A group of civil and environmental engineering graduate students at the University of Wisconsin-Madison is designing an affordable, easy-to-use test that will allow residents to identify lead in their tap water.
For the students, it’s literally a golden opportunity to make a big difference in human health: Their system—a color-changing solution that detects lead in tap water—uses gold nanorods attached to silica nanoparticles.
The solution turns from a wine-red color to colorless when lead is present. PhD student Hanwei Wang says that’s due to an effect called “localized surface plasmon resonance.” For gold, that means the electrons in nanoparticles—which are smaller than a wave of visible light—resonate with light waves and produce different shades depending on the nanoparticles’ size and shape.
“When lead is present, there’s a chemical reaction happening that etches the gold nanorods, shortening them,” Wang says. “That changes the color of the water with the solution in it. The higher the concentration of lead, the lighter the water sample’s color becomes.”
In fact, in the team’s experiments lead turns the red solution clear. The students have used colorimetric sensing, a form of spectroscopy, to evaluate the test results.
Now the students will work on calibrating the solution. They’ve used pure water for their experiments so far, but Wang notes that tap water isn’t only H2O—especially in parts of the Midwest that have hard water with high mineral content.
These vials show the solution Haoran Wei’s research group is using for lead testing. Red, like on the left, means no lead is present, and it turns colorless when lead triggers a chemical reaction. Photo: Joel Hallberg.
“The challenge is that mineral ions can cause nanoparticles to aggregate, or clump together, and the sensor won’t work,” Wang says. “With the design of our gold nanorods, the silica nanoparticles attached to gold nanorods can prevent them from aggregating, even in the mineral-rich tap water like we have in Madison. So we’ve already proved the stability of our sensor in tap water, but we need to keep testing for additional quantitative analysis.”
When that work is done, they’ll pair it with a smartphone app so that people can easily use it at home. “We’ve been thinking about how we can develop a sensor using just tap water with a sensing element,” UW-Madison civil and environmental engineering assistant professor Haoran Wei says. “There’s some color change in the sensing element, and we can develop an algorithm to analyze the color change. That means a user could take a photo with the smartphone, and then use the app for analysis.”
Because the project is in its early phases—it will run through summer 2026—the team is still working on the specifics—for example, how certain aspects of the smartphone app might work. So for now, says Wei—an expert in detecting contaminants in water, and the students’ advisor—it’s primarily a proof of concept.
The project is funded through the U.S. Environmental Protection Agency’s People, Prosperity, and the Planet (P3) Program, which is a competition that supports student teams across the United States who are working on ideas for a more sustainable future. It’s one of many ongoing efforts to combat the lingering effects of lead pipes across the country. Though lead pipes were banned across the United States in the 1980s, many places with older construction still rely on them to deliver drinking water. Lead is a potent neurotoxin and can cause significant damage to the brain and nervous system, as well as other parts of the body.
“Unfortunately, those old pipes sometimes release lead ions into the water, especially when the source water changes,” Wei says. “That can make the chemistry change, like in Flint, Michigan, when they changed the water source to the Flint River. That led to corrosion in the pipes, which released lead into the tap water.”
For Wei’s students, who are also studying high lead levels in clusters in major cities and how that impacts local communities, the project is a chance to be a part of a solution for a problem that has lasted for decades.
Wang sees it as a way to empower ordinary citizens to get information that might otherwise be difficult to obtain. “It can be difficult to even understand how serious the situation is, because the conventional, gold-standard method for lead analysis is mass spectroscopy. It’s time-consuming and requires trained personnel, so it’s expensive. But we want to make it easier so that if someone is interested in finding out how much lead is in their water, they can just do it in their home.”
Featured image caption: Civil and environmental engineering assistant professor Haoran Wei, left, and PhD student Hanwei Wang work in a lab on a solution that they’ll use as part of a project to develop a low-cost, at-home method to detect lead in drinking water. Photo: Joel Hallberg.