Analytical device and method for detecting chlamydia trachomatis and neisseria gonorrhoeae.

Background of the Invention

The present invention is generally directed to a device and method for accurately detecting <u style="single">Chlamydia trachomatis</u> and <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> antigens. The detection of these two types of antigens is complicated by the difficulty in obtaining sufficient quantity of sample to test and by the low concentration of antigen present in such samples. Therefore it is desirable to design a device and method whereby minimal amounts of sample can be accurately tested and minimal amounts of the particular antigen detected.

One device which can be employed to identify antigens by performing a binding assay is TESTPACK™ manufactured by Abbott Laboratories, Abbott Park, Illinois and disclosed in U.S. Application Serial Nos. 784,416 filed October 4, 1985, and 831,013 filed February 18, 1986 (both herein incorporated reference). Generally the device employs an enzyme immunoassay technique and comprises a plurality of substantially spherical, solid particles immobilized within a porous fiber matrix. The particles may have a substance coated on their surface which is capable of reacting with analyte present in a sample. The sample is brought into contact with the porous matrix where analyte present in the sample binds to the microparticle surface where it can be detected.

Other methods have been developed to identify <u style="single">Chlamydia trachomatis</u> and <u style="single">Neisseria gonorrhoeae</u> as disclosed in U.S. Patent 4,497,899 and 4,497,900. In particular these patents disclose absorbing the respective antigens onto a solid phase where they are then treated with antibody, washed, treated with antiglobulin, washed and, finally the amount of antiglobulin bound to the antigen antibody complex determined. Despite these methods, further improvements are necessary to identify small concentrations of antigen or analyze small quantities of sample for <u style="single">Chlamydia</u><u style="single">trachomatis</u> or <u style="single">Neisseria</u><u style="single">gonorrhoeae</u>. These problems have been identified and their solutions are the subject matter of the present invention.

Summary of the Invention

In one aspect, the present invention is directed toward a solid-phase assay device useful in a binding assay to determine the presence of <u style="single">Chlamydia</u><u style="single">trachomatis</u> or <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> antigen in a sample. The solid-phase device comprises a substantially planar layer of a material having a porous matrix of fibers and characterized by a plurality of substantially spherical, solid particles comprising polytetrafluoroethylene having an average diameter of from 0.1 to 10 microns. The particles are retained and immobilized within the matrix upon the fibers. The substantially planar layer has a first, sample-contacting surface and a second surface opposed to the first surface, and is disposed in the device such that, when the device is performing the assay, at least a portion of the sample contacting the first surface passes through the substantially planar layer to the second surface. The polytetrafluoroethylene particles serve to bind the antigen which can then be identified by immunoenzyme technique. The device can further employ on-board controls to assure accurate identification and readily recognizable results.

In another aspect, the present invention is directed toward a method for performing a binding assay to determine the presence of <u style="single">Chlamydia</u><u style="single">trachomatis</u> or <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> antigen in a test sample. The steps comprise: <ul id="ul0001" list-style="none"><li>a) contacting a porous matrix of fibers having a plurality of substantially spherical, solid particles comprising polytetrafluorethylene having an average diameter of from 0.1 to 10 microns, the particles being retained and immobilized within the matrix upon the fibers, whereby antigen in the sample becomes bound to the particles forming an antigen complex on the particles;</li><li>b) contacting the antigen complex on the particles with a second substance capable of reaction with the antigen which is labeled with a substance capable of producing a detectable response in the presence of the antigen and an indicator substance, whereby the labeled substance becomes bound to the antigen complex on the particles;</li><li>c) removing unbound labeled substance from the material;</li><li>d) contacting the complex with the indicator substance; and</li><li>e) detecting the response produced as a function of the presence or amount of the antigen in the sample.</li></ul>

In yet another aspect, the subject invention is directed toward a method for detecting the presence of <u style="single">Chlamydia</u><u style="single">trachomatis</u> or <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> antigen in a fluid sample. This method comprises the steps of: <ul id="ul0002" list-style="none"><li>a) incubating with a fluid sample a plurality of substantially spherical, solid particles comprising polytetrafluoroethylene having an average diameter of from about 0.1 to about 10 microns, whereby the antigen becomes bound to the particles forming an antigen complex on the particles; and</li><li>b) contacting a porous, fibrous matrix with the incubated particles, whereby at least a portion of the particles become retained and immobilized within the matrix upon at least a portion of the fibers.</li></ul>

The bound particle complex is observed by treatment with an enzyme-conjugated antibody or antigen which is treated with an indicator substance such that the comples can be observed either visually or with instrumentation.

