The concept behind the artemisinin biosensor is relatively straightforward: a synthetic novel
protein is expressed constitutively in an E. coli cell, and forms a complex with artemisinin that
produces a color. A sample of a suspect medicine can then be added to a culture of this biosensor
to determine its artemisinin content. If artemisinin is not present, or is present in small
concentrations—as happens in some substandard medicines—the change in color will be less
noticeable than would be seen with authentic artemisinin. Because we do not want the cell walls
of E. coli to interfere with the diffusion of either artemisinin or the binding protein, a genetic
device that lyses the bacterial cells is also included. It is controlled by an inducible promoter,
however, so that the bacteria can produce sufficient protein for artemisinin to be the limiting
factor before lysing.
