GB2168809A - Photometer apparatus - Google Patents

Abstract

A photometer apparatus comprises a housing (21, Figure 1, not shown) accommodating a conventional light emitting diode (LED) (47) and an operatively associated photodetector (not shown), the housing (21) having an opening (26) into which a support member (30) carrying a microtitre tray (31, Figure 3, not shown) can be inserted and selector means for releasably engaging the housing (21) with the support member (30) such that a specific well in a microtitre tray in the opening of the housing can be located at a predetermined position between the LED and the detector, the resultant output from the detector being visually displayed to give a reading to provide a measure of the intensity of light transmitted through the substance in the specific well. The selector means may comprise spring-loaded ball-bearings mounted adjacent the housing end walls and co-operable with channels in support member flanges (35), (36, Figure 3), or alternatively there may be used bearing members mounted in an LED housing and engageable with apertures in the underside of the support member (Figure 13, not shown). <IMAGE>

Description

SPECIFICATION Photometer apparatus This invention relates to a photometer apparatus for selectively locating each well of a microtitre tray in a predetermined position in a housing. In particular the invention relates to a photometer apparatus for performing enzyme immunoassay (EIA) tests in microtitre trays. Enzyme immunoassay (EIA) is a widely used diagnostic technique. The technique is applicable to a wide spectrum of biological materials, and the more sophisticated versions can measure extremely low levels, e.g.

picogram amounts of hormones.

In the case of most ElAs the measured response is a colour-produced by the action of an enzyme on a substrate in the presence of a chromogen.

The colour can in the case of "yes/no" tests be assessed visually and give adequate results. The interpretation of other tests may depend on the actual concentration of a particular metabolite, rather than on its presence or absence. The above tests are often carried out in a photometer using a microtitre tray which has a 12 x 8 array of microtitration wells.

In one known type of photometer a light emitting diode (LED) is mounted in a spring urged collimator which is located in turn in each of the microtitration wells.

A photodiode located below the microtitration well detects the intensity of light passing through the liquid under test.

The LED and photodiode are thus mounted in alignment opposite each other and the microtitre tray is manually moved to locate each well in between the LED and photodiode.

As the microtitre tray is moved to locate the collimator from one well to an adjacent well the collimator is urged upwards against the wall between the two adjacent wells. This can cause particles to be abraded off both the collimator and the wall and such particles may adversely affect readings taken by the photometer. However, it is necessary in order to locate the collimator correctly over a well that the collimator actually projects down into the well.

It is therefore an object of the invention to provide an apparatus for performing tests using microtitre trays, in which each well of a microtitre tray can be accurately located between a light source and photodetector.

In some EIA tests it is desirable to make an objective assessment of the colour response at two or more wavelengths. Thus, it is another object of the invention to provide a photometer apparatus in which there is provided two or more light sources and in which each well of a microtitre tray can be selectively positioned between one of said two or more light sources and a respective photodetector.

According to the invention there is provided a photometer apparatus comprising a housing incorporating a source of electromagnetic radiation and an operatively associated detector, and a support member for holding at least one well, the housing having an opening for receiving the well(s) accommodated on or in the said support member, and selector means for releasably engaging the housing with the support means such that a selected well is located within the said opening in the housing at a predetermined position operatively relative to the electromagnetic radiation source and the associated detector.

Preferably the wells comprise a microtitre tray.

The support member preferably has an index means including a plurality of shallow recesses, each of which recesses correspond to a unique well in the microtitre tray, the housing having said selector means for releasably engaging in a selected one of the recesses, such that the well corresponding with said one recess is located within the opening at the predetermined position.

The support member is preferably elongate and has an oblong recess for holding the microtitre tray, the support member further including a flange disposed adjacent each shorter side of the oblong recess.

In a first example of the invention each flange of the support member has a plurality of shallow recesses, each one of the recesses in each flange corresponding with a unique well in the microtitre tray.

The plurality of recesses in each flange are preferably defined by the intersections of two sets of shallow criss-crossing channels formed in the upper surfaces of the flanges. Further one set of the shallow criss-crossing channels preferably comprises twelve channels which lie parallel to the longer axis of the support member and the other set of the channels comprises eight channels which lie perpendicular to said one set of channels.

