Assay device and method
An assay method and device can perform at least one (e.g., at least two) assays on a single aliquot of a sample liquid. The device can mix a sample liquid with assay reagents including magnetically susceptible particles. The device is configured to create a sample liquid-air interface with the sample liquid. The magnetically susceptible particles can be located (via an applied magnetic field) at the liquid-air interface when a second liquid contacts the interface to form a liquid-liquid interface. The magnetic particles travel across the liquid-liquid interface to the second liquid. The magnetically susceptible particles are configured to trans-port an analyte across the interface into the second liquid. An assay for the analyte is performed in the second liquid. An assay for another analyte can also be performed in the sample liquid.
1. A device comprising:
an inlet in fluid connection with a first portion of a channel, the inlet configured to receive a first liquid;
a second portion of the channel connected to the first portion of the channel at a junction;
magnetically susceptible particles disposed in the first portion of the channel;
a capillary stop at the junction, wherein at the junction the cross sectional area of the first portion of the channel is less than the cross sectional area of the second portion of the channel, and wherein the junction of the first and second portions of the channel is substantially orthogonal to the longitudinal axis of the first portion of the channel and the longitudinal axis of the second portion of the channel, and wherein the first and second portions of the channel have a common longitudinal axis, wherein the capillary stop is configured to form, with the first liquid received by the inlet, a liquid interface at the junction;
a reservoir containing a quantity of second liquid and configured to deliver second liquid released from the reservoir into the second portion of the channel such that the second liquid flows towards the junction; and
at least one sensor configured on the second portion of the channel to detect a signal from the second liquid, and
wherein the device is configured to direct the flow of the second liquid across the face of the first liquid at the interface in a direction substantially orthogonal to the direction of flow of the first liquid in the first portion of the channel immediately before the interface.
2. The device of claim 1 wherein the first liquid is a quantity of human blood.
3. The device of claim 1 wherein said magnetically susceptible particles are clustered in the first liquid at the interface.
4. The device of claim 1 wherein the second liquid is a buffer solution.
5. The device of claim 1 , wherein said immediately before the interface is at distance D before the interface, wherein D is less than 10 mm.
6. The device of claim 1 , wherein at the junction, the first portion of the channel has height h 1 and the second portion of the channel has height h 2 , wherein h 2 >h 1 and the ratio h 1 :h 2 is at least 1:2 and wherein at the junction the first portion of the channel has a cross-sectional area A 1 , and the second portion or the channel has a cross-sectional area A 2 , wherein A 1 <A 2 and the ratio of A 1 :A 2 is at least 1:3 and wherein at the junction the first portion of the channel has a width w 2 , and the second portion of the channel has a width w 5 , wherein w 5 >w 2 and the ratio w 2 :w 5 is at least 1:3 and wherein at the junction of the first and second portions of the channel a base of the second portion of the channel is sloped between a region of the second portion of the channel distal of the junction and having height h 3 and a region of the second portion of the channel at the junction and having height h 2 , wherein h 2 >h 3 .
7. The device of claim 1 , wherein a wall of the second portion of the channel has a capillary stop, an upper edge of a slope extending across the second portion of the channel from a region at the capillary stop towards the opposing wall of the second portion of the channel and wherein the upper edge of the slope extends obliquely across the channel and towards the junction.
8. The device of claim 1 , wherein the second portion of the channel has a first region distal to the junction wherein the channel has a width w 6 and height h 3 , the second portion of the channel having a tapered neck region formed between the first region and the junction in which the channel width and height increases to height h 2 and width w 5 at the junction, and wherein the first portion of the channel is rectangular in cross section and has height h 1 and width w 2 , wherein h 1 is at least about 0.06 mm and w 2 is at least about 1.0 mm and wherein at the junction of the first and second portions of the channel the second portion of the channel is generally rectangular in cross section and has a height h 2 , and width w 5 , wherein h 2 is at least about 0.35 mm and w 5 is at least about 9 mm and wherein the second portion of the channel has a height h 3 and a width w 6 at distance d 2 from the junction, wherein d 2 is at least about 3.5 mm, and wherein the second portion of the channel has height h 2 and width w 5 at the junction of the first and second channel portions, wherein h 2 >h 3 and w 5 >w 6 .