Agarose gel loading buffer

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Loading dye is mixed with DNA samples for use in agarose gel electrophoresis. It generally contains a dye to assess how "fast" your gel is running and a reagent to render your samples denser than the running buffer (so that the samples sink in the well).



  • Ficoll
  • sucrose


  • xylene cyanol (Sigma X4126)
  • bromophenol blue (Sigma B8026)
  • Orange G


Ficoll & Orange G

  • Ficoll 400 (in 68-558F)
  • Deionized water
  • Orange G dye

Dissolve 1.5 g of Ficoll in 10 mL of deionized water. Add very small amounts of Orange G dye such that the loading dye is dark orange. Store in small aliquots at 4°C (room temperature is okay too). To use, add and mix 1/5th volume of loading dye to DNA solutions prior to loading into the wells of gels.

Specific recipes


  • Orange G: generally runs very fast (<100 bp)
  • Bromophenol blue: purple, generally runs at ~500bp (depending on percentage agarose)
  • Xylene cyanol: blue, runs at ~4kb