LUMINESCENCE OR FLUORESCENCE MONITORING APPARATUS AND METHOD

Abstract: A monitor for use in sample testing comprises a sample chamber for receiving a vessel containing a light-emitting substance, and an avalanche photodiode for receiving the emitted light and connected to a circuit for measuring the light received by the avalanche photodiode. The use of an avalanche photodiode enables the monitor to be portable and robust and to be included in a portable kit for carrying out hygiene monitoring in the field.

Description: Luminescence or Fluorescence Monitoring Apparatus and Method This invention relates to an apparatus and method fo monitor ing luminescent or fluorescent light emission, an particularly but not solely for use in hygiene monitoring. It is known to test for bacteria or other living cell by taking a sample and releasing adenosine tr iphosphate (ATP contained within the cells using an appropriate reagent togethe with the enzyme luciferase in order to cause the emission o light. The light output is related to the concentration of AT in the sample. The light output is however very small an h i ther to the l ight de tect ing appar atus has made use of photomultiplier tube in order to provide a measurable electrica s ignal output. Photomultipliers require a high voltage powe supply, normally only available in the laboratory. Hithert testing for living cells has been carried out by taking a sampl in the f ield, then analysing the sample at a central laborator either by conventional culture techniques using plate counts, or using luminescence monitoring apparatus with which the laborator is equipped, together with a power supply appropr iate for th photomultiplier tube of that apparatus. In accordance with this invention, there is provided monitor for use in sample testing, comprising a sample chamber for receiving a vessel containing a light-emitting substance and a photodetector for receiving the emitted light and connected to an electr ical circuit for measur ing the light received by the photodetector, in which the photodetector comprises an avalanche photodiode. The avalanche photodiode is a semi-conductor device which is extremely light-sensitive and responds to a low level of received light to provide a measurable electrical output signal. The circuitry for the avalanche photodiode does not require as h i gh a vo l t ag e o r a s h i gh a c u r r e n t po w e r s upp ly as photomultipliers, and can be powered by batteries. Furthermore the avalanche photodiode is, in contrast with photomultipl ier. robust and not adversely affected by exposure to intense ligh Thus the monitor in accordance with this invention can be portable device. The monitor in accordance with this invention may b used for measuring the light emitted by substances spontaneousl and it may be used for measuring the light emitted by substance once excited by exposure to light (i.e. fluorescent substances and references in this specification to a luminescence monito (or to a light-emi ting substance) are intended to include monitor measuring light produced by fluorescence (or to fluorescent substance). Also in accordance with this invention, there i provided a monitor for use in sample testing, comprising sample chamber for receiving a vessel containing a light-emittin substance, the chamber being formed in its side wall with a ligh outlet for passing light to a photodetector, and means fo adjusting the vertical position of the vessel relative to sai light outlet. The vertical adjustment enables the sample containin vessel to be positioned such that the centre oϋ its sample o e.g. liquid is aligned with the outlet which is passing light t the photodetector. Thus a relatively small sample may be take and contained in the vessel, yet it can be ensured that th photodetector receives the maximum of the light emitted by th sample. One use of the monitor is for hygiene monitoring. I accordance with this invention there is provided a method o hygiene monitoring, comprising wiping a swab over a surface to b tested, placing the swab in a pipette tip, coupling a pipette t the pipette tip and using the pipette to draw a quantity o breakage reagent into the pipette, and subsequently expelling th breakage reagent from the pipette tip and into a sample vesse which already contains an enzyme, such that if the swab sampl included bacteria or other living cells, light is now emitte from the liquid in the sample vessel. This hygiene monitoring method is particularly suite to being carried out in the field, using a kit comprising steril swabs, sterile pipette tips, a container of breakage reagent sample vessels already charged with enzyme, and a portabl luminescence monitor. These items can all be carried in carrying case. Thus also in accordance with this invention, there i provided a kit for use in hygiene monitoring comprising portable carrying case containing a luminescence monitor, plurality of swabs, a plurality of pipette tips, a pipette fo coupling to each pipette tip, a plurality of sample vessels pre charged with enzyme, and a container of breakage reagent Preferably also a holder is provided for gripping each swab. The monitor described above may be used for a wid variety of other sample testing applications, for example testin raw and final products in the food industry, pharmaceutial preparations, water quality and