Combined multiple-displacement amplification and PCR in an emulsion microdroplet
The methods and systems described herein provide an improved emulsion droplet based nucleic acid amplification method, which allows nucleic acids contained in biological systems to be detected, quantitated and/or sorted based on their sequence as detected with nucleic acid amplification techniques, e.g., polymerase chain reaction (PCR). The nucleic acids can be free floating or contained within living or nonliving structures, including particles, viruses, and cells. The nucleic acids can include, e.g., DNA or RNA.
1. A nucleic acid amplification method comprising:
(a) encapsulating a target nucleic acid and amplification reagents in an emulsion microdroplet, wherein the amplification reagents comprise non-specific amplification reagents and PCR amplification reagents;
(b) non-specifically amplifying the target nucleic acid, thereby producing a non-specific amplification product in the emulsion microdroplet;
(c) amplifying the non-specific amplification product of (b) by PCR amplification, thereby producing a PCR amplification product in the emulsion microdroplet; and
(d) detecting the PCR amplification product of (c).
2. The method of claim 1 , wherein non-specifically amplifying the nucleic acid comprises amplifying the nucleic acid by Multiple Displacement Amplification (MDA).
3. The method of claim 2 , wherein the MDA comprises amplification of the nucleic acid with a polymerase which is active under buffer conditions under which Taq DNA polymerase is active.
4. The method of claim 3 , wherein the polymerase is a B st polymerase.
5. The method of claim 1 , wherein the PCR amplification reagents comprise Taq DNA polymerase.
6. The method of claim 1 , wherein the emulsion microdroplet is a multiple-emulsion microdroplet comprising a first miscible phase fluid surrounded by an immiscible shell, wherein the multiple-emulsion microdroplet is positioned in a second miscible phase carrier fluid.
7. The method of claim 6 , wherein the second miscible phase carrier fluid is a buffered aqueous phase carrier fluid.
8. The method of claim 6 , wherein the first and second miscible phase fluids are the same.
9. The method of claim 1 , further comprising labeling the PCR amplification product with a detectable label prior to (d).
10. The method of claim 1 , wherein the PCR amplification reagents comprise detectably labeled primers and/or probes.
11. The method of claim 9 , wherein the detectable label is a fluorescent label, and wherein the method further comprises sorting emulsion microdroplets via fluorescence activating cell sorting (FACS).
12. The method of claim 11 , further comprising pooling nucleic acid sequences from the sorted emulsion microdroplets, thereby providing an enriched pool of target nucleic acid sequences.
13. The method of claim 1 , wherein (a) comprises encapsulating a single cell comprising the nucleic acid in an emulsion microdroplet, and wherein the method further comprises lysing the single cell prior to (b).
14. The method of claim 1 , wherein no more than 10 fg of the target nucleic acid is present the emulsion microdroplet prior to (b).
15. The method of claim 1 , further comprising sequencing the PCR amplification product.
16. The method of claim 1 , wherein the PCR amplification reagents comprise one or more primers that hybridize to the non-specific amplification product.
17. The method of claim 1 , wherein the target nucleic acid comprises a nucleic acid sequence that is not present in the PCR amplification product.
18. The method of claim 6 , wherein encapsulating the amplification reagents comprises introducing the non-specific amplification reagents into the second miscible phase carrier fluid, wherein the non-specific amplification reagents diffuse from the second miscible phase carrier fluid through the immiscible shell and into the first miscible phase fluid of the multiple-emulsion microdroplet.
19. The method of claim 1 , wherein the emulsion microdroplet comprises monodisperse microdroplets.
20. The method of claim 6 , wherein encapsulating the amplification reagents comprises introducing the PCR amplification reagents into the second miscible phase carrier fluid, wherein the PCR amplification reagents diffuse from the second miscible phase carrier fluid through the immiscible shell and into the first miscible phase fluid of the multiple-emulsion microdroplet.