Abstract:
An apparatus for and method of enabling enhanced, selective agitation of liquid containing a solid-phase reagent. The apparatus includes at least one liquid-bearing container, a circular tray, and a motor. The liquid-bearing container(s) includes at least one internal baffle that imparts turbulent agitation to the liquid when flowing from one end of the container to an opposite end. The circular tray is adapted for selective rotation about a vertical axis of rotation. The rotary circular tray assembly includes container-receiving stations that selectively retain a respective liquid-bearing container in an inclined or pitched orientation with respect to a horizontal plane. The motor creates centrifugal force, which causes liquid in the container(s) to travel from the first end of the container to the second end of the container via the internal baffle(s), agitating the liquid and the solid-phase portions of the reagent. When gravitational force exceeds the centrifugal force, liquid in the container(s) travels from the second end of the container to the first end of the container via the internal baffle(s), again agitating the liquid and the solid-phase portions of the reagent.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to reagent trays for automated immunoassay systems, and more particularly to rotary reagent tray assemblies that are structured and arranged to promote homogenous mixing of solid-phase reagents using rotary motion of the ring and centrifugal force. 
         [0003]    Previous immunoassay systems have included linear reagent trays for holding reagent packs, such as ReadyPack reagent packs manufactured by Siemens Healthcare Diagnostics, Inc. of Tarrytown, N.Y. Typically, linear reagent trays are adapted to rock about a point of rotation so that the rocking, back-and-forth motion maintains most of the solid-phase portion of the reagent in suspension. However, even with automatic rocking motion, it is not always possible to suspend all solid-phase portions of the reagent adequately. As a result, some reagent packs must be manually mixed and agitated before being installed in the reagent tray. A further problem with applying a rocking motion is that the motion must be continuously applied to the reagent packs so that the solid-phase portion of the reagent does not settle out. This “24/7” approach produces more wear and tear on the system and also affects the on-board stability of the reagent. 
         [0004]    U.S. Pat. No. 5,451,528 to Raymoure et al. (the “&#39;528 Patent”) purports to disclose methods of modifying a liquid assay reagent for prolonged longevity. The method includes adding an inert material to the liquid assay reagent. In addition, according to the &#39;528 patent, the liquid assay reagent is automatically agitated by the back-and-forth motion of a reagent carousel onto which reagent packs containing the liquid assay reagent are loaded. The acceleration, velocity, distance moved, and pause-asymmetry can be changed to provide “rapid assay reagent resuspension without foaming or bubble formation.” In short, the &#39;528 patent relies on centripetal forces and the hurky-jerky movement of the carousel to “slosh” the liquid assay reagent sufficiently to maintain the solid-phase portions of the reagent in suspension. 
         [0005]    However, “sloshing” due to hurky-jerky centripetal forces can result in solid-phase portions of the reagent adhering to the sides or walls and even to the lid of the liquid-carrying container. Such a result would reduce the percentage or concentration of the solid-phase portion in the reagent. 
         [0006]    Accordingly, it would be desirable to provide a rotary reagent tray assembly that is adapted to use the movement and energy of the tray rotation and stopping to mix and agitate the solid-phase portion of a liquid assay reagent, and, thereby, to eliminate the need for manual mixing/agitation prior to installation of the reagent packs in the reagent tray. Moreover, it would be desirable to provide a rotary reagent tray that is adapted to use centrifugal forces resulting from the rotational movement of a rotary reagent tray to mix and agitate the solid-phase portion of a liquid assay reagent, and, thereby, eliminate the possibility of loss of some of the solid-phase portion through adherence to an inner surface of the reagent pack due to uncontrolled centripetal “sloshing”. 
         [0007]    In comparison with linear reagent trays that use a rocking, back-and-forth movement to suspend solid-phase portions, rotary reagent trays increase the capacity of the reagent tray while minimizing the footprint of the tray. Moreover, advantageously, lateral travel requirements of the aspirating reagent probe are reduced and can result in replacement of a three-axis of control probe with a simpler, two-axis probe mechanism. 