The selector means used with this first example of the invention preferably comprises a ball bearing mounted adjacent each end of the housing and spring urged downwards to project into the opening for engagement with the recesses in a respective flange. At each intersection of two channels an enlarged recess is formed and as the support member is moved relative to the ball bearing, the latter is urged into the enlarged recess to releasably hold the support member at a particular recess, such that the corresponding well of the microtitre tray is located at a predetermined position within the housing.

In a second example of the invention it is preferred that the support member has a recess therein for holding the microtitre tray, the recess having a base member with a plurality of spacedapart apertures therein the said apertures in use being in alignment with the wells of the microtitre tray accommodated in the recess.

Further in this second example the preferred selector means comprises one or more ball bearings mounted in a unit located in the housing and adapted to engage one or more of the apertures in the base of the support member such that a selected well in the microtitre tray corresponding to the aperture(s) is located within the opening at the predetermined position.

The predetermined position within the housing is preferably defined by a light emitting diode (LED) and a photodetector positioned directly opposite each other on spaced apart opposing wall members of the housing which define the opening.

The housing preferably also includes first circuit means to energise the LED and second circuit means to drive a meter in response to the output of the photodetector to provide a measure of the intensity of light transmitted through a substance in the selected microtitration well.

The invention will have application in enzyme immunoassay (ElA) tests and more particularly when measuring the optical density of the blue (490 nm) or red (650 nm) absorption lines in chromogens.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 7 is a perspective view of an apparatus according to the invention, Figure 2 is a perspective view of the support member shown in Figure 1, Figure 3 is a plan view of the support member of Figure 2 showing a microtitre tray in position, Figure 4 is a cut-away perspective view of the housing and support member of the apparatus shown in Figure 1, Figure 5 is an end view of the housing of the apparatus of Figure 1 looking in the direction of arrow A, Figure 6 is a diagrammatic view of the bearing assembly in the apparatus of Figure 1, Figures 7 and 8 are diagrammatic plan views showing the housing in dotted outline with the support member in two different positions in the housing, Figure 9 is a perspective view of another embodiment of the support member, Figure 10 is a perspective view of a second embodiment of the support member, Figure 1 7 is a plan view of the support member of Figure 10, Figure 12 is a perspective view of a combined LED and bearing assembly unit, and Figure 13 is a cut-away perspective view of the apparatus with the support member of Figure 10 and the combined LED and bearing assembly of Figure 12.

Referring now to Figures 1-9 of the accompanying drawings wherein similar numerals have been used to indicate like parts, there is shown therein, a photometer apparatus 20 according to the invention. The photometer apparatus indicated generally at 20 comprises a housing 21 including a substantially hollow base member 22 on which is secured in conventional manner a similarly shaped cover member 23. The cover member 23 and the base member 22 have central interior substantially flat spaced apart wall members 24, 25 respectively. Defined between the wall members 24, 25 is a central elongate opening 26 which extends between end walls 27, 28 of the housing 21.

The invention further provides a hollow elongate support member 30 for holding a conventional microtitre tray 31. The support member 30 has a central oblong recess 32 defined between four sidewalls 33. A peripheral ledge 34 is formed at the base of the sidewalls 33 and the microtitre tray 31 is supported on the peripheral ledge 34. The support member 30 includes flanges 35, 36 disposed adjacent the transverse or shorter sides of the central oblong recess 32.Each of the flanges 35, 36 has an index means which comprises one set of eight channels Xi (X1, X2, X3, X4, X5, X6, X7, X8) which lie in a direction parallel to the longer axis of the support member 30 and another set of twelve channels Yi (Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8, Y9, Y10, Y11, Y12) which lie transverse to the Xi channels and thus define a total of ninety-six (96) intersecting locations, each of which is generally denoted (Xi, Yi). As will be explained later, each one of these intersecting locations (Xi, Yi) denotes a shallow recess which corresponds with a unique well in the microtitre tray 31.

As is well known the microtitre tray 31 has an array of microtitration wells each of which can be individually identified by one letter A, B, C, D, E, F, G or H and a number ranging from one (1) to twelve (12). The microtitre tray thus has a total of ninetysix (96) microtitration wells which are arranged in eight (8) rows (A-H) of twelve (12) wells. It will be noted from Figure 3 that each of the rows (A-H) is aligned with a respective channel Xi in the flanges 35, 36.

