WO2015087092A2

WO2015087092A2 - Assay apparatus

Info

Publication number: WO2015087092A2
Application number: PCT/GB2014/053703
Authority: WO
Inventors: Nasr-Eddine Djennati; Andrew Mitchell
Original assignee: Bio Amd Holdings Limited
Priority date: 2013-12-13
Filing date: 2014-12-15
Publication date: 2015-06-18
Also published as: GB201322099D0; WO2015087092A3

Abstract

An assay apparatus for determining properties of a sample. The apparatus has first and second chambers for receiving a sample. The first and second chambers are linked by a conduit along which at least part of the sample may travel so that the sample can move from the first chamber to the second chamber in series. The apparatus also has a slot extending from the conduit and a valve body comprising magnetic or magnetically susceptible material which is housed at least substantially within the slot. The valve body is movable between a first position in which the valve body is arranged at least substantially outside the conduit and a second position in which the valve body extends across the conduit thereby restricting a sample from travelling along the conduit from the first chamber to the second chamber. The valve body is slidably movable between the two positions by an external magnetic field.

Description

ASSAY APPARATUS

Technical Field of the Invention

The present invention relates to assay apparatus, for example, assay apparatus for testing low volumes of fluids of interest. Background to the Invention

Assay strips are widely used in the medical field to determine different characteristics of a sample of interest. Assay strips can be used to measure the coagulation characteristics of a sample of blood by determining, for example, the promothrombin time (PT) of blood or plasma, activated partial thromboplastin time (APPT), activated clotting time (ACT), protein C activation time (PCAT). Assays can also be used to determine non-clotting properties of a sample of interest such as the blood or plasma viscosity and blood haematocrit.

A known system for determining properties of a sample of interest such as blood is disclosed in PCT/GB2011/051292 which describes apparatus having a chamber for receiving at least one sample. The chamber is arranged to receive a quantity of the sample of interest and typically contains a reagent that is intended to react with the sample. The type of reagent used is specific to the test intended to be conducted on the sample of interest. The chamber also contains a rotor which is arranged to rotate under the influence of an external magnetic field. The rotation speed of the rotor within the chamber is measured by an external detector so that as a sample of blood within the chamber begins to clot, the reduction in speed of rotation due to friction between the sample and the rotor can be determined. By measuring the reduction in rotation speed of the rotor, the apparatus can be used to determine, for example, the PT properties of a sample of blood.

A problem with such apparatus is that it is not capable of determining the properties of a sample when the test on the sample requires the use of more than one reagent used in sequence. For example, the APTT, which measure the activity of the intrinsic and common pathways of coagulation, is determined by mixing the sample of interest with more than one reagent. Another test that involves more than one reagent involves the use of an in- vitro diagnostic device intended to be used for the quantitative measurement of direct thrombin inhibitors (DTI), such as hirudin, Argatroban ® and dabigatran in human citrate plasmas.

It is an object of the present invention to provide an improved assay apparatus that is capable of carrying out tests on a substance of interest that involves the use of more than one reagent.

