Cheap strong dye with COOH group?

WS via (by novalidaddress from
Wed Aug 3 16:23:44 EST 2011

Dear experts,

I am looking for a dye that I could attach by covalent coupling to
amino groups of a protein. A mild chemistry like carbodiimide/NHS
activation (makes succinimide esters, like those frequently used quite
expensive fluorescent dyes for antibody labeling)  is preferred, I can
do this step myself and also attach a spacer like 6-amino-caproic
acid, if required.

Ideal properties are: strong colour, stable against light, absorption
at 500 to 550 nm or longer (visible or at least shorter than 900nm,
that I may trace it with a UV/Vis photometer), if possible: also
fluorescent (I don't care much about color, as long as it is visible).
Should not impair water solubility of proteins after coupling. And be
so cheap, that my boss doesn't kill me when I order a few grams of it.

Any suggestions? All input is welcome!

By chance, I came across Gallocyanine (eg see
I have found that it is used in a formulation as DNA-stain (Einarson's
Gallocyanine Chrome Alum, a possible replacement for HE, but no
covalent coupling is used). Might it be worth a try?

Thanks for your help!


By chance

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