       SUMMARY OF TEE INVENTION 
       [0008]    An apparatus for and method of enabling enhanced, selective agitation of liquid containing a solid-phase reagent are disclosed. The apparatus includes at least one liquid-bearing container, a circular tray, and a motor. The liquid-bearing container(s) has a first end and an opposite second end between which is disposed at least one internal baffle. The internal baffle imparts turbulent agitation to the liquid when flowing from one end of the container to an opposite end. 
         [0009]    The circular tray is adapted for selective rotation about a vertical axis of rotation. The rotary circular tray has plural container-receiving stations arranged radially in a circle on the tray. Each station is further adapted to receive and to selectively retain a respective liquid-bearing container in an orientation whereby the container is inclined or pitched with respect to a horizontal plane. Moreover, the first end of the container, which is proximate the axis of rotation, is disposed lower than the second end of the container, which is distant from the axis of rotation. 
         [0010]    The motor is in driving engagement with the tray and is, further, adapted for selectively rotating the tray. 
         [0011]    In pertinent part, centrifugal force, which is associated with the rotation or rotational acceleration of the tray by the motor, causes liquid in the container(s) to travel from the first end of the container to the second end of the container via the internal baffle(s), causing the liquid and the solid-phase portions of the reagent therein to be agitated so as to promote continued suspension or resuspension of the solid-phase portions. When gravitational force, which is associated with the cessation of rotation or the rotational deceleration of the tray by the motor, exceeds the centrifugal force, liquid in the container(s) travels from the second end of the container to the first end of the container via the internal baffle(s), again causing the liquid and the solid-phase portions of the reagent therein to be agitated so as to promote continued suspension or resuspension of the solid-phase portions. 
         [0012]    The method of selectively agitating liquid in a container includes providing the liquid-bearing container(s); providing the rotatable circular tray; disposing the container(s) on a respective container-receiving station associated with the tray; selectively rotating the tray so that centrifugal force generated causes liquid in the container(s) to travel from the first end of the container to the second end via the internal baffle(s), which causes the liquid and the solid-phase portions of the reagent therein to be agitated so as to promote continued suspension or resuspension of the solid-phase portions, and selectively decelerating or stopping the tray so that gravitational force exceeds the centrifugal force, causing liquid in the container(s) to travel from the second end of the container to the first end of the container via the internal baffle(s), again causing the liquid and the solid-phase portions of the reagent therein to be agitated so as to promote continued suspension or resuspension of the solid-phase portions. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be more fully understood by reference to the following Detailed Description of the invention in conjunction with the Drawings, of which: 
           [0014]      FIG. 1  shows an illustrative schematic of a rotary reagent tray assembly and reagent compartment for an assay testing system; 
           [0015]      FIG. 2  shows an illustrative schematic of the rotary reagent tray assembly of  FIG. 1  with the cover of the ancillary tray removed; 
           [0016]      FIG. 3  shows a cross-section of the rotary reagent tray assembly of  FIG. 1 ; 
           [0017]      FIG. 4  shows an illustrative schematics of plan (A) and elevation (B) views a reagent pack; 
           [0018]      FIG. 5  shows an exemplary triangular motion profile; 
           [0019]      FIG. 6  shows an exemplary trapezoidal motion profile; and 
           [0020]      FIG. 7  shows a cross-section of an alternative embodiment of a rotary reagent tray assembly having a direct drive motor. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring to  FIGS. 1-3 , a rotary reagent tray or carousel assembly will be described. The rotary reagent tray assembly  10  is structured and arranged to hold a plurality of primary reagent packs  35  and/or ancillary reagent packs  20 , respectively, in a primary tray  12  and an ancillary tray  14 . The primary tray  12  and the ancillary tray  14  are arranged in the rotary reagent tray assembly  10  coaxially and concentric with one another about a vertical axis  29 . Although the invention will be described in terms of having both a primary tray  12  and an ancillary tray  14 , the invention could also be practiced using just a primary reagent tray. 
