Assay device having controllable sample size
Disclosed is an assay device which comprises a liquid sample addition zone, a reagent zone, a detection zone, and a wicking zone, all defining a fluid flow path. The device further comprises a reagent addition zone along and in fluid communication with the fluid flow path downstream of the sample addition zone and upstream of the detection zone. An interrupting wash is added at this reagent addition zone in accordance with the method of the subject invention to control sample volume. The interrupting wash fluid is added at a predetermined fill volume on the chip device and also serves to wash the detection channel and fill the remaining chip volume.
1. A method of controlling sample size in an assay device, said assay device comprising a substrate having a planar top surface, said method comprising:
providing a liquid sample addition zone on the planar top surface of the substrate;
providing a reagent zone on the planar top surface of the substrate, the reagent zone being provided downstream and in fluid communication with the sample addition zone and containing a reagent, said reagent including a material that produces a detectable signal in the presence of a sample;
providing a detection zone on the planar top surface of the substrate in fluid communication with the reagent zone;
providing a wicking zone on the planar top surface of the substrate in fluid communication with the detection zone having a capacity to receive liquid sample flowing from the detection zone, wherein the sample addition zone, the reagent zone, the detection zone and the wicking zone define a fluid flow path formed on the planar top surface of the substrate, the fluid flow path being configured to enable capillary flow from the sample addition zone to the wicking zone by means of projections formed on the planar top surface of the substrate, the projections having height and width dimensions, as well as spacing between adjacent projections that spontaneously create lateral capillary flow along the fluid flow path;
further providing a fluid addition zone on the planar top surface of the substrate, the fluid addition zone being along and in fluid communication with the fluid flow path downstream of the sample addition zone and the reagent zone and upstream of the detection zone;
adding sample to the sample addition zone, wherein the sample moves through the fluid flow path due to the capillary action of the projections;
allowing the sample to mix with the reagent in the reagent zone; and
controlling sample size within the fluid flow path by adding an interrupting fluid to the fluid addition zone after the sample has passed through the reagent zone, mixed with the reagent, and moved a predetermined percentage into the wicking zone, the added fluid creating a dome-shaped droplet that interrupts the capillary flow of sample along the fluid flow path.
2. The method as claimed in claim 1 including the step of adding a wash reagent as the fluid added to the fluid addition zone.
3. The method as claimed in claim 1 wherein the sample is whole blood and further including the step of adding a fluid to the sample addition zone, the fluid including a surfactant.
4. A method as claimed in claim 3 wherein the surfactant is deposited on the sample addition zone before the sample is added to the sample addition zone.
5. A method as claimed in claim 1 further comprising providing a filter on the sample addition zone, wherein sample passes through the filter before entering the fluid flow path.
6. A method as claimed in claim 1 further comprising providing a hydrophilic tape at least partially covering the detection zone.
7. A method as claimed in claim 1 , in which the fluid is added after the sample has filled at least 20% of the wicking zone.
8. A method as claimed in claim 1 , in which the fluid is added after the sample has filled at least 50% of the wicking zone.