The piercing device  380  performs substantially the same function as the piercing device  280  described above, and therefore like reference numerals preceded by the numeral “3” are used to indicate like elements. 
         [0057]    The piercing device  380  shown in  FIGS. 6A-6D  is substantially the same as the piercing device  280  shown in  FIG. 5  with a slightly different piercing element. As shown best in  FIG. 6D , the piercing element  395  is tapered on a bias such that the pointed tip  382  is offset from the longitudinal axis  384  of the piercing element. In this embodiment, the opening  397  to the passageway  381  extend along the longitudinal axis  384  from the base surface  389  to the pointed tip  382  such that the opening essentially begins at the pointed tip  382 . One advantage of this embodiment is that an open fluid passageway  381  is established almost immediately after the septum of a container is punctured. 
         [0058]    It is envisioned that the piercing device  280 ,  380  could be easily attached to a container by the user. However, in some instances, the piercing device can be pre-install to the top end of each container and would be discarded with the container  220  after the liquid reagent is utilized. Referring now to  FIGS. 7A and 7B , the piercing device  380  is shown attached to the top end of a container  320 . As shown in  FIG. 7A , the piercing device  380  is movably attached to the end of the container  320  in a un-actuated position. In this un-actuated position, the piercing element  395  is not in contact with the septum  326  and the container  320  is still sealed. The protrusions  385  are disposed in a groove  321  in the top end of the container  320  to secure the device  380  on the container  320 . Fingers  387  extend beyond the top end of the container  320  and help prevent inadvertent penetration of the septum by the piercing element during shipping or handling. 
         [0059]    To pierce the septum of the container  320 , the user pushes down on the piercing device  380  in the direction indicated by line B to actuate the piercing device  380  causing the piercing element  395  to pierce the septum  326  and vent the container  320  to atmosphere. Alternatively, the cover  50  of a liquid storage apparatus  10  described above can actuate a plurality of piercing devices  380  when the cover  50  is closed.  FIG. 7B  shows the piercing device  380  in the actuated position. Once manipulated into the actuated position, the fingers  387  engage the groove  321  and secure the piercing device  380  into the actuated position and remain in the actuated position even after the user removes their finger or opens the cover  50 . 
         [0060]    Referring now to  FIG. 8 , a fully loaded liquid storage apparatus  10  is shown. A series of air vents  58  are fluidly coupled to the passageways  81  of the needles  80  or piercing devices, which allow direct venting of the containers  20  to the atmosphere. As the liquid reagents are withdrawn from the containers  20 , air can freely enter the containers  20  through the passageways to replace the liquid volume as it is removed. Replacing the space occupied by the liquid with air or other gas maintains a consistent operating pressure in the containers  20 , i.e., no vacuum build-up, thus helping prevent dispensing errors at selector valves in the liquid handling system. 
         [0061]    Liquid reagents used in some microfluidic systems have toxic vapors or have an unpleasant odor. The air vents  58  can be fluidly coupled to a filter (not shown) such as a biological grade filter or to a laboratory ventilation system to eliminate the odors or toxic vapors. In further embodiments, the liquids being stored may be extremely volatile in which case a one way check valve or a series of check valves may be included to allow air to flow into the containers after liquid is withdrawn. In yet a further embodiment, certain reagents may be reactive with oxygen and therefore the air vents  58  may be fluidly coupled to an inert gas system to prevent the reagents from degrading. 