         [0022]    The primary reagent tray  12  is shown mechanically coupled to a primary motor  11  via a drive shaft  13 , a drive pulley  44 , and a pulley belt  15 . The primary motor  11 , drive shaft  13 , drive pulley  44 , and pulley belt  15  are structured and arranged to provide independent, bi-directional movement to the primary reagent tray  12  by applying torque to the drive shaft  13 . 
         [0023]    The pulley belt  15  is disposed between a pair of idler wheels  22 , around a drive wheel  24  that is mechanically coupled to the motor  11 , and around the drive shaft  13  or an extension thereof. The drive shaft  13  includes a head portion that is mechanically and/or frictionally coupled to an inner peripheral portion  16  of the primary reagent tray  12 . As a result, when the drive shaft  13  rotates, accelerates, decelerates or stops, so does the primary reagent tray  12 . Alternatively, the embodied motive means for the primary reagent tray  12  can be replaced by a direct-drive primary motor  71  co-located with the drive shaft  73  as shown in  FIG. 7 . Bearings  72  are provided to support the drive shaft  73 . 
         [0024]    The ancillary reagent tray  14  is mechanically coupled to an ancillary motor  21  via a drive wheel  23  at an outer peripheral surface  25 . The ancillary motor  21  and drive wheel are structured and arranged to provide independent, bi-directional movement to the ancillary reagent tray  14  by applying a centripetal or tangential force to the outer peripheral surface  25  of the ancillary reagent tray  14 . 
         [0025]    Although the figures illustrate the primary reagent tray  12  and the ancillary tray  14  of rotary reagent tray assembly being driven, respectively, from an inner peripheral portion  16  and from an outer peripheral surface  25 , that is done for descriptive purposes only. Those of ordinary skill in the art can appreciate that a rotary reagent tray assembly  10  structured and arranged as previously described could also include a primary reagent tray  12  and the ancillary tray  14  that are driven instead, respectively, from an outer peripheral surface and from an inner peripheral surface. 
         [0026]    The ancillary reagent tray  14  includes an annular, flat or substantially flat, bottom portion  18  that has a plurality of seating areas  27 , each of which is structured and arranged for storing and holding a respective ancillary reagent pack  20 . Adjacent, cooperating spring-biased clips  55  can be used to securely fasten and hold the ancillary reagent pack  20  in a discrete seating area  27 . 
         [0027]    Referring to  FIG. 1  and  FIG. 3 , the ancillary reagent tray  14  optionally can be protected by a non-moving cover portion  19  that is structured and arranged to enclose the ancillary reagent tray  14  and the ancillary reagent packs  20  disposed therein, to control the temperature thereof, and to provide structural support to at least one cooling device  26 , e.g., at least one thermoelectric Peltier device. Although  FIG. 1  and  FIG. 3  show a rotary reagent tray assembly  10  with a cooling device-supporting cover portion  19 , the tray assembly  10  can be operated without either as shown in  FIG. 2 . 
         [0028]      FIG. 7  shows alternative internal and external cooling devices for a rotary reagent tray assembly  10 . According to the embodiment shown in  FIG. 7 , for external conduction, the tray assembly  10  includes at least one cooling device  26 , e.g., a thermoelectric Peltier device, which is disposed on the bottom portion of the tray assembly  10  proximate the rotary motor  71  and rotating shaft  73 , which will produce a great deal of heat. Internal cooling is performed by forced air convection. More specifically, a fan assembly  74  is centrally disposed at or near the axis of rotation of the shaft  73 . The fan assembly  74  is structured and arranged to create forced-air circulation as shown by the arrows  77 . A plurality of cooling fins  76  are provided on the bottom portion of the tray assembly  10 . The cooling fins  76  are thermally coupled to the bottom portion, which, in turn, is thermally coupled to the at least one cooling device  26 . 
         [0029]    In operation, the at least one cooling device  26  is structured and arranged to remove heat from cool the fins  76 , which remove heat from the circulating forced-air  77 . The fan assembly  74  draws air that has been cooled by the cooling fins  76  via an air duct  75 . The cooled air then circulates in the air space above the ancillary reagent packs  20 ; around the primary reagent packs  18 ; and back through the cooling fins  76 . 
