WO2000019201A1

WO2000019201A1 - Biological assay compositions containing non-interfering, foam-inhibiting and foam-collapsing agents

Info

Publication number: WO2000019201A1
Application number: PCT/US1999/022113
Authority: WO
Inventors: Martha Louise Garrity; Ronald N. Diamond
Original assignee: Quest Diagnostics Investments Incorporated
Priority date: 1998-09-25
Filing date: 1999-09-23
Publication date: 2000-04-06
Also published as: AU6059299A

Abstract

There are provided compositions, manufactures and methods for performing biological assays, particularly immunoassays in which the generation and persistence of foam, that can interfere with the assay, is inhibited. Such compositions include, for example silicone-based anti-foaming agents, silicone-glycol emulsions, and polyalkylsiloxane. In a preferred method, the compositions and/or manufactures are used in conjunction with an automated biological assay apparatus which includes a pipetting means which is equipped with a clot detection means.

Description

BIOLOGICAL ASSAY COMPOSITIONS CONTAINING NON-INTERFERING, FOAM-INHIBITING AND FOAM-COLLAPSING AGENTS

Field of the Invention

The present invention relates to biological assay compositions which contain an anti-foaming agent, manufactures; such as, biological assay reagent cartridges containing the composition, and methods for using the same, either alone or in conjunction with a pipetting means clot detection device.

Background of the Invention

Agents which act to collapse foams are known and have been used in various applications including, processed foods, petrochemicals, paper manufacturing, and pharmaceuticals. In the present invention, however, anti-foaming agents are used in sensitive biological assays. Biological assays such as immunoassays are well known in the art. Additionally, the use of automated test instruments to perform such assays is known. In a particular application, biological assays are carried out on an automated assay instrument, which utilizes cartridges, typically disposable cartridges. The cartridge may contain vials, which contain various reagents used in carrying out a particular assay.

Reagents are typically aqueous buffers containing the active species, for example, an antibody, an antibody conjugate, an antigen, an antigen conjugate and in some instances, magnetic particles. Additives to the reagents to improve the performance of the assay may include proteins, and blocking agents. These additives promote the formation of foam when the reagent is either deliberately mixed or by, for example, jostling of the reagent container during shipping or in preparation for use. Therefore, the formation of foam, typically at the surface of a reagent is a common problem. The foam is often very difficult to disrupt. Without outside intervention, it may take several hours for the foam to dissipate. Alternatively, the foam can be removed from the container, but this procedure is time-consuming, tedious, causes loss of reagent and risks contamination of the reagent by the use of instruments, such as pipettes to remove the foam. In some instances reagent containers are completely sealed. A pipette probe can be used to puncture the seal and remove reagent from the container. The puncture is typically very small and the seal material closes on the puncture preventing contamination and loss of fluid by evaporation and any resulting concentration changes. Removal of foam from such sealed containers, if the advantages of such sealed containers are to be kept, makes manual removal of foam extremely difficult, if not practically impossible. The formation of foam also causes problems when the reagent is used on an automated assay instrument which includes a clot detection feature. Many automated pipetting systems used on such assay instruments feature sensors, usually differential pressure sensors, which are used to provide assurance that an aspiration or dispensation of a sample was properly executed. However, the determination of the presence of foam with the clot detection procedure is not effective when the total sample size is small, i.e., about 5 uL to about 200 uL, particularly about 20 uL or less, because the pressure drop which must be detected in order to indicate the presence of a clot is too small. Therefore, when such small samples are involved, in order to ensure proper pipetting volumes are obtained it is important to avoid the presence of foam. The anti-foaming agents disperse into the thin films surrounding the entrapped gases, i.e., the walls of the foam, and lower the surface tension of the walls, thereby causing the foam to collapse.

Accordingly, it would be desirable to provide methods, compositions and manufactures, such as cartridges containing the claimed compositions, which would both help to prevent foam formation and to collapse any foam which did form ("anti-foaming agents"). In particular, it would be desirable to provide a system comprising an automated assay instrument with clot detection used with reagent containers having anti-foaming agents and a method for using anti-foaming agent containing biological assay reagent containers on such instruments.

Summary of the Invention

The present invention is directed to a biological diagnostic reagent which includes an anti-foaming agent. The anti-foaming agent must not interfere with or alter the result of the assay. Rather, the result of the assay, e.g., an analyte concentration, obtained with the anti-foam agent present must not be significantly different from the result obtained when the anti-foam agent is absent.

