Controlling Fluid Flow Through An Assay Device

Abstract

An assay device includes: a detection zone which includes a first set of projections which are capable of generating capillary flow. A wicking zone (WZ) has a capacity to receive liquid sample flowing from the detection zone and includes a second set of projections which are capable of generating capillary flow. The WZ is rectangular in shape and the longer side of the rectangle extends in the direction of flow to thereby reduce the pressure gradient in the assay device which increases the total flow time of liquid sample compared to a WZ having equal length sides and same volume. At least a portion of the second set of projections have at least one dimension selected from a diameter, a center-to-center spacing, or a gap between projections that is different from the first set of projections, and is selected to increase the total flow time of the sample.

What is claimed is: 
     
         1 . An assay device comprising:
 a liquid sample zone;   a reagent zone downstream and in fluid communication with the sample zone containing a reagent material;   a detection zone in fluid communication with the reagent zone, wherein the detection zone comprises a substrate and a first set of projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface; and   a wicking zone in fluid communication with the detection zone having a capacity to receive liquid sample flowing from the detection zone,   wherein the wicking zone comprises a substrate and a second set of projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface,   wherein the wicking zone is rectangular in shape and the longer side of the rectangle extends in the direction of flow to thereby reduce the pressure gradient in the assay device which increases the total flow time of liquid sample compared to a wicking zone having equal length sides and same volume, and   further wherein at least a portion of the second set of projections have at least one dimension selected from a diameter, a center-to-center spacing, or a gap between projections that is different from the first set of projections, and is selected to increase the total flow time of the sample through the device.   
     
     
         2 . An assay device as claimed in  claim 1 , wherein the reagent material comprises a labeled reagent material, and the detection zone has capture elements bound thereto. 
     
     
         3 . An assay device as claimed in  claim 1 , wherein the longer/shorter side ratio of the wicking zone is greater than 1 and less than 10:1 
     
     
         4 . An assay device as claimed in  claim 1 , wherein the sample receiving zone, the reagent zone, the detection zone and the wicking zone define a fluid flow path. 
     
     
         5 . An assay device as claimed in  claim 4 , wherein the fluid flow path intersects the shorter side of the wicking zone at the midpoint thereof. 
     
     
         6 . An assay device as claimed in  claim 1 , wherein the portion of the second set of projections is located at the beginning of the wicking zone, where the sample and other materials enters the wicking zone. 
     
     
         7 . An assay device as claimed in  claim 1 , wherein total area of the assay device is ≦900 mm 2 . 
     
     
         8 . An assay device as claimed in  claim 1 , wherein the assay device is capable of using a sample size of ≦30 μl. 
     
     
         9 . An assay device comprising:
 a liquid sample addition zone;   a reagent zone downstream and in fluid communication with the sample addition zone containing a reagent material;   a detection zone in fluid communication with the reagent; and   a wicking zone in fluid communication with the capture zone having a capacity to receive liquid sample flowing from the detection zone,   wherein the wicking zone comprises a substrate and a second set of projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface, and   wherein the wicking zone is circular in shape which increases the pressure gradient in the assay device which decreases the total flow time of liquid sample compared to a square wicking zone having equal length sides.   
     
     
         10 . An assay device as claimed in  claim 9 , wherein the sample receiving zone, the reagent zone, and the detection zone define a fluid flow path. 
     
     
         11 . An assay device as claimed in  claim 10 , wherein flow path directs the sample to the center of the wicking zone and the sample flows in all directions from the center. 
     
     
         12 . An assay device as claimed in  claim 9 , wherein the detection zone comprises a substrate and a first set of projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface, and wherein further wherein at least a portion of the second set of projections have at least one dimension selected from a diameter, a center-to-center spacing, or a gap between projections that is different from the first set of projections, and is selected to decrease the total flow time of the sample through the device. 
     
     
         13 . An assay device comprising:
 a liquid sample zone;   a reagent zone downstream and in fluid communication with the sample zone containing a reagent material;   a detection zone in fluid communication with the reagent zone; and   a wicking zone in fluid communication with the detection zone having a capacity to receive liquid sample flowing from the detection zone,   wherein the wicking zone comprises a substrate and projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface, and   wherein the wicking zone comprises barriers which provide a tortuous path for the fluid to follow, increasing the length of the flow path in the wicking zone which decreases the pressure gradient in the assay device which decreases the total flow time of liquid sample compared to an identically sized wicking zone having no barriers.   
     
     
         14 . An assay device as claimed in  claim 13 , wherein the reagent material comprises a labeled reagent material, and the detection zone has capture elements bound thereto. 
     
     
         15 . An assay device comprising:
 a liquid sample zone;   a reagent zone downstream and in fluid communication with the sample zone containing a reagent material;   a detection zone in fluid communication with the reagent zone; and   a wicking zone in fluid communication with the detection zone having a capacity to receive liquid sample flowing from the detection zone,   wherein the wicking zone comprises a substrate and a set of projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface, and   wherein the projections are arranged in a row by row configuration and the gap between the rows of pillars is greater than the gap between pillars within a row.   
     
     
         16 . An assay device as claimed in  claim 15 , wherein the reagent material comprises a labeled reagent material, and the detection zone has capture elements bound thereto. 
     
     
         17 . An assay device as claimed in  claim 1 , wherein the fluid flow path intersects the wicking zone at the midpoint thereof. 
     
     
         18 . An assay device as claimed in  claim 16 , wherein the ratio of gap between the rows of pillars to the gap between pillars within a row is at least 2.5, more preferably >4. 
     
     
         19 . A method of controlling the flow rate of a sample through an assay device that comprises:
 providing a liquid sample zone;   providing a reagent zone downstream and in fluid communication with the sample zone containing a reagent material;   providing a detection zone in fluid communication with the reagent zone;   providing a wicking zone in fluid communication with the detection zone having a capacity to receive liquid sample flowing from the detection zone, wherein the wicking zone comprises a substrate and projections which extend substantially vertically from the substrate, wherein the projections have a height, cross-section and a distance between one another that defines a capillary space between the projections capable of generating capillary flow parallel to the substrate surface,   selecting the macroscopic dimensions of the wicking zone, wherein if a decreased total flow time of sample is desired, then the pressure gradient in the wicking zone is increased by at least one of decreasing the length of the flow path in the wicking zone relative to a square wicking zone with the same area and height (the same volume) and the same pillar arrangement, and if an increase in total flow time of sample is desired, then the pressure gradient in the wicking zone is decreased by at least one of increasing the length of the flow path relative to a square wicking zone with the same area and height (the same volume) and the same pillar arrangement or by increasing the pillar density at the flow channel prior to fluid entering the wicking zone.   
     
     
         20 . A method as claimed in  claim 19 , wherein the reagent material comprises a labeled reagent material, and the detection zone has capture elements bound thereto. 
     
     
         21 . A method as claimed in  claim 19 , wherein the length of the flow path in the wicking zone is increased by providing barriers in the wicking zone to provide a tortuous path for the fluid to follow. 
     
     
         22 . A method as claimed in  claim 19 , wherein the length of the flow path in the wicking zone is increased by increasing the length of the wicking zone relative to the width. 
     
     
         23 . A method as claimed in  claim 19 , wherein the length of the flow path in the wicking zone is decreased by selecting a round wicking zone. 
     
     
         24 . A method as claimed in  claim 23 , wherein the flow path transports sample to the center of the wicking zone and the sample flows in all directions from the center.