         [0030]    The cover portion  19  includes a planar or substantially planar, annular upper portion  28  on which the cooling device(s)  26  can be releasably attached, an outer peripheral surface  25  having at least one loading port  39  for introducing and removing the ancillary reagent packs  20 , and an inner surface or inner skirt  37 . 
         [0031]    The loading port  39  is provided in the outer peripheral surface  25  and permits automatic and/or manual horizontal or substantially horizontal loading and unloading of new or used ancillary reagent packs  20 . The dimensions of the ancillary port(s)  20  can be varied to enable insertion/removal of a single ancillary reagent pack  20  or the insertion/removal of multiple ancillary reagent packs  20  simultaneously. To load an ancillary reagent pack  20 , the ancillary reagent tray  14  is rotated until a vacant seating area  27  or a seating area  27  currently housing an empty ancillary reagent pack  20  is placed in registration with the ancillary loading port  39 . If the seating area  27  is vacant, then an unused ancillary reagent pack  20  can be manually or automatically inserted into the vacant seating area  27  via the loading port  39 . If, on the other hand, a used ancillary reagent pack  20  is occupying a needed seating area  27 , the used ancillary reagent pack  20  is first removed manually or automatically before a fresh ancillary reagent pack  20  is manually or automatically inserted into the now vacant seating area  27  via the loading port  39 . 
         [0032]    A reagent probe access area  31  is located in the inner skirt  37  (if there is one) proximate to the at least one pipettor (not shown) that aspirate(s) reagent from the reagent packs. Probe access to the primary reagent pack  35  or to the ancillary reagent pack  20  is provided through at least one hole or opening  32  in a portion of the cover portion  19  of the ancillary tray  14  (if there is one). Because any one container can be positioned beneath at least one hole or opening  32 , an aspiration probe movable in X and Z directions only can be employed, in contrast to a probe used with a linear array of containers, which requires the ability to move the probe in X-, Y-, and Z-axes. Probe access holes or openings  32  are structured and arranged to enable the tip(s) of at least one pipettor to puncture the lid of and to aspirate a desired volume of a reagent from a liquid-carrying container  20  or  35 . 
         [0033]    A single probe access hole or opening  32  disposed in the annular upper portion  28  of the cover portion  19  and multiple access holes  32  disposed in the skirt  37  are shown in  FIG. 1  for illustrative purposes only. Those of ordinary skill in the art can appreciate the variations that can be made with the number of redundant pipettors and the number of holes or openings  32 . 
         [0034]    The primary reagent tray  12  includes an annular bottom portion  33  that is structured and arranged to provide a plurality of container-receiving areas or seating areas  38  each of which is structured and arranged for holding a respective reagent pack  35 . A discussion of the seating area  38  and the reagent packs  35  is provided below. 
         [0035]    The primary reagent tray  12  is protected by the inner skirt  37  of the cover portion  19  (if there is one), by the annular, flat or substantially flat, bottom portion  18  of the ancillary reagent tray  14 , by an inner core cover  34 , and by a non-moving outer peripheral surface  36 . At least one loading port  30  is provided in the outer peripheral surface  36 . The loading port(s)  30  permits automatic and/or manual, horizontal or substantially horizontal loading and unloading of new or used primary reagent packs  35 . The dimensions of the loading port(s)  30  can be varied to enable insertion/removal of a single reagent pack  35  or the insertion/removal of multiple reagent packs  35  simultaneously. 
         [0036]    To load a reagent pack  35 , the primary reagent tray  12  is rotated until a vacant seating area  38  or an empty reagent pack  35  that needs to be removed is placed in registration with the loading port(s)  30 . If the seating area  38  is vacant, then an unused reagent pack  35  can be manually or automatically inserted into the vacant seating area  38  via the loading port  30 . Adjacent spring-biased clipping devices  59  are adapted to hold an installed reagent pack  35  securely within the seating area  38 . Alternatively, a used reagent pack  35  can first be removed manually or automatically from the reagent tray  12  before an unused reagent pack  35  is manually or automatically inserted into the now vacant seating area  38  via the loading port  30 . 
