Our Sensor

The goal of our project is to design a biosensor to rapidly identify cattle known as super shedders. Super shedders are cattle that excrete extremely large numbers of E.coli O157:H7 a subgroup of E. coli referred to as Enterohemorrhagic E. coli (EHEC). EHEC organisms produce a toxin called Shiga toxin or verotoxin. This toxin binds to blood cells and lyses them resulting in hemolytic-uremic syndrome (HUS) in humans and can be deadly.

Supershedders excrete E. coli O157:H7 in the range of 10 ⁷ to 10 ¹⁰ exceeding normal cattle by 3-6 logs and can contaminate other cattles in the same holding penn as well as the meat downstream. Supershedders are thought to be the reason for 95% of the E. coli O157:H7 contamination in the industry.

We are building a DNA-based biosensor that specifically detects the gene called stx2 that is common to all EHEC organisms. Our device will be useful for the detection of not only the O157:H7 strain of E.coli but for the other EHEC strains as well. Click on the components below to learn more about their design and function. View our animation below to see how the system would actually work!

The FerriTALE System:

As seen in the video above our goal is to develop a strip based assay that can alert us upon detection of pathogenic DNA sequence, namely Stx 2. We will immobilize a TALE-Ferritin scaffold (a FerriTALE!) to a nitrocellulose strip. The TALE protein that has been immoblized will bind to a unique oligonucleotide sequence that is approximately 18-20 base pairs in size on the Stx 2 gene. This immobile component of our system (Figure 1) will effectively capture our target DNA on the strip. A second TALE attached to our reporter (Prussian blue ferritin or β-lactamase) that targets a different target sequence on Stx 2 will then be run along the nitrocellulose as a mobile component. The TALE-reporter complex will only bind if the second oligo sequence is present. Following this we will add a substrate solution and in the presence of both the TALEs we will see a colour output on the strip.

TALEs are modular and can be used platform technology implying TALEs can be engineered to detect any DNA of interest. We are using TALE proteins as our sensory element. TALEs are very powerful tools since they can be engineered to bind to any 12 to 31bp sequence of DNA (source: Golden Gate TALEN and TAL Effector Kit 2.0). Therefore, by just swapping the TALEs in our PLASMID XYZ, one can detect any DNA of interest. To further ease this process, we have incorporated a KasI restriction cut site at the end of all TALEs in all the constructs. Using the KasI restriction enzyme and one of the biobrick prefix enzymes one can incorporate their own engineered TALE into the part, and use it for detecting their DNA of interest.