WO1994017212A1

WO1994017212A1 - Slide immunoassay detection system

Info

Publication number: WO1994017212A1
Application number: PCT/US1994/001182
Authority: WO
Inventors: Adrian Gropper; Mark Pearce; Rosemary Maurtagh Petrone; Klint R. Wright
Original assignee: Cambridge Biotech Corporation
Priority date: 1993-01-28
Filing date: 1994-01-27
Publication date: 1994-08-04
Also published as: AU6100694A

Abstract

A system and method for detecting and measuring an agglutination reaction as the agglutination reaction occurs at multiple sites distributed over a test slide's reaction chamber (typically a capillary channel). The detection system employs light stimulus sources having light emitting diodes, optical detection receivers having photodiodes, analog-to-digital converters, a microprocessor, and a liquid crystal display. Diffracted light is transmitted through a capillary action test slide's capillary channels at various strategical points and received by optical detectors, to monitor agglutination reaction dynamically. As the liquid assay flows through the channel(s), each photodiode synergistically with microprocessor control and measurement software, monitors the dynamic changes in optical density of the assay liquid. Each measurement is quantitized to result in a statistical calculation which can be compared to a set of thresholds (generated empirically) stored in the memory of the device. The agglutination reaction can then be characterized and displayed.

Description

Slide Immunoassay Detection System

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Background of the Invention

1. Field Of The Invention

The present invention relates generally to a system for detecting 10 agglutination reaction, and more particularly to a system for detecting and measuring agglutination reaction as the agglutination reaction occurs.

2. Related Art

Agglutination reagents are used for diagnostic test purposes to determine antigenic substances (e.g. hormones, antibodies, etc.). An

15 agglutination reagent is mixed with a sample (e.g. , blood) to react with the reagent on a slide or in a test tube. Then in a lab situation, a human will determine through visual observation whether there was an agglutination reaction or not.

The problem associated with this method of testing is that it relies

20 entirely upon the visual acuity and training of the person performing the test.

Agglutination tests are limited by the ability of the human eye to detect differences between reacted and unreacted particles. As differences between the sizes of reacted and unreacted particles decreases, error and subjectivity of a visual reading increases. Human subjectivity can contribute to

25 inconsistent and inaccurate test results. Accordingly, agglutination detection systems have been developed to measure agglutination reactions, and provide accurate and consistent test results.

A. U.S. Patent No. 4,597,944

One such system is described in U.S. Patent No. 4,597,944 entitled

"Agglutination Reagent Detection System" to Cottingham (hereinafter the '944 patent). The '944 patent utilizes a light emitter diode to direct light toward a slide. Light is then refracted and diffracted from a mirror underneath the slide and detected by a photo detector. A kinetic activator (an air pump) blows air on the mixture deposited on the slide, so that agglutination particles flow across the slide. As the particles flow across the slide they can be counted by the photo detector.

One problem associated with the '944 patent is that it employs a technique of back-scattering light. This¹ involves setting up and aligning intricate optics. Additionally, the optical set-up tends to be expensive to manufacture and is fragile, making the system vulnerable to breakage. A second limitation of the '944 patent is that it requires kinetic energy to create movement of the agglutination reagents. An air pump requires significant power consumption, precise alignment and calibration. Thus, an air pump adds to the expense of the system.

A further problem associated with the '944 patent is the assumption that agglutination is uniform over a given area. Since uniformity cannot be guaranteed, this assumption may provide for a system with a higher percentage of inaccurate test results than desired. Additionally, an air pump tends to evaporate the fluids on the slide, also limiting accuracy. B. U.S. Patent No. 4,806,015

Another agglutination detection system is described in U.S. Patent No. 4,806,015 entitled "Agglutination Detection Apparatus" to Cottingham (hereinafter the '015 patent). The '015 patent employs a laser-light-source mounted on a moving carriage. A beam from the laser is directed through diffraction optics (including a polarizer, a collimating lens, a reflecting prism and an optical focusing assembly) to transform a collimated laser beam to form a diffraction limited spot. This spot is then focused within a gap on a slide. The beam passes through the slide, diverges and impinges on a photo diode detector. A signal can then be processed by a circuit and displayed.

