Back in 2019, a team of researchers at Northwestern University developed a cheap testing system for the detection of fluoride levels in water. The following year, project leader Prof. Julius Lucks introduced a new system that could detect 17 different contaminants in a single drop of water, and now that setup has been updated to not only confirm contamination but also indicate concentration levels.
The original development was published in Nature Biotechnology and dubbed RNA output sensors activated by ligand induction, or ROSALIND for short. Employing cell-free synthetic biology – where the "molecular machinery" of cells (such as DNA, RNA and proteins) are removed and reprogrammed to perform new tasks – the team snipped out the parts of bacteria that enabled them to "taste things in their water" and used this mechanism to test for contaminants in water.
If one of 17 contaminants were present in the single drop of test water, the output sensors would glow green as a simple positive/negative visual gauge.
"We found out how bacteria naturally taste things in their water," said Lucks. "They do so with little molecular-level ‘taste buds.’ Cell-free synthetic biology allows us to take those little molecular taste buds out and put them into a test tube. We can then ‘re-wire’ them to produce a visual signal. It glows to let the user quickly and easily see if there’s a contaminant in the water."
Now the research team says that it's managed to add a kind of "molecular brain" logic circuit to the latest iteration of ROSALIND. The setup still uses the "molecular taste buds" to detect contamination in a sample, but each of the freeze-dried pellets dropped in the array of eight small test tubes was reprogrammed to have different sensitivity to contaminants.
So, if only the test tube to the left of the array glowed green then the sample concentration was low. If all eight test tubes reacted to the sample, then "there is a big problem." The setup has so far successfully indicated levels of zinc, an antibiotic and an industrial metabolite in field tests, taking minutes to deliver the results.
"After we introduced ROSALIND, people said they wanted a platform that could also give concentration amounts," explained Lucks. "Different contaminants at different levels require different strategies. If you have a low level of lead in your water, for example, then you might be able to tolerate it by flushing your water lines ahead of using them. But if you have high levels, then you need to stop drinking your water immediately and replace your water line."
The end goal of the project is to produce an inexpensive hand-held device that will allow folks to test their own drinking water, on the spot and continuously monitor the water source over time.
A paper on the development of ROSALIND 2.0 has been published in the journal Nature Chemical Biology.
Source: Northwestern University
