Debbie Knight

Photo of the Week

In photo log on April 24, 2012 at 9:00 am

This is a poster (slightly customized) that hangs in my lab. It was “designed” during a time when we did quite a bit of work with viruses. And the only way to figure out how much virus there was in an experiment was to do a “plaque assay.”

The way we did a plaque assay was we added a solution with virus in it to some cells that were growing in a tissue culture plate. Let it incubate for an hour or so, so that the virus could attach and enter the cells before we washed off any virus solution that didn’t get in. Because this virus tended to blow up the cell when it was ready to spread to other cells, we would add a layer of agarose/media (think cherry jello) to the cells.  This “jello” fed the cells (the media part) and held the virus in one area (the agarose part). This forced any newly made viral particles to infect only neighboring cells and not the entire cell layer. After several cycles of blowing up cells and infecting neighboring cells, a “hole” was made in the cell lawn — we call this a plaque.

When the plaques were big enough to see with a low-power microscope (called a dissecting scope), we “fixed” the cells/virus in place with a solution of formalin. This killed the cells/virus and allowed us to stain the cells and count the plaques.

A plaque assay to count the amount of virus in a solution. The cell monolayer is stained with the dye crystal violet which turns the cells purple. The "holes" or clear areas are areas of viral infection. This image was borrowed from

For large experiments, it wasn’t so fun to count plaque assays — you might say it was a pain in the “assay.”  Hence the poster.


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