While the beam is focused at the slide, a motor is used to drive a gear train which causes the carriage to move. After a scan is completed, the motor is reversed and a second scan is made to collect more data. The process repeats itself in this fashion. The system measures the size of particles by calculating the distance travelled by the beam between successive readings.

It is possible to also detect the number of particles detected after each successive scan.

There are a number of problems associated with the '015 patent. The '015 patent employs a moving carriage, which requires an intricate scanning mechanism utilizing many parts. This tends to make the apparatus of the '015 patent heavier than desired for convenient transport. Additionally, the use of a motor mechanism to move the scanning mechanism requires significant power and is expensive to manufacture. The use of a pin-point focused laser mechanism is also expensive. Additionally, the pin-point laser system tends to make the system fragile, therefore limiting human handling of the system and further decreasing its effective mobility.

To summarize, the overall problem with current agglutination detection systems (as the types mentioned above) is that they are more expensive to manufacture than desired; they consume more power to operate than desired: they are not portable; they all employ moving parts; they are very fragile; and they do not detect certain types of agglutination reactions.

One area in which agglutination detection is paramount is the detection of antibodies to Human Immunodeficiency Virus (HIV) in serum, plasma or whole blood. Such a detection system is needed to operate in the "field" such as in rural areas of Africa or other developing countries where there might not be access to electrical power. Therefore, the detection system must not require much power and provide a simple reading or even a diagnosis. The detection system must be able to operate on commonly used consumer batteries and be able to take hundreds of readings on a single set of batteries.

The detection system should be easily used by untrained personnel, such as in clinics in developing countries, or by lay individuals for home usage. The detection system must be inexpensive to manufacture, making it inexpensive enough to be acquired by clinics and doctor offices throughout the world and with individuals for family usage. What is also needed is a detection system that is light weight, portable and sturdy enough for everyday human handling including repetitive portable transport.

Summary of the Invention

The present invention is directed to a system and method for detecting and measuring an agglutination reaction as the agglutination reaction occurs at multiple sites distributed over a test slide's reaction chamber, not just at the endpoint.

Detection is achieved by a slide agglutination detection system. The detection system employs a capillary action test slide with a mixing well, a first capillary channel, a second capillary channel, a third capillary channel, and a viewing window. Optical detection is performed by three Light Emitting Diodes (LEDs) and three corresponding photodiodes. Each LED and corresponding photodiode is strategically located to monitor different stages of agglutination on a test slide. For instance, the first photometric sensing device (LED and photodiode) is positioned to monitor liquid assay flow at a position in the first capillary channel of the test slide (early stages of agglutination). The second photometric sensing device is positioned to monitor liquid assay flow in a position In the second capillary channel of the test slide (intermediate stages of agglutination) and the third photometric sensing device is positioned to monitor liquid assay flow in the third capillary channel of the test slide (late stages of agglutination).

As agglutination particles pass through the three positions the detection system monitors (via LEDs and photodiodes) the agglutination of particles based upon their light scattering properties. In other words, as the liquid assay flows through the channels of the test slide each photodiode, synergistically with microprocessor control and measurement software, monitors the dynamic changes in optical density of the assay liquid. The major measurement principle of the detection system is quantization of the temporal variability of light transmitted through the liquid assay. The detection system employs diffracted and unfocused light sources (LEDs).

Light transmitted through the channels of the test slide is converted to digital electrical signals by the photodiodes and an analog-to-digital converter.

