Bio-Rad Criterion™ TBE-Urea Precast Gels - Manual (Page 23)

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Criterion Stain Free
™
System
5
5.1 Introduction
The Criterion Stain Free system, which comprises the Gel Doc ™ EZ imager, Image Lab ™ software,
and Criterion ™ TGX Stain-Free ™ and Criterion Stain Free precast gels, eliminates the time-consuming
staining and destaining steps required by other protein detection methods. Criterion TGX (Tris-Glycine
eXtended shelf life) Stain-Free gels include a proprietary modification that extends their shelf life to
12 months and enhances separation characteristics relative to conventional gel types. Criterion TGX
Stain-Free and Criterion Stain Free gels also include unique trihalo compounds that allow rapid
fluorescent detection of proteins with the Gel Doc EZ imager — without staining.
The trihalo compounds in the gels react with tryptophan residues in a UV-induced reaction to
produce fluorescence, which can be easily detected by the Gel Doc EZ imager within gels or on low-
fluorescence PVDF membranes. Activation of the trihalo compounds in the gels adds 58 Da moieties
to available tryptophan residues and is required for protein visualization. Proteins that do not contain
tryptophan residues cannot be detected using this system. The sensitivity of the Criterion Stain Free
system is comparable to staining with Coomassie Brilliant Blue for proteins with a tryptophan content
>1.5%; sensitivity superior to Coomassie staining is possible for proteins with a tryptophan content >3%.
Molecular weights of proteins are estimated by a regression method using Image Lab software. The
software generates a standard curve using the molecular weight and relative mobility (R
f
) of standard
proteins (R
f
= distance migrated by the protein/distance migrated by the dye front). The standard curve
is then used to estimate the molecular weights of sample proteins.
Benefits of the Criterion Stain Free system include:
n
Elimination of staining and destaining steps for faster results
n
Automated gel imaging and analysis
n
No background variability within a gel or between gels (as is often seen with standard
Coomassie staining)
n
Reduced organic waste by not requiring acetic acid and methanol for staining or destaining
n
Visualization of transferred (blotted) proteins on low-fluorescence PVDF membranes