The subject invention is characterized by employing microparticles of polytetrafluorethylene to effectively bind the <u style="single">Chlamydia</u><u style="single">trachomatis</u> or <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> antigen. Polytetrafluoroethylene has been found to be superior to other microparticles. This is especially valuable because generally the samples of interest are small in quantity or low in concentration of antigen.

Brief Description of the Drawings

<ul id="ul0003" list-style="none"><li>Fig. 1 is a side view in partial cross section of an analytical device suitable for use in the subject invention.</li><li>Fig. 2. is a top plan view of the device of Fig. 1.</li><li>Figs. 3A, 3B, 3C and 4A, 4B, 4C are top plan views of various embodiments of the device of Fig. 1 and depicting various examples of control areas.</li><li>Fig 5. is a perspective view of the device of Fig. 1, showing pre-filter assembly removed from the body of the device.</li></ul>

Detailed Description of the Invention

The present invention is directed toward an improved method for identifying <u style="single">Chlamydia</u><u style="single">trachomatis</u> (<u style="single">Chlamydia</u>) and <u style="single">Neisseria</u><u style="single">gonorrhoeae</u> (<u style="single">gonorrhoeae</u>) antigen present in a sample. In particular the subject device and method is adapted to detecting the presence of small quantities of <u style="single">Chlaymdia</u> and <u style="single">gonorrhoeae</u> antigens present in a biological fluid.

Generally the device and method employ an improved form of a solid-phase immunoassay technique for performing colormetric or other enzyme immunoassay analysis of biological fluids. The device as depicted in Fig. 1 shows a cross-sectioned view of the various components necessary to understanding the subject improvements.

The device 10 comprises a substantially planar, generally circular, disk-shaped reaction matrix 12. The matrix 12 contains the special particles of the invention, as described herein, and is disposed within the device 10 such that the various chemical reactions and changes necessary to perform a binding assay can take place therein for visual or instrumental detection.

The matrix 12 has a sample-contacting surface 12a and a surface 12b opposed therefrom. The filter matrix 12 is a "porous" filter matrix meaning that the matrix is composed of a material into which fluids can flow and easily pass through. Appropriate materials can include glass fibers, cellulose, nylon, or other fibrous materials well know in the art. One perferred material is "Whatman GF/D" glass fiber filter paper (Whatman Reeve Angel, Inc., Clifton, New Jersey) which has a nominal thickness of 0.032 inch; however, thickness is not a critical factor.

The device 10 additionally includes a carrier 14 within which the matrix 12 is disposed. The carrier 14 can be made of any suitable material such as plastic, metal or other rigid or semi-rigid substance. Especially preferred as a material for the carrier 14 is a plastic commercially known as "ABS", and available from the Monsanto Company, St. Louis, Missouri. In the preferred embodiment shown, the carrier 14 completely surrounds the matrix 12 and functions as a support and holder therefore. In order to accomplish this function, the carrier 14 has a generally circular flange 16 for supporting and tightly holding the matrix 12. A fluid chamber is generally defined by sidewalls formed by an outer wall surface 16a of the flange 16 and a base wall formed by the sample contacting surface 12a of the matrix 12.

The device 10 further comprises absorbent means 20 disposed in the carrier 14, as shown, for absorbing fluids during use of the assay device. The absorbent means 20 of the device 10 can comprise one or more layers of material and is in physical contact, as shown, with the barrier material 18, when used, or with the reaction matrix 12. This especially advantageous feature enables excess fluid, during the performance of an assay using the device 10, to be easily absorbed, as necessary, after passage of such excess fluid from the reaction matrix 12 during the assay procedure. The absorbent means 20 can be virtually any moisture of fluid-retaining material, e.g., that available from James River, and designated "105 point" or "50 point", or, as is especially preferred, a combination of one or more layers of each of the foregoing.

Barrier means is provided for restricting fluid flow in the solid phase analytical devices. This aspect is particularly advantageous when used in solid phase analytical devices having a permeable reaction surface or matrix, or filter layer, and an absorbant layer for absorbing fluids used in the device to permit the flow of fluids from the reaction surface to the absorbant means or layer while preventing the back flow of fluids from the absorbant layer to the reaction matrix.

As shown in Fig. 1,the barrier means comprises a layer of barrier material 18 extending under the matrix 12 and within the carrier 14. The barrier material 18 is in contact with the surface 12b of the matrix 12, and functions, when the device is in use, to restrict fluid passing through the matrix 12, to and through the surface 12b, and into the layer 18, from re-contacting the surface 12b. Layer 18 is employed as a fluid restrictive layer and to help prevent or eliminate "background" interference in the matrix 12. However, this feature is not essential or critical to the basic functions of concepts of the matrix 12, and can be omitted from the device if desired. If omitted, the device generally will perform satisfactorily in an assay, but possibly with less sensitivity (diminished detectable response).