Summary of the Invention According to a first aspect of the present invention, there is provided an assay apparatus for determining properties of a sample comprising first and second chambers for receiving a sample, wherein the first chamber has an inlet and an outlet and the second chamber has an inlet, and wherein the outlet of the first chamber is connected to the inlet of the second chamber by a conduit along which at least part of the sample may travel so that the sample can move from the first chamber to the second chamber in series, the apparatus further comprising a slot extending from the conduit and a valve body comprising magnetic or magnetically susceptible material which is slidably mounted at least substantially within the slot and which is slidable between a first position in which the valve body is arranged at least substantially outside the conduit and a second position in which the valve body extends across the conduit thereby restricting a sample from travelling along the conduit from the first chamber to the second chamber, the valve body being movable between the two positions by an external magnetic field. Advantageously, apparatus according to the present invention can be used to conduct tests on samples that require the use of more than one reagent. An assay apparatus according to the present invention therefore allows immunoassay tests requiring two or more different reagents used in sequence, which would normally only be possible in laboratories where technical operator intervention is necessary, to be performed automatically in hand held instruments using small volumes of a sample. By slidably mounting the valve body within the slot, the orientation of the valve body may be kept substantially the same when moving between the two positions so that the position of the poles of the valve body can be kept substantially the same, thereby ensuring a reliable and consistent movement. The valve body and slot may be arranged relative to the conduit such that the valve body is substantially perpendicular to the conduit when the valve body is in the second position. The valve body may conform substantially to the shape of the slot. The slot may define a path along which the valve body may travel between the first and second positions. The valve body may be shaped and dimensioned so that it is confined to move substantially along a plane between the first and second positions. The shape and dimensions of the valve body and slot respectively may be such that the valve body is confined to move between the first and second positions so that the orientation of the valve body stays substantially the same between the two positions. The shape and dimensions of the valve body and slot respectively may be such that the valve body is confined to move between the first and second positions with a close sliding fit.

The slot may extend from at least one side of the conduit. The slot may extend in at least two different directions from the conduit. The slot may extend from opposite sides respectively of the conduit so that, in the second position, the valve body extends from outside the conduit on one side of the conduit across the conduit and beyond the other side of the conduit on the opposite side respectively of the conduit. The slot may extend from all sides of the conduit so that the slot surrounds the conduit and so that, in the second position, the valve body extends beyond all sides of a perimeter of the conduit.

The valve body may comprise a substantially planar surface which extends across the conduit when the valve body is in the second position. The valve body may comprise two substantially flat opposing sides. The valve body may be substantially cuboidal.

Each chamber may be associated with an air vent which extends from the chambers to outside the apparatus. Each air vent may comprise a capillary tube which is dimensioned to permit the flow of air but restrict the flow of liquid.

The apparatus may comprise two separate sets of chambers and conduits. Each set may comprise the same number of chambers and conduits. One set may be used for conducting a control test on a sample of interest and the other set may be used to test the sample of interest. The apparatus may comprise more than two chambers arranged in series and each chamber may be connected in series by a corresponding conduit. Each conduit may comprise a slot and a valve body slidably mounted at least substantially within the slot and arranged to move between the first position and the second position. Each valve body may be independently moveable between first and second positions. The or each valve body may be moved between first and second positions by a corresponding external magnetic field. The or each external magnetic field may be a uni-directional magnetic field and the direction of the magnetic field may be changed to attract or repel the gate between first and second positions.

The apparatus may further comprise a controller which controls the or each external magnetic field so that the or each gate can be set to either a closed or an open position. The controller may comprise a timer that determines when the controller sets the or each gate to either a closed or an open position. The apparatus may further comprise a substantially cylindrical magnet within each chamber which may be urged to rotate within the chamber by an external magnetic field. Each chamber may comprise a support to separate the corresponding chamber magnet from walls of the chamber. The support may comprise pillars upon which the chamber magnet rests. Detailed Description of the Invention

In order that the invention may be more clearly understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Fig. 1 shows a plan view of a sample strip used as part of the present invention. Fig. 2 shows a side view of the sample strip shown in Fig. 1;

Fig. 3 shows the sample strip shown in Fig. 1 including magnetic rotors;

Fig. 4 shows a side view of the sample strip shown in Fig. 3; Fig. 5 shows apparatus according to the present invention;

Fig. 6 shows a cross section view of the apparatus shown in Fig. 5;

Fig. 7 shows an alternative sample strip used as part of the present invention;

Fig. 8 shows the sample strip shown in Fig. 7 including magnetic rotors; and Fig. 9 is a perspective exploded view of an alternative sample strip used as part of the present invention;

Fig. 10 is an enlarged cross section view across a valve part of the strip shown in

Fig. 9 when the valve body is in an open position;

Fig. 11 is an enlarged cross section view across the valve part shown in Fig. 10 when the valve body is in a closed position;

