Droplet-based high throughput screening involves encapsulating reagents in individual microdroplets – just nanoliters or picoliters in size - each of which serves as an independent reaction vessel. Specifically, the reagents in question are usually chemical compounds or single cells, while the microdroplets comprise an aqueous core surrounded by an immiscible carrier oil.
Compared to conventional plate-based screening methods, the use of microdroplets offers several advantages. These include lower reaction volumes, which save on expensive reagents and precious sample material, as well as the capacity to process extremely large sample numbers.
Using microdroplets, thousands of samples can be screened within minutes, whereas conventional plate-based methods will take hours. Droplet-based high throughput screening can be used for a broad range of applications. These include synthetic biology, diagnostics, and many different biological and chemical assays, along with drug screening and directed evolution.
However, droplet-based high throughput screening is especially useful for single-cell analysis since it enables parameters such as protein secretion, enzyme activity, and clonal colony formation to be studied on an individual basis.So how is droplet-based high throughput screening applied to single-cell analysis?
Let’s just take a step back and consider that most single-cell analysis studies involve labeling cells with fluorophore-conjugated antibodies before isolating different target populations with a cell sorter. Because conventional cell sorters do not allow the use of oil as the sheath fluid, the water-in-oil droplets must first be encapsulated in another aqueous phase to produce a double emulsion – something which adds an extra level of complexity to the experiment.
Not only are the resultant double emulsions often highly polydisperse, but they are also unable to withstand the physical shock of conventional cell sorting. In addition, the individual double emulsion droplets cannot be easily dispensed into microplates due to their small size, which prohibits downstream applications such as antibody discovery and cell line development.
To overcome the technical challenges of droplet-based single-cell analysis, cell sorting technologies have had to evolve. The On-chip Droplet Selector combines microfluidics, flow cytometry, and liquid dispensing technologies all in one system to allow the gentle isolation and dispensing of individual emulsion droplets in a single step.
Key features include the use of air-over-liquid flow shift sorting, which differs mainly from conventional sorting in that it uses pressurized air to generate a short liquid pulse for directing the target droplets into the collection reservoir.
As well as eliminating all of the damaging steps associated with conventional cell sorting methods – including the associated risk of droplet breakage – air-over-liquid flow shift sorting allows for the use of oil as the sheath fluid since it works by regulating the liquid flow within the microchannels.
Importantly, the On-chip Droplet Selector provides the option to dispense single sorted droplets into the wells of up to three microtiter plates, with a dispensing accuracy of over 90%, making previously unworkable experiments possible. With proven utility for methods that include detecting microorganisms grown in droplets, and performing high throughput screening for enzyme-producing strains, the On-chip Droplet Selector helps researchers tackle even the most challenging single-cell applications.
To learn more about On-chip Droplet Selector, visit onchipbio.com
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