Our project focuses on the detection of cigarette smoke in the air. Our SmoColi cells detect two different toxic substances contained in cigarette smoke, acetaldehyde and xylene, and display their concentrations visually by display of a spatially varying, fluorescent light output signal. Depending on the interpretation, SmoColi can thus either serve as a health assistant device, warning of dangerous smoke concentrations in the air, or as a “partymeter”, monitoring the progress of a certain party (under the creative assumption that the progress of the party is measured by the amount of smoke in the air).

Project description

Cigarette smoke detector

We engineer a gas induced system in E.coli such that our cells can detect acetaldehyde, which is a substance found in cigarette smoke. Upon binding of acetaldehyde to AlcR, AlcR acts as an inhibitor of gene transcription. This is where our genetically engineered circuit starts. With a number of inhibitors and activators, our circuit gives rise to a GFP output upon sensing acetaldehyde in a certain range of concentration. Our circuit then acts as an acetaldehyde band-pass filter.

Our genetically engineered cells are cultivated in a microfluidic channel and are constantly supplied with a flow of growth medium containing acetaldehyde. They are designed to degrade acetaldehyde, such that a concentration gradient is created along the flow direction within the channel.

Since our cells detect only a certain concentration range of acetaldehyde, as the gradient moves through the channel with varying initial concentration, the GFP stripe that certain cells produce will also "move along". Furthermore, our system acts as a low-pass filter which produces AHL molecules once the acetaldehyde concentration is below a certain threshold (the lower threshold for the previously described band-pass filter). Thus, cells that are on the right side of the GFP stripe will produce AHL (assuming the flow direction is from left to right).

As the stripe moves through the channel, AHL is always produced to its right and flows along in the channel. Moreover, we feed back some of the produced AHL to the channel again, by a "recycling channel", so that even the cells to the left of the stripe are supplied with AHL. As soon as the stripe moves to the end of the channel, no more cells produce AHL and the recycling ceases after a while. The absence of AHL then triggers RFP production by the entire culture.

Thus, with increasing acetaldehyde concentration in our channel one can see a moving green stripe. Once it reaches the end of the channel, the entire culture turns red.