clinical samples. In these cases, a modified monitoring kit is appropriate. Therefore further in accordance with this invention, there is provided a kit for use in sample testing, comprising a portable carrying case containing a luminescence monitor, a plurality of pipette tips, a pipette for coupling to each pipette tip, a plurality of sample vessels, and containers of breakage reagent and enzyme. In use of this kit, the sample to be tested is introduced into a sample vessel and then using the pipette with a tip coupled to it, appropriate quantities of the breakage reagent and of the enzyme are also introduced into the sample vessel. The sample vessel is finally placed in the luminescence monitor to measure the light emission. Embodiments of this invention will now be desribed by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a plan view of a hygiene monitoring kit shown with its carrying case open; FIGURE 2 is a side view of the kit shown in Figure 1; FIGURE 3 is an enlarged plan view of a reagent kit of the hygiene monitoring kit; FIGURE 4 is a section through a pipette tip when receiving a swab from a swab holder; FIGURE 5 is a section through the pipette tip when engaged with a pipette; FIGURE 6 is a section through one form of sample chamber of a portable luminescence monitor of the kit; FIGURE 7 is a section through another form of sample chamber; FIGURE 8 is a section through a further form of sample chamber; FIGURE 9 is a plan view of the sample chamber shown in Figure 8; FIGURE 10 is a block diagram of the circuit of the monitor, and FIGURE 11 is a plan view of another embodiment of sample testing kit shown with its carrying case open. Referring to Figures 1 and 2, a portable hygiene monitoring kit comprises a carrying case having upper and lower halves 10, 12 which are hinged to each other at 11. When closed together and fastened by means of integral catches, the case may be carried by means of a handle 13. When opened up as shown, the two halves of the case lie flat on an e.g. table or benchtop. In the interior of the case, each half receives a number of items or components of the kit within recesses formed in inserts 14, 15 of plastics foam cushioning material. In the lower half 12 of the casing, there is disposed a portable luminescence monitor 16, a reagent kit 17 and a pack of sterile stencils 18. The luminescence monitor 16 may be powered by batteries housed within its own casing, but additionally or instead a power pack 19 may be provided. In the upper half 10 of the case, there is disposed a swab holder 20 and a pipette 21. Further a pipette holder 22 is mounted in the upper half 10 of the case and is movable between a first position in which it is laid flat into a rece in the foam insert 14 and an upright position as shown in Figu 2. Referring to Figure 3, the reagent kit 17 comprises plurality of cuvettes 24, a plurality of strips of sterile swa 25, a plurality of sterile pipette tips 26 and a bottle of liqu extractant 27. Each of the cuvettes 24 contains a corre quantity of appropriate enzyme, either powdered or freeze dri onto the inner surface of the cuvette, and the cuvette is clos by a cap. As shown in Figure 4, each swab comprises a short ste 28 provided with an absorbent head 29. Each pipette tip has barrel portion 30, a tapering lower end 31 and an upper e shaped to fit onto the lower end of the pipette. In use of the hygiene monitoring kit, a swab is take out of its individual packaging, and gripped in the lower end o the swab holder 20. The latter has a tubular lower end 32 whic is split to form gripping fingers, which are caused to open u when an actuator at the upper end of the swab holder is depresse (so that the gripping end 32 may be engaged over the free end o the swab stem), and which will close up again (to grip the swa stem) when the actuator is released. Then by holding the swa holder, the user wipes the head 29 of the swab over a surface t be tested. Once the sample has in this manner been taken, th swab is released into a pipette tip, as shown in Figure 4. Next the pipette 21 is engaged to the pipette tip, a shown in Figure 5. Then the pipette is used to draw up predetermined volume (say 500^ιl) of breakage reagent 33 from th extractant bottle 27. The pipette is engaged with the pipett holder 22 and allowed to stand for a predetermined time perio (e.g 60 seconds). During this period the breakage reagent break into any bacteria or other living cells which have been picked u on the swab during the sampling process, and releases the AT contained within the cells. Then the breakage reagent 33 within the pipette tip i ejected into a cuvette containing the appropriate enzyme. Th pipette is used to alternately eject the liquid and draw it u again two or three times, in order to ensure adequate mixing Having now mixed the enzyme with the breakage reagent, then i there were any living cells on the swab, the ATP will react wit the enzyme to commence light emission, the strength of the ligh emission (number of photons emitted) being related to th concentration of bacteria present. After mixing the breakag reagent into the cuvette, the cuvette is placed in the portabl luminescence monitor so that the light output can be measure over a predetermined period of time, to provide a measure of th concentration of bacteria in the sample obtained. It is a featur