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08
Apr
Which Agarose Concentration Should You Actually Be Using?
A practical guide to optimizing DNA resolution and band sharpness.
Quick question: why does your lab use the gel concentration it uses?
If the answer is "because that's what we've always used" or "because the protocol I learned from used it" — you're in good company. Most labs land on 1% agarose and stay there. It works well enough for most things, and changing something that's working is low on everyone's priority list.
But "works well enough for most things" and "optimized for your specific application" aren't the same thing. Choosing the right concentration for the right fragment size can meaningfully improve band resolution, sharpen separation of closely spaced fragments, and reduce run times. It's one of the easiest protocol optimizations available — and it mostly just requires knowing what to choose.
Here's the practical guide.
The Basic Logic
Agarose forms a molecular sieve — a mesh of tangled polymer through which DNA fragments migrate under an electric field. The concentration of agarose determines the pore size of that mesh.
- Higher concentration = smaller pores = better resolution for small fragments
- Lower concentration = larger pores = better resolution for large fragments
Put a large fragment through a high-concentration gel and it barely moves — poor separation. Put small fragments through a low-concentration gel and they all run out the front together — also poor separation.
Concentration by Application
0.8% — For the big stuff
Use for: Large genomic DNA fragments, BAC inserts, restriction fragments above 5 kb, Southern blot preps.
At 0.8%, the pores are large enough that even multi-kilobase fragments can migrate and separate. For anything above 10 kb, this is often your only option in standard agarose. Heads-up: gels at this concentration are more fragile than denser gels, so handle carefully when transferring.
1.0% — The general-purpose workhorse
Use for: Routine PCR verification, plasmid restriction digests, cDNA inserts, any workflow covering the 500 bp–10 kb range.
This is the "tolerably well" option — useful precisely because it doesn't fail dramatically at either end of the size range. For most routine gel runs where the question is "did this PCR work and is it the right size?", 1% gets the job done.
1.2% — PCR product sweet spot
Use for: Routine PCR verification in the 200 bp–5 kb range, any workflow where you want noticeably sharper bands than 1%.
The jump from 1% to 1.2% produces a visible improvement in band sharpness for typical PCR amplicons. If you're running PCR verification all day, this is probably the upgrade with the best ratio of improvement to effort.
1.5% — For when it matters that bands don't overlap
Use for: Genotyping assays, RFLP analysis, any workflow where you need to distinguish between fragments that differ by less than 200–300 bp.
At 1.5%, band separation in the 100 bp–3 kb range is noticeably tighter. If a 50 bp size difference determines the answer, 1% isn't going to give you the resolution you need.
2.0% — Small fragment territory
Use for: miRNA detection, small RNA analysis, short PCR products (under 500 bp), microsatellite assays, MLPA.
At 2%, the gel matrix is dense enough to resolve fragments that would be difficult at lower concentrations. Anything above about 3 kb will migrate very slowly or not at all.
Custom concentrations (0.75%–2.5%): Some workflows live outside the standard range. Biofargo manufactures AgaroPrep gels at custom concentrations on request, with the same machine-manufacturing quality, GelRed® pre-incorporation, and lot documentation.
Quick Reference Chart
| Fragment Size | Best Concentration | Typical Use Case |
|---|---|---|
| > 5 kb | 0.8% | Genomic DNA, large restriction fragments |
| 500 bp – 10 kb | 1.0% | General-purpose, plasmid digests |
| 200 bp – 5 kb | 1.2% | Routine PCR verification |
| 100 bp – 3 kb | 1.5% | Genotyping, RFLP, close-band resolution |
| 50 bp – 1.5 kb | 2.0% | miRNA, short PCR products |
| < 50 bp | 2.5%+ (custom) | Oligonucleotides, siRNA |
One More Thing: Agarose Type Matters Too
Standard agarose (what AgaroPrep uses) is appropriate for nearly all analytical electrophoresis. Two specialty types are worth knowing about:
- Low-melting-point (LMP) agarose: For gel extraction — allows elution without denaturation.
- High-resolution agarose: Engineered for tighter separation in the 50–500 bp range (AFLP, RFLP).
Ready to Optimize Your Run?
AgaroPrep gels are available in 1.0%, 1.2%, 1.5%, and 2.0% as standard stock. Every kit includes loading buffer, DNA marker, and TAE granules.
Biofargo team
