Scientists at Rice University have developed a special type of nanocrystal that can kill bacteria in water when exposed to visible light.
These tiny structures, called halide perovskite nanocrystals (HPNCs), are effective, stable, and easy to produce, making them a promising tool for water treatment and possibly even future medical applications.
This breakthrough, led by scientist Yifan Zhu and his colleagues, is detailed in the journal Nano Letters.
HPNCs are materials with unique properties that make them useful for many applications, including solar power, bioimaging, and speeding up chemical reactions using light (a process called photocatalysis).
One of their most exciting abilities is producing reactive oxygen species—molecules that destroy bacteria and other contaminants in water.
However, a major problem has been their instability, especially in water and biological fluids. These materials degrade quickly when exposed to moisture and light, limiting their use in real-world settings.
“These materials are cheap and easy to make, but they’ve always had a stability issue,” explained Jun Lou, a professor at Rice University and co-author of the study.
To tackle the stability problem, the researchers developed a new method to protect the HPNCs without affecting their ability to work.
They coated the nanocrystals with two layers of silicon dioxide (the main ingredient in glass). Silicon dioxide is transparent, allowing light to pass through, but it also protects the nanocrystals from degrading.
In early tests, using just one layer of silicon dioxide wasn’t enough. The single-layer coating only partially protected the HPNCs, and they lost more than half of their antimicrobial power within a day. Adding a thicker coating blocked the light and made the crystals less effective. The solution was a double-layer coating, designed with just the right thickness for both layers.
“Two coats are more effective than one thicker coat,” said Lou. “It’s not just about thickness—we needed a specific method to make the layers work together.”
How effective are the new HPNCs?
The researchers tested their newly coated HPNCs in water using two types of nanocrystals: one made with lead and another with bismuth. Lead-based HPNCs performed slightly better, but both types showed remarkable results under visible light. When exposed to low levels of light for six hours, the nanocrystals destroyed more than 90% of E. coli bacteria in the water.
Importantly, the double-layer coating not only protected the nanocrystals from breaking down but also limited the amount of lead leaching into the water. After four days, the amount of lead released was far below safety limits set by the World Health Organization.
Bismuth-based HPNCs were slightly less effective but avoided the use of lead entirely, making them a safer option for medical or environmental applications.
The ability to kill bacteria in water using only visible light could have far-reaching benefits, especially as antibiotic resistance becomes a growing global concern. HPNCs could help clean water in areas with limited resources or serve as a more eco-friendly alternative to chemical disinfectants.
“Removing bacteria from water is just one example of how these materials can be used,” said Zhu. “In the future, we might develop HPNCs that can target other types of contaminants or even be used in medicine.”
While the results are promising, the researchers note that more testing is needed before HPNCs can be used in real-world applications. They must undergo safety evaluations and prove their effectiveness under practical conditions, such as in large-scale water treatment systems.
However, the potential for these nanocrystals is clear. By combining cost-effectiveness, stability, and powerful antibacterial properties, HPNCs could provide innovative solutions to pressing global issues like water contamination and disease prevention.
After years of research, Lou is optimistic about the future. “We’ve invested a lot of time and effort into these materials, and now they are getting closer to becoming a reality,” he said.
Whether cleaning water, developing safer disinfectants, or creating innovative medical treatments, these nanocrystals may soon play a vital role in improving health and the environment.
