Method uses synthetic biology to detect dangerous fluoride concentrations in drinking water

Synthetic biologists at Northwestern University have developed a simple, inexpensive new test that can detect dangerous levels of fluoride in drinking water.

The system costs only pennies and only takes a drop and a sip: drop a tiny drop of water into a prepared test tube, rock the tube once to mix and wait. If the water turns yellow, there is an excessive amount of fluoride that exceeds the EPA’s most stringent regulatory standards.

This method is very different from current tests, which cost hundreds of dollars and which often require scientific expertise to apply.

Researchers tested the system both in the laboratory at Northwestern and in the field in Costa Rica, where fluoride is naturally abundant near the Irazu volcano. When ingested in large amounts over a long period of time, fluoride can cause skeletal fluorosis, a painful condition that hardens bones and joints.

Americans tend to think of the health benefits of small doses of fluoride that strengthen teeth. But elsewhere in the world, particularly in parts of Africa, Asia, and Central America, fluoride occurs naturally in amounts that are dangerous to consume.

“In the United States, we hear about fluoride all the time because it’s found in toothpaste and city water supplies,” said Julius Lucks of Northwestern, who led the project. “It makes calcium fluoride, which is very hard, and thus strengthens our tooth enamel. But above a certain level, fluoride also hardens the joints. In the US this is mostly not an issue, but in other countries it can be a debilitating problem if not identified and addressed. “

The research was published online in the journal ACS Synthetic Biology last week (December 13th).

Lucks is Associate Professor of Chemical and Bioengineering at the McCormick School of Engineering and a member of the Northwestern Center for Synthetic Biology. The work was carried out in collaboration with Michael Jewett, Professor of Chemical and Bioengineering at McCormick and Director of the Center for Synthetic Biology. Doctoral students Walter Thavarajah, Adam Silverman and Matthew Verosloff led the research.

Success in the field test

Fluoride is a naturally occurring element that can seep into the groundwater from the bedrock. Fluoride is also found in volcanic ash and is particularly common in regions around volcanoes.

Home to three volcanic range systems, Costa Rica seemed like a natural place to test the device in the field. Matthew Verosloff, a Ph.D. Candidate in Lucks’ laboratory, traveled to Costa Rica and took various water samples – from mud puddles, ponds and ditches.

“Every test on these field samples worked,” said Lucks. “It’s exciting that it works in the lab, but it’s much more important to know that it works in the field. We want it to be a simple, practical solution for people with the greatest needs. Our goal is to empower individuals to monitor the presence of fluoride in their own water. “

How it works

Although the device is easy to use, the prepared test tube houses an ingenious synthetic biological reaction. Lucks spent years understanding the mechanisms behind RNA folding. In his new test he uses this folding mechanism.

“RNA folds into a small bag and waits for a fluoride ion,” he explained. “The Ion fits perfectly in this pocket. When the ion shows up, the RNA expresses a gene that stains the water yellow. If the ion doesn’t show up, the RNA changes shape and stops the process. It’s literally a switch. “

According to Lucks, organisms already fulfill this function in nature. “Fluoride is toxic to bacteria,” he said. “They use RNA to detect fluoride in the cell, then they make a protein to pump it out and detoxify.”

Lucks’ system works the same way. But instead of producing a protein pump, his test produces a protein enzyme that makes a yellow pigment so people can see the results with a simple look.

The Lucks team freeze-dried the RNA reaction, which looks like a tiny cotton ball, and placed it in a test tube. In this form the reaction is safe and has a long shelf life. A small pipette accompanies the test tube. When placed in water, the pipette will take up exactly 20 microliters – just the tiny drop needed to rehydrate the reaction. From there, it takes two hours to get a result that Lucks wants to speed up in future iterations.

“We are currently limiting ourselves to testing for fluoride,” said Thavarajah, the first author of the paper. “But we’re trying to design other RNAs to meet all possible targets.”