New Protein-Based Sensor Detects Rare Earth Metals Utilized in Smartphones and Other Technologies

Lanthanides—the rare earth metals utilized in many technologies, including smartphones—could be detected in a more efficient and cost-effective manner with a novel protein-based sensor.

A new sensor changes its fluorescence when it binds to lanthanides (Ln), rare earth metals used in smartphones and other technologies, potentially providing a more efficient and cost-effective way to detect these elusive metals. (Image credit: Cotruvo Lab, Penn State)

When this novel sensor binds to these metals, it changes its fluorescence. The sensor was developed from a protein by Penn State researchers, who had recently described this protein and subsequently utilized it for studying the biology of bacteria that make use of lanthanides.

A study detailing the sensor was published online in the Journal of the American Chemical Society.

Lanthanides are used in a variety of current technologies, including the screens and electronics of smartphones, batteries of electric cars, satellites, and lasers. These elements are called rare earths, and they include chemical elements of atomic weight 57 to 71 on the periodic table. Rare earths are challenging and expensive to extract from the environment or from industrial samples, like waste water from mines or coal waste products. We developed a protein-based sensor that can detect tiny amounts of lanthanides in a sample, letting us know if it’s worth investing resources to extract these important metals.

Joseph Cotruvo, Jr., Study Senior Author, Assistant Professor, and Louis Martarano Career Development Professor, Department of Chemistry, Penn State University.

A fluorescent sensor used for detecting calcium was redesigned by the researchers, replacing the part of the sensor that adheres to calcium with a protein they recently found to be many million times better at sticking to lanthanides when compared to other kinds of metals. When the protein binds to lanthanides, they undergo a change in shape. These lanthanides are important for the fluorescence of the sensor to “turn on.”

The gold standard for detecting each element that is present in a sample is a mass spectrometry technique called ICP-MS,” stated Cotruvo. “This technique is very sensitive, but it requires specialized instrumentation that most labs don’t have, and it’s not cheap. The protein-based sensor that we developed allows us to detect the total amount of lanthanides in a sample. It doesn’t identify each individual element, but it can be done rapidly and inexpensively at the location of sampling.”

In addition, the team utilized the sensor to analyze the biology of certain bacterial species that use lanthanides—the bacteria from which the lanthanide-binding protein was initially found.

Previous studies had identified lanthanides in the periplasm of the bacteria. Periplasm is a space existing between membranes close to the cell exterior, but now with the help of the sensor, the researchers also identified lanthanides in the microorganism’s cytosol—the fluid filling the cell.

We found that the lightest of the lanthanides—lanthanum through neodymium on the periodic table—get into the cytosol, but the heavier ones don’t. We’re still trying to understand exactly how and why that is, but this tells us that there are proteins in the cytosol that handle lanthanides, which we didn’t know before. Understanding what is behind this high uptake selectivity could also be useful in developing new methods to separate one lanthanide from another, which is currently a very difficult problem.

Joseph Cotruvo, Jr., Study Senior Author, Assistant Professor, and Louis Martarano Career Development Professor, Department of Chemistry, Penn State University.

The bacteria use lanthanides just like how a majority of bacteria use iron, established the researchers. They secrete tiny molecules that bind firmly to the metal, and the whole complex is taken inside the cell. This shows that there are tiny molecules that probably stick to lanthanides much more firmly than the extremely selective sensor.

We hope to further study these small molecules and any proteins in the cytosol, which could end up being better at binding to lanthanides than the protein we used in the sensor. Investigating how each of these bind and interact with lanthanides may give us inspiration for how to replicate these processes when collecting lanthanides for use in current technologies.

Joseph Cotruvo, Jr., Study Senior Author, Assistant Professor, and Louis Martarano Career Development Professor, Department of Chemistry, Penn State University.

Besides Cotruvo, the research group includes Jackson Ho and Joseph Mattocks at Penn State. The Penn State Eberly College of Science Department of Chemistry and the Penn State Huck Institutes of the Life Sciences funded the study.

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