Hydrogel encapsulation:

First, we are encapsulating the biosensor to contain its spread and protect it during deployment. The hydrogel capsule is made of sodium alginate crosslinked in CaCl2. When created, the gel capsule will have 5–50 nanometer pores [1], allowing for the exchange of metal ions between the environment and the capsule’s matrix solution. The E. coli bacteria will not escape the capsule due to the nanoscale pores, thus preventing horizontal gene transfer. Gene transfer could increase environmental threats after spreading antibiotic-resistant genes to other wild species. Currently, we have tested and validated that the cells in the hydrogels are viable after five days as documented on the Experiment and Results page. The next step is to validate that the hydrogels prevent the bacteria from escaping, as postulated by literature [1][2].

Agarose Gel Cast:

Our robust bacterial containment strategy relies on a 1% agarose gel cylinder measuring about 100nm in diameter, creating a formidable barrier. This gel's size advantage over the bacteria, which are only 0.5µm in radius [2], ensures their confinement. Moreover, the agarose gel acts as a semi-permeable membrane, allowing metal ions to pass through while effectively blocking the bacteria's escape. Importantly, this system aligns with our commitment to environmental sustainability, as agarose is a biodegradable and eco-friendly material. We have further bolstered our confidence in this strategy through testing, consistently demonstrating its efficacy as shown in our hardware section. Our containment approach combines size advantage, semi-permeability, eco-friendliness, and some empirical evidence to provide a robust and convincing safeguard against bacterial escape while upholding environmental values.

: Agarose gel cast mould

As a further precautionary measure, after the removing the biosensor from the hole in the ground, shine UV light into the hole for a few minutes to kill any bacteria that might have escaped into the environment. This provides an all-round safety measure for our project.

UV kill switch:

Our final security layer involves the incorporation of a UV promoter that triggers the production of autolytic enzymes within the bacteria. In case of any escape beyond the previous containment measures, exposure to UV radiation will lead to the complete self-destruction of the organisms. Even in cases of inadequate UV exposure, the UV-induced promoter ensures the production of autolytic enzymes, effectively eliminating any stray engineered organisms. The UV kill switch has been integrated into the various sensing modules as shown in the genetic circuits on the Parts page.