It will be noted that the channels (Xi), (Yi) on each of the flanges 35, 36 define an array of eighty-four (84) areas 60 the top surface of which lie flush with the top surface 61 of the support member 30. Each of these areas 60 provides an indicator for a corresponding well in the microtitre tray 31, and together with twelve (12) additional indicators provided on the top surface 61 of the support member 30 adjacent to the X1 channels, provide a total of ninety-six (96) indicators, one for each well in the microtitre tray 31. As shown in the drawings the indicators in each flange are are ranged in eight (8) rows (A-H) of twelve (1-12) indicators and, for example, indocator A7 corresponds with the microtitration well A-7 as will be described in more detail later.

Referring to Figures 5 and 6, a nylon ball bearing 40, is mounted in the wall member 24, adjacent each end wall 27, 28 of the cover member 23 and in the centre thereof. The two bearings 40 (only one shown), are mounted such that they project downwards slightly into the opening 26. Each of the bearings 40 is urged downwards by a respective coil spring 41, which is held in a respective housing 42 (only one shown). The housings 42 are secured to the wall member 24 in conventional manner by means of small bolts 43 and nuts 44.

The downward travel of the bearing 40 into the opening 26 is restricted since the aperture 45, in the wall member 24, through which the bearing 40 projects, is of slightly smaller diameter than that of the bearing 40. Thus, the bearing 40 is unable to be removed from the housing 42 through the aperture 45. However, the bearing 40 can be pushed upwards thus compressing the spring 41 so that the circumference of the bearing is flush with the exposed surface 46 of the wall member 24.

A light emitting diode (LED) 47 is mounted centrally in the wall member 24 (Figure 4) in alignment with the two ball bearings 40. The LED 47 may have any suitable emission spectrum characteristics but in particular it may be of the blue (490 nm) type or red (650 nm) type. A photodetector (not shown) is mounted in the wall member 25 directly opposite the LED 47. The LED 47 is energised by a battery power supply (not shown) contained within the housing 21 via any suitable electrical circuit (not shown) also contained with the housing 21. The output from the photodetector is converted by a suitable circuit (not shown) in the housing 21, into a reading on a digital display 48 mounted in the cover member 23.The apparatus 20 is also provided with a conventional on/off switch 49 for the circuits and a zero adjustment switch 50 which is used in conventional manner to adjust for ambient light levels.

Referring to Figure 5 there is also shown a marker 51 at the end wall 27 of the cover member 23 an apex 52 of which is displaced slightly to the left relative to the ball bearing 40. A similar marker 51 is also provided at the end wall 28 of the cover member 23 and this marker is also slightly displaced relative to the bearing 40. (See Figures 7 and 8).

In use, a substance which it is desired to test is placed in the wells of the microtitre tray 31. The microtitre tray 31 is placed in the support member 30 as shown in Figure 3. The support member 30 containing the microtitre tray 31 is then inserted into the opening 26 in the housing 21. To locate a particular well of the microtitre tray 31 at the predetermined position within the housing i.e. between the LED 47 and the photodetector (not shown), the support member 30 is moved until the apex 52 of each of the markers 51, is aligned with the relevant indicator in the respective flanges 35, 36. The reason that the marker 51 is slightly displaced relative to the respective ball bearing 40, is of course that the indicators in each of the flanges 35, 36 are slightly displaced relative to an adjacent Xi channel.

As the support member 30 is moved in the housing 21 the ball bearings 40 engage in the channels (Xi) and (Yi) in the respective flanges 35, 36. When the support member 30 is moved to a position so that the ball bearings 40 lie between an adjacent pair of the indicators 60, the ball bearings 40 are urged upwards in the housing 42 against the coil spring 41. This is because the width of the individual channels Xi, Yi are much narrower than the diameter of ball bearings 40. However, when the support member 30 is in a position so that the ball bearings 40 lie at the intersection of two channels (Xi, Yi), for example (X1, Y7) as shown in Figure 7, then the ball bearings 40 are able to move downwards to a greater extent in the housing 42, so that they are engaged in the enlarged recess defined at the intersection of the two channels (X1, X7).To move the support member 30 to another position it is necessary to overcome the force of the coil spring 41 as it must be compressed when the ball bearings 40 are moved from one intersection of two channels (Xi, Yi) to another.

In Figure 7 the ball bearings 40 are engaged at the intersection of two channels (X1, X7) in the respective flanges 35, 36. Further, the apex 52 of the markers 51 adjacent each end of the housing 21 are aligned with the indicators A-7 in the respective flanges 35, 36. In this position of the support member 30, the seventh well in row A of the microtitre tray 31 is located in the predetermined position, between the LED 47 and the photodetector in the housing 21. Thus, the invention enables each well of a microtitre tray 31 to be selectively located between the LED 47 and the photodetector in the housing 21. Furthermore, the support member 30 is releasably engaged with the housing 21, by the ball bearings 40 which are forced downwards into the selected recess at the intersection of two channels (Xi, Yi).