Fig. 12 is a perspective exploded view of an alternative sample strip used as part of the present invention;

Fig. 13 is an enlarged cross section view across a valve part of the strip shown in

Fig. 12 when the valve body is in an open position; Fig. 14 is an enlarged cross section view across the valve part shown in Fig. 13 when the valve body is in a closed position;

With reference to the drawings, there is shown a first embodiment of an assay strip 1 having a substantially planar body 2 made from plastics material. A first chamber 3 having an inlet and an outlet and a second chamber 5 having an inlet are etched into an upper face of the body 2. The two chambers 3, 5 are connected by a conduit or capillary tube 7 which runs along the strip between the outlet of the first chamber 3 and the inlet of the second chamber 5. The strip further comprises a reservoir 9 at one end which is connected to the first chamber by a further conduit 11. The reservoir 9 forms a deposition area where a sample fluid may be presented to the strip 1 so that the sample can flow along the first conduit 11 to the first chamber 3 and along the linking conduit 7 to the second chamber 5. The volume of the reservoir 9 is substantially equivalent to the combine volume of the chambers 3, 5 and conduits 7, 11 to ensure that a sufficient volume of sample is presented to the strip 1 for testing purposes. The strip 1 further comprises a lid 13 to cover the chambers 3, 5, conduits 7, 11 and reservoir 9 so that the sample is restricted to flow along those elements of the strip 1.

The diameter of each conduit 7, 11 is chosen so that a sample of interest such as blood will flow along the conduits 7, 11 without assistance. To encourage this capillary motion, the internal surface of each conduit 7, 11 is treated with corona discharge plasma to form a hydrophilic coating. The lid 13 is provided with air vents 15, 17 that are arranged to sit over the first and second chambers 3, 5 when positioned on the strip 1 to further encourage capillary motion of the sample along the flow path and avoid trap air bubbles.

The strip 1 further comprises a recess or slot 21 which extends substantially perpendicularly from one side of and below the conduit 7, downstream from the first chamber 3 between the first chamber 3 and the second chamber 5. A substantially cuboidal valve or gate 19 made from magnetic material is slidably mounted within the slot 21. The slot 21 defines a path along which the gate 19 may travel. The gate 19 has a first position in which it is seated and supported within the slot 21 outside the conduit flow path. In this open position, a sample may flow unobstructed across the slot and along the conduit 7. The gate also has a second position in which the gate 19 extends across the conduit 7, thereby restricting a sample from flowing along the conduit 7 from the first chamber 3 to the second chamber 5. The size and dimensions of the gate valve 19 are chosen such that it fits snugly within the slot 21 with a close fit and such that the gate 19 is outside the conduit 7 in the first position and substantially blocks the conduit 7 in the second position. The gate 19 is free to slide between the first and second positions in response to an external magnetic field and at least one side of the gate 19 is supported by the slot 21 between the first and second positions.

Contained within each chamber 3, 5 is a substantially cylindrical rotor 23 made from sintered neodymium magnetic material. Optionally, the material is encased in another material such as plastic to minimise the effect of the neodymium on the blood sample. Each rotor 23 is magnetised such that its poles are on opposite sides respectively of the rotor 23 across its diameter. This is to enable rotation of the rotors 23 when subjected to an alternating magnetic field.