The layer 18 can comprise any suitable material capable of restrictive, substantially "one-way" flow of fluid or moisture. Examples of especially suitable materials for this purpose are polyethylene weave materials manufactured and sold by Ethyl Visqueen Corp., Baton Rouge, Louisiana under the designations "X-6057" (1.0 mil) and "X-6108" (1.25 mil) as well as those materials described in U.S. Patents 3,939,135 and 4,342,314. Another suitable material is "Lydair™ Grade 254" from Lydall, Inc., Manchester, Connecticut.

Referring now in more detail to Figs. 1, 2 and 5 of the drawings, the analytical device 10 of the invention can optionally include a filtering means 22 disposed over surface 12a of the reaction matrix 12. The filtering means 22 can be press-fitted into the carrier 14 by means of a retaining ring 22a, and preferably has a removable portion 22b having a handle portion 22c. The means 22 is further composed, for example, of a suitable porous of fibrous material 22d such as a glass or cellulose filter membrane in a plastic surround; especially preferred are "Lydair™ Grade 254" from Lydall, and "GF/F" or "GF/D" from Whatman Reeve Angel, Inc., Clifton, New Jersey, either singly or in combination.

Even though device 10, as described above, can produce a visually-readable response, an instrumental determination can also be made of a detectable response therefrom, e.g., corresponding to the reflectance of visible light, or intensity of fluorescence or the like, produced by the matrix 12 as a result of the chemical and biological reactions and changes which occur therein when an assay is performed. Accordingly, the detectable response from the device 10 can be measured by, for example, a reflectometer.

A generalized example of how a direct diagnositc assay is performed with the instant device is as follows: <ul id="ul0004" list-style="none"><li>Step a) Application of a test sample containing the antigen or antibody to be determined to the reaction matrix having microparticles immobilized thereon;</li><li>Step b) Application of an enzyme-conjugated antibody or antigen to the antigen or antibody of Step a);</li><li>Step c) Washing, to remove unbound material; and</li><li>Step d) Application of an indicator substance which, in the presence of the enzyme portion of the conjugate of Step b), produces a detectable color or other response in the reaction matrix.</li></ul>

In another aspect, the subject invention can be employed by incubating the sample with a plurality of the spherical, solid particles comprising polytetrafluoroethylene. After the analyte becomes bound to the particles, the particles are contacted with a porous, fibrous matrix, whereby at least a portion of the particles become retained and immobilized within the matrix. The bound particles are then treated with an enzyme-conjugated antibody or antigen. The particles are washed to remove excess enzyme-conjugate and an indicator substance is added to produce a detectable color or other response. In yet another aspect, the subject spherical, solid particles comprising polytetrafluoroethylene can be employed as the solid phase components in the methods described in U.S. Patents 4,497,899 and 4,497,900.

In the subject invention, the methods and device are characterized by employing a plurality of substantially spherical, solid particles comprising polytetrafluoroethylene to bind the analyte. An example of polytetrafluoroethylene particles are Teflon™ particles, a trademark of DuPont E.I. De Nemours &amp; Co., Wilmington, Delaware. Preferably the particles are homopolymers of polytetrafluorethylene; however, derivations of polytetrafluoroethylene can also be employed.

The polytetrafluoroethylene particles are deposited into a fiber matrix (either before or after binding the antigen, depending upon the method employed) where they are retained and immobilized. "Retained and immobilized" means that the particles, once upon the fibers of the material, are not capable of substantial movement to positions elsewhere within the material, (i.e., to other fibers), or cannot be removed completely from the material without destruction thereof. No special treatment is necessary to retain and immobilize the particles on the fiber matrix, as they have been found to readily adhere to the fibers upon exposure thereto.

The particles have an average individual diameter of from about 0.1 to about 10 microns more preferably from about 2 to about 5 microns in diameter and an average density of about 2.14 gm/cm³. It is to be recognized that the particles can be present as aggregates which can exceed 200 microns in diameter. The particles are substantially uncoated and in fact it has been found that this is the preferred method for performing the assay for <u style="single">Chlamydia</u> and <u style="single">gonorrhoeae</u> antigens. However, further embodiments can include coating the particles with antibody or other substances to assist in the binding of antigen.

The polytetrafluoroethylene microparticles are extremely stable under a variety of conditions and therefore can be employed with a wide range of samples containing the <u style="single">Chlamydia</u> or <u style="single">gonorrhoeae</u> antigens. For example, the microparticles are resistant to strong acids and bases as well as most organic solvents. The microparticles are also stable from -240° to 260°C and because they are hydrophobic they absorb minimal amounts of water.

