Electricity sensor harnesses a shark's secret weapon | Science News for Students

Electricity sensor harnesses a shark's secret weapon

This new material changes in response to tiny electric fields at sea
Apr 17, 2018 — 6:45 am EST
reef shark

Sharks have an uncanny ability to sense tiny electrical fields. It helps them home in on prey. A new electronic sensor now mimics that ability — and works in saltwater.


This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Sharks have a secret weapon in their snouts that helps them hunt prey. It's an organ that can sense faint electrical signals given off by other, delicious creatures. Now, engineers in Indiana have made a new material for electronics that mimics the shark's sensor. It even works in salt water, which is usually a harsh environment for electronics. (Drop your smartphone in the ocean, for instance, and that’s the end of the phone.)

The new device may be useful in ways from studying marine life to building new tools for submarines. It’s made from a substance called samarium nickelate, or SNO. And it can detect some of the weakest electric fields found in the sea.

Many marine animals, from tiny clams to big fish, produce electric signals. Sharks and other ocean predators, including skates and rays, sense those electric fields. They do it using organs known as ampullae (AM-puh-lay) of Lorenzini. Scientists call such tissues electroreceptors because they detect electric fields. 

The ampullae look like a line of small holes, or pores, near the mouth on a shark's snout. Those pores lead to short channels filled with a jelly-like substance. At the other end of the channels, behind the jelly, are special sensing cells. 

When a fish swims nearby that gives off an electric field, those cells send signals to the shark's brain: “Dinner!” 

The new SNO detects electricity, too. It's an example of a quantum material. That means it has electronic properties — ones that scientists can't fully explain. (These properties, called quantum effects, are due to the weird behaviors of atoms at the smallest scales.) Even though scientists don't understand exactly why a quantum material does what it does, they still can study its effects. 

The researchers described their new type of SNO in the January 2018 Nature.

This doping is a good thing

Shriram Ramanathan works at Purdue University in West Lafayette, Ind. The materials engineer led a team that designed the new sensor. SNOs have been Ramanathan’s focus for eight years. Their appeal? They act differently in different situations. At room temperature or cooler, for instance, an SNO will let some electric charge pass through. That makes it a semiconductor. But at a toasty 130° Celsius (266° Fahrenheit), it becomes a true conductor. That means it freely allows charge to flow through it. 

In 2014, Ramanathan and his team found another way to change an SNO. They added protons, which are particles with positive charges. Adding extra molecules or protons to a material is called “doping.” It made the SNO an insulator at room temperature. That means it does not let electric charges pass through. Importantly, it showed the scientists how to adjust the properties of the material. They could “tune” the material to be more or less conductive at temps below 130 °C by simply adding or removing protons. 

By tuning it in this way, the researchers can make their SNO more sharklike. In the last few years, for instance, scientists have discovered that the jelly in those shark pores is good at conducting protons. They suspect those protons make the shark more sensitive to electric fields. They do the same thing for the new SNO: Added protons make it super-sensitive. The doped SNO also works in salt water — another similarity to sharks.

quantum sensor
This small rectangle is a sensor that can detect tiny electric fields in the sea. It's made from a quantum material.
Purdue University image/Marshall Farthing

When the new SNO senses an electric field, its resistivity goes up. That means it blocks electric charges from passing through. At the same time, it becomes transparent. So an SNO in the water can reveal electric fields both by how it conducts electricity and by its appearance. 

Unlike a shark, the new material is dark and shiny. In their latest study, the researchers worked with a slice no bigger than the nail on your pinkie. They tested its sensing power using salt water samples in the lab. The SNO detected fields as weak as 4.5 microvolts, which is about the strength of a field given off by a sea snail. They soon plan to take it to sea, for more testing. 

Smart sensing

Gustau Catalán did not work on the new study. He’s a physicist at the Catalan Institute of Nanoscience and Nanotechnology in Barcelona, Spain. Catalán is an expert on perovskite nickelates, the family of materials that includes SNO. 

He's encouraged by the development of the sensor. He sees its use in the ocean as a “natural and promising” application. That's because protons make SNOs better at sensing, and protons are plentiful in the sea. “A proton is just a hydrogen atom minus an electron,” he says, and there's plenty of hydrogen in water. “That's what the 'H' stands for in 'H2O.'” 

Submarines could use SNO-based sensors to find other vessels or nearby fish. The sensors might be used to track the movements of animals, or to make other measurements in water. 