         [0062]    Referring no to  FIG. 9 , a syringe pump system  400  for withdrawing, mixing, and delivering liquid volumes is shown. The syringe pump system  400  includes a syringe  410  having a plunger  420 . The plunger  420  is coupled to a plunger actuator  430  that mechanically moves the plunger  420  up and down to fill and evacuate fluid in the syringe  410 . The syringe  410  is fluidly coupled to a reagent selector valve  440  via a syringe port orifice  450 , which is in turn fluidly coupled to the liquid reagent containers. The selector valve  440  has a plurality of inlets (not shown), each of the inlets corresponding to one of the liquid reagent containers, and one or more outlets (not shown) corresponding to one or more piece of analytical equipment. The selector valve  440  controls the flow of liquid reagents into the syringe  410  and distribution of the liquid mixture out to analytical equipment. 
         [0063]    In operation, the selector valve  440  is set to a particular reagent. The plunger  420  is then pulled down by the actuator  430  creating a pressure drop drawing a predetermined volume of liquid from a specific reagent container, through a conduit, through the selector valve  440 , and into the syringe  410 . The selector valve  440  can then be changed to an outlet port and the plunger  420  is actuated in an upward direction thereby discharging the liquid to the analytical equipment. 
         [0064]    Alternatively, some assays require a combination of several different liquid reagents. In this instance, the selector valve  440  can be set to a particular inlet port corresponding to a certain reagent such as, for example, Reagent  1 . The plunger  420  is then actuated drawing a predetermined volume of Reagent  1  into the syringe  410  as described above. The selector valve  440  is then changed to a different inlet port corresponding to a different reagent such as, for example, Reagent  2 . The plunger  420  is then actuated drawings a predetermined volume of Reagent  2  into the syringe  410 . Once the two reagents are in the syringe  410  they essentially form a mixture of Reagents  1  and  2 , which can then be dispensed to the analytical equipment as described above. 
         [0065]    Furthermore, in some assays, the plurality of reagents must be sufficiently well mixed to form a relatively homogeneous solution. There are several factors that effect mixing performance including, for example, viscosity of each reagent, volumes of each reagent, miscibility of reagents, total volume to be mixed, and geometry of the syringe. Several fluid dynamic phenomena occur within the syringe pump system  400  that are highly effective at promoting sufficient mixing such as cavitation and turbulence. For example, when the plunger  420  is pulled down very quickly, a significant pressure drop is generated at the orifice  450  of the syringe  410 . This pressure drop depends on the size of the orifice  450 , the diameter of the syringe  410 , the speed of the plunger  420  movement, and the total change in volume of the syringe  410 . This inertial cavitation provides a low pressure void into which the fluid flows causing increased mixing through the eddies and vortices occurring at the interface between the void and the liquid. 
         [0066]    During the mixing process, if Reynolds numbers greater than 1,000 can be achieved creating transitional flow, or better still, greater than 2,000 creating turbulent flow, mixing will occur throughout the syringe  410  volume. However, with lower velocities and therefore lower Reynolds numbers, the cavitation and layering of reagents also can provide effective mixing. For layering of reagents, small volume reagents should generally be added in between layers of the highest volume reagents. The highest volume reagents are added at higher flow rates to create Reynolds numbers in excess of 2,500. Furthermore, it may be necessary to add an individual reagent to the syringe  410  multiple times stacking them up in the syringe  410  and disturbing them during the filling/mixing process several times as the formulation is prepared to ensure proper mixing. One reason for “stacking” certain reagents is to avoid damaging the reagents by localized heating and/or shock waves caused by cavitation. One example of such stacking of reagents is provided in Example 1 below. 
       EXAMPLE 1 
       [0067]      
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                 Volume 
                 Aspiration Speed 
               
