Team:Technion Israel/Design
Introduction
FlashLab, a novel detection tool based on the chemotaxis system of E. coli
bacteria
. It utilizes chemotaxis to concentrate bacteria expressing a chromo-protein, this in turn, creates a visible gradient in color – detection of a target material.
FlashLab is an application of the S.Tar project. S.Tar is a platform for programmable chemotaxis which allows the user to select the material that will induce a bacterial chemotactic response. For more information please visit S.Tar page.
Using S.Tar technology, FlashLab can detect a variety of materials: hormones, amino acids, organic compounds etc.
Fig. 1: A steps scheme of the FlashLab concept: Add bacteria expressing the chemoreceptor of your choice and a chromo protein to a fluidic chip . Add the sample in question to said chip. If the sample contains the substance that is recognized by the chemoreceptor, a displacement of the bacteria will become visible. If not, then the no displacement will be seen.
Fig. 2:The geometry of a commercial fluidic chip.
The chip is open on the button part and closed with a standard microscope cover glass (0.3[mm] thick).
FlashLab setup
The setup of the device is composed of two parts, as shown below (Figure 3): a. The channel is filled with colored E. coli bacteria suspended in motility buffer. b. The sample is loaded into one of the entry slots.
Fig. 3: The chip setup.
FlashLab test
Once the sample is loaded, it diffuses into the channel. If the sample contains a repellent, the bacteria will react and move away from it as shown below:
Fig. 4: Chemotaxis reaction in the chip.
The chemotactic response will result in visible changes in the bacterial concentration throughout the chip: Very low concentration in the immediate area of the slot in which the sample was loaded, adjacent to a higher concentration of bacteria created due to the fleeing bacterial population. (right picture, figure 1:4). These changes will be visible to the naked eye, as the higher concentration of colored bacteria results in darker color (blue gradient, figures 1:3 and 1:4).
If the sample does not contain the target material, the bacteria will not react and no gradient will be formed.
For more information see mathematical model.
Results
FlashLab parts
The setup for the device is as shown in "Design and Implementation". The bacteria, UU E.coli strain with a cloned Tar-PctA receptor , was taken from a petri dish and diluted in of motility buffer. The Chemo-repellent used was of TCE in concentration of 0.02[M] while the control was motility buffer. The pictures were taken in differential of 5[min] apart.
Fig. XYZ:ABC.
After 20[min] , a noticeable color gradient is formed in the channel. on the far left, a relatively light shade. adjacent to it, an area with a darker tone and from there up to the right end of the channel, the color did not change at all. This fits the theory perfectly, as the lighter shade is caused by colored bacteria moving away from the repellent. The darker shade is the clustering of bacteria in the chemo-repellent diffusion limit. All other bacteria in the channel, were not exposed to the repellent and did not react accordingly.
==========For more information see chip experiment protocol==========
Outlook
FlashLab has advatages as a detection tool:
- Cheap The only major cost is the fluidic chip and one costs about 15$ and can be reuse multible times.
- Fast as shown in the expermints, it takes about 30 minutes for detection. This is faster then most other bacterial detection (based on transecription and translation) and most laboratory tests (HPLC).
- Verstile The S.tar system enable this device to detect verity of materials: hormones, amino acids, PCE etc.
- Senstive: Bacteria can sense extrimly small traces of target material.
- Easy to use: The set up of the system is an easy, two parts process. To reuse the chip you only need to flush the channel with water and dry.
References:
1. KELLER, Evelyn F.; SEGEL, Lee A. Model for chemotaxis. Journal of theoretical biology, 1971, 30.2: 225-234.