The shape and dimensions of each rotor 23 is chosen such that it can freely rotate within its chamber 3, 5 but such that its lateral movement along the length of the chamber 3, 5 is limited. The shape and dimensions of each rotor are also chosen so that a space is formed between the rotor 23 and its corresponding chamber 3, 5, A quantity of dried clotting reagent which is intended to be mixed with the sample is deposited within the space formed between the rotor 23 and the chamber 3, 5. Different reagents may be deposited in each respective chamber 3, 5 depending on the type of test to be conducted on the sample. At the base of each chamber 3, 5 is formed four small pillars 25 arranged at each corner of the chamber to support the rotors 23 and separate the rotors 23 from the base wall. Separating the rotors 23 from the base wail of the corresponding chambers 3, 5 facilitates reagent disposition within the chambers 3, 5, A sampl e strip reader 27 is also provided comprising a slot into which the sample strip 1 may be inserted for measurements to be taken. The slot is shaped and configured to receive the sample strip in a relatively tight fit. The sample strip reader 27 also comprises electrical coils (solenoids) or electromagnetic field generators 31 which are positioned such that, when the sample strip 1 is inserted into the reader 27, the chambers 3, 5 are adjacent and in close proximity to the coils 31 . The coils 31 are arranged in an array around each chamber and oriented to extend substantially perpendicularly away from its corresponding chamber 3, 5 such that one end lies adjacent its chamber 3, 5. Each coil 31 of the array is paired with its diametrically opposed coil and arranged to be energised and de-energised in pairs in sequence. Thus, when a current is passed through one pair of diametrically opposed coils 31, a magnetic pole is created adjacent the chamber 3, 5. Each pair of coils 31 are powered by a small battery unit 32 contained within the reader 27 and are configured to generate a DC magnetic field between the pairs along their respective axes, A dedicated DC coil 40 is positioned within the reader 27 such that when the assay strip 1 is inserted into the reader 27, the coil 40 i s adj acent the gate 19. The coil 40 is arranged to generate a static uni-directional field that is capable of repelling the gate 19 out from the first position and to the second position across the conduit 7 to block the flow of the sample. By reversing the current through the coil, the gate 19 can be attracted back to the first position to permit the sample to flow from the first chamber 3 to the second chamber 5. Thus, the DC coil 40 moves the gate 19 between open and closed positions. The DC coil 40 is controlled by an electronic control device 34 which comprises a timer to control the operation of the DC coil and thus control when the gate 19 is moved between positions. This timing depends on the time required by the particular assay being conducted to mix the first reagent with the sampl e (blood, plasma or other fluids) and then mix the sample with the second reagent.

A heating elem ent 33 i s provided toward the upper surface of the reader 27 and is positioned to be substantially parallel with the upper face of the sample strip 1 and adjacent the two chambers 3, 5. The heating element 33 is also powered by the battery unit and serves to maintain the temperature of the sample at 37°C (human body temperature) so as to replicate the conditions in the body. To maintain the sample at the desired temperature, a temperature sensor is provided toward the lower portion of the reader 27 adjacent the lower section of the sample strip 1 so that the temperature of the sample in the chambers 3, 5 can be monitored and the operation of the heating element 33 adjusted accordingly. The operation of the heating element 33 and the coils 3 1 is also controlled by the electronic control means 34.

To determine the time at which the sample enters the chambers 3, 5, an optical detector 37 is provided which monitors the light levels within the chambers 3, 5. When the sample enters the chambers 3, 5 and fills the respective spaces between the rotors 23 and chamber walls, the light level drops to a predetermined level which signifies the starting time for the test (T zero). Measurement of the properties of the sample is facilitated by two magnetic field detectors e.g. Hall Effect sensors 39 which are positioned within the reader 27 such that they are substantially parallel with and adjacent to respective chambers 3, 5 when the sample strip 1 is inserted into the reader 27.

In use, the sample strip 1 is inserted into the reader 27 and a blood sample is deposited on the reservoir 9. When the sample strip 1 is in place, diametrically opposed pairs of coils 31 are energised and then de-energised in sequence around the array shown in Fig, 6. Thus, one pair of diametrically opposed coils is energised to generate a DC field between the pair, then de-energised to turn off the DC field and the next pair of coils in the sequence is energised and de-energised and so on (4 pairs in Fig 6) to generate a rotating magnetic field across the two rotors 23. When the pole of a rotor 23 and the pole of an adjacent coil 31 are alike at their closest proximity, the two poles repel one another and cause the rotor 23 to rotate. As the rotor 23 rotates within its chamber 3, 5, the opposite pole of the rotor 23 moves closer to and is attracted by the opposite pole of the coil 31. At the point at which the two opposite poles are at their closest proximity, the magnetic field generated by the coil 31 is reversed and the aforementioned process repeats itself around the array to maintain the rotating action of the rotors 23.