In accordance with one aspect of the present invention there is provided a biological assay reagent composition. The composition includes a liquid phase. The liquid phase contains a diagnostic reagent and an anti-foaming agent. The anti-foaming agent does not alter the result provided by the biological assay reagent composition compared to the result obtained in the absence of the anti-foaming agent.

In a preferred embodiment, the anti-foaming agent includes a silicone-base. In another preferred embodiment, the anti-foaming agent comprises a silicone- glycol emulsion.

In yet another preferred embodiment the anti-foaming agent comprises a polyalkylsiloxane.

In accordance with another aspect of the present invention there is provided a biological assay. The biological assay includes a first liquid phase contained in a first container. The first liquid phase includes a diluent and an anti-foaming agent. The assay also includes a second liquid phase contained in a second container. The second liquid phase includes a specific binding partner and an anti-foaming agent. The assay also includes a third liquid phase contained in a third container. The third liquid phase includes a fluid, at least one solid particle and an anti-foaming agent. It is important that the anti-foaming agent does not alter the result provided by the biological assay compared to the result obtained in the absence of the anti-foaming agent.

In a particular embodiment, the specific binding partner is an antibody, more particularly it can be a biotinylated antibody. In another embodiment the assay includes a second antibody that is detectably labeled.

In yet another aspect of the present invention there is provided a reagent cartridge for use in an automated assay instrument, for performing assays. The cartridge has at least one reagent containing chamber. The reagent cartridge includes the composition described above contained in at least one of the reagent containing chambers.

In a further aspect of the present invention there is provided a method of performing a biological assay. The method includes the steps of combining a sample to be assayed with a diagnostic reagent and an anti-foaming agent. At least one of the sample and diagnostic reagent is in a liquid phase, the anti-foaming agent being added to at least one of the liquid phases.

In a preferred embodiment, the method further includes the step of performing the biological assay while using a pipetting means to provide an aliquot from at least one of the liquid phases containing an anti-foaming agent, and which clot detection means includes a clot detection device. The clot detection device including a pressure drop sensing means.

In another preferred embodiment, the liquid phase that the pipetting means provides an aliquot from is of a volume insufficient to provide to the pressure drop sensing means the pressure difference between a first pressure drop when foam is present versus a second pressure drop when foam is not present.

In yet another aspect of the present invention there is provided a system which includes an automated biological assay instrument. The instrument includes a clot detection device. The system also includes a reagent cartridge including a biological assay reagent composition for providing a diagnostic result. The composition includes a liquid phase. The liquid phase contains a diagnostic reagent and an anti-foaming agent. It is important that the anti-foaming agent does not significantly interfere with the result provided by the biological assay reagent composition compared to the result obtained in the absence of the anti-foaming agent.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, various features of preferred embodiments of the invention.

Description of the Figures

The detailed description of the invention will be made with reference to the accompanying figures, where, as appropriate, like numerals designate corresponding parts of the figures. The figures are meant to be generally illustrative of various examples of the present invention, but are merely examples and are not meant to be limiting of the scope of the invention.

FIGS. 1A-C illustrate a cartridge for use with the present compositions of the present invention, which cartridge is suitable for use on an automated assay device.

Detailed Description of the Invention

The present invention is useful for facilitating the performance of biological assays, such as immunoassays, particularly medically useful diagnostic immunoassays, by assisting to prevent foam formation in at least one or all of the reagents and/or sample used to perform such assays and to collapse any foam which has formed in at least one or all of the reagents and/or sample. In a preferred embodiment, the assay is run on an automated test instrument An example of an automated test instrument on which assays, such as biological assays of the present invention, can be run, is the Nichols Advantage® automated assay platform, available from Nichols Institute

Diagnostics, San Juan Capistrano, California. Other automated test instruments, as are known in the art, are also within the scope of the present invention.