Once the required well is in position between the LED 47 and the photodetector, a test may be made on the substance in the well by switching on the LED 47 and the photodetector and using the circuits in conventional manner.

In Figure 8 another position of the support member 30 is shown. In this position each marker 51 has its respective apex 52 aligned with the respective indicator 2 in row E in the flanges 35, 36 and accordingly, the well 2 in row E of the microtitre tray 31 is aligned with the LED 47 and the photodetector. Furthermore, the ball bearings 40 are located in the respective flanges 35, 36 at the intersection of channels X5 and Y2.

It will be clear therefore, that in positioning a particular well of the microtitre tray 31, between the LED 47 and the photodetector, it is only necessary to move the support member 30 until the corresponding indicator 60 in each of the flanges 35, 36 is aligned with the respective marker 51 in the housing 21.

It will also be apparent that if another diode is mounted in the housing 21, adjacent to the diode 47, then another marker similar to the marker 51 may be provided on the cover member 23, adjacent to the marker 51, so that a well of the microtitre tray 31 may be positioned between this other diode and another corresponding photodetector.

As shown in Figure 9 the recess 32 of the support member 30 may be provided with a peripheral upstanding curtain member 70, the uppermost edge 71 of which fits snugly against the exposed surface 46 of the wall member 24, so that all ambient light is precluded from the region of the microtitre tray 31 during operation of the apparatus.

This enables more accurate results to be obtained.

Referring to Figures 10-13 of the accompanying drawings there is provided a support member 130 for holding a conventional microtitre tray (not shown). The support member 130 has a central oblong recess 132 defined between four sidewalls 133. The recess 132 of the support member 130 has a base 140. The support member 130 has in the recess 132 peripheral recess flanges 134 which in use support a microtitre tray in position. The base 140 is provided with a plurality of spaced apart apertures 141 which in use correspond exactly with the wells in the microtitre tray. The support member 130 includes flanges 135 and 136 disposed adjacent the transverse or shorter sides of the central oblong recess 32. The flanges 135 and 136 are each provided with an index sheet 135a and 136a adhesively affixed to the flanges 135,136 respectively in the format as illustrated particularly in Figure 11.The flanges 135,136 are secured to the support member 130 by securing screws 142.

Referring to Figure 12 of the accompanying drawings there is provided an LED and bearing assembly unit comprising a housing 150 accommodating two LED's 151 (blue type) and 152 (red type) and associated circuit means and two bearings 153 and 154. The housing 150 is adapted to accommodate securing screws 155 which are used to mount the unit in position on the base member 22 - as shown in Figure 13. Photodetectors (not shown) are provided in the cover member 23 directly opposite the LEDS. 151 and 152, and the output from the photodetectors is converted by conventional circuit (not shown) in the cover 23 into a reading on a digital display 48 mounted on the cover 23.

In its position of use the bearings 153 and 154 engage the apertures 141 in the base 140, as shown in Figure 13, to locate a well in the microtitre tray in correct position relative to the LEDs 151,152.

The indexd sheets 135a and 136a cooperate with the markers 51,52 on an end wall 27 of the cover member 23 to indicate the particular well of the microtitre tray which is ppsitioned between one of the two LED's 151,152 and the complementary photodetector. The index sheet 135a refers to the position of a well relative to the LED 153 and the index sheet 136a refers to the position of a well relative to the LED 154. In this-embodiment the microtitre tray support member 130 is inserted into the housing 21 such that the relevant index sheet 135a, 136a is located in association with the marker 51,52.

The manner of operation of the second embodiment of the invention as described above is substantially as already described in relation to the first embodiment.

The selector means of the second embodiment, indicating the bearings 151,152 engaging in apertures 141 in the support member base 140, operates very efficiently and since the bearings 151,152 are adjacent the LED's 153,154 the accuracy of location is always good and the location tolerances necessarily employed during manufacture are not as high as demanded by the selector means employed in the first embodiment.

Some advantages of the invention are as follows.

First, the use of LED's for conducting optical tests enables the photometer apparatus to be made portable since the LED's require only a small power supply which can be contained within the housing. This enables the Portable Photometer to be made available to individual medical and veterinary practices, to local laboratories and even to the public at large.