Through capillary action, the sample proceeds from the reservoir 9 to the first chamber 3 via the conduit 1 1 and gradually fill s the first chamber 3. At this stage, the DC coil 40 is set to repel the gate 19 and urge it into the closed position so that the sample is restricted from flowing along the linking conduit 7 into the second chamber 5. Rotation of the rotors 23 helps to dissolve and mix (re-suspend) the reagent in the first chamber 3 with the sample.

When the reagent has mixed with the sample in the first chamber 3, the DC coil 40 is set to attract the gate 19 and thus withdraw it from the linking conduit 7 to the open position within the slot 21 so that the sample can flow into the second chamber 5. Activation of the DC coil to move the gate to an open position may be set to occur at a predetermined time (dependent upon the type of test being conducted) as controlled by the electronic control means 34, When the sample flows into the second chamber 5, it mixes with the reagent contained therein so that measurements can be taken.

The rotating magnetic field of each rotor 23 gives rise to peak outputs detected by the adjacent Hail Effect sensor 39. The peak output corresponds to the point at which a pole of the rotor 23 passes in closest proximity to an adjacent sensor 39. By measuring the time between the peak outputs of the sensor 39 it is possible to determine the rotational velocity of the rotors 23. When the chambers 3, 5 contain a predetermined quantity of the sample, which is indicated by a specific drop in light intensity as measured by the optical detector 37, the test start time is triggered. As the blood sample within the first chamber 3 and second chamber 5 coagulates and the viscosity of the sample changes, the resistance of the sample to the rotation of the rotors 23 increases, thereby reducing the rotational velocity of the rotors 23 as detected by the respective sensors 39. When a predetermined rotational velocity is measured which corresponds to coagulation of the sample, the timer is stopped and the property of the sample is determined. Whilst two chambers in sequence are disclosed in this embodiment, it is envisaged that further chambers could be linked in series to enable tests requiring multiple reagents. The number of chambers would correspond to the number of separate reagents required for a particular test.

and chambers is provided which branch off from the same reservoir of the first set. The second set has the same number of chambers and conduits as the first set and is used to conduct a reference/control test on the sample. The first set is used as the test channel. In all other respects, the second embodiment shares the same features as the first embodiment and operates in the same way. With reference to Figs. 9, 10 and 1 1 , in a third embodiment, the assay strip 301 shares many of the same features as the first embodiment and comprises a body 302 made from plastics material comprising a first chamber 303 having an inlet and an outlet and a second chamber 305 having an inlet. The two chambers 303, 305 are connected by a first conduit 307 which is formed in the body 302 and runs from the outlet of the first chamber 303 to the inlet of the second chamber 305. The strip 301 further comprises a reservoir 309 which forms a deposition area for a sample and which is linked to the inlet of the first chamber 303 by a second conduit 31 1.

A substantially cuboidal slot or recess extends from one side of the first conduit 307 and beneath the conduit 307 and defines a space adjacent the conduit 307. The slot 321 forms a housing for a valve body 319 which is made from magnetic material or magnetically susceptible material and which is slidably mounted within the slot 321. The valve 319 comprises a substantially cuboidal, planar body which is shaped and configured to fit within the slot 321 and its lengt i s chosen such that the valve body 319 fits substantially entirely within the space adjacent the conduit 307. Thus, the valve body 319 has two extreme positions, a first position in which it is seated within the space adjacent to, and outside of the flow path of, the conduit 307 and a second position in which the valve body 319 extends transversely across the conduit 307 so that a planar surface of the valve 19 extends substantially perpendicularly across the flow path of the conduit 307, thereby blocking the conduit. A part of the valve body 319 forms a sidewall of the conduit 307 when the valve body 319 is in the first position so that the sample flows along the conduit 307 and is restricted from entering the space of the slot 321 in which the valve body 319 is seated. The assay strip 301 further comprises a first air vent 350 which extends from the first chamber 303 to the upper side of the body 302 so that an airflow path is defined between the first chamber 303 and outside the strip. Likewise, a second air vent 352 extends from the second chamber 305 to the upper side of the body 302 and defines an airflow path from the second chamber 305 to outside the strip 301. Both vents 350, 352 comprise a duct or capillary leading from the respective chambers 303, 305 that extend into a larger aperture. The respective diameters of the ducts are chosen to permit the flow of air but restrict the flow of any sample contained within the chambers 303,305.