       Reagent Packs 
       [0037]    A reagent pack for keeping fluids with or without solid-phase portions mixed or suspended is disclosed in U.S. Pat. No. 5,788,928 (the “&#39;928 Patent”) currently assigned to Siemens Healthcare Diagnostics, Inc. of Tarrytown, N.Y., and which is incorporated in its entirety herein by reference. 
         [0038]    The &#39;928 reagent pack includes a sub-divided chamber whose sub-chambers are separated by a throat region that is defined by baffles, e.g., an S-shaped channel (or S-channel). Although the reagent packs described in the &#39;928 patent were designed for the rocking action of a linear reagent tray, reagent packs having the same properties are also suitable for use with the rotary reagent tray assembly described herein. 
         [0039]    Referring to  FIG. 4 , the reagent packs  35  that make up a portion of the present invention are designed so that the effects of the bi-directional, rotational movement of the rotary reagent tray assembly  10  and, furthermore, of the periodic stopping of the same adequately mix and/or keep suspended solid-phase reagent portions contained within the liquid portion of the reagent. More specifically, the design of the reagent packs  35 , which includes a narrowed throat region  40  between adjacent sub-chambers  41  and  42 , in combination with the centrifugal forces that are generated by the rotating reagent tray assembly  10 , force all or some portion of the reagent outwards through the restrictive channel  40 . 
         [0040]    The reagent pack  35  has an inner end  52  and an outer end  54 . As shown in  FIG. 2 , the inner end  52  is closest to the vertical axis  29  of the rotary reagent tray assembly  10  and the outer end  54  is closest to the loading port  30  when aligned therewith. Walls and surfaces that are described in the &#39;928 patent divide each reagent pack  35  into a plurality of chambers  41 - 44 . Each chamber  41 - 44  is structured and arranged to store a reagent used by the immunoassay system. The reagent can be soluble, which requires little or no agitation for homogenous distribution, or non-soluble, which requires agitation for continuous distribution. 
         [0041]    The bottom surface  53  within each of these chambers  41 - 44  is inclined or pitched toward a single location within the respective chamber, to facilitate complete or substantial aspiration of material stored therein. In a preferred embodiment, this location takes the form of a depression  48  (or sump) disposed in the bottom  53  of a chamber  43  and  44 . 
         [0042]    At least one of the chambers of each reagent pack  35  can be provided with a pair of opposing, offset baffles  56 ,  58 . In particular, a larger chamber can be divided into two sub-chambers  41  and  42  of substantially equal volume, each of the sub-chambers  41  and  42  is interconnected by the narrow throat region  40 , which can include baffles  56  and  58 . Each of the baffles  56  and  58  extends from a respective side wall into the larger chamber towards the opposite side wall. The baffles  56  and  58  can be vertically disposed from the floor surface  53  to the upper edge of the side wall, and preferably extend across at least half the width of the reagent pack  35  toward the opposing side wall. 
         [0043]    The benefit of such a configuration is realized when suspended solid-phase reagent materials are introduced into the sub-divided chamber and the reagent pack  35  is subjected to a centrifugal force due to the rotation of the primary reagent tray  12 . The applied centrifugal force causes fluid to travel from the inner end  52  towards the outer end  54  (arrow A), which is to say, from the first sub-chamber  42  through the baffles  56  and  58  at the narrow throat  40  into the second sub-chamber  41 . When no or an inadequate centrifugal force is applied to the reagent packs  35 , head pressure and the pitch of the reagent pack  35  cause the fluid to travel from the second sub-chamber  41  through the baffles  56  and  58  at the narrow throat  40  into the first sub-chamber  42 . 
         [0044]    Fluent material, carrying the suspended solid-phase reagent portions, greatly accelerates as it passes through the throat  40 , resulting in significant agitation of the solid-phase reagent portion and the fluid carrier through currents circulating about the perimeter of the sub-chambers  41  and  42 . Complete, homogenous distribution is achieved rapidly, with the exact speed of mixing depending upon, inter alia, the pitch of the reagent pack, the rotational velocity, the reagent intermixed, the type and viscosity of the fluid carrier, temperature, and so forth. 