Second, the use of the housing 21 having the opening 26 readily excludes most ambient light from the microtitre tray 31 and the photodetector.

The use of the curtain 70 effectively excludes all ambient light from the region of the microtitre tray 31, thus increasing the accuracy of test results.

Third, the substance in the wells of the microtitre tray 31 does not come into contact with the LED 47 and thus there is no cross-contamination of substance from one well to another which is a problem with conventional equipment.

Fourth, it is possible to mount two or more LED's 47 in the housing 21 and still use the index means. This is important since it is often desirable to conduct tests using LED's which have different emission spectrum characteristics.

Fifth, each well in a microtitre tray can be readily located in position between a LED and a corresponding photodetector.

Claims (15)

1. A photometer apparatus comprising a housing incorporating a source of electromagnetic radiation and an operatively associated detector, and a support member for holding at least one well, the housing having an opening for receiving the weli(s) accommodated on or in the said support member, and selector means for releasably engaging the housing with the support means such that a selected well is located within the said opening in the housing at a predetermined position operatively relative to the electromagnetic radiation source and the associated detector.

2. A photometer apparatus as claimed in Claim 1, in which the support member accommodates a microtitre tray having a plurality of spaced apart wells arranged in a predetermined format.

3. A photometer apparatus as claimed in Claim 2, wherein the support member has an index means including a plurality of shallow recesses, each of which recesses corresponds to a unique well in the microtitre tray, the housing having selector means for releasably engaging in a selected one of the recesses, such that the well corresponding with said one recess is located within the opening at the predetermined position.

4. A photometer apparatus as claimed in Claim 2, wherein the support member is elongate and has an oblong recess for holding the microtitre tray, the support member further including a flange disposed adjacent each shorter side of the oblong recess, each flange having a plurality of shallow recesses, each one of the recesses in each flange corresponding with a unique well in the microtitre tray.

5. A photometer apparatus as claimed in Claim 4, wherein the plurality of recesses in each flange are defined by the intersections of two sets of shallow criss-crossing channels formed in the upper surfaces of the flanges.

6. A photometer apparatus as claimed in Claim 5, wherein one set of the shallow criss-crossing channels comprises eight channels which lie paral lel to the longer axis of the support member and the other set of shallow criss-crossing channels comprises twelve channels which lie perpendicular to said one set of channels.

7. A photometer apparatus as claimed in any preceding Claim, wherein the selector means comprises a ball bearing mounted adjacent each end of the housing, and spring urged downwards to project into the opening for engagement with the recess in a respective flange.

8. A photometer apparatus as claimed in Claim 1, wherein the predetermined position within the housing is defined between a source of electromagnetic radiation and an operatively associated detector such that, in use, radiation emitted from the source is received by the detector after transmission through the selected well.

9. A photometer apparatus as claimed in Claim 8, wherein the source of electromagnetic radiation is a light emitting diode (LED) and the detector is a photodetector, the light emitting diode and photodetector being positioned directly opposite each other, on spaced apart opposing wall members of the housing which define the opening.

10. A photometer apparatus as claimed in Claim 9, wherein the housing includes first circuit means to energise the LED and second circuit means to drive a meter in response to the output of the photodetector, to provide a measure of the intensity of light transmitted through a substance in the selected well.

11. A photometer apparatus as claimed in any preceding claim, wherein the recess for holding the microtitre tray has a peripheral upstanding curtain member, the uppermost edge of which, in use, fits snugly against the exposed surface of the adjacent wall member to preclude ambient light from the region of the microtitre tray.

12. A photometer apparatus as claimed in Claim 1, in which the support member has a recess therein for holding the microtitre tray, the recess having a base member with a plurality of spacedapart apertures therein the said apertures in use being in alignment with the wells of the microtitre tray accommodated in the recess.

13. A photometer apparatus as claimed in Claim 12, in which the selector means comprises one or more ball bearings mounted in a unit located in the housing and adapted to engage one or more of the apertures in the base of the support member such that a selected well in the microtitre tray corresponding to the aperture(s) is located within the opening at the predetermined position.

14. A photometer apparatus as claimed in Claim 13, in which the unit holding the ball bearing(s) also houses at least one light emitting diode (LED) and associated electric circuitry.

15. A photometer apparatus substantially as herein described with reference to Figures 1-8, Figure 9 and Figures 10-13 of the accompanying drawings.