Getting SNO to sense electrical fields was challenging, Ramanathan says, and took three steps. The first was creating the material. (He estimates it took two or three years to get the recipe right.) The second was discovering that doping SNO with protons improved the material's properties. (That work took another three to four years.) Finally, his team had to figure out how to tune the material’s conductivity for particular uses. That meant finding the right way to add protons to the SNO. While testing this doped SNO, they discovered it works in salt water. 

Ramanathan still isn't done. His ultimate goal is to use SNOs to create devices that can learn in the same way the brain learns, by remembering and forgetting things. Doping SNOs, he says, is like building in memory about how to respond to something in the environment. 

He envisions SNO-based materials, such as smart windows, that can remember when to darken or lighten a room based on the light coming in from outside. 

 Indeed, he observes, “Sensing is a form of intelligence.” 

Power Words

(more about Power Words)

ampullae of Lorenzini     (singular: ampulla) Bottle-shaped sensory cells on members of the shark family (including skates and rays). Located on their snouts, these cells are filled with a jelly-like substance that is able to detect extremely tiny electrical signals, and then help relay this information to the animals’ brains. As such, each of these serves as an "electroreceptor." These cells are named for the 17th Century Italian scientist who first described them.

application     A particular use or function of something.

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

conductive     Able to carry an electric current.

conductor     (in physics and engineering) A material through which an electrical current can flow.

doping     (in electronics) The deliberate insertion of something into a crystalline or other semiconductor material. For instance, manufacturers may dope a material with electrons or protons.

electric charge     The physical property responsible for electric force; it can be negative or positive.

electric field     A region around a charged particle or object within which a force would be exerted on other charged particles or objects.

electronics     Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

engineer     A person who uses science to solve problems. As a verb, to engineer means to design a device, material or process that will solve some problem or unmet need.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

hydrogen     The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.

intelligence     The ability to collect and apply knowledge and skills.

marine     Having to do with the ocean world or environment.

materials engineering     The design of new substances, focusing on how their atomic and molecular structure affects their overall properties. Materials engineers can create new materials or gain important insights by probing existing materials. Their analyses of a material’s overall properties (such as density, strength and melting point) can lead to the creation of novel materials that are tailor-made for some new use. 

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

organ     (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that makes sense of nerve signals and a plant’s roots are organs that take in nutrients and moisture.

pore     A tiny hole in a surface. On the skin, substances such as oil, water and sweat pass through these openings.

predator     (adjective: predatory) A creature that preys on other animals for most or all of its food.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

proton     A subatomic particle that is one of the basic building blocks of the atoms that make up matter. Protons belong to the family of particles known as hadrons.

quantum     (pl. quanta) A term that refers to the smallest amount of anything, especially of energy or subatomic mass.

rays     (in biology) Members of the shark family, these kite-shaped fish species resemble a flattened shark with wide fins that resemble wings.

resistor      An electric or electronic component that works to cut the flow of electricity in a electricity in a circuit, and, at the same time, to lower the voltage.

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

semiconductor     A material that sometimes conducts electricity. Semiconductors are important parts of computer chips and certain new electronic technologies, such as light-emitting diodes.

sensor     A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.

sharks     A family of primitive fishes that rely on skeletons formed of cartilage, not bone. Like skates and rays, they belong to a group known as elasmobranchs. Then tend to grow and mature slowly and have few young. Some lay eggs, others give birth to live young.

smartphone     A cell (or mobile) phone that can perform a host of functions, including search for information on the internet.

subatomic     Anything smaller than an atom, which is the smallest bit of matter that has all the properties of whatever chemical element it is (like hydrogen, iron or calcium).

submarine     A term for beneath the oceans. (in transportation) A ship designed to move through the oceans, totally submerged. Such ships — especially those used in research — are also known as submersibles.

tissue     Made of cells, it’s any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.


Journal: Z. Zheng et al. Perovskite nickelates as electric-field sensors in salt water. Nature. Vol. 553, January 4, 2018, p. 68. doi:10.1038/nature25008.

Journal: J. Shi et al. Colossal resistance switching and band gap modulation in a perovskite nickelate by electron doping. Nature Communications. Vol. 5, published online Sept. 3, 2014. doi:10.1038/ncomms5860.

Journal: A. Sand. The function of the ampullae of Lorenzini, with some observations on the effect of temperature on sensory rhythms. Proceedings of the Royal Society B. Vol. 125, August 5, 1938. doi: 10.1098/rspb.1938.0041.