The detection system then collects and quantitizes the temporal variability of light transmitted through the channels to produce various statistical calculations. The results of the statistical calculations are compared to a set of thresholds (empirical data) stored in memory of the detection system. The reaction can then be characterized as positive, negative or indeterminate. This information can be presented as a display, stored in memory, sent to a host computer as well as sent to a printing device. Features and Advantages of the Invention

One feature of the present invention is the employment of multiple photometric detectors strategically located at various positions on a test slide. This enables an agglutination reaction to be sampled dynamically while it is proceeding. Additionally, this enables the detection of multiple types of agglutination assays, including detection of strong agglutination reactions, which occur before mechanisms of conventional detection systems are able to monitor the reaction.

Another feature of the present invention is the employment of a capillary action test slide (capillary action as sole driving force of fluid) and stationary photometric devices. This eliminates all moving parts significantly reducing the size and power requirements of the system. Additionally, this enables for a system that is light weight and portable.

A further feature of the present invention is the employment of non- collimated light. This also reduces the size, power and costs associated with the detection system.

An additional feature of the present invention is a detection system that can be operated with minimal training making the present invention suitable for low technology centers. All operations are self contained in the system. The only human procedure necessary to operate the system is the insertion of a test slide and depositing of liquid assay. The results generated by the system are self contained and produced automatically.

Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. Brief Description of the Drawings

Figure 1 shows an exemplary agglutination test slide that functions with capillary action.

Figure 2 is a circuit block diagram of the slide agglutination detection system of the invention.

Figure 3 shows three points where photometric transmittance is positioned to monitor agglutination of assay liquid capillary flow (indicated by arrows) in a test slide.

Figure 4 shows a side view of an agglutination slide captured mechanically between the LED (stimulus light source) and photodiode (optical channel receiver).

Figure 5A is a flow chart illustrating the operation of a detection system of the invention.

Figure 5B is a continuation of the flow chart from Figure 5A Figure 5C is a continuation of the flow chart from Figure 5A and 5B.

Figure 6 is a top view of the detection system of the invention.

The left-most digit of a reference number identifies the drawing in which the reference number first appears.

Detailed Description of the Preferred Embodiments

1.0 Overview

The present invention was developed to be employed in unsophisticated clinical field-use environments, modern hospital laboratories, doctor offices or households. Operation of the present invention can be performed by individuals who have little to no medical training. The present invention detects and measures an agglutination reaction as the agglutination reaction occurs at multiple sites distributed over a test slide's reaction chamber, not just at the endpoint.

The preferred embodiments of the present invention are described in four sections below. Section 2.0 describes an exemplary capillary action agglutination test slide. Section 3.0 introduces the structure of the present invention. Section 4.0 describes the photometric detection apparatus. Section

5.0 describes how the present invention operates.

2.0 Exemplary Agglutination Test Slide

Figure 1 shows an exemplary agglutination test slide 102 that functions with capillary action. The agglutination test slide is fully described in U.S.

Patent No. 4,775,515 to Cottingham, herein incorporated by reference.

Agglutination test slide 102 includes: a mixing well 104; capillary channels A, B, and C (a capillary channel is sometimes referred to as a "reaction chamber"); a viewing window 112; and air vents 1 14. Arrows indicate direction of capillary flow of fluid. Capillary agglutination occurs as follows: an immunoassay reagent and sample (e.g., blood) are deposited in mixing well 104. When the mixture enters capillary channel A, capillary action is initiated. Capillary action is the sole driving force for mixing the reagent and sample (there is no need for a rotator, or blower driving force).

As the sample is allowed to interact with the reagent (while traveling through the channels) there is increased contact of reagent with antibodies that might be present in the sample. Such contact will cause the antibodies to bind with the reagent to form agglutination particles. In conventional systems, agglutination reaction is observed after the mixture has reached the viewing window 112. At this point, a detection system of the type mentioned above (the '015 patent) can be used to scan the viewing window 1 12 to interpret the results of the test. But such scanning techniques require moving parts, which as described above is not desired (more expense, power, etc.)

