New sensor detects rare metals used in smartphones

A new protein-based sensor that changes its fluorescence when it binds to these metals could be a more efficient and cost-effective way to detect lanthanides, rare earth metals used in smartphones and other technologies. A team of Penn State researchers developed the sensor from a recently described protein and then used it to explore the biology of bacteria that use lanthanides. A study describing the sensor appears online in the Journal of the American Chemical Society.

"Lanthanides are used in a variety of current technologies, including screens and electronics for smartphones, electric car batteries, satellites and lasers," said Joseph Cotruvo, Jr., assistant professor and professor. from chemistry to Louis Martarano's career development department at Penn State and lead author of the study. "These elements are called rare earths and include chemical elements of atomic weight from 57 to 71 in the periodic table.Rare earth is difficult and expensive to extract from the environment or from samples. industrial, such as mine wastewater or coal waste.We developed a protein-based sensor capable of detecting minute amounts of lanthanides in a sample, thus allowing us to know how well it is worthwhile. 39, invest resources to extract these important metals. "

The research team has redesigned a fluorescent sensor used to detect calcium, replacing the portion of the sensor that binds to calcium with a newly discovered protein that binds lanthanides several million times better than other metals. . The protein undergoes a change of shape when it binds to the lanthanides, which is essential for the fluorescence of the sensor to "turn on".

"The ideal method for detecting each element present in a sample is a mass spectrometry technique called ICP-MS," said Cotruvo. "This technique is very sensitive, but it requires specialized instrumentation that most laboratories do not have, and it's not expensive." The protein-based sensor that we developed allows us to detect the total amount of lanthanides in a sample.identify each individual element, but this can be done quickly and inexpensively at the place of sampling. "

The research team also used the sensor to study the biology of a type of bacterium that uses lanthanides – the bacterium behind the discovery of the lanthanide binding protein. Previous studies had detected lanthanides in the periplasm of the bacteria – a space located between the membranes near the outside of the cell – but, with the help of the sensor, the team also detected lanthanides in the cytosol of the bacteria – the fluid that fills the cell.

"We found that the lighter lanthanides – lanthanum by neodymium on the periodic table – enter the cytosol, but not the heaviest," said Cotruvo. "We are still trying to understand exactly how and why, but it tells us that there are proteins in the cytosol that handle lanthanides, which we did not know before." Understanding what lies behind this high selectivity could also be useful to develop new methods to separate lanthanides from others, which is currently a very difficult problem. "

The team also determined that bacteria absorb lanthanides, much like many bacteria absorb iron; they secrete small molecules that bind tightly to the metal and the entire complex is introduced into the cell. This reveals that there are small molecules that can bind to lanthanides even more closely than the highly selective sensor.

"We hope to further investigate these small molecules and all cytosol proteins, which could ultimately bind better to lanthanides than the protein we used in the sensor," Cotruvo said. "The study of how each of these elements binds and interacts with lanthanides can give us an inspiration to replicate these processes when collecting lanthanides for use in current technologies."

In addition to Cotruvo, the research team includes Joseph Mattocks and Jackson Ho at Penn State.