(From left) Purdue University doctoral student Derek Schwanz, professor Shriram Ramanathan and postdoctoral research associate Zhen Zhang have led work to develop a material that mimics a shark's ‘sixth sense’. Photo: Purdue University image/Marshall Farthing.
(From left) Purdue University doctoral student Derek Schwanz, professor Shriram Ramanathan and postdoctoral research associate Zhen Zhang have led work to develop a material that mimics a shark's ‘sixth sense’. Photo: Purdue University image/Marshall Farthing.

A ‘quantum material’ that mimics a shark's ability to detect the minute electric fields of small prey has been shown to perform well in ocean-like conditions, suggesting potential applications ranging from defense to marine biology.

The material maintains its functional stability and does not corrode after being immersed in saltwater, a prerequisite for ocean sensing. Surprisingly, it also functions well in the cold, ambient temperatures typical of seawater, said Shriram Ramanathan, a professor of materials engineering at Purdue University.

Such a technology might be used to study ocean organisms and ecosystems, and to monitor the movement of ships for military and commercial maritime applications.

"So, it has potentially very broad interest in many disciplines," said Ramanathan, who led the research to develop the sensor, working with a team that included Purdue postdoctoral research associate Zhen Zhang and graduate student Derek Schwanz.

Their findings are detailed in a paper in Nature. The paper's lead authors are Zhang and Schwanz, working with colleagues at Argonne National Laboratory, Rutgers University, the US National Institute of Standards and Technology (NIST), the Massachusetts Institute of Technology, the Canadian Light Source at the University of Saskatchewan, Columbia University and the University of Massachusetts.

The new sensor was inspired by an organ near a shark's mouth called the ampullae of Lorenzini, which is capable of detecting small electric fields generated by prey animals. "This organ is able to interact with its environment by exchanging ions from seawater, imparting the so-called sixth sense to sharks," Zhang said.

The organ contains a jelly that conducts ions from seawater to a specialized membrane located at the bottom of the ampulla. Sensing cells in the membrane allow the shark to detect the bioelectric fields emitted by prey fish.

The new sensor is made of a material called samarium nickelate, which is a quantum material, meaning its performance taps into quantum mechanical effects. Samarium nickelate belongs to a class of quantum materials called strongly correlated electron systems, which have exotic electronic and magnetic properties. Because this material can conduct protons very quickly, the researchers wondered whether they might use it to develop a sensor that mimics the shark's organ.

"We have been working on this for a few years," Ramanathan said. "We show that these sensors can detect electrical potentials well below 1 volt, on the order of millivolts, which is comparable to electric potentials emanated by marine organisms. The material is very sensitive. We calculated the detection distance of our device and find a similar length scale to what has been reported for electroreceptors in sharks."

The quantum effect causes the material to undergo a dramatic ‘phase change’ from a conductor to an insulator, allowing it to act as a sensitive detector. The material also exchanges mass with the environment, as protons from the water move into the material and then return to the water, going back and forth.

"Having a material like that is very powerful," Schwanz said.

In contrast, metals such as aluminium immediately form an oxide coating when placed in seawater. This reaction protects against corrosion but prevents further interaction with the environment.

"Here, we start with the oxide material and we are able to maintain its functionality, which is very rare," Ramanathan said. The material also changes optical properties, becoming more transparent as it becomes more insulating.

"If the material transmits light differently, then you can use light as a probe to study the property of the material and that is very powerful. Now you have multiple ways to study a material, electrically and optically."

The researchers tested the material by immersing it in simulated ocean water environments designed to cover the wide range of temperatures and pHs found in the Earth's oceans. In future work, they plan to test the devices in real oceans instead, and may team up with biologists to apply the technology to broader studies.

A technique called neutron reflectometry was performed at NIST. Adding protons to the crystal lattice of the quantum material causes the lattice to swell slightly. Shining a neutron beam on the material allows researchers to detect this swelling and determine that the protons moved into the material.

"Neutrons are very sensitive to hydrogen, making neutron reflectometry the ideal technique to determine whether or not the swelling and huge resistance change is caused by hydrogen entering the material from salt water," said Joseph Dura, a NIST physicist.

This story is adapted from material from Purdue University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.