of the enzyme that a constant light output is produced so tha this step is not time dependent. Referring to Figure 1, the portable luminescenc monitor includes a socket 34 in its upper surface, into which th cuvette is placed. The socket is then covered over in light tight manner. Within the monitor, a photodetector is positione to receive the light emitted from the liquid within the cuvette In the example shown, the photodetector comprises an avalanch photodiode. Such a photodiode is extremely light sensitive ye its circuitry requires a low voltage and current power supply, s rendering it suitable for the portable hygiene monitoring syste being described. The avalanche photodiode requires an operatin temperature of typically +5°C to 0°C and its circuitry i arranged to cool it to this level. The monitor may include digital display, or an analog display, or a printer or a plotte to provide the measurement data. Figure 6 shows one embodiment of cuvette receivin chamber of the luminescence monitor. A socket 34 is formed i the upper side of the monitor casing and receives the tubula cuvette 24, to rest on a spring-loaded platform 35. An arm 36 i mounted on a post 37 which is rotatably mounted to the monito casing, and a plunger 38 depends from the lower side of the ar 36. In use, the cuvette 24 is placed in the socket 34, then th arm 36 is turned until the plunger 38 lies above the cuvette, an then the arm is depressed until it lies against the upper side o the monitor. In this position, the arm 36 seats onto an O-rin seal 39 on the monitor casing to ensure light-tightness. I depressing the arm 36, the plunger 38 displaces the cuvett downwardly into the socket 34. An O-ring seal 40 on the plunge seals with the inside of the socket 34 to enhance the light tightness. The cuvette needs to be positioned so that the centr of its small column of liquid is aligned with an orifice 41 i the side of the socket 34, through which the light from th liquid is passed to the detector. Different reactions wil require different volumes of liquid, so that they will requir different vertical positions for the cuvette for effective ligh collection. This requirement is achieved by turning an adjustin screw 42 which is threaded through the arm 36 and which carrie the plunger 38 at its lower end. The adjusting screw preferabl has a number of predetermined settings, each one corresponding t a different reaction liquid volume or protocol, and serving t depress the cuvette to its required level. Figure 7 shows an alternative arrangement in which th vertical adjustment of the cuvette 24 is achieved by means of a adjusting screw 42 on the underside of the monitor, acting on th platform 35 on which the cuvette stands. In this case, a sprin loaded plunger 38 is closed onto the top of the cuvette once th cuvette is placed into the socket 34. Figures 8 and 9 show a sample chamber for the monitor comprising a body 50 formed with socket 34 for receiving the cuvette. A top part 51 of the body 50 is circular and receives a rotatable cap 56 which has a peripheral skirt encircling the top part 51 of the body 50. The cap 56 is mounted on a stem 57 which passes through the part 51 and is journalled therein for rotation. The top and skirt of the cap 56 are cut-away over an angular portion as shown at 62. A lower part 52 of the body 50 is formed with a through passage 58 perpendicular to the axis of the socket 34. At one end of this passage, and to one side of the sample tube or cuvette when received in the socket, there is mounted a concave mirror 59. In the passage 58 on the other side of the cuvette are mounted the lens 60 of an optical system for focussing light from the sample in the cuvette onto the avalanche photodiode APD. In use of the sample chamber shown in Figures 8 and 9, the cuvette is placed into the socket 34 whilst the cap 56 is in the position shown, i.e. so that the socket 34 is exposed through the cut away 62 of the cap. Then the cap 56 is turned through 180°, to cover the top of the socket 34. The cap 56 and body part 51 are precision-made so that the sample chamber is light-tight when closed. A microswitch is included in the body part 51 and closes as the cap reaches its closed position, to turn on the counter of the APD circuit for a predetermined time, e.g. 10 seconds, as will be described with reference to Figure 10. The cuvette rests with its bottom on a stem 62. Provision for vertical adjustment of the cuvette may be made by mounting this stem 62 to extend through the bottom of the body part 52 along its axis. This adjusting stem may be displaced in the vertical direction by a manually operable screw such as shown in Figure 7. The provision for vertical adjustment of the cuvette may also be used to allow for different height cuvettes, which are typically 47mm or 55mm in height. Referring to Figure 10, there is shown the circuit in which the avalanche photodiode APD is connected. The circuit comprises a temperature stabilising system for the avalanche photodiode, comprising a Peltier effect heat pump HP mounted adjacent the APD and supplied with current from a temperature control circuit TC for cooling the APD. A temperature sensing thermistor TS is also mounted adjacent the APD and controls via the circuit TC the magnitude of the current supplied to the Peltier heat pump HP. The output signal from the APD