Create a biosensor using a cell-free extract of Saccharomyces cerevisae yeast, plus a GFP transformed yeast plasmid to produce a green fluorescence when amatoxin is not present. In the presence of amatoxin, the extract does not produce fluorescence because the toxin inhibits RNA polymerase II, preventing protein production. The control is the cell-free extract containing the GFP yeast plasmid and water, which produces green fluorescence.