Method for rapid and large-scale generation of droplets and droplet libraries
Provided is a method of generating droplets that includes aspirating a first liquid into a tube, positioning the tube over a receiving liquid, and ejecting the first liquid to generate a plurality of droplets that contact the receiving liquid and remain discrete even after contacting the receiving liquid. Whereas many other droplet generators require complex microfluidics, the present methods allow generation of droplets without the need for microfluidics. The methods can be performed with existing commercially available macro-fluidic liquid handling devices. The methods can be used for digital PCR, digital MDA, enzyme screening, single cell analysis, and other applications involving droplets.
1 . A method of generating droplets, comprising:
aspirating a first liquid into a lumen of a tube through an opening in the tube, wherein the tube is part of a piezo-electric droplet generator;
positioning the opening over a receiving liquid;
ejecting the first liquid from the opening to generate a first plurality of droplets that contacts the receiving liquid,
wherein the first plurality of droplets and the second plurality of droplets remain discrete and 50% or more of the first plurality of droplets do not merge after contacting the receiving liquid;
washing the tube with a washing liquid;
aspirating a second liquid into the tube through the opening;
positioning the opening over the receiving liquid; and
ejecting the second liquid from the opening to generate a second plurality of droplets that contacts the receiving liquid thus creating a library comprised of the first plurality of droplets and the second plurality of droplets,
wherein the second plurality of droplets remain discrete and 50% or more of the second plurality of droplets do not merge after contacting the receiving liquid.
2 . The method of claim 1 , repeating the aspirating, positioning, and ejecting steps for a total of 5 or more liquids and optionally for a total of 10 or more liquids.
3 . The method of claim 1 , wherein each liquid being aspirated and ejected comprises water and the receiving liquid comprises oil or wherein each liquid being aspirated and ejected comprises oil and the receiving liquid comprises water.
4 . The method of claim 1 , wherein the receiving liquid comprises a surfactant, wherein the surfactant is optionally a fluorosurfactant, and wherein the receiving liquid optionally comprises 0.5% w/v or more of the surfactant.
5 . The method of claim 1 , further comprising stirring or agitating the receiving liquid during each ejecting step, optionally wherein the ejecting comprises applying an oscillating force to the ejected liquid, wherein each oscillation corresponds to a single droplet, and optionally wherein the droplets are generated at a rate of 50 Hz or more and optionally at a rate of 500 Hz or more.
6 . The method of claim 1 , wherein the opening of the tube has a cross-sectional area of 100 mm 2 or less.
7 . The method of claim 1 , further comprising fluorescently tagging or barcoding the generated droplets.
8 . The method of claim 1 , wherein 95% or more of the droplets have a volume ranging from 10 pl to 2,000 pl.
9 . The method of claim 1 , wherein a total of 100 or more droplets are generated, and optionally wherein a total of 10,000 or more droplets are generated.
10 . The method of claim 1 , wherein 90% or more of the droplets do not combine with another droplet after contacting the receiving liquid, and optionally wherein 90% or more of the droplets have a volume that is within 20% of the median droplet volume.
11 . The method of claim 1 , wherein each aspirated liquid is present in a well plate before being aspirated and/or is part of a pool of liquid having a volume of 100 μl or more and/or wherein each aspiration step comprises aspirating 0.5 μl or more of liquid.
12 . The method of claim 1 ,
wherein the first liquid comprises a nucleic acid and a polymerase chain reaction (PCR) reagent, further comprising incubating a first droplet under conditions effective for the formation of a PCR amplification product from the nucleic acid, wherein the method is a method of performing digital PCR; or
wherein the first liquid comprises a nucleic acid and the second liquid comprises a PCR reagent, further comprising merging a first droplet with a second droplet to form a combined droplet and incubating the combined droplet under conditions effective for the formation of a PCR amplification product from the nucleic acid, wherein the method is a method of performing digital PCR.
13 . The method of claim 12 , further comprising repeating the digital PCR on ten nucleic acids present in ten different liquids and optionally wherein the PCR reagent is a barcoded or fluorescently labelled primer.
14 . The method of claim 1 ,
wherein the first liquid comprises a nucleic acid and a multiple displacement amplification (MDA) reagent, further comprising incubating the first plurality of droplets under conditions effective for the formation of MDA amplification products from the nucleic acid, wherein the method is a method of performing digital MDA, or
wherein the first liquid comprises a nucleic acid and the second liquid comprises a MDA reagent, further comprising merging a first droplet with a second droplet to form a combined droplet and incubating the combined droplet under conditions effective for the formation of MDA amplification products from the nucleic acid, wherein the method is a method of performing digital MDA.
15 . The method of claim 14 , further comprising repeating the digital MDA on ten nucleic acids present in ten different liquids and optionally wherein the MDA reagent is a barcoded or fluorescently labelled primer.
16 . The method of claim 1 ,
wherein the first liquid comprises a substrate and an enzyme hypothesized to be able to metabolize the substrate, further comprising incubating the first plurality of droplets under conditions hypothesized to be effective for metabolism of the substrate, wherein the method is a method of enzyme screening, or
wherein the first liquid comprises a substrate and the second liquid comprises an enzyme hypothesized to be able to metabolize the substrate, further comprising merging a first droplet with a second droplet to form a combined droplet and incubating the combined droplet under conditions hypothesized to be effective for metabolism of the substrate, wherein the method is a method of enzyme screening.
17 . The method of claim 1 ,
wherein the first liquid comprises a single cell analysis reagent, wherein the first liquid further comprises a single cell and a lysing reagent or contents from a single lysed cell, further comprising incubating the first plurality of droplets under conditions effective for single cell analysis, wherein the method is a method of single cell analysis, or
wherein the first liquid comprises a single cell analysis reagent, wherein the second liquid comprises a single cell and a lysing reagent or contents from a single lysed cell, further comprising merging a first droplet and a second droplet to form a combined droplet and incubating the combined droplet under conditions effective for single cell analysis, wherein the method is a method of single cell analysis.
18 . The method of claim 17 , wherein the single cell analysis is selected from genomic analysis, transcriptome analysis, proteomic analysis, and metabolomic analysis.
19 . The method of claim 1 , wherein the first liquid comprises a nucleic acid conjugated to part of a drug candidate or to a whole drug candidate, further comprising assessing an interaction of the drug candidate with a biological target, wherein optionally the interaction is a binding assay, wherein optionally the nucleic acid is a DNA oligomer, wherein optionally the biological target is a cell receptor, and wherein optionally the drug candidate is a small molecule.