WO1998032019A1

WO1998032019A1 - Device for detecting an analyte and an analytical method

Info

Publication number: WO1998032019A1
Application number: PCT/EP1998/000156
Authority: WO
Inventors: Hermanus Johannes Maria Kreuwel; Wilhelmus Maria Carpay
Original assignee: Akzo Nobel N.V.
Priority date: 1997-01-14
Filing date: 1998-01-12
Publication date: 1998-07-23
Also published as: AU6208998A

Abstract

Device for the autonomous detection of an analyte, wherein the sample liquid is transported through a conduit. The conduit comprises a detection zone which is operatively connected to an absorber element. By absorption of sample liquid, the absorber element is capable of increasing the flow of sample liquid through the detection zone after a predetermined reaction time.

Description

Device for detecting an analyte and an analytical method

The present invention relates to a device for the autonomous, specific detection of an analyte, said device comprising a means through which a sample liquid can be transported, said means comprising a proximal end to receive the sample liquid, a detection zone having an upstream end and a downstream end, and a distal end, said detection zone at the downstream distal end being operatively connected to an absorber element capable of absorbing the sample liquid and maintaining a flow of sample liquid through the means. A device according to the preamble is disclosed in

EP 0 291 194. Here the means through which the sample liquid can be transported is a porous carrier, for example an oblong rectangular nitrocellulose strip. A section of the porous strip comprises an immobilized reagent and acts as the detec- tion zone. Sample can be applied, indirectly via a proximal absorber element or directly, to the proximal end of the strip. The sample liquid is transported by the capillary action of the porous strip towards the distal end of the strip. A mobile reagent is supplied between the proximal end and the detection zone. The porous strip comprises a further section extending from the detection zone towards the distal end of the porous strip and this section functions as an integrated absorber element, capable of washing at least parts of the excess mobile reagent and aspecifically-bound reagent from the detection zone. Said device is autonomous in the sense that, after application of the sample, no further operations are required for the detection reaction to occur and to obtain a reading.

The above device has several disadvantages. A par- ticular drawback is the fact that the porous carrier imposes limitations, for instance with respect to the flow of sample liquid through the means. The object of the present invention is to improve on the device according to the preamble.

To this end the device according to the invention is characterized in that the absorber element is capable of increasing the flow of sample liquid through the means, and in particular through the detection zone, after a predetermined reaction time, by absorption of sample liquid.

Thus, the device according to the present invention allows for a controlled flow rate of sample liquid through the means, said flow rate being adapted to the stage of the assay performed. For example, the device according to the present invention may provide a quick wash step after the reaction of analyte and reagent, resulting in a faster assay and a reduced background. Control over the flow rate allows the transport function of the means to be separated from other functions, such as the suitability of the means as a substrate for immobilizing the reagent in the detection zone. Thus, the present invention gives the expert a greater degree of freedom when developing assays. According to a preferred embodiment the means through which the sample liquid is to be transported is a conduit .

Using a conduit as the means through which the sample liquid is to be transported reduces loss of mobile reagent due to adsorption or physical entrapment and in addition reduces the loss of analyte due to aspecific binding of the analyte to the means. Furthermore, a conduit has a very low flow resistance for the sample liquid, allowing the absorber element to achieve a wider range of sample liquid flow rates.

A very interesting embodiment is characterized in that the conduit is capable of passing sample liquid pushed from the proximal end towards the distal end at least up to the detection zone, and preferably up to the absorber element. O

3

The timing of sample flow rates through the conduit at any particular time -between the application of the sample and obtaining a reading and of the addition of reagents, would essentially be controlled by the absorber element only. According to a preferred embodiment the absorber element is capable of at least a twofold increase of the flow of sample liquid through the means, and preferably of at least a fivefold increase of flow.

The term twofold (or fivefold) increase is intended to mean an increase of a sample flow rate through the means to a sample flow rate which is twice, or five times as high.

Thus, an attractive saving in time and reduction of background can be achieved.

According to a preferred embodiment the proximal end of the means is capable of receiving a sample taker comprising the sample liquid.

This allows for the delivery of a controlled volume of sample liquid to the device. It is also possible to use the sample taker to push the liquid into the conduit, as described for one of the other preferred embodiments.