The use of clot detection devices and methods in conjunction with pipetting means is known in the art. Also, such clot detection devices and methods can be used in conjunction with an automated biological assay instrument, as is generally known in the art. For example, clot detection means and methods are disclosed in United States Patent Nos. 4,893,515; 5,503,036 and 5,723,795, all of which are incorporated herein by reference. However, the presence of foam in samples which are being pipetted can interfere with the functioning of clot detection means and methods, as follows: Typically, if the pipette means in aspirating a sample encounters a clot, a pressure detecting means which is a part of the clot detection means will register a pressure drop in a conduit line behind the clot. Due to the clot, the sample volume will be incorrect and the automated assay instrument is designed to either repipette the sample until the correct volume is obtained and/or to flag a particular test result as an error and/or alert an instrument operator as to the problem. However, if the sample volume is small enough, typically, less than about 20 uL, during pipette aspiration of a foam-containing sample, the pressure may not drop detectably with respect to the normal pressure drop detected when a non-foam containing small volume sample is pipetted, even though an incorrect volume of sample is being pipetted. For example, if the volume from which the pipette draws an aliquot is about 10 uL and the pipette is set to draw 5 uL, the normal pressure drop, detected by the pressure sensing means, in a non-foam containing sample might typically be about 10 millibars. The actual pressure drop will depend upon the operating characteristics of the aspirating pump which creates the vacuum that the pipetting means uses to draw up the sample. The pressure drop will typically range between about 5 millibars and about 50 millibars. If the sample contains foam, the pressure drop will be less, for example 9.5 millibars. However, the difference between a 10 millibar drop and a 9.5 millibar drop is not enough for the pressure sensing means to reliably distinguish between. Therefore, eliminating foam from small volume samples is important, even when the assays are performed on instruments with clot detection means. However, the inventive compositions can be used in any assay in which, regardless of sample size, any resulting pressure drop difference between a foam and a non-foam containing sample, upon sample pipetting is too small to detect. Also, if the sample contains bubbles of foam at the surface, the fluid sensor of the pipetting means can incorrectly detect the bubble surface as the liquid surface and position the pipette probe in the foam. This foam will defeat the function of liquid level detectors which use various means such as changes in conductivity or ultrasonic signals top detect a liquid level and position a pipette means accordingly, because the detectors often cannot differentiate between foam and liquid.

Therefore, for all of the foregoing reasons, the prevention or disruption of foam to begin with is important. By using an anti-foaming agent in conjunction with the clot detection means and methods, an advantage is obtained regarding reproducible and accurate sample size, with respect to the use of either anti-foaming agents alone or clot detection means alone.

Typical assays which can be performed, and are within the scope of the present invention, include, but are not limited to, assays for the following analytes: ACTH, Cortisol, Free T3, Free T4, Thyroid Stimulating Hormone ("TSH"), Thyroglobulin, Thyroglobulin-autoantibodies, Thyroid Peroxidase ("TPO")-autoantibodies, TSH receptor, TSH receptor-antibodies, renin, DHEA, DHEA-sulfate, FSH, LH, Prolactin,

Calcitonin, Deoxypridonoline, PTH, Osteocalcin, 25-Hydroxyvitamin D, 1,25, dihydroxy Vitamin D, Human Growth Hormone, IGF, and Tumor Markers, such as, but not limited to : PSA, AFP, CEA, CA 15-3, NSE, TPA, Cancer antigen ("CA") 19-9, CA 72-4, CA 125. Assays of combinations of the above can also be performed. By "anti-foaming" is meant that the formation and persistence of any foam formed in an assay reagent or sample to be added to a reagent or to which a reagent is added is less than the amount of foam formed and the time the foam persists in the absence of the anti-foaming agent. The anti-foaming agent of the present invention must be suitable for use with a biological assay. The anti-foaming agent must therefore not significantly alter the results obtained from the assay. By "not significantly alter" is meant that the result obtained with the anti-foaming agent present is as useful for its intended purpose. For example, if the result is an analyte concentration for a clinically relevant medical diagnostic assay, any change in the concentration obtained with the anti-foaming agent present will not lead to a clinically important change in the concentration obtained. In a preferred embodiment, the anti-foaming agent minimally, i.e., non-statistically significant, if at all, alters the result provided by the biological assay reagent composition compared to the result obtained in the absence of the anti- foaming agent.

By "analyte concentration" is meant any information regarding, for example, either the amount of an analyte present, e.g., in units such as mols, or the weight of an analyte present such as in mg, either of which may be further characterized in relation to their presence per unit volume or weight of a liquid. However, any units and any physical characteristics which allow for the medically or biochemically relevant comparison of different samples are within the scope of the present invention and the term "analyte concentration."

