A protein-based sensor developed by the researchers at the Pennsylvania State University promises to make detection of valuable rare earth metals easier.

In a new paper, a team of researchers from Pennsylvania State University described a new protein-based sensor that changes its fluorescence as it binds to the metal. The method is based on an existing fluorescent sensor used to detect calcium.

The researchers said that their protein-based sensor offers an efficient and cost-effective way to find lanthanides, the rare earth metals often found in smartphones and other consumer electronics.

The study appears in the Journal of the American Chemical Society.

A Lanthanide Sensor

To create the sensor, the researchers reengineered the fluorescent sensor used to find calcium by removing the substance that binds to the calcium and switching it with the a newly discovered protein that binds with lanthanides. They said that the protein is a "several million times better at binding to lanthanides than other metals."

When the protein binds to the lanthanide, it changes its shape that switches on the fluorescence of the sensor.

"The protein-based sensor that we developed allows us to detect the total amount of lanthanides in a sample," explained Joseph Cortruvo Jr., a professor at Pennsylvania State University and the senior author of the study. "It doesn't identify each individual element, but it can be done rapidly and inexpensively at the location of sampling."

Studying Lanthanides In Bacteria

The researchers also used the new sensor to study the bacteria known to use lanthanides. Previous experiments found traces of the rare earth metal in the periplasm of the bacteria, but the new research also confirmed the presence of lanthanides in the cytosol of the organism.

"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," explained Cortruvo. "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."

Moreover, the study revealed that the bacteria secrete small molecules that bind and take in lanthanide. The process is similar to how other bacteria take in iron.

Investigating the bacteria could lead to the development of new methods of collecting lanthanides and separating one lanthanide from another.

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