Additionally, scanning techniques which measure the agglutination reaction at any single point in time and space (e.g. , when the fluid reaches the viewing window 1 12) are unreliable at extremes of agglutination because only a small fraction of the reaction mixture is sampled. For instance, when an agglutination reaction occurs there is a possibility that a sample will produce high agglutination titers and the agglutination reaction will begin to form almost instantaneously. The agglutination reaction will take place before it reaches the viewing window 1 12 and therefore may be measured as a false negative reading.

3.0 Structure of Slide Agglutination Detection System

Figure 2 is a circuit block diagram of the slide agglutination detection system (detection system) 200. Detection system 200 includes: a power supply 202, a constant current supply circuit 204, light stimulus sources 205 (shown in dotted lines) having light emitting diodes (LEDs) 206, optical detection receivers 207 (shown in dotted lines) having photodiodes 208, analog-to-digital converters 210 (are integrated components of microprocessor 212 in the preferred embodiment), a microprocessor 212, a micro switch 214, an interface and host connector 218, a tone alert 220 and a liquid crystal display

(LCD) 222. All electrical components of the agglutination detection system 200, would be apparent to a person skilled in the relevant art.

Slide agglutination detection system 200 is specifically tailored to operate at low levels of power. To enhance convenience and simplify field operation an internal battery (not shown) is the system's primary power supply

202. The preferred batteries are consumer types, (i.e., two D-size cell). Alkaline batteries can provide a service life to test 1000 slides. In the preferred embodiment microprocessor 212 is a MC68HC1 1 F1 available from Motorola Corporation, Schamburg, Illinois, U.S.A. Microprocessor 212 is the heart of slide agglutination detection system 200. It generally controls all functions including: control of the pulse frequency for LEDs 206, control of the LCD 222, control of photodiode 208 actuation, control of tone alert 220, and half-duplex communication to and from a host 218 (optional), or output device (e.g., printer). All internal elements of microprocessor 212 (such as timing, control, registers, etc.) are not shown. In the preferred embodiment, memory 250 is an EEPROM 250. Other types of memory (e.g., ROM), can be employed.

4.0 Optical Detection Set-up

Referring to Figure 2, optical detection is performed by three LEDs 206A, 206B and 206C, and corresponding photo-detectors (photodiodes) 208A, 208B and 208C, respectively. Each LED 206 and corresponding photodiode 208 is strategically located to monitor different stages of agglutination on a test slide. More or less than three LEDs and photodiodes can be employed.

In the preferred embodiment, detection system 200 employs the agglutination slide shown in Figure 1 and described above. However, any agglutination slide that employs a reaction chamber can be used. Additionally, it is possible to force fluid through the reaction chambers of the test slide 102 without the use of capillary action.

Figure 3 shows three points 302A, 302B and 303C where photometric transmittance is positioned to monitor agglutination of assay liquid capillary flow (indicated by arrows) in test slide 102. Referring to Figure 3, each point

302 A, 302B and 302C correspond to the three channels A, B and C, respectively, of the agglutination test slide 102. At each point 302 is an LED 206 and a corresponding photodiode 208. Point 302A is representative of the earliest stages of agglutination that take place in agglutination test slide 102. Point 302B is located mid-way between the mixing well 104 and the viewing window 1 12. Point 302B is representative of the early-to-midpoint stages of agglutination. Point 302C is located in front of the viewing window 112 and is representative of the late stages of agglutination. The photometric transmittance configuration represented in Figure 3 is designed for detection of multiple latex agglutination assays or other particle reagents.

As agglutination particles 403 pass through points 302A, 302B and 302C, the detection system 200 monitors (via LEDs 206 and photodiodes 208) the agglutination of particles based upon their light scattering properties. This eliminates all moving parts and enables the reaction to be sampled while it is proceeding. The agglutination reaction can therefore be read as a rate and end-point rather than an end-point alone. Figure 4 shows a side view of an agglutination slide 102 captured mechanically between the LED 206 (stimulus light source) and photodiode 208 (optical channel receiver). Referring to Figure 4, the agglutination test slide 102 rests upon an opaque plastic mask 406 of the detection system 200 (part of the detection system chassis 422). LED 206 is mounted on chassis 422A. LED 206 emits a divergent light (non-collimated) 420 which passes through a channel (A,B or C) 408 of the agglutination test slide 102.