Additionally, the term "analyte concentration" includes values provided by indirect measurements of analyte concentration, such as, chemiluminescent, fluorescent, electrical, chemical or otherwise machine or human detectable signals which either provide medically or biochemically relevant information or which can be mathematically manipulated to provide analyte concentrations as the term is defined in the preceding paragraph.

Examples of anti-foaming agents include, but are not limited to, the following: a silicone-based anti-foaming agent, a silicone-glycol emulsion anti-foaming agent, a polyalkylsiloxane anti-foaming agent. Such anti-foaming are readily available from commercial suppliers. The anti-foaming agents should be soluble or dilutable in an aqueous phase. The anti-foaming agents can be provided as fluids, compounds, for example, silicone fluids containing a suspension of finely powdered silica or emulsions. Emulsions are preferred for applications in which water is the predominant phase. Also, the anti-foaming agents disclosed in U.S. Patent No. 5,556,902, incorporated herein by reference, are within the scope of the present invention. In a particular embodiment, Dow Corning® Antifoam 2210 ("2210") is the antifoaming agent used in the compositions of the present invention. 2210 is a silicone-glycol emulsion, comprising 90% water, 6% polypropylene glycol and 2% polydimethylsiloxane. The active ingredient of 2210 provided at 10% of the composition. 2210 has a specific gravity of 1.0 at 25 Degrees C and a consistency of 2,500 cp at 25 Degrees C. The 2210 emulsifier is non-ionic and the pH is 7.0. In addition, Dow Corning® Antifoam 1920 is within the scope of the present invention.

Other anti-foaming agents which have good shelf-life stability, as would be known to those of ordinary skill in the art, and which are compatible with aqueous systems and which do not significantly interfere with the results obtained in the biological assay to which it is added, for example due to the anti-foaming agents effectiveness at low concentrations, such as about less than 100 ppm, are within the scope of the present invention.

The anti-foaming agent is preferably present in a final concentration in an amount from about 1 to about 1000 ppm. More preferably, the anti-foaming agent is present in a final concentration in an amount from about 1 to about 500 ppm. Even more preferably, the anti-foaming agent is present in a final concentration in an amount from about 1 to about 50 ppm. In one particular embodiment the anti-foaming agent is present in a final concentration in an amount of about 20 ppm. The final concentration can refer to the concentration in a particular reagent or sample or the final concentration in a mixture of reagents and/or sample(s).

Assays within the scope of the present invention can include solid-phase particles. The solid-phase particle of the present invention can include a particle comprised of, but not limited to: glass, latex, plastic, metal and combinations thereof. Such a particle can have a size of from about 0.01 microns to about 1 cm, more preferably from about 0.05 microns to about 100 microns, and most preferably from about 0.05 microns to about 10 microns. In a preferred embodiment, the solid-phase particle is a magnetic particle, particularly a paramagnetic particle, as are known in the art. Typically, about 5 ug to about 100 ug of paramagnetic particles are used per assay. However, the term particle is not meant to be limited to particular shape of particle. For example, spherical, irregular, flat discs, solid, perforated and combinations of the above are within the scope of the present invention.

In a preferred embodiment, the solid-phase particle is associated with a specific- binding moiety. The specific -binding moiety can be integral to the particle, such as a surface feature(s) which allows the particle to preferentially bind with other moieties or the particle can have associated with it the specific -binding moiety. In a preferred embodiment the specific -binding partner is coated on the solid-phase particle, and more preferably is covalently attached to the solid-phase particle. Such specific -binding moieties include, but are not limited to: antibodies, lectins, and proteins, such as but not limited to streptavidin, avidin, avidin derivatives, or an anti-linker-moiety antibody, such as an anti-biotin antibody.

The compositions of the present invention can be added into any reagent liquid, including buffer liquids, or the sample to be assayed, so long as the anti-foaming agent is present at the time that an aliquot of liquid is to be removed from a container in which it is contained. In a method of the present invention the anti-foaming agent need not be present in the reagents, kit, product, composition or cartridge supplied, but can be added by the user of the assay at any time before or just prior to the removal of an aliquot of liquid or liquid and solid particles from the container in which they are contained.

