How this instrument works
Resuspension, in molecular biology, is dissolving a dry-shipped oligonucleotide (a short synthetic DNA or RNA strand, such as a primer) in a buffer — typically nuclease-free water or TE buffer — to bring it to a usable working concentration. Custom oligo orders ship as a dried pellet with a known yield, in nanomoles (nmol), printed on the tube or specification sheet; how much buffer you add to that pellet determines the final concentration of the resulting stock solution.
The calculation follows directly from the definition of molar concentration: volume needed (in microliters) equals the amount of oligo (in nanomoles) times 1000, divided by the desired concentration (in micromolar) — the factor of 1000 converts nanomoles to the same 10^-6-scale units that micromolar concentration and microliter volume are both built on. A commonly used shortcut follows from this: to make a standard 100 uM stock, just multiply the nmol amount by 10 to get the microliters of buffer needed.
This calculator performs the resuspension-volume arithmetic only, using the oligo amount and target concentration you already know from your order and protocol — it doesn't know your specific oligo's actual synthesis yield or recommend a particular working concentration for a given downstream application (PCR, sequencing, cloning), both of which should come from your own order specification sheet and lab protocol.
- Enter the oligo's synthesis yield, in nanomoles, into Amount of oligonucleotide (nmol) — found on the tube label or specification sheet from the synthesis order.
- Enter the concentration you want the resuspended stock to end up at into Desired concentration (uM).
- Read Required diluent volume (uL) below the inputs — this is how much buffer (typically nuclease-free water or TE buffer) to add to the dry pellet.
- For the common 100 uM stock target, a quick shortcut is to multiply the nmol amount by 10 directly, without needing this calculator at all.
Worked example — a 10 nmol oligo to a 100 uM stock
Enter 10 into Amount of oligonucleotide (nmol) and 100 into Desired concentration (uM) — a common combination, since 100 uM is the standard working-stock concentration most oligo suppliers recommend as a versatile default. Required diluent volume (uL) reads 100 uL: (10 x 1000) / 100 = 100.
Adding exactly 100 uL of nuclease-free water or TE buffer to that dry 10 nmol pellet, then mixing until fully dissolved, produces a 100 uM stock — which matches the quick mental-math shortcut of simply multiplying the nmol figure by 10 (10 nmol x 10 = 100 uL) that most labs use for this specific, very common target concentration.
Questions
Where do I find the nmol amount for my oligo?
It's printed on the tube label the oligo shipped in, and also listed in the 'amount of oligo' or 'yield' section of the specification sheet that comes with a custom synthesis order. This figure varies from one synthesis run to the next depending on the oligo's length and the synthesis scale ordered, so it needs to be read off your specific order rather than assumed.
Why is 100 uM such a common target concentration?
Because it's concentrated enough to dilute down conveniently for almost any downstream application (PCR primers, hybridization probes, sequencing reactions) while still being a round, easy-to-remember number, which is why most oligo suppliers recommend it as a default working-stock concentration. It isn't a required concentration, though — any target concentration your specific protocol calls for works with the same formula.
What buffer should I actually resuspend the oligo in?
Nuclease-free water or TE buffer (Tris-EDTA) are the two most common choices — water is simpler and works for short-term use, while TE buffer's EDTA chelates trace metal ions that can otherwise promote nuclease activity or degradation, making it a better choice for longer-term storage. This calculator only computes the volume needed; which buffer to use is a separate protocol decision usually specified by your lab or the oligo supplier's own guidance.
Does the oligo's length or sequence change this calculation?
No, not directly — the formula only needs the amount already expressed in nanomoles (a molar unit) and the target concentration, both of which already account for the specific oligo's molecular weight implicitly. Length and sequence matter earlier, when the synthesis yield itself was determined (a longer oligo of the same mass represents fewer nanomoles), but by the time you're reading nmol off the tube label, that's already been accounted for.
What if I want the concentration in nM or mM instead of uM?
Convert your target concentration to micromolar (uM) before entering it, since Desired concentration (uM) expects that specific unit — divide a nanomolar (nM) target by 1000 to get uM, or multiply a millimolar (mM) target by 1000 to get uM. Getting the concentration unit right matters a great deal here, since the required volume is inversely proportional to it.