Photodiode 208 is mounted on chassis 422B in the path of photons produced by LED 206 and monitors the light transmitted through the slide 102. Pin-hole 404 (diameter) determines the volume of agglutination reaction mixture that is sampled for each transmission measurement. When LED 206 sprays light, the photodiode 208 collects the number of photons that hit it per square area per unit time. Pin-hole 404 enables employment of less expensive photometric devices (LED and photodiode) instead of a laser or laser diode and associated optics for producing collimated light (although more expensive photometric devices can be used as a mechanism for monitoring the test slide 102).

As the liquid assay 402 flows through the channel 408, each photodiode 208, synergistically with microprocessor 212 control and measurement software (to be described), monitors the dynamic changes in optical density of the assay liquid. If the dynamic changes are sufficiently abrupt, the system will identify the event as the leading edge of the assay liquid (reagent) 402 and store the time of its occurrence.

The microprocessor 212 monitors the optical density of the assay liquid by accumulating its variability for a multitude of seven measurements at each point 302B and 302C at preset periods of time (8 seconds each) relative to the leading edges (determined as above). For each of the seven measurements there are a total of 32 transmittance samples (8 sec * 4 samples/second) accumulated by the microprocessor 212. Variability is calculated as the difference of each sample from the running average of all the samples measured from a particular photodiode 208.

The results of the variability measurements (some times referred to as statistical counts) described above are manipulated (as described later) to arrive at a single quantitative estimate of agglutination. This number is compared to a set of thresholds stored in memory 250 to determine if the result is to be reported as positive, negative or indeterminate/unreliable. These stored thresholds and the manipulations of the (14 total) variability measurements are characteristic of a particular agglutination test. In the preferred embodiment the reaction is characterized (for testing of HIV) as positive, negative or indeterminate and the information is presented on the LCD display 222. It can also be stored in memory 250 along with the quantitative result and the other intermediate information for subsequent communication to a host computer (optional) or output device (optional). 5.0 Operation and Detailed Description of Detection System

The operation of detection system 200 is generally illustrated in flow charts shown in Figures 5A, 5B, and 5C. It should be noted that the flow charts shown in Figures 5A-5C provide those skilled in the relevant art with the ability to code a computer program. The source code can be stored in memory 250 or as firmware in the microprocessor 212. The operation as well as a more detailed description of the hardware will now be described by referring to Figures 5A, 5B and 5C and corresponding hardware diagrams of Figures 1 , 2, 3, 4 and 6. Figure 5A is a flow chart illustrating the activation phase of detection system 200. In step 502, the detection system 200 is "off. " The microprocessor 212 is in standby mode (low power) awaiting activation. The microprocessor 212 will remain in standby mode ("NO" path of decisional block 504) until an agglutination test slide 102 is inserted into a slot shown in Figure 6. Referring to Figure 6 is a top view of the detection system 200.

Referring to Figures 2 and 6, when the test slide 102 is fully inserted into a slot 602 of detection system 200, the slide switch 214 is actuated thereby sending an active power control signal 213 to the microprocessor 212 ("YES" path of decisional block 504). The slide 102 is inserted in slot 602 with no liquid assay added to the mixing well 104.

In step 506, microprocessor 212 performs a power-on self test on detection system 200. The microprocessor 212 verifies the integrity of the system 200 firmware by calculating the firmware's "checksum. " The microprocessor 212 also prepares the detection system 200 for use by initializing data variables to known values and initializing the photometric subsystem.

