This year we want to focus on landmine detection based on synthetic biology. We employed bacteria to detect landmines with an elaborate device. The concept of our project is to turn our bacteria into a landmine detector, so that, once the bacteria discover a landmine, it will emit fluoresce, which can trigger our designed device to transmit signal. To construct the device, we conducted a series of experiments to prove the feasibility of our concept.
Response to DNT
As the core part, we first need to demonstrate that the yqjF promoter can be activated by 2,4-Dinitrotoluene (DNT). For this purpose, we constructed a vector that contains the yqjF promoter upstream of a reporter gene, EGFP. After transforming the reporter vector into bacteria, we tested the expression of the reporter gene when the bacteria were cultured in the presence of different concentrations of DNT. As shown in Fig. 1, we could clearly detect the DNT that could induce the expression of EGFP, but the fluorescent signal was barely detectable without DNT. In addition, we also improved and stably expressed the yhaJ, a transcription factor of the yqjF promoter, and optimized the yqjF promoter. Overall, we have successfully reduced the detection threshold to 0.1 mg/L.
Fig. 1. Assay to evaluate the DNT detection threshold of the wild-type yqjF promoter.
Fig. 2. Assay to evaluate the DNT detection threshold of the yhaJ mutations.
Detecting landmines is dangerous, while it is irresponsible and unsafe to spread bacteria directly over a minefield. Therefore, we designed a device to carry the engineered bacteria and help us detect landmines in minefields, and the device can directly capture the fluorescent signals emitted by the bacteria. The bacteria are fixed inside the device and a circuit system is also installed to detect the fluorescence. Once the bacteria sense the DNT, they will emit fluorescence under the excitation light that has been installed interiorly. Then, the photoresistor in the circuit can receive the fluorescence signal through a filter and generate electrical signal that can be transmitted to our smartphone to determine landmine presence remotely. As shown in Fig. 3, in response to DNT induction, the fluorescence emitted by the engineered bacteria can be successfully detected by the photosensitive resistor. The intensity of the generated signal showed a DNT concentration-dependent manner, indicating that our device could readily detect the fluorescence signal emitted by the engineered bacteria.
Fig. 3. The effects of the EGFP expression on resistance value in response to different conditions.
Through a series of experiments, we demonstrated that the chemical signal, DNT, Can be detected by engineered bacteria and lead to the production of fluorescent. Then, the fluorescent light can be converted to electrical signal through the photoresistor installed on the circuit. The designated software would process the data and determine the location of landmines. In conclusion, we eventually proved the feasibility of the concept of our project.