Ultra-sensitive detection of molecules or particles using beads or other capture objects
The present invention relates to systems and methods for detecting analyte molecules or particles in a fluid sample and in some cases, determining a measure of the concentration of the molecules or particles in the fluid sample. Methods of the present invention may comprise immobilizing a plurality of analyte molecules or particles with respect to a plurality of capture objects. At least a portion of the plurality of capture objects may be spatially separated into a plurality of locations. A measure of the concentration of analyte molecules in a fluid sample may be determined, at least in part, on the number of reaction vessels comprising an analyte molecule immobilized with respect to a capture object. In some cases, the assay may additionally comprise steps including binding ligands, precursor labeling agents, and/or enzymatic components.
1. A method for determining a measure of the concentration of analyte molecules or particles in a fluid sample, comprising:
providing a plurality of capture objects that each are associated with either at least one analyte molecule or particle of the fluid sample or are free of any analyte molecules or particles of the fluid sample;
individually addressing at least a portion of the capture objects and determining the fraction of said capture objects associated with at least one analyte molecule or particle of the fluid sample; and
determining a measure of the concentration of analyte molecules or particles in the fluid sample based at least in part on the fraction of capture objects subjected to the addressing step determined to be associated with at least one analyte molecule or particle of the fluid sample,
wherein the capture objects comprise or are each contained within a liquid droplet that is immiscible within a fluid in which the droplet is suspended during at least the addressing step, and
wherein the step of individually addressing at least a portion of the capture objects comprises flowing at least a portion of the capture objects comprising or contained wihtin liquid droplets through a flow channel such that the at least a portion of the capture objects pass by a detection system.
2. The method of claim 1 , wherein the capture objects each include a binding surface having affinity for at least one type of analyte molecule or particle.
3. The method of claim 2 , comprising a step of immobilizing analyte molecules or particles with respect to the plurality of capture objects such that a statistically significant fraction of the capture objects associate with a single analyte molecule or particle and a statistically significant fraction of the capture objects are free of any analyte molecule or particle.
4. The method of claim 3 , comprising a step of individually isolating at least a portion of the capture objects subjected to the immobilizing step from the remainder of the capture objects.
5. The method of claim 1 , wherein at least a portion of the analyte molecules or particles are associated with at least one binding ligand.
6. The method of claim 1 , wherein the analyte molecules or particles comprise an enzymatic component.
7. The method of claim 5 , wherein the binding ligand comprises an enzymatic component.
8. The method of claim 1 , wherein the concentration of analyte molecules or particles in the fluid samples is less than about 50×10 −15 M.
9. The method of claim 1 , wherein the concentration of analyte molecules or particles in the fluid sample is determined at least in part by comparison of a measured parameter to a calibration standard.
10. The method of claim 1 , wherein the addressing step uses optical techniques.
11. The method of claim 1 , wherein a statistically significant fraction of the capture objects is associated with a single analyte molecule or particle and a statistically significant fraction of the capture objects is free of any analyte molecule or particle.
12. The method of claim 1 , comprising a step of individually isolating at least a portion of the capture objects from a remainder of the capture objects.
13. The method of claim 1 , wherein the liquid droplet is a microfluidic droplet.
14. A method for determining a measure of the concentration of a plurality of types of analyte molecules or particles, said plurality including at least a first type of analyte molecules or particles and a second type of analyte molecules or particles in a fluid sample, comprising:
providing a plurality of a first type of capture objects and a plurality of a second type of capture objects, wherein the first type of capture objects are each associated with either at least one first type of analyte molecule or particle of the fluid sample or are free of any analyte molecules or particles of the fluid sample, and the second type of capture objects are each associated with either at least one second type of analyte molecule or particle of the fluid sample or are free of any analyte molecules or particles of the fluid sample;
individually addressing at least a portion of the capture objects and determining the fraction of said first type of capture objects associated with at least first type of one analyte molecule or particle of the fluid sample and the fraction of said second type of capture objects associated with at least one second type of analyte molecule or particle of the fluid sample;
determining a measure of the concentration of first type of analyte molecules or particles in the fluid sample based at least in part on the fraction of first type of capture objects subjected to the addressing step determined to be associated with at least one first type of analyte molecule or particle of the fluid sample; and
determining a measure of the concentration of second type of analyte molecules or particles in the fluid sample based at least in part on the fraction of second type of capture objects subjected to the addressing step determined to be associated with at least one second type of analyte molecule or particle of the fluid sample,
wherein the first type of capture objects and/or the second type of capture objects comprise or are each contained within a liquid droplet that is immiscible within a fluid in which the droplet is suspended during at least the addressing step, and
wherein the step of individually addressing at least a portion of the capture objects comprises flowing at least a portion of the first type of capture objects and/or second type of capture objects comprising or contained within liquid droplets through a flow channel such that the at least a portion of the first type of capture objects and/or second type of capture objects pass by a detection system.
15. The method of claim 1 , wherein the step of flowing the at least a portion of the capture objects through a flow channel is performed such that the at least a portion of the capture objects passes by the detection system single file.
16. The method of claim 1 , wherein determining the fraction of said capture objects associated with at least one analyte molecule or particle of the fluid sample comprises using the detection system to determine whether each capture object passed by the detection system is associated with an analyte molecule or particle of the fluid sample or is free of any analyte molecules or particles of the fluid sample.
17. The method of claim 1 , wherein the capture objects are beads that are each contained within a liquid droplet that is immiscible within a fluid in which the droplet is suspended during at least the addressing step.
18. The method of claim 12 , wherein the step of isolating at least a portion of the capture objects comprises feeding the at least a portion of the capture objects into a column.