Fluidic Test Cassette

Abstract

A disposable cassette for detecting nucleic acids or performing other assays. The cassette can be inserted into a base station during use. The cassette has numerous features to ensure correct operation of the device under gravity, such as vent pockets for enabling the flow of sample fluid from one chamber to the next when the vent pocket is unsealed. The vent pockets have protrusions to help prevent accidental resealing. The cassette also can have a gasket to ensure free air movement between open vent pockets. A flexible circuit with patterned metallic electrical components disposed on a heat stable material can be in direct contact with fluid in the chambers and has resistive heating elements aligned with the vent pockets and the chambers. The detection chamber, which houses a lateral flow detection strip can have a space below the strip that has sufficient capacity to accommodate an entire volume of the sample fluid entering the detection chamber at a height that enables the fluid to flow up the detection strip by capillary action without flooding or otherwise bypassing regions of the detection strip. The space can also contain detection particles. Recesses in in the cassette channels or chambers can have structures such as ridges or grooves to direct fluid flow to enhance rehydration of lyophilized reagents disposed in the recess. Flow diverters in the chambers can reduce the flow velocity of the sample fluid and increase the effective fluid flow path length, enabling more accurate control of fluid flow in the cassette.

1 . A cassette for detecting a target nucleic acid, the cassette comprising:
 a plurality of chambers;   a plurality of vent pockets connected to said chambers; and   a heat labile material for sealing one or more of said vent pockets;   wherein at least one said vent pocket comprises a protrusion.   
     
     
         2 . The cassette of  claim 1  wherein said protrusion comprises a dimple or an asperity. 
     
     
         3 . The cassette of  claim 1  wherein said protrusion sufficiently prevents molten heat labile material from attaching to a heat stable material disposed adjacent to said heat labile material to prevent resealing of said vent pocket after said heat labile material is ruptured. 
     
     
         4 . A cassette for detecting a target nucleic acid, the cassette comprising:
 a plurality of chambers;   a plurality of vent pockets connected to said chambers;   a heat labile material for sealing one or more of said vent pockets;   a heat stable material; and   a gasket disposed between said heat labile material and said heat stable material, said gasket comprising an opening encompassing said plurality of vent pockets.   
     
     
         5 . The cassette of  claim 4  wherein said gasket is sufficiently thick to provide a sufficient air volume to equilibrate pressures and ensure free air movement between open vent pockets. 
     
     
         6 . The cassette of  claim 4  further comprising a flexible circuit, said flexible circuit comprising patterned metallic electrical components disposed on said heat stable material. 
     
     
         7 . The cassette of  claim 6  wherein said gasket comprises a second opening, or is limited in dimension, such that said flexible circuit will be in direct contact with fluid in at least one of the chambers. 
     
     
         8 . The cassette of  claim 6  wherein said electrical components comprise resistive heating elements or conductive traces. 
     
     
         9 . The cassette of  claim 8  wherein said resistive heating elements are aligned with said vent pockets and said chambers. 
     
     
         10 . The cassette of  claim 4  comprising one or more ambient temperature sensors for adjusting a heating temperature, heating time, and/or heating rate of one or more of said chambers. 
     
     
         11 . A cassette for detecting a target nucleic acid, the cassette comprising:
 a vertically oriented detection chamber;   a lateral flow detection strip disposed in said detection chamber oriented such that a sample receiving end of said detection strip is at the bottom end of said detection strip; and   a space in said detection chamber below said lateral flow detection strip for receiving fluid comprising amplified target nucleic acids;   said space comprising sufficient capacity to accommodate an entire volume of the fluid at a height that enables the fluid to flow up the detection strip by capillary action without flooding or otherwise bypassing regions of the detection strip.   
     
     
         12 . The cassette of  claim 11  wherein said space comprises detection particles. 
     
     
         13 . The cassette of  claim 12  wherein said detection particles are selected from the group consisting of dye polystyrene microspheres, latex, colloidal gold, colloidal cellulose, nanogold, and semiconductor nanocrystals. 
     