               
                   
                 Reagent 
                 (μL) 
                 (μL/second) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Water 
                 22.5 
                 250 
               
               
                   
                 Reagent 1 
                 12 
                 20 
               
               
                   
                 Reagent 2 
                 12 
                 15 
               
               
                   
                 Reagent 3 
                 6 
                 10 
               
               
                   
                 Water 
                 20 
                 250 
               
               
                   
                 Reagent 4 
                 6 
                 20 
               
               
                   
                 Water 
                 20 
                 250 
               
               
                   
                 Reagent 1 
                 10 
                 20 
               
               
                   
                 Reagent 2 
                 10 
                 15 
               
               
                   
                 Reagent 3 
                 5 
                 10 
               
               
                   
                 Water 
                 20 
                 250 
               
               
                   
                 Reagent 4 
                 6 
                 20 
               
               
                   
                 Water 
                 20 
                 250 
               
               
                   
                 Reagent 1 
                 10 
                 20 
               
               
                   
                 Reagent 2 
                 10 
                 15 
               
               
                   
                 Reagent 3 
                 5 
                 10 
               
               
                   
                 Water 
                 9.7 
                 250 
               
               
                   
                 Reagent 4 
                 6 
                 20 
               
               
                   
                 Water 
                 39.8 
                 250 
               
               
                   
                   
               
             
          
         
       
     
         [0068]    Analytical equipment utilizing liquid reagents can be damaged if gasses are allowed to enter the liquid handling system. One way of preventing this damage is to provide liquid level sensors for the entire apparatus or a level sensor at each individual container. Referring now to  FIGS. 10A and 10B , the liquid storage apparatus  10  further includes a liquid level sensor  70 . As shown in  FIG. 10A , the liquid level sensor  70  includes a photo sensor  72  and a light-emitting diode (LED)  74 . The liquid level sensor  70  is positioned on a circuit board  76  below each of the containers  20  along the flow path between the aperture  64  of the lower needle  60  and the outlet  73  to the liquids handling system. The photo sensor  72  is located on the opposite side of the flow path from the LED  74 . This type of liquid level sensor  70  is known as an optical level sensor and can sense the presence or absence of fluid bases on the light transmitted from the LED  74  thought the flow path. Other types of liquid level sensors that can be used with the liquid storage apparatus  10  include, for example, ultrasonic level sensors and capacitance level sensors. 
         [0069]    The liquid level sensors can be configured to shut down the equipment when the liquid in the containers has been fully utilized or to provide notification to the user when the liquid level is either getting low or is completely empty. As shown in  FIG. 10B , a LED  78  is attached to the circuit board  76  next to the container  20 . The LED  78  provides a visual indication to the user when that particular container  20  is empty. The LEDs may also be configured to provide a visual indication of where certain containers  20  should be loaded for particular experimental procedures. 
         [0070]    As shown in  FIGS. 1 ,  2 , and  8 , all of the containers  20  are the same size and shape. Referring now to  FIG. 11 , a liquid storage apparatus  110  is shown with one container  130  larger than the other containers  120 . The tops and bottoms of all of the containers  120 ,  130  are symmetrical having the same size and shape. The top and bottom cavities  142 ,  152  are also the same size and shape such that the containers  120 ,  130  can be loaded in either direction. This universal interface design allows a variety of different container sizes to be used in the liquid storage apparatus  110 . In alternative embodiments, the tops and bottoms of the bottles  120 ,  130  and the top and bottom cavities  142 ,  152  are not all symmetrical (i.e., different sizes and shapes) which can prevent liquid reagents from being loaded in the wrong location. 
         [0071]    As mentioned above, the liquid storage apparatus  110  of the present invention is designed for a wide variety of applications. In certain applications, such as single sequencing of DNA molecules, the liquid reagents can be very expensive. The user can customize the liquid storage apparatus  110  with larger containers for reagents that are used more frequently and smaller containers for those reagents that are used less frequently or in smaller quantities. Additionally, container cartridge assemblies can be designed for specific applications so that the liquid in each container of the assembly is used up at approximately the same time. 
         [0072]    The liquid storage apparatus  10  can be a stand-alone apparatus that can be connected to a variety of lab equipment or it may be integrated into an individual piece of equipment. Referring now to  FIG. 12A-12E , the frame  40  is integrated into a compartment of a single molecule sequencing device  90 . To load the reagents, the user simply slides open the compartment  92  and opens the cover  94 . Individual containers and/or cartridge assemblies are inserted into the appropriate locations. The liquid storage compartment  92  may be subdivided to store liquids at different temperatures. 
         [0073]    The disclosed embodiments are exemplary. The invention is not limited by or only to the disclosed exemplary embodiments. Also, various changes to and combinations of the disclosed exemplary embodiments are possible and within this disclosure.