         [0045]    Further, the container-receiving stations or seating areas  38  of the annular portion of the primary reagent tray  12  are pitched or inclined so that, when disposed therein, the reagent packs  35  are pitched downward towards the vertical axis  29  at an angle. The benefits of pitching the reagent packs  35  include: when the tray  12  is stopped, the pressure head and the effects of gravity will draw a portion of the reagent inwards towards the inner end  52  and through the restrictive channel  40 , which, advantageously, mixes the solid-phase reagent portion and re-suspends and re-mixes any settled solid-phase portions. 
         [0046]    Reagent packs  35 —such as ReadyPacks manufactured by 
         [0047]    Siemens Healthcare Diagnostics, Inc. of Tarrytown, N.Y.—are or should be specifically designed to be placed in and held in a seating area  38  at an angle that is five (5) degrees below the horizontal during aspiration of the reagent from the reagent pack. However, steeper pack angles of 20 degrees below the horizontal or more provide greater mixing. When pack angles exceed the pre-established five degrees for aspiration, the rotary reagent tray assembly  10  may include a raising means that is adapted to elevate the lower end of the reagent pack  35 , say from 20 degrees below the horizontal to 5 degrees below horizontal. Preferably, reagent packs  35  are raised at a single pre-designated location(s), e.g., proximate the reagent aspiration probe and the reagent probe access area  31 . 
         [0048]    Each of the chambers  41 - 44  is covered with a lid, e.g., a HDPE lid. Each lid is structured and arranged to include plural apertures  45 ,  46 , and  49  that protect the chamber contents from contamination but that are easily penetrable by a reagent probe. Moreover, an important criteria is that the aperture-covering material remains inactive with the enclosed reagent. For example a combination of polyester and ethyl vinyl acetate (EVA) films, or a combination of polyester and HDPE films, and so forth can be used. Alternatively, a single layer of film is employed. 
         [0049]    The apertures  45 ,  46 , and  49  are substantially aligned with respective underlying chambers  43 ,  44 , and  42 , and, more preferably, with reagent pack chamber floor depressions  48 . Each aperture  45 ,  46 , and  49  may be covered separately, or all can be covered by a continuous portion of aperture covering material. 
       Operation of the Rotary Reagent Tray Assembly and Motion Profiles 
       [0050]    Those of ordinary skill in the art can appreciate that there are a myriad of variables that can affect the proper function, i.e., continuous and proper mixing, suspension, and/or resuspension of solid-phase reagent portions, of the rotary reagent tray assembly, e.g., diameter of the tray, distance of the reagent pack from the vertical axis, the pitch angle of the reagent packs, reagent pack design (S-channel or other), and motion profiles, just to name a few. This section will address motion profiles and how they can be used to best advantage to ensure that the solid-phase reagent portions are suspended and properly mixed within the appropriate sub-chamber immediately prior to aspiration. 
         [0051]    One of the limitations of conventional linear rocking mixers is that the motion profile cannot be changed to increase the energy and “sloshing” of the reagent significantly. Thus, rotary mixing is superior to rocking mixing, inter alia, in its ability to re-suspend solid-phase reagent portions within the fluid reagent solution. Indeed, as described in greater detail below, the acceleration/deceleration, maximum velocity, stopping, and other parameters can be altered to increase the instantaneous energy and “sloshing” of the reagent. 
         [0052]      FIG. 5  and  FIG. 6  illustrate, respectively, a triangular motion profile and a trapezoidal motion profile. The triangular motion profile includes a steadily increasing rotational velocity and a steadily decreasing velocity after some peak velocity is reached. The rapid and steadily increasing velocity makes triangular motion profiles more ideal for initial start-up and for reagents that require more violent mixing. 
         [0053]    In contrast, the trapezoidal motion profile ( FIG. 6 ) includes a steadily increasing rotational velocity that flattens out for a period of time followed by a steadily decreasing velocity. Trapezoidal motion profiles are better for maintaining already suspended solid-phased portions in suspension. 
