We wanted to create a detector, thus we could have designed it like following:
Where X is the molecule to detect, and Z the fluorescent signal. However, with this design, the communication between the bacteria (quorum sensing) wouldn’t have worked really well, we would have needed an important quantity of X at the initial time to be able to obtain an important diffusion that we could actually see. Indeed, the evolution of X would have been like following:
Thus, the next idea was to amplify X:
Like this, as soon as it would be detected, by a bacterium, the bacterium would re-create some X, and the quorum sensing would work, as we would have this evolution of X:
Thanks to the quorum sensing if we detect X, we can easily measure it.
Now, we had a last problem: the false positives. Indeed, we have a detector, so we don’t want to have a signal if there is nothing to detect. Thus, we decided to add a classic feed forward loop, because it is known to reduce the false positives. Finally, we got our system:
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