The invention also relates to a method of detecting an analyte in a sample liquid by

1) applying the sample liquid to a device comprising a means through which the sample liquid is to be trans- ported, said means comprising a proximal end to which the sample liquid is applied and a distal end;

2) transporting the sample liquid towards the distal end;

3) supplying a reagent from a reagent zone between the proximal end and the distal end of the means to the sample liquid;

4) keeping the reagent and the sample liquid in contact for a predetermined reaction time; 5) passing the reagent and the sample liquid after the predetermined reaction time over a detection zone located at or downstream of the reagent zone; and

6) washing the detection zone using an absorber element at the downstream end of the detection zone.

According to the invention the method is characterized in that after the predetermined reaction time the flow of sample liquid through the detection zone is increased by an absorber element capable of increasing the flow of sample liquid through the detection zone as the absorber element. Thus the detection zone is washed thoroughly and quickly.

According to a preferred embodiment, the means comprises a conduit, and sample liquid is pushed through the conduit until the sample liquid is in contact with an absorbing zone, after which the device autonomously maintains a flow for a predetermined time to allow a reaction to occur, after which the flow is increased to wash the detection zone. Advantageously, the sample taker may be used to push the sample liquid to the detection zone, and more preferably the sample taker is used to push the sample liquid to the absorber element as the absorbing zone.

If the sample liquid is pushed to the detection zone, this zone determines the flow rate of sample liquid for a comparatively short time. If the sample liquid is pushed to the absorber element, this absorber element fully controls the flow rate of sample liquid. If, for instance, it is desired to remove proteins interfering with the assay or detection from the sample liquid, it is possible to use a hydrophobic section, for example a macroporous pad, to absorb the proteins. In devices according to the state of the art, the presence of a hydrophobic section would result in a stop of capillary flow.

The invention will now be illustrated by way of example with reference to the drawing, in which Fig. 1 shows a schematic cross-section of a device according to the invention;

The device for the specific detection of an analyte shown m Fig. 1 comprises a single conduit 1 having a proxi- mal end 2 and a distal end 3. The conduit 1 is provided with a porous pad 4. This pad 4 comprises an immobilised reagent in a detection zone 5. A mobile reagent 6 is provided m a reagent zone between the proximal end 2 and the pad 4. A sample liquid comprising the analyte, if any, can be applied to the proximal end 2. Downstream of the detection zone 5 an absorber element 7 is provided. According to the invention, this absorber element 7 is arranged to increase the flow rate of the sample liquid through and along the conduit 1, and more m particular through the detection zone 5. This may be achieved in one of several ways. Some non-limitmg examples will be discussed. The absorber element 7 may comprise a section 8 with increased geometrical dimensions, as is shown m Fig. 1. However, section 8 may also have a more hydrophillic character, for example due to the presence or lack of a coat- mg. Alternatively, the capillary structure may be modified. Another possibility is the presence of flow-enhancing reagent. The flow rate may also be controlled using viscosity as the parameter. For example, a substance increasing the viscosity of the sample liquid may be added to the sample liquid upstream from section 8, for example between the detection zone 5 and section 8, said substance being diluted or degraded m section 8.

The mobile reagent 6 is dissolved or dispersed m the sample liquid. Depending on the type of assay, the mobile reagent 6 may react with the analyte, as is the case for an lmmunological sandwich assay. There the mobile reagent 6 is usually a labelled antibody or lmmunologically active fragment thereof capable of specifically binding the analyte. The label may be any of those known m the art, and is preferably a particle, such as a carbon, gold or latex particle. In case of an immunological sandwich assay the detection zone 5 will comprise antibodies capable of binding the bound analyte.

After a predetermined reaction time the absorber element 7 increases the speed with which the sample liquid flows through the conduit 1 and m particular the detection zone 5. Thus any surplus of mobile reagent is quickly and effectively removed.

Though the conduit 1 may have the capability to transport liquid by capillary action over a part or its full length, be it by the conduit 1 itself or any porous material in the conduit 1, the conduit 1 according to the invention allows for the increased transport of sample liquid as generated by the absorber element 7, preferably by a factor of at least 2 and more preferably by a factor of at least 5.

However, the conduit may be over at least part of its length incapable of supporting autonomous capillary transport of sample liquid. This may be the case if a hydrophobic zone is provided to remove certain components from the sample liquid.

In such a case, or indeed whenever it is desirable, the sample liquid is forced through the conduit 1, for example using a sample taker 9. A basic sample taker 9 comprises a handle 10 and an absorber element 11. The sample taker 9 and the proximal end 2 may be designed such that the proximal end 2 is capable of receiving the sample taker 9 such that a predetermined amount of sample liquid is pushed into the conduit 1. In any case, the sample liquid must be pushed beyond any zone incapable of supporting capillary transport, and preferably up to the detection zone 5 and more preferably up to the absorber element 7. After that, the device operates autonomously.