In step 508, the internal clock starts counting. This clock provides a relative time base to measure and record events. In step 510, the microprocessor 212 sends a light control signal 252 to constant current supply 204, which controls the frequency that LEDs 206 "flash" on and off. The microprocessor 212. via constant current supply 204, directs LEDs 206 to produce one light flash. At this point, air is in channels A, B and C. Photodiode 208 detects light produced by LED 206 and transmits an analog voltage signal 254, corresponding to the intensity of the light, to an analog-to-digital converter 210. This digital voltage (representing air) is read by the microprocessor and stored in memory 250 for later use. In step 512, microprocessor 212 sends an identification number to the LCD display via bus 250. The identification number allows the user to identify and label the agglutination test slide 102.

Steps 502-512 occur in approximately one second and represent the start-up of the system 200. At this point the liquid reagent (in the preferred embodiment the liquid reagent is Recombigen^® of Cambridge Biotech Corporation, Worcester, Massachusetts, U.S. A, see U.S. patent No.

4,753,873 to Beltz et al.) and the sample' to be tested, can be added to the mixing well 104. Referring to Figure 3, once added to mixing well 104, the liquid assay flows in channel A from mixing well 104 towards point 302A.

In step 514, the instrument is fully powered-up and ready to start the agglutination test. Accordingly, microprocessor 212 sends a light control signal 252 to constant current supply 204 to activate LEDs 206A, 206B and 206C. LEDs 206 will "flash" on and off 4 times per second. Each time an LED 206 produces light, photodiode 208 detects the light and transmits an analog voltage signal 254 to an analog-to-digital converter 256. Microprocessor 212 will continuously read the digital voltage from A/D converter 210 and compare it with digital voltage obtained in step 510 representative of air, according to the "NO" path of decisional block 516.

When liquid assay reaches point 302A, photodiode 208A senses a change in voltage to processor 212, since the intensity of light changes as the liquid assay arrives and flows past point 302A. Microprocessor 212 detects the change in digital voltages by comparing each voltage reading from A/D converter 210A with the digital voltage stored in step 510. It takes between 5 to 20 seconds for the liquid assay to reach the first point 302A. Fluid speed in channels A, B and C is dependant on humidity, temperature, slide composition, capillary gap dimension and sample constituents, and other associated factors. When liquid assay is detected the operation of system 200 continues, according to the "YES" path of decisional step 516.

In step 518, microprocessor 212 collects one data point reading from point 302A and stores it in memory 250. Voltage levels from A/D converter 210A depend on the light level received from the photodiode 210A.

Variability is calculated as the difference of each sample reading from the running average of all the samples measured from a particular photodiode 208 A.

After taking a reading at point 302A, microprocessor 212 monitors point 302B until the liquid assay is detected.

In step 522, microprocessor 212 monitors the optical density of the assay liquid by accumulating the variability for a multitude of seven measurements at point 302B. Microprocessor 212 samples digital voltages from A/D converter 210B every 4 times per second (for a total of 56 seconds) until all seven variability measurements are collected. After the first reading is made at point 302B, microprocessor 212 activates LED 206C to monitor when liquid assay reaches point 302C. Microprocessor 212 will not collect data from point 302B until liquid assay is detected, as shown in decisional step 524. However, it is contemplated to simultaneously detect and monitor fluid at different points 302.

In step 526, microprocessor 212 initiates collection of 224 (56 * 4 = 224) digital voltage readings from A/D converter 210C. Microprocessor 212 samples digital voltages from A/D converter 4 times per second. Once microprocessor 212 starts collecting data from point 302C, it also initiates a 56 second countdown timer (internal to microprocessor 212), as shown in step 528.

In step 530, microprocessor 212 displays the countdown time on LCD display 222. The countdown time is displayed on LCD display 222 until time is elapsed, as indicated in decisional step 532.

