What is Emulsion PCR?
“Emulsion PCR is a PCR variation
that some NGS technologies use to
replicate DNA sequences.
It is conducted on a bead surface
within tiny water bubbles floating on
an oil solution.”
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Principle
The basic principle of ePCR is dilution and
compartmentalization of template molecules in water
droplets in a water-in-oil emulsion.
Each droplet contains a single template molecule and
functions as a micro-PCR reactor.
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Procedure
Fragmentation of DNA
•The sample is fragmented ranging from 300 to
800bp.
Ligation of adapters
•Adapters with one end sticky and one blunt are ligated
with fragments.
•Phosphates are removed from sticky ends to avoid
dimerization.
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Procedure
Formation of clonal bead populations
•Beads coated with
streptavidin are used.
•Beads have primers that
matches the adapters used.
•Each bead is emulsified in a water-in-oil droplet with
PCR reagents (DNA polymerase, primers, buffers,
dNTPs).
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Formation of clonal bead
populations
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Amplification
Denaturation to single strands
•The double stranded DNA's with adapters are
then denatured by heating the DNA up to 95 °C.
Annealing of ssDNA
•The ssDNA is then attached to the beads.
•Reverse strand (bottom strand or 3’-5’ strand) anneal
to the f-primer on bead surface and r-primer anneal
to the forward strand (top strand or 5’-3’ strand)
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Amplification
Extension
•Polymerase amplifies the forward strand (5’-3’)
starting from beads towards the primer site.
•The reverse strand is amplified starting from primer
towards the bead site.
Cycle
•Each newly formed double-strand is denatured,
allowing for the strand to ligate to another site on the
surface of the bead. Eventually, 1 million copies of
the target is amplified on the surface of each bead.
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Procedure
Emulsion Breaking
•After amplification, the emulsions are broken using
isopropanol and detergent buffer. The solution is
then vortexed, centrifuged, and magnetically
separated.
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