The compositions of the present invention can be used in all types of assays, particularly those assays in which the accuracy and reproducibility of the volume pipetted of at least one of the components of the assay is important and where the formation of foam will interfere with obtaining accurate and reproducible sample volumes. For example, direct, competitive, simultaneous, sequential and sandwich assays as are known in the art are within the scope of the present invention. Examples of typical assays employing the compositions and methods of the present invention are set forth below.

EXAMPLE 1 THYROID STIMULATING HORMONE ASSAY WITH

ANTI-FOAMING AGENT

The assays which are performed using the methods and compositions of the present invention, are in a preferred embodiment, immunoassays using solid-phase particles, particularly magnetic particles. Such assays are generally carried out as either a simultaneous assay or as a sequential assay. However, other assay formats and modifications are within the scope of the present invention.

The TSH assay components included the following: 1) an assay diluent which is composed of equine serum; 2) an antibody solution containing an biotinylated anti-TSH antibody and an acridinium ester, i.e., chemiluminescent labeled, anti-TSH antibody in a PBS buffer including proteins, such as BSA; and, 3) a PBS buffer including proteins and streptavidin coated magnetic particles. An anti-foaming agent (Dow Corning® 2210) was added to each of the components of the TSH assay. The anti-foaming agent was added to a final concentration of 20 ppm. When a container containing the components with the anti-foaming agent was shaken, the foam bubbles formed dissipated within seconds. In contrast, when a container containing the components without the anti-foaming agent was shaken, the foam bubbles formed did not dissipate until about 24 hours had passed.

The concentration of the analyte in the sample to be assayed is determined by using a standard curve. The signal which is detected and which correlates to analyte concentration may be given in Relative Light Units ("RLU"), if for example, a chemiluminescent signal is being used to detect analyte or lack thereof. The standard curve is a curve generated by obtaining signals from samples containing known amounts of an analyte. Samples containing unknown amounts of analyte can be compared to the standard curve and the amount of analyte present in the sample can thereby be determined. Addition of the anti-foaming agent to the reagents did not significantly impact the RLU values obtained for the standard curve as compared to the standard curve obtained without addition of anti-foaming agent.

Standard Control System RLU DC2210 ) @ 20 ppm RLU Relative %

0 333 349 105%

2 489 5 -08 104%

3 672 ( 688 102%

4 3416 3489 102%

5 14644 1 15026 103%

6 27622 28458 103%

7 50180 5 -1873 103%

8 112669 ] 113557 101%

9 181739 ] 181325 100%

Further, the anti-foaming agent did not affect the stability of the assay reagents. An accelerated stability study was conducted by heating the containers containing the reagents and the anti-foaming agent and heating containers containing the reagents without anti-foaming agents to 45 degrees C for 3 days.

The heated reagents recovered, on average, 90% of the non-heat stressed signal whether or not the anti-foaming agent was present. Additionally, the anti-foaming agent maintained its anti-foaming properties even after the heat stress. Based on the rate of foam bubble dissipation after heat stressing, using Arrehenius calculations, the shelf-life of the reagent/anti-foaming agent compositions should be over one year at 4 degrees C. This determination is based on the fact that most chemical reactions, including decomposition, follow Arrhenius behavior which means that the rate of reaction or decomposition is related to the temperature according to the equation K = A exp (- E/RT). A is a constant. R is the gas constant. E is the activation energy of the reaction and T is the temperature in Kelvin. This relationship enables the estimation of shelf -life of reagents at 4 degrees C by accelerated stability studies. Thus heating a reagent to 45 degrees for 1 day results in approximately the same amount of decomposition as 3 months at 4 degrees C. One week at 37 degrees C is equal to 10.4 months at 4 degrees C.

Most significantly, the patient correlation for the TSH assay with and without the anti-foaming agent is excellent. For 45 patient samples, the slope was 0.998 with a Y axis intercept of 0.003 and a correlation coefficient of 0.999.

EXAMPLE 2 CORTISOL COMPETITION ASSAY WITH ANTI-FOAMING AGENT

The assay components included the following: 1) an assay diluent which is composed of PBS; 2) an antigen solution containing a biotinylated Cortisol molecule; 3) an antibody solution containing an acridinium ester, i.e., chemiluminescently labeled, anti-Cortisol antibody in a PBS buffer including proteins such as BSA; and, 4) a buffer, preferably citrate, including proteins and streptavidin coated magnetic particles. An anti-foaming agent (Dow Corning® 2210) was added to each of the components of the Cortisol assay. The anti-foaming agent was added to a final concentration of 20 ppm. When a container containing the components with the anti-foaming agent was shaken, the foam bubbles formed dissipated within seconds. In contrast, when a container containing the components without the anti-foaming agent was shaken, the foam bubbles formed did not dissipate until about 24 hours had passed.