Steps 534-538 involve utilizing and storing data collected from channels A, B and C. In the preferred embodiment, the agglutination test is for detection of antibodies to HIV. However, collection of data can be tailored (empirically) for other specific agglutination applications. In step 534, the data collected from points 302A, 302B and 302C are reduced. The sample reading from channel A (point 302A) is ignored although the edge time is important for error detection. The seven channel B samples (point 302B) are sorted, and the single highest and three lowest voltage readings are ignored. The remaining three samples are summed together to arrive at a "Bsum. " The seven channel C samples (point 302B) are sorted and the single highest and three lowest samples are ignored. The remaining three samples are summed together to arrive at a "Csum. " Bsum or Csum quantitatively represent agglutination as a percentage of an arbitrary scale. Such a scale can be used to convert a raw data unit (variability number) into a medical unit (result) (i.e., positive and negative). Such a conversion factor can be stored in a "table look-up" in memory 250.

In the preferred embodiment, the greater of the two sums (Bsum or Csum) is used to index a medical unit in the look-up table. The greater of Csum or Bsum therefore indicate if a person is HIV positive or negative. The reasoning for using the greater of two sums (Bsum or Csum) is to prevent false negatives from occurring due to over agglutination. In some rare instances there are samples with such a high agglutination titers that the agglutination begins to form almost instantaneously. The agglutination reaction takes place before it reaches the point 302C (and viewing window 112). The agglutination has completely stopped and only a clear non- agglutinating solution reaches the point 302C. If the results were based only on the data collected from point 302C the result would be a false negative. In the instance of this specific HIV assay, this has been empirically determined to be more reliable then other tested combinations of the accumulated variability numbers. The greater of Csum or Bsum therefore indicate if a person is HIV positive or negative. A number 0-to-9 indicates a HIV negative reading. A number of 15-to-100 indicates a HIV positive reading. And a number 10-to-14 indicates a indeterminate reading.

In step 536, the results are stored in memory 250. In step 538, microprocessor 212 displays the results on LCD display

222. Normally, microprocessor 212 sends an actuation signal 232 to a tone alert 230 (speaker or buzzer) to activate a short beep indicating the availability of a result. Once a result is displayed, microprocessor 212 starts a shut down mode timer for the system 200, in step 540. Shut down mode causes the system to transition from high power to low power/standby mode after a time period of 30 seconds.

As indicated in decisional step 542, if the slide 102 is removed from system 200 at any time, the system will return to stand-by mode according to path C ("YES") of decisional block 542. If 30 seconds has elapsed and the slide 102 has not been removed, the system will automatically transition to standby mode, as indicated in step 546 and return to step 502 via path D.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

What is Claimed is:

1. A slide detection system for measuring agglutination of particles in a liquid assay as an agglutination reaction is proceeding, comprising: a test slide, having channel for transportation of the liquid assay from a first point to an end point; wherein the agglutination reaction takes place as said liquid assay travels from said first point to said end point; photometric means, positioned between said first point and said end point, for monitoring said channel for any dynamic changes in optical density of said liquid assay as said liquid assay travels past said photometric device toward said endpoint, and for producing an electrical signal representative of said changes in optical density of said liquid assay; and a microprocessor, coupled to said photometric means, for (a) controlling when said photometric means monitors said channel, (b) for receiving said electrical signal, (c) for identifying dynamic changes in optical density of said liquid assay as a plurality of agglutination particles flow pass said photometric means, (d) for cumulating said dynamic changes in optical density of said liquid assay in a processor counter, and (e) for comparing said quantity to a set of thresholds stored in a memory device to produce an agglutination characterization result.

2. The slide detection system of claim 1, wherein said photometric means comprises: a light emitting diode operable to produce light; a photodiode, opposite said light emitting diode, operable to sense light and produce an electrical signal indicative of the intensity of said light; wherein said test slide is between said light emitting diode and said photodiode; and and a pin-hole, between said photodiode and said test slide, for limiting scattering effects of light from said light emitting diode to define a volume of said liquid assay that is measured by said photodiode.

3. The slide detection system, of claim 1 wherein said agglutination characterization result indicates whether a liquid assay is Human Immunodeficient Virus- 1 , positive or negative; and/or Human Immunodeficient Virus-2, positive or negative.

4. The slide detection system of claim 2, wherein said electrical signal is convened from an analog voltage to a digital voltage by an analog-to-digital converter coupled between said photodiode and said microprocessor.

