Resuspending Dry Oligos

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IMPORTANT — BEFORE OPENING DRY OLIGOS
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• Loose DNA can easily be lost when opening the tube, especially due to
  electrostatic attraction (e.g., when wearing latex gloves).

⚠️ ALWAYS BRIEFLY CENTRIFUGE OLIGOS BEFORE OPENING
FOR THE FIRST TIME AFTER DELIVERY TO AVOID LOSS OF THE DNA PELLET.

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RESUSPENSION BEHAVIOR OF DRIED DNA
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Pure, dried DNA generally dissolves readily in aqueous solution, but drying behavior
can vary:

A) Filamentous / fibrous appearance
• Occurs if the oligo solution freezes during lyophilization (Speed-Vac).
• Appears like a fine piece of tissue or Kimwipe.
• Dissolves almost instantly in aqueous solution.
• Highly prone to “flying out of the tube” — centrifuge before opening.

B) Clear film coating tube walls or bottom
• Occurs if the DNA does not freeze during drying.
• Fully soluble, but may require:
  - Vigorous vortexing for several minutes
  - Heating to accelerate dissolution
• Especially true for large-yield (milligram-scale) oligos.

C) Phosphorothioate-modified oligos
• Particularly difficult to resuspend.
• Can be shipped in aqueous solution upon request (they are quite stable).

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STOCK SOLUTION PREPARATION
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• Dissolve stock oligo in TE buffer:
  - 10 mM Tris, pH 8.0
  - 1 mM EDTA

• DNA stored frozen in TE is stable for YEARS.

RECOMMENDED FREEZER STOCK
• Prepare a 100 µM stock solution.
• Add a volume of TE (µL) equal to 10× the number of nanomoles listed on the spec sheet.

Example:
• 50 nmol oligo + 500 µL TE → 100 µM stock solution

• Freeze this stock and thaw infrequently.

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WORKING SOLUTIONS FOR PCR
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• Dilute 100 µM stock 1:10 in water → 10 µM working solution.
• Typical PCR primer concentration:
  - 0.1–0.5 µM final

Example:
• Add 1 µL of 10 µM primer to a 20 µL PCR reaction:
  → Final primer concentration = 0.5 µM
  → 10 picomoles of oligo per reaction

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WORKING IN MASS UNITS (OPTIONAL)
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• Spec sheets list oligo quantity as:
  - OD260 units
  - milligrams (mg) DNA

CONVERSION
• 1 OD260 = 33 µg single-stranded DNA

Typical values:
• Average 20-mer MW ≈ 7,500 g/mol
• 1 OD260 = 33 µg ≈ 4.4 nmol

Example (mass-based stock):
• Dissolve 500 µg DNA in 500 µL TE:
  → 1 µg/µL stock
  → ≈133 picomoles/µL

• This stock should be diluted further before use.

PCR guidance:
• ~10 picomoles (≈75 ng for a 20-mer) is sufficient for a single 20 µL PCR reaction.

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SUMMARY
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• Always centrifuge before opening shipped oligos.
• Resuspension behavior varies by drying morphology and modification.
• Use TE buffer for long-term storage.
• Prepare concentrated freezer stocks and dilute for working solutions.
• Typical PCR reactions require only picomole quantities of oligo.