As in the above example, addition of the anti-foaming agent to the reagents did not impact the RLU values obtained for the standard curve as compared to the standard curve obtained without addition of anti-foaming agent. lard Control System RLU DC2210 @ 20 ppm RLU Relative %

0 5459 5293 97%

1 10143 10183 100%

2 16177 16304 101%

3 25626 26152 102%

4 41306 42049 102%

5 55303 56486 102%

The anti-foaming agent did not affect the stability of the assay reagents. An accelerated stability study was conducted by heating the containers containing the reagents and the anti-foaming agent and heating containers containing the reagents without anti-foaming agents to 37 degrees C for 11 days. The anti-foaming agent maintained its anti-foaming properties even after the heat stress.

Most significantly, the patient correlation for the Cortisol assay with and without the anti-foaming agent is excellent. For 30 patient samples, the slope was 1.01 with a Y axis intercept of 0.9 and a correlation coefficient of 0.99. Another lot of

Cortisol reagents gave similar results for 20 patient samples with a slope of 1.01 with a Y axis intercept of 0.55 and a correlation coefficient of 1.00.

FIGS. 1A-1C depict a reagent cartridge 432 which is within the scope of the present invention. Other reagent cartridges for used in automated assay devices are within the scope of the present invention. The cartridge 432 in general is an elongate prismatic body 434 consisting of a base portion 436, and one or more removably attached add-on portions 438, each molded of polymer material. At the forward end 440 of the base portion 436, the base portion 436 defines a vertically extending bore 442 in which an agitation container 444 is rotationally received captively. The agitation container 444 includes an upper radially extending flange portion 446, which is disposed adjacent to an upper flange portion 448 of the body 434. A molded resilient integral hook portion 450 extends from the flange 448 over flange 446 to captively retain agitation container 444 in the bore 442. The body 434 has a lower edge 452, which at the forward end 440 of the module bounds an opening 454. Agitation container 444 includes circumferentially continuous gear portion 456 exposed in this opening. Above the opening 454, the body 434 includes sensor tab 458, which is receivable into a sensor opening 460 at the rear of recess 416 to inform a computer system on an automated assay instrument (not shown) where a particular reagent module has been inserted into the slots 430. Above the sensor tab 458, the body 434 includes a pair of spaced apart resilient detent tongues 462. These tongues are receivable on opposite sides of a positioning key 464 at the rear of a recess (not shown) and engage opposite detents (not shown) to removably retain cartridge 432 in a particular slot (not shown).

Internally, agitation container 444 includes vertically extending agitation fins 472, see FIG. 1C, so that rotary oscillation of this container effected by reciprocation of a rack (not shown) stirs the contents of container 444. Container 444 is used to hold a reagent liquid which includes solid-phase particles, such as magnetic beads. The agitation of this container prevents the beads from settling, so that they may be transferred along with the liquid contained therein into a container, such as a cuvette, by a probe of an automated assay instrument (not shown). Container 444 includes a slit septum, 474, as shown in FIG. lC. Base portion 436 further includes three recesses 476, within which respective reagent containers 478 are removably received. The reagent containers 478 each include a slit septum 478' closing the top opening of these containers, but through which a probe (not shown) may access the reagent liquid in these containers. At the rear of base portion 436 is defined a pair of vertically extending spaced apart guide rails 482. The guide rails 482 cooperate with the remainder of body 434 to define a pair of oppositely opening vertically extending grooves 484, each ending vertically upwardly at an abutment surface 486 adjacent to the upper flange 448 of body

434. The add-on portion 438 has a pair of elongate vertically extending inwardly facing engagement tongues 448, which are vertically receivable in sliding engagement into the grooves 484. Add-on portion 438 includes a lid 490 defining an opening 492 closed by slit septum 494 by which the probe (not shown) may access the liquid reagent in these add-on portions 438.

