We've discussed the problem of fertilizer use in Thailand before. Not knowing the nutrient content of the soil you are farming generally leads to over-fertilizing your fields, wasting money and having a negative impact on the health of your plants. It also cultivates an unhealthy over-dependency on large chemical fertilizer companies. To fix this, networks have begun offering "soil clinics" to help test soil for nitrogen, phosphorous, and potassium content (NPK) and offering recommendations on how much and what type of fertilizer to use.
The kits used to test the soil cost 5,000 Thai Baht and are good for only 60 tests. The test requires multiple steps, involves many chemicals and is a bit cumbersome. Well trained staff are able to process hundreds of soil samples using multiple test kits in a single day, but could there be an easier way? Would it be possible to develop a handheld biosensor to measure NPK? Could a sensor post even give real-time NPK readings? And could all of this be done with the aid of synthetic biology?
Imagine three strains of E. coli bacteria each designed to detect NPK respectively, then admit light by incorporating genes from fireflies involved in bioluminescence. Creating biosensors using engineered E. coli bacteria using bioluminescence as an indicator is already commonly done for many projects seen at MIT's annual iGEM competition. Cambridge's iGEM team even created an open source device that could quantify the amount of light emitted so you could not only detect the presence of a certain element, but also detect how much was present.
We'd like to put all of this together to create an NPK biosensor suite. There's probably a lot of problems that have to be overcome, and lots of questions that need to be answered, like how many tests could you perform and how would you recharge the handheld device of bacteria after a test is performed? How long would it take to perform a test and get answers? How accurate would it be?
Whether or not a device can be made now is only part of the point of pursuing this. By pursuing practical projects using the tools of synthetic biology, the groundwork can be laid now for the future when tools and practical solutions are easier to obtain. If an NPK sensor can't be made now, surely it will be within reach in the future, but only if we keep up with developments being made in the fields most likely to produce such solutions.
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