Thus, the volume of sample liquid squeezed out of the sample taker 9 suffices to fill the conduit 1 up to the point where capillary action takes over. The capillary action generated by the absorber element 7 should be enough to draw sample liquid from the absorber element 11.

According to a preferred embodiment, the absorber element 7 is capable of maintaining a flow for a predeter- mined reaction time and subsequently an increased flow for a predetermined wash time.

Alternatively the flow is increased when the sample liquid contacts the absorber element 7.

According to a preferred embodiment the mobile reagent 6 remains substantially in the reagent zone until the sample liquid reaches the detection zone 5, and more preferably until the sample liquid reaches the absorber element 7.

Thus the device, and more in particular the absorber element 7, can control the reaction conditions. To remain substantially in the reagent zone, that is, not passing the detection zone 5, the mobile reagent 6 may be a slowly solubilizing or dispersing compound or may be comprised in a matrix allowing for the suitably slow release. If the reagent remains substantially in the reagent zone, this may result in a more sensitive competition assay. Analyte in the sample liquid pushed up to the detection zone 5, and in particular to the absorber element 7, has a chance to occupy binding sites in the reaction zone 5 before the mobile reagent has.

The device according to the invention may be used to detect any kind of analyte, for example antigens using antibodies or specific DNA or RNA sequences using complementary sequences . It goes without saying that the device may contain several detection zones for different analytes.

Claims

1. Device for the autonomous, specific detection of an analyte, said device comprising a means through which a sample liquid is to be transported, said means comprising a proximal end to receive the sample liquid, a detection zone having an upstream end and a downstream end, and a distal end, said detection zone at the downstream distal end being operatively connected to an absorber element capable of absorbing the sample liquid and maintaining a flow of sample liquid through the means, characterized in that the absorber element is capable of increasing the flow of sample liquid through the means, and in particular through the detection zone, after a predetermined reaction time, by absorption of sample liquid.

2. Device according to claim 1, characterized in that the means through which the sample liquid is to be transported is a conduit.

3. Device according to claim 2, characterized in that the conduit is capable of passing sample liquid pushed from the proximal end towards the distal end at least up to the detection zone.

4. Device according to any of the preceding claims, characterized in that the absorber element is capable of at least a twofold increase of the flow of sample liquid through the means .

5. Device according to claim 4, characterized in that the absorber element is capable of at least a fivefold increase of flow.

6. Device according to any of the claims 2 to 5, characterized in that the conduit is over at least part of its length incapable of supporting autonomous capillary transport of sample liquid.

7. Device according to any of the previous claims, characterized in that t-he absorber element is capable of maintaining a flow for a predetermined reaction time and subsequently an increased flow for a predetermined wash time.

8. Device according to any of the preceding claims, characterized in that the proximal end of the means is arranged to receive a sample taker comprising the sample liquid.

9. Method of detecting an analyte in a sample liquid by

1) applying the sample liquid to a device comprising a means through which the sample liquid can be transported, said means comprising a proximal end to which the sample liquid is applied and a distal end; 2) transporting the sample liquid towards the distal end;

3) supplying a reagent from a reagent zone between the proximal end and the distal end of the means to the sample liquid; 4) keeping the reagent and the sample liquid in contact for a predetermined reaction time;

5) passing the reagent and the sample liquid after the predetermined reaction time over a detection zone located at or downstream of the reagent zone; and 6) washing the detection zone using an absorber element at the downstream end of the detection zone; characterized in that after the predetermined reaction time the flow of sample liquid through the detection zone is increased by an absorber element capable of increasing the flow of sample liquid through the detection zone as the absorber element.

10. Method according to claim 9, characterized in that the means comprises a conduit, and sample liquid is pushed through the conduit until the sample liquid is in con- tact with an absorbing zone, after which the device autono- ously maintains a flow for a predetermined time to allow a reaction to occur, after which the flow is increased to wash the detection zone.

11. Method according to claim 10, characterized in that a sample taker is used to push the sample liquid to the detection zone as the absorbing zone.

12. Method according to claim 11, characterized in that the sample taker is used to push the sample liquid to the absorber element as the absorbing zone.

13. Method according to any of the claims 10 to 12, characterized in that as the reagent a reagent is used that remains substantially in the reagent zone until the sample liquid reaches the detection zone.

14. Method according to claim 13, characterized in that as the reagent a reagent is used that remains substantially in the reagent zone until the sample liquid reaches the absorber element.