Add-on portions 438 at their side opposite the base portion 436 define features replicating those of the base portion, so that additional add-on portions may be interlocked to form the regent cartridges 432, as is indicated in phantom lines, viewing FIG. 1A. Either the base portion 436 or add-on portions 438 may accept a handle member 496 and configured with engagement tongues like those referenced above with respect to numeral 488. This handle member 496 is engageable with the base portion 436 or with one of the add-on portions 438 in order to facilitate manual grasping and easy insertion and removal of the reagent cartridges 432 at slots 430. At a side surface 498, reagent cartridge 432 can carry a bar code tag 500, which allows for identification by the assay instrument (not shown) of the particular reagents provided to the instrument in each cartridge 432.

The presently disclosed embodiments are to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

What is claimed is:

1. A biological assay reagent composition for providing a diagnostic result, the composition comprising a liquid phase, the liquid phase containing a diagnostic reagent and an anti-foaming agent, wherein the anti-foaming agent does not significantly alter the result provided by the biological assay reagent composition compared to the result obtained in the absence of the anti-foaming agent.

2. The reagent composition of claim 1 wherein the anti-foaming agent includes a silicone-base.

3. The reagent composition of claim 1 wherein the anti-foaming agent comprises a silicone-glycol emulsion.

4. The reagent composition of claim 1 wherein the anti-foaming agent comprises a polyalkylsiloxane.

5. The reagent composition of claim 1 wherein the anti-foaming agent is present in an amount from about 1 to about 500 ppm.

6. The reagent composition of claim 1 wherein the anti-foaming agent is present in an amount from about 1 to about 50 ppm.

7. A biological assay comprising a first liquid phase contained in a first container, the first liquid phase comprising a diluent and an anti-foaming agent, a second liquid phase contained in a second container, the second liquid phase comprising a specific binding partner and an anti-foaming agent and a third liquid phase contained in a third container, the third liquid phase comprising a fluid, at least one solid particle and an anti- foaming agent, wherein the anti-foaming agent does not significantly alter the result provided by the biological assay compared to the result obtained in the absence of the anti- foaming agent.

8. The biological assay of claim 7 wherein the specific binding partner comprises an antibody.

9. The biological assay of claim 8 wherein the antibody is a biotinylated antibody.

10. The biological assay of claim 9 further comprising a second antibody, wherein the second antibody is detectably labeled.

11. The biological assay of claim 10 wherein the second antibody is an acridinium labeled antibody.

12. The biological assay of claim 7 wherein the anti-foaming agent includes a silicone-base.

13. The biological assay of claim 7 wherein the anti-foaming agent comprises a silicone-glycol emulsion.

14. The biological assay of claim 7 wherein the anti-foaming agent comprises a polyalkylsiloxane.

15. The biological assay of claim 7 wherein the anti-foaming agent is present in an amount from about 1 to about 500 ppm.

16. The biological assay of claim 7 wherein the anti-foaming agent is present in an amount from about 1 to about 50 ppm.

17. A reagent cartridge for use in an automated assay instrument, for performing assays, the cartridge having at least one reagent containing chamber, the reagent cartridge comprising the composition of claim 1 contained in at least one of the reagent containing chambers.

18. A method for performing a biological assay comprising the steps of: combining a sample to be assayed with a diagnostic reagent and an anti-foaming agent, wherein at least one of the sample and diagnostic reagent is in a liquid phase, the anti- foaming agent being added to at least one of the liquid phases.

19. The method for claim 18 further comprising the step of performing the biological assay while using a pipetting means to provide an aliquot from at least one of the liquid phases containing an anti-foaming agent, and which pipetting means includes a clot detection device, wherein the clot detection device including a pressure drop sensing means.

20. The method of claim 19 wherein the liquid phase that the pipetting means provides an aliquot from is of a volume insufficient to provide to the pressure drop sensing means the pressure difference between a first pressure drop when foam is present versus a second pressure drop when foam is not present.

21. A system comprising an automated biological assay instrument, the instrument including a clot detection device and a reagent cartridge comprising a biological assay reagent composition for providing a diagnostic result, the composition comprising a liquid phase, the liquid phase containing a diagnostic reagent and an anti-foaming agent, wherein the anti-foaming agent does not significantly alter the result provided by the biological assay reagent composition compared to the result obtained in the absence of the anti-foaming agent.