         [0054]    The immunoassay system and/or the rotary reagent tray assembly  10  further includes a controller, e.g., a processor, microprocessor, and the like, that is structured and arranged to control at least one of: velocity, rate of acceleration, rate of deceleration, stopping, and direction of rotation of the motor. Moreover, the controller is adapted to operate the rotary reagent tray periodically, randomly, intermittently, at a prescheduled time, in accordance with one of a plurality of pre-established motion profiles, and on-command. 
       Initial Re-suspension Testing Results 
       [0055]    In order to evaluate the effectiveness of the rotary reagent tray assembly and of mixing the solid-phase reagent portion, rotary mixing was compared with manual mixing using S-channel packs in each instance. For the comparison, aHBS, CEA, and H2n assays were specifically chosen because the three assays are notorious for experiencing re-suspension issues. 
         [0056]    The degree of mixing was evaluated subjectively and objectively using visual and absorbance measurement techniques, respectively. For the former, the “amount” of mixing was characterized using the number of traversals of the S-channel. In the case of the latter, absorbance was measured at 600 nm and aliquots were sampled from top, middle and bottom layers of the reagent. 
         [0057]    The results of absorbance testing for manual and rotary fixture mixing in connection with aHBS, CEA, and H2n assays were performed using a linear Centaur fixture manufactured by Siemens Healthcare Diagnostics, Inc. of Tarrytown, N.Y. and a rotary reagent tray assembly. The intra-layer absorbance averages for manual and rotary fixture mixing for each assay confirm that a rotary reagent tray assembly with Readypacks is fully capable of suspending the solid-phase reagent portion. 
       On-Board Stability Testing 
       [0058]    As previously mentioned, arresting motion of the rotary reagent tray has many benefits. First, it allows motors and controllers to be shut off, which reduces heat output, saves energy, and reduces wear and tear on the system. Second, when rotary motion is stopped, solid-phase particles in the reagent come to rest, which improves, inter alia, the on-board stability of the solid-phase reagent. 
         [0059]    On-Board stability (OBS) is a measure of the usable and useful life of a discrete reagent once the reagent pack has been first opened and made available for use. In short, OBS is a measure of the “shelf-life” of the reagent once it is on-system, which, on average, can range from 7 to 45 days. 
         [0060]    OBS is affected by oxidation and/or other chemical reactions that may affect the reagent and, more pertinent to the present invention, to the effect that constant mechanical mixing may have on the solid-phase portions of the reagent, i.e., disaggregation, wear on particles, and the like. As previously mentioned, a back-and-forth rocking-type motion requires 24 hours, 7 day a week application. 
         [0061]    Typically, the more movement and agitation to which the solid-phase particles are subjected, the shorter the OBS life. 
         [0062]    Hence, advantageously, non-operation or downtime of the rotary tray equates into extended OBS life of the solid-phase reagent. Indeed, with the rotary reagent tray assembly of the present invention, functioning of the assay system can be stopped at the end of an 8-hour shift, which is likely to cause the OBS to increase, yet, after a shutdown and substantial settling time, the solid-phase portions can be resuspended using an appropriate motion profile, e.g., a triangular motion profile. Indeed, one of the many advantages of the rotary reagent tray assembly is that it provides better mixing at start-up compared to linear-type or other rotary-type reagent trays. 
         [0063]    OBS data for a linear (Centaur) reagent tray and a rotary reagent tray assembly using TUp and DIG reagents was collected. TUp and DIG reagents were chosen due to their relatively short OBS—respectively four and three days. The rotary reagent tray and the linear (Centaur) reagent tray were run continuously with five (5) seconds of rocking followed by ten (10) seconds idle for five (5) days. The rotary profile includes three (3) 180-degree moves in eight (8) seconds to model the supposed worst case. The results demonstrate no adverse impact to OBS for reagents that are mixed using a rotary reagent tray assembly versus a linear, rocking reagent tray. 
         [0064]    Although the invention is described through the above-described exemplary embodiments, it will be understood by those of ordinary skill in the art that modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. Accordingly, the invention should not be viewed as limited, except by the scope and spirit of the appended claims.