     
         14 . The cassette of  claim 12  wherein said detection particles comprise oligonucleotides complementary to a sequence of the amplified target nucleic acids or ligands capable of binding to the amplified target nucleic acids. 
     
     
         15 . The cassette of  claim 14  wherein the ligands are selected from the group consisting of biotin, streptavidin, a hapten or an antibody. 
     
     
         16 . The cassette of  claim 12  wherein the detection particles have been dried, lyophilized, or present on at least a portion of the interior surface as a dried mixture of detection particles in a carrier to facilitate resuspension of the detection particles. 
     
     
         17 . The cassette of  claim 16  wherein the carrier comprises a polysaccharide, a detergent, or a protein. 
     
     
         18 . The cassette of  claim 12  wherein a capillary pool of the fluid forms in the space, providing improved mixing and dispersion of the detection particles to facilitate comingling of the detection particles with the amplified target nucleic acid. 
     
     
         19 . The cassette of  claim 11  for performing an assay having a volume less than about 200 μL. 
     
     
         20 . The cassette of  claim 19  wherein the assay has a volume less than about 60 μL. 
     
     
         21 . A cassette for detecting a target nucleic acid, the cassette comprising one or more recesses for containing at least one lyophilized or dried reagent, at least one of said recesses comprising one or more structures for directing fluids to facilitate rehydration of the at least one dried or lyophilized reagent, said recesses disposed in one or more channels connected to said chambers or in one or more of said channels. 
     
     
         22 . The cassette of  claim 21  wherein said structures comprise ridges, grooves, dimples, or combinations thereof. 
     
     
         23 . A cassette for detecting a target nucleic acid, the cassette comprising at least one chamber comprising a feature to prevent fluid vertically entering a top of said chamber from flowing directly into an outlet of said chamber. 
     
     
         24 . The cassette of  claim 23  wherein said feature deflects the fluid to the side of said chamber opposite from said outlet. 
     
     
         25 . The cassette of  claim 23  wherein a resulting flow path of the fluid comprises a horizontal component, thereby sufficiently increasing an effective length of the flow path and sufficiently decreasing a flow velocity of the fluid to restrict an amount of fluid exiting said outlet. 
     
     
         26 . The cassette of  claim 23  wherein said feature creates a swirling of fluid within said chamber, thereby increasing mixing of reagents within the fluid. 
     
     
         27 . The cassette of  claim 23  wherein said feature is triangular or trapezoidal in shape. 
     
     
         28 . The cassette of  claim 23  wherein said outlet is tapered. 
     
     
         29 . The cassette of  claim 23  wherein a channel located downstream of said outlet comprises turns for increasing an effective length of said channel. 
     
     
         30 . The cassette of  claim 23  wherein said feature is located near or at a bottom of said chamber or near a middle of said chamber. 
     
     
         31 . A method of controlling vertical flow of a fluid through a chamber in a cassette for detecting a target nucleic acid, the method comprising deflecting a flow of fluid entering a top of the chamber, thereby preventing the fluid from flowing directly into an outlet of the chamber. 
     
     
         32 . The method of  claim 31  comprising reducing a flow velocity of the fluid, thereby reducing a distance the fluid flows down a channel connected to the outlet before the fluid stops. 
     
     
         33 . The method of  claim 31  comprising dividing a flow of the fluid into the chamber into a first fluid flow that contacts a wall of the chamber and is directed upward, and a second fluid flow that enters the outlet. 
     
     
         34 . The method of  claim 33  further comprising creating a swirling of the fluid in the first fluid flow in the chamber, thereby increasing mixing of reagents within the fluid. 
     
     
         35 . The method of  claim 33  wherein the second fluid flow forms a meniscus and travels through a channel connected to the outlet, the meniscus increasing pressure in closed air space in the channel downstream of the fluid until the pressure stops the flow of fluid in the channel. 
     
     
         36 . The method of  claim 35  wherein the outlet is tapered, thereby increasing compressible air volume at the entrance to the outlet. 
     
     
         37 . The method of  claim 31  comprising providing turns in a channel connected to the outlet, thereby increasing an effective path length of the channel and reducing a flow velocity of fluid in the channel.