is passed to a detector circuit DC which includes a comparator for comparing the signal with a threshold and providing a pulse of predetermined width and amplitude for each signal exceeding t threshold. These pulses are passed to a counter C. The circu further comprises a control logic circuit CL to which t microswitch MS in the sample chamber is connected: when t chamber closes and so closes the microswitch, a 10 second tim in the control logic CL is started and the counter C is enabl for the corresponding time interval. At the end of this, t count is displayed on the numerical display ND. The circuit of Figure 10 further includes a supp circuit PSC powered from rechargeable batteries B and providi the required supplies for the control logic, temperature contro detector, counter and display circuits. The circuit of Figure may be connected to an external power supply unit PSU f operation and/or for recharging the batteries B. Referring to Figure 11, there is shown anothe embodiment of portable hygiene monitoring kit comprising carrying case having upper and lower halves 80,82 hinged to eac other at 81, and which can be closed together and fastened b means of integral catches so that the case can be carried b means of a handle 83. When opened up as shown, the two halves o the case lie flat. In the inside of each half of the case, ther is a piece of plastics foam cushioning material 84,85 formed wit recesses in which the various components of the kit are receive In the lower half there is disposed the portable luminescenc monitor 86 having a sample chamber 88 of the type shown i Figures 8 and 9, an on/off switch 90 and a visual display 92. Th monitor includes batteries to power its circuits but a powe supply unit PSU is also provided together with electrical leads for connecting the monitor to the mains for powering it and/o recharging its batteries. A pack of individually packaged steril swabs is provided at 94 and sterile pipette tips are provided a 96. A rack 98 is also provided, including a number of cuvette 100, and bottles of breakage reagent and enzyme 102, 104. In th upper half of the case, two or more pipettes 106 are provided. In use of the kit shown in Figure 11, a swab is wipe over the surface to be tested, then placed into a cuvette which predetermined volumes of breakage reagent and then enzy are added, using one of the pipettes with one of the pipette ti coupled to it. The cuvette is allowed to stand for predetermined period in the rack 98, and is then placed into t sample chamber and the latter is closed: the count appearing o the display 92 at the end of the integrating period (typically 1 seconds) of the monitor is recorded as a measure of the microbia activity of the sample taken up by the swab.

Claims: CLAIMS 1. A monitor for use in sample testing, comprising sample chamber for receiving a vessel containing a light-emittin substance and a photodetector for receiving the emitted light an connected to an electrical circuit for measuring the ligh received by the photodetector, in which the photodetecto comprises an avalanche photodiode. 2. A monitor as claimed in claim 1, in which th electrical circuit comprises a counter which counts the discret signals issuing from the avalanche photodiode within predetermined period of time. 3. A monitor for use in sample testing, comprising sample chamber for receiving a vessel containing a light-emittin substance, the chamber being formed in a side wall with a ligh outlet for passing light to a photodetector, and means for adjusting the vertical position of the vessel relative to sai light outlet. 4. A monitor as claimed in claim 3, in which the adjusting means comprises an element on which the sample vessel rests, the vertical position of which element is presettable. 5. A monitor as claimed in claim 3, in which the adjusting means comprises a spring-loaded element on which the sample vessel rests, and means for bearing against the top of the sample vessel to depress it through a presettable distance. 6. A method of hygiene monitoring, comprising wiping a swab over a surface to be tested, placing the swab in a pipette tip, coupling a pipette to the pipette tip and using the pipette to draw a quantity of breakage reagent into the pipette, and subsequently expelling the breakage reagent from the pipette tip and into a sample vessel which already contains an enzyme, such that if the swab sample included bacteria or other living cells, light is now emitted from the liquid in the sample vessel. 7. A kit for use in hygiene monitoring, comprising a portable carrying case containing a luminescence monitor, a plurality of swabs, a plurality of pipette tips, a pipette for coupling to each pipette tip, a plurality of sample vessels pre- charged with enzyme, and a container of breakage reagent. 8. A kit as claimed in claim 7, further comprising a holder for gripping each swab.- 9. A kit for use in sample testing, comprising a portable carrying case containing a luminescence monitor, a plurality of pipette tips, a pipette for coupling to each pipette tip, a plurality of sample vessels, and containers of breakage reagent and enzyme.

Inventors: GOODFIELD CLIVE, JOHNSON IAN ROY, GOODFIELD, CLIVE, JOHNSON, IAN, ROY
Applicants: BIOTRACE LTD, BIOTRACE LTD.
Application year: 1989
Main classification: G01N21
IPC codes: C12M1, C12Q1, G01J1, G01N1, G01N21