Smart trick for marking replicas?

Sean Stevens stevens at
Tue Jun 13 21:54:35 EST 1995

jkortes at (Jarkko Kortesmaa) wrote:
>Dear netters,
>I have marked the position of replica filters on the plate by stabbing
>through the filter into the plate agar as suggested in Current Protocols.
>Finding the needle holes after hybrization and marking them on the film
>is time-consuming and not very convenient. Also, this method usually is
>so inaccurate that distinguishing between two plaques near each other for
>sure may be impossible, which means further screening/other extra analysis.
>In Clontech¥s library manual, they recommended stabbing the filter with a
>needle attached to a radioactive ink containing syringe. This way, the
>positions of the holes should be seen directly on the film. IMHO, sounds
>VERY messy. Has anyone tried this? How active must the ink be?
>Do you have a clever method for this?
>Jarkko Kortesmaa		Dept. of Biochemistry and Biocenter Oulu
>jkortes at		University of Oulu
>				Finland

There is a simple way to improve visibility without changing methods-I dip my needle into black india ink before stabbing through to the plate-the ink seeps into the agar in a limited range and easily identifies the spot. Just be sure not to load the needle with too much ink. I would use the smallest gauge needle you have. Good luck.


Sean Stevens  The Rockefeller University  NY NY  10021
stevens at

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