In the performance of an immunoassay for <u style="single">Chlamydia</u> and <u style="single">gonorrhoeae</u> it has been discovered that the polytetrafluoroethylene microparticles provide superior results as compared to other potential polymeric particles. This is demonstrated in the following examples:

Example I

Various microparticles were compared for their ability to bind antigen in an enzyme immunoassay specific for <u style="single">Chlamydia</u>.

In the method, <u style="single">Chlamydia</u> antigens were absorbed by microparticle suspensions. The bound analyte was separated from unbound analyte by centrifugation and the absorbed analyte detected using rabbit anti-<u style="single">Chlamydia</u> and goat anti-rabbit globulin conjugated to horseradish peroxide to detect immune complexes. The indicator employed were ortho phenylene diamine. Following color development the microparticles were removed by centrifugation and the supernatants transferred to cuvettes for measuring relative absorbance at 492 nm with a spectrophotometer.

In this experiment, the capacity of each type of microparticle to absorb analyte in a suspension containing <u style="single">Chlamydia</u> was measured. Non-specific binding was also evaluated by testing in parallel each type of microparticle in diluent solutions containing no analyte (blank)

The results obtained for seven types of microparticles were as follows: <tables id="tabl0001" num="0001"><img file="EP0264036A2_D0001.tif" /></tables>

The results show that the polytetrafluoro­ethylene microparticle has a superior capacity to absorb analyte when exposed to the microorganism. Also the polytetrafluoroethylene showed low non-specific binding.

Example II

The sensitivity of the polytetrafluoroethylene particles was further demonstrated by measuring the absorbancy at 492 nm when exposed to decreasing levels of microorganism. A similar centrifugal enzyme immunoassay technique was employed as in Example I. The absorbancy measured at varying concentrations of <u style="single">Chlamydia</u> is shown below: <tables id="tabl0002" num="0002"><img file="EP0264036A2_D0002.tif" /></tables>

The results indicate excellent sensitivity to as low as 50,000 organisms per millimeter with over a three-fold difference between the blank and the sample at this level.

Example III

The sensitivity of the polytetrafluoroethylene particles was further evaluated in the instant solid-phase device (TESTPACK™) by immobilizing microparticles in the glass fibrous matrix to form the reaction matrix. The reaction matrix was then treated with <u style="single">Chlamydia</u> microorganisms at various levels of concentration and then visual colormetric change and reflectance was measured after treatment with an indicator substance.

The results were as follows: <tables id="tabl0003" num="0003"><img file="EP0264036A2_D0003.tif" /></tables>

The signal was measured visually on a scale of 1 to 4 for color intensity for positive results with 4 being a blue-black color and 1 being a light blue color. The signal was also quantified by a reflectometer which measured percent reflectance. The perecent reflectance corresponded to the color intensity with the lowest reflectance indicating a very dark color.

The results indicate that a positve result could be detected for as low as 5 x 10² microorganisms per milliliter. Visually, at the 5 x 10² microorganism level a slight color was perceptable to the point a positive reaction was indicated although not within the color scale; however, the instrumentation signal showed a definite difference between the blank and the 5 x 10² microorganisms per milliliter level. These results show an excellent sensitivity of the subject device and method to low concentrations of <u style="single">Chlamydia</u>.

While all the above examples have employed <u style="single">Chlamydia</u>, the device and method is equally applicable to the identification of <u style="single">gonorrhoeae</u> antigens.

The subject invention can also provide "on-board" control areas to simultaneously display detectable responses corresponding to a positive control (which will display a detectable response indicative of a valid assay result, regardless of the presence or absence of an analyte of interest in a test sample), and a negative control (which will display a detectable response change only if the assay results are invalid). In this aspect of the invention, the same volume of a test sample and assay reagents are simultaneously placed in contact with the procedural controls and test areas, thereby avoiding the necessity of separate control tests as generally practiced in the art.

Referring to Figures 3A-C and 4A-C on-board negative and positive control areas 30 and 32, respectively, can be provided on the reaction surface or matrix 12 of the analytical device 10. The analyte binding area 34 indicates a positive test result to the user. Generally the control areas 32 and 34 are configured to provide a readily recognizable result to the user as shown in Figure 3C.

The negative control area 30 is formed by maintaining the area 30 free of substances which will retain the enzyme label or other signal response material during the assay. The positive control area 32 is formed by providing a substance capable of binding the enzyme label or other signal response material regardless of the presence of the antigen of interest. The analyte binding area 34 is formed by coating the microparticles of polytetrafluoroethylene at this position to bind the antigen of interest. In other embodiments the device can contain only the analyte binding area 34 and other configurations of areas 30, 32, and 34 can be employed.