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 engineered two gas induced systems in E.coli, such that our cells can either detect acetaldehyde or xylene, both being toxic substances found in cigarette smoke. Upon binding of acetaldehyde to AlcR, AlcR acts as an inhibitor of gene transcription. Similarly, upon binding to xylene, XylR is acting as a trainscriptional activator. Thus, acetaldehyde or xylene act as the input for our synthetic signal transduction and processing device. With a number of inhibitors and activators, our circuit gives rise to a GFP output upon sensing acetaldehyde or xylene in a certain, upper- and lower-bounded range of concentration (band-pass filter).

The SmoColis, our genetically engineered cells, are cultivated in a microfluidic channel. Acetaldehyde or xylene enter the channel at one end by diffusion from a sample medium, and are degraded inside the channel by the SmoColi cells, such that a concentration gradient is established. Thus, the cells are exposed to a spatially varying concentration of acetaldehyde or xylene.

Since our cells only produce fluorescence proteins when exposed to a certain concentration range of acetaldehyde or xylene, only a few cells at the right distance from the channel entrance produce a fluorescence signal for a given concentration of acetaldehyde or xylene in the sample medium. For increasing or decreasing concentrations of the toxic molecules in the sample, the "GFP stripe" will also change its position. Thus, the distance of the stripe from the sample medium is directly correlated to the acetaldehyde or xylene concentration, which should be measured, and can be used to quantify the concentration.

Furthermore, both systems act as low-pass filters which produce AHL molecules once the acetaldehyde (xylene) 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 sample medium is at the left). As the stripe moves through the channel, AHL is always produced to its right and flows along in the channel. However, as soon as the stripe moves to the end of the channel, no more cells produce AHL. The absence of AHL then triggers RFP production by the entire culture.

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