Circuit Design
The quest began with the search for ways to curb the problem of capturing and detecting noxious gases and harmful chemicals. The task was to make a circuit with feedback positive and negative loops for increasing the sensitivity and specificity of detection. We came up with a novel circuit that can be modified easily for detecting various pollutants. Some pollutants activate, whereas others repress, a promoter. For eg. CO activates the COOA promoter whereas Acetaldehyde represses the XylR promoter. The circuit we have designed can be used for both kinds of pollutants.
Circuit 1 and Circuit 2 represent circuits for activator and repressor type pollutants respectively.
Ciruit 1
Different pollutants with their activating circuits and respective promoters can be used to replace module 3 accordingly. Examples of pollutants acting as positive regulators include CO, Xylene, NO etc.
Ciruit 2
Different pollutants that can negatively regulate their respective promoters can replace the first part of module 3 accordingly.
The circuit can be divided into 3 parts. The bottom circuit gives a color when there is no pollutant. It
signifies the number of cells alive and and capable of forming chromoprotein. In the presence of a
pollutant, the topmost part detects the pollutant and activates the formation of a second
chromoprotein in the middle circuit. Simultaneously, it inhibits the production of the first
chromoprotein. This results in the differential color formation depending upon the concentration of
pollutant [1]. It has been documented that positive feedbacks have stabilizing effects on circuits. Also,
negative feedback loops make systems robust against alterations and noise [1].
Reference:
1. Cinquin, O., & Demongeot, J. (2002). Roles of positive and negative feedback in
biological systems. Comptes rendus biologies, 325(11), 1085-1095.
