Alpha System

The Alpha System is the preliminary design we planned for a biosensor that can detect various materials at low concentrations.
The main goal of our design is to make the bio sensor capable of detecting harmful substances at far lower concentrations than existing bio-sensors. To do this, we designed a system which produces a chain reaction resulting from the input of a single molecule. This system utilizes a Cell-to-cell communication channel called quorum sensing, to make it possible for a cell which sensed a single molecule of the material detected to “inform” the surrounding cells of the existence of this toxin, causing them to produce a signaling molecule, and then inform their neighbors and so on, creating a chain reaction.
Unlike other biosensors, our system is meant to be as versatile as possible- with a minor change at the genetic level it can detect molecule A instead of molecule B. That saves us the need to construct an entirely different detector for every dangerous material out there.
*Maybe a picture of a bun and a heavy metal frightened because of safie*
The alpha system consists of three gates:
*picture of a cell with the schemes of the three gates*
Each gate plays an important role in the detection process inside the cell, but the system as a whole is also based on communication between bacteria via quorum sensing.

Gate 1

Built and Biobricked

The goal of the first gate is to produce the quorum sensing molecule, AHL, when a material of interest is present in the bacteria's environment. As a result, this part can be replaced by any bio-sensor which uses AHL production as its output.

The construct includes a changeable promoter for the detection of the material of interest. In the example above the promoter is Ptet which is repressed by tetR; when tetracycline or its analog ATC is present, tetR is removed.
When the material is present it will get into the cell, attach to the promoter and the transcription of the LuxI gene will begin. LuxI gene encodes for an AHL synthase. AHL is a signal molecule that can diffuse freely into the cell and out.
The NheI restriction site was added to the construct so that the promoter activating the gate can be easily changed. EcoRI restriction site is found at the beginning of the prefix, and by a simple restriction reaction with the two enzymes we could take the promoter out and replace it with a different one.

But why do we want our bacteria to produce AHL molecules? How does it help us to see if a toxin or an allergen is present in our sample?
Continue reading about gate 2 and 3 to find out

Gate 2

Built and Biobricked

The gate serves as a sensitivity tuner, allowing us to control on the timing of the measurement. When we want to start our measurement we just need to add IPTG to the bacteria solution.

The gate consists of the Plac promoter and the LuxR gene. When IPTG is added to a sample containing our bacteria, LuxR gene is transcribed. LuxR is a transcriptioninal activator that binds directly to the AHL molecules, so that a LuxR-AHL complex is formed.

And what happens in our system when the complex LuxR-AHL is formed?
Read the next sections about gates 3 to find out

Gate 3

Failed to build

Gate 3 enables us to see if our material of interest is present in a random sample by producing GFP and amplifying the signal.

This construct is the final part of our alpha system. The promoter of the gate is the Plux promoter which undergoes activation when the complex LuxR-AHL dimer binds to it. If the promoter is activated we get the production of a reporter gene (GFP) and the LuxI gene.
As been said in the gate 1 section, LuxI transcription results in AHL molecules.

To conclude Alpha System is a 3 gate construct that produces GFP upon substance detection and signals other cells around to produce GFP as well:

*picture*