The first air vent 350 encourages the flow of a sample from the reservoir 309 to the first chamber 303 and the second air vent 352 encourages the flow of the sample from the first chamber 303 to the second chamber 305 when the valve body 319 is set to an open position. The upper surface of the body 302 which comprises the exposed features ofthe strip 301 is substantially sealed by a laminated cover 313. The cover 313 is pierced at regions adjacent the two air vents 350, 352 to allow air from the vents to escape the strip 301 .

The assay strip 301 is compatible with the strip reader 27 ofthe first embodiment so that when the assay strip 301 is inserted into the strip reader 27, the valve body 319 may be moved between the first and second positions by the DC coil 40 so that the conduit can be blocked and unblocked as desired to restrict or permit the flow of a sample from the first chamber 303 to the second chamber 305.

With reference to Figs. 12, 13 and 14, in a fourth embodiment, the assay strip 401 comprises a body 402 made from two interfacing halves 402a, 402b of plastics material which each comprise one half of features of the assay strip 401 etched therein. Thus, when the two halves 402a, 402b are brought together in an appropriate orientation, they define a first chamber 403 having an inlet and an outlet and a second chamber 405 having an inlet. The two chambers 403, 405 are connected by a first conduit 407 which runs from the outlet of the first chamber 403 to the inlet of the second chamber 405. The strip 401 further comprises a reservoir 409 which forms a deposition area for a sample and which is linked to the inlet of the first chamber 403 by a second conduit 41 1 .

The two halves 402a, 402b both comprise formations arranged along the first conduit 407 which together define a substantially cuboidai slot or recess 421 extending substantially perpendicularly from all sides of the conduit first conduit 407. The slot 421 defines a passage along which a valve body 419 may slide. The valve body 419 is shaped and configured to fit within the slot 421 and its length is chosen such that the valve body 419 can fit substantially entirely within a space of the slot 421 adjacent the conduit 407 and outside of the conduit's flow path.

The valve body 419 has two extreme positions, a first position in which it is seated within the space adjacent the conduit 407, as shown in Fig, 13, and a second position in which the valve body 419 extends transversely across the conduit 407, thereby blocking the conduit, as shown in Fig. 14. Since the slot 421 extends from and surrounds the conduit 407, the face of the valve body 419 may be arranged to be substantially perpendicular to and extend around the opening of the conduit 407, thereby ensuring a more effective blockade against the flow of a sample along the conduit 407.

The assay strip 401 further comprises a first air vent 450 which extends from the first chamber 403 to the upper side of the body 402 so that an airflow path is defined between the first chamber 403 and outside the strip. Likewise, a second air vent 452 extends from the second chamber 405 to the upper side of the body 402 and defines an airflow path from the second chamber 405 to outside the strip 401. As with the third embodiment each air vent comprises a capillar}' tube or duct leading from the chambers 403, 405 to a larger exit aperture. The first air vent 450 encourages the flow of a sample from the reservoir 409 to the first chamber 403 and the second air vent 452 encourages the flow of the sample from the first chamber 403 to the second chamber 405 when the valve body 419 is set to an open position.

The assay strip 401 of the fourth embodiment is also compatible with the strip reader 27 of the first embodiment so that when the assay strip 401 is inserted into the strip reader 27, the valve body 419 may be moved between the first and second positions by the DC coil 40 so that the conduit can be blocked and unblocked as desired to restrict or permit the flow of a sample from the first chamber 403 to the second chamber 405.

