Cleanliness is the key to health
Engineers from Northwestern University have developed an inexpensive, easy-to-use portable device that can determine within a few minutes whether water is suitable for drinking. It uses powerful programmable genetic networks that mimic electronic circuits to perform a range of logical functions. For example, on the basis of DNA, researchers assembled cell-free molecules into an analog–to-digital converter (ADC) - a circuit found in almost all electronic devices. In the water quality control device, the ADC analyzes the analog input (pollutants) and generates a digital output (a visual signal to inform the user).
The device is equipped with eight small test tubes that glow green when a contaminant is detected. The number of green-burning test tubes depends on how much harmful impurities are in the sample. If only one test tube is lit, it means that the water sample is clean or has traces of contamination, and if all eight are lit, the water is heavily polluted. The researchers programmed each tube for a different threshold of contamination, one with the lowest threshold is lit constantly.
The new system is based on the work that the authors published in the journal Nature Biotechnology in July 2020. In it, they reported on ROSALIND (named after the famous chemist Rosalind Franklin and abbreviated from RNA output sensors activated by ligand induction – sensors for the output of RNA activated by ligand induction). ROSALIND is able to capture 17 different pollutants in one drop of water. If the test detected a contaminant exceeding the norm, it glowed green, giving a simple, easy-to-read result.
To improve ROSALIND, the group used the principles of non-cellular synthetic biology. The researchers extracted molecular mechanisms, including DNA, RNA and proteins, from cells, and then rearranged them to perform new tasks.
They found out how bacteria naturally feel the "taste" of molecules in their environment – this is due to the so-called "taste receptors" at the molecular level. Cell-free synthetic biology made it possible to remove these receptors from cells and place them in a test tube. Then they were given the ability to glow when in contact with certain substances.
The molecular brain
So, in the new version, called ROSALIND 2.0, the researchers added a "molecular brain" – a genetic network that allows you to perform calculations using programmable interactions between chains of nucleic acids.
The researchers sublimated this "brain" to make it resistant to storage, and placed it in test tubes. Adding a drop of water to each tube triggers a network of reactions and interactions, ultimately causing the sublimated granules to glow in the presence of a contaminant.
The researchers demonstrated that ROSALIND 2.0 can successfully determine the concentrations of zinc, an antibiotic and an industrial metabolite, and not just give a positive or negative result, which is very important.
The ultimate goal of the developers is the opportunity for ordinary users to regularly test the water at home.
Article by J.K.Jung et al. Programming cell-free biosensors with DNA strand displacement circuits is published in the journal Nature Chemical Biology.