Ethidium Bromide Fluorescence

NJ njuni at
Thu Jul 26 20:55:32 EST 2001

in article 60805a5e.0107250646.1292beb7 at, Bill Atkins at
billatkins at wrote on 7/25/01 11:46 PM:

> Why does ethidium bromide only fluoresce in the prescense of DNA?
> Thanks,
> Bill

Free EtBr also emits fluorescence when irradiated with longer wave length
(~302 and ~366 nm) of UV. This is why you get higher background fluorescence
when you observe EtBr-stained gels under longer wave lengths of UV (in this
case, we can recognize DNA bands just because EtBr accumulates in DNA, I
suppose...). In the case of EtBr-DNA complex, DNA absorbs shorter wave
length (~254 nm) of UV, which is not absorbed by EtBr itself, and transmits
excitation energy to intercalating EtBr, yielding greater fluorescence but
lower background fluorescence from free EtBr. See Molecular Cloning.

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