The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. An assay apparatus for determining properties of a sample comprising first and second chambers for receiving a sample, wherein the first chamber has an inlet and an outlet and the second chamber has an inlet, and wherein the outlet of the first chamber is connected to the inlet of the second chamber by a conduit along which at least part of the sample may travel so that the sample can move from the first chamber to the second chamber in series, the apparatus further comprising a slot extending from the conduit and a valve body comprising magnetic or magnetically susceptible material which is slidably mounted at least substantially within the slot and which is slidable between a first position in which the valve body is arranged at least substantially outside the conduit and a second position in which the valve body extends across the conduit thereby restricting a sample from travelling along the conduit from the first chamber to the second chamber, the valve body being movable between the two positions by an external magnetic field.

2. An assay apparatus as claimed in claim 1, wherein the valve body and slot are arranged relative to the conduit such that the valve body is substantially perpendicular to the conduit when the valve body is in the second position.

3. An assay apparatus as claimed in any preceding claim, wherein the valve body conforms substantially to the shape of the slot.

4. An assay apparatus as claimed in any preceding claim, wherein the slot defines a path along which the valve body may travel between the first and second positions.

5. An assay apparatus as claimed in any preceding claim, wherein the valve body is shaped and dimensioned so that it is confined to move substantially along a plane between the first and second positions.

6. An assay apparatus as claimed in claim 5, wherein the shape and dimensions of the valve body and slot respectively are such that the valve body is confined to move between the first and second positions so that the orientation of the valve body stays substantially the same between the two positions.

7. An assay apparatus as claimed in claim 5 or claim 6, wherein the shape and dimensions of the valve body and slot respectively are such that the valve body is confined to move between the first and second positions with a close sliding fit.

8. An assay apparatus as claimed in any preceding claim, wherein the slot extends from at least one side of the conduit.

9. An assay apparatus as claimed in claim 8, wherein the slot extends in at least two different directions from the conduit.

10. An assay apparatus as claimed in claim 9, wherein the slot extends from opposite sides respectively of the conduit so that, in the second position, the valve body extends from outside the conduit on one side of the conduit across the conduit and beyond the other side of the conduit on the opposite side respectively of the conduit.

11. An assay apparatus as claimed in any preceding claim, wherein the slot extends from all sides of the conduit so that the slot surrounds the conduit and so that, in the second position, the valve body extends beyond all sides of a perimeter of the conduit.

12. An assay apparatus as claimed in any preceding claim, wherein the valve body comprises a substantially planar surface which extends across the conduit when the valve body is in the second position.

13. An assay apparatus as claimed in any preceding claim, wherein the valve body comprises two substantially flat opposing sides.

14. An assay apparatus as claimed in any preceding claim, wherein the valve body is substantially cuboidal.

15. An assay apparatus as claimed in any preceding claim, wherein each chamber is associated with an air vent which extends from the chambers to outside the apparatus.

16. An assay apparatus as claimed in claim 14, wherein each air vent comprises a capillary tube which is dimensioned to permit the flow of air but restrict the flow of liquid.

17. An assay apparatus as claimed in any preceding claim comprising two

separate sets of chambers and conduits.

18. An assay apparatus as claimed in claim 16, wherein each set comprises the same number of chambers and conduits.

19. An assay apparatus as claimed in claim 16 or claim 17, wherein one set is used for conducting a control test on a sample of interest and the other set is used to test the sample of interest.

20. An assay apparatus as claimed in any preceding claim, comprising more than two chambers arranged in series, wherein each chamber is connected in series by a corresponding conduit.

21. An assay apparatus as claimed in any of claims 12 to 19, wherein each conduit comprises a slot and a valve body slidably mounted at least substantially within the slot and arranged to move between the first position and the second position.

22. An assay apparatus as claimed in claim 20, wherein each valve body is

independently moveable between first and second positions.