actually we using Safe stains in lab . but i think for the cloning purposes use of EthBR is better than of safe stain
Although it is not my field but I found the following in one article:
EtBr is the most common reagent used to stain DNA in agarose gels. When exposed to uv light, electrons in the aromatic ring of the ethidium molecule are activated, which leads to the release of energy (light) as the electrons return to ground state. EtBr works by intercalating itself in the DNA molecule in a concentration dependent manner. This allows for an estimation of the amount of DNA in any particular DNA band based on its intensity. Because of its positive charge, the use of EtBr reduces the DNA migration rate by 15%. EtBr is a suspect mutagen and carcinogen, therefore one must exercise care when handling agarose gels containing it. In addition, EtBr is considered a hazardous waste and must be disposed of appropriately. Alternative stains for DNA in agarose gels include SYBR Gold, SYBR green, Crystal Violet and Methyl Blue. Of these, Methyl Blue and Crystal Violet do not require exposure of the gel to uv light for visualization of DNA bands, thereby reducing the probability of mutation if recovery of the DNA fragment from the gel is desired. However, their sensitivities are lower than that of EtBr. SYBR gold and SYBR green are both highly sensitive, uv dependent dyes with lower toxicity than EtBr, but they are considerably more expensive. Moreover, all of the alternative dyes either cannot be or do not work well when added directly to the gel, therefore the gel will have to be post stained after electrophoresis. Because of cost, ease of use, and sensitivity, EtBr still remains the dye of choice for many researchers. However, in certain situations, such as when hazardous waste disposal is difficult or when young students are performing an experiment, a less toxic dye may be preferred.
Loading dyes used in gel electrophoresis serve three major purposes. First they add density to the sample, allowing it to sink into the gel. Second, the dyes provide color and simplify the loading process. Finally, the dyes move at standard rates through the gel, allowing for the estimation of the distance that DNA fragments have migrated.
The exact sizes of separated DNA fragments can be determined by plotting the log of the molecular weight for the different bands of a DNA standard against the distance traveled by each band. The DNA standard contains a mixture of DNA fragments of pre-determined sizes that can be compared against the unknown DNA samples. It is important to note that different forms of DNA move through the gel at different rates. Supercoiled plasmidDNA, because of its compact conformation, moves through the gel fastest, followed by a linear DNA fragment of the same size, with the open circular form traveling the slowest.
In conclusion, since the adoption of agarose gels in the 1970s for the separation of DNA, it has proven to be one of the most useful and versatile techniques in biological sciences research.
https://www.jove.com/video/3923/agarose-gel-electrophoresis-for-the-separation-of-dna-fragments
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