5. The slide detection system of claim 1 , further comprising a second and third photometric means, positioned between said first point and said end point.

6. The slide detection system of claim 1 , wherein said test slide is a capillary action test slide.

7. The slide detection system of claim 1 , wherein in said channel is a capillary channel.

8. A method for measuring agglutination of particles in a liquid assay as an agglutination reaction is proceeding in a slide detection system: having a test slide with a mixing well, a first capillary channel, a second capillary channel, and a viewing window, said detection system also having a first photometric sensing device positioned to monitor liquid assay flow at a position in said first capillary channel and a second photometric sensing device positioned to monitor liquid assay flow in a position in said second capillary channel, said detection system also having a microprocessor to control said photometric sensing devices and to receive signals from said photometric sensing devices indicating an agglutination particle event, said method comprising the steps of: (a) depositing the liquid assay in the mixing well; (b) detecting liquid assay in the position in said first capillary channel; (c) collecting a plurality of digital signals from the first photometric sensing device; (d) detecting a liquid assay in the position in said second capillary channel; (e) collecting a plurality of signals from the second photometric sensing device; (f) adding said plurality of digital signals together from said first photo metric sensing device to arrive at a first sum; (g) adding said plurality of digital signals together from said second photometric sensing device to arrive at second sum; (h) comparing said first sum to said second sum to determine which is larger; (i) choosing the sum which is larger; (j) employing said larger sum as a mechanism for indexing a threshold value stored in the system; and (k) displaying said threshold.

9. A slide detection system for measuring agglutination of particles in a liquid assay as an agglutination reaction is proceeding, comprising: a capillary action test slide, having a mixing well connected in series with a first capillary channel connected in series with a second capillary channel connected in series with a viewing window, said capillary action test slide operable to transport the liquid assay from said mixing well to said viewing window; wherein the agglutination reaction takes place as said liquid assay travels from said mixing well to said viewing window, a first photometric sensing means, located at a point on said first capillary channel, for measuring changes in optical density of the liquid assay as it flows past said first photometric sensing means; a second photometric sensing means, located at a point on said second capillary channel, for measuring changes in optical density of the liquid assay as it flows past said second photometric sensing means; and a microprocessor, coupled to said first and second photometric means, operable to control said photometric sensing means and collect data from said first and second photometric sensing means at preset periods of times representing variability of the optical density of the liquid assay measured at said preset periods of times from said first and second photometric sensing means.

10. The system of claim 9, wherein said microprocessor is further operable to calculate the total variability of the liquid assay at said first photometric sensing means by summing all said collected data to arrive at a single quantitative estimate of agglutination and comparing said quantitative estimate to a set of thresholds stored in said system.

1 1. The system of claim 9, wherein said first photometric sensing means comprises: a light emitting diode operable to produce light; a photodiode, opposite said light emitting diode, operable to sense light and produce an electrical signal indicative of the intensity of said light; wherein said capillary action test slide is between said light emitting diode and said photodiode; and and a pin-hole, between said photodiode and said capillary action test, for limiting scattering effects of light from said light emitting diode to define a volume of said liquid assay that is measured by said photodiode.

12. The system of claim 9, wherein said second photometric sensing means comprises: a light emitting diode operable to produce light; a photodiode, opposite said light emitting diode, operable to sense light and produce an electrical signal indicative of the intensity of said light; wherein said capillary action test slide is between said light emitting diode and said photodiode; and and a pin-hole, between said photodiode and said capillary action test, for limiting scattering effects of light from said light emitting diode to define a volume of said liquid assay that is measured by said photodiode.

13. The system of claim 11 , wherein said electrical signal is converted from an analog voltage to a digital voltage by an analog-to-digital converter coupled between said photodiode and said microprocessor.

14. The system of claim 12, wherein said electrical signal is converted from an analog voltage to a digital voltage by an analog-to-digital converter coupled between said photodiode and said microprocessor.