Water sensor quickly detects algal poison | Science News for Students

Water sensor quickly detects algal poison

This cheaper, more sensitive test could be used to scout for evidence of harmful drinking water
Nov 4, 2016 — 7:00 am EST
Algae waves

Waves at Pelee Island in Lake Erie can turn bright green during a harmful algae bloom, but chemical testing is necessary to know whether the water is toxic to people.

T. Archer, National Oceanographic and Atmospheric Administration

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

Periodically, algae in lakes and streams will encounter a food bonanza. Within days, the growth of these one-celled organisms can mushroom into what scientists refer to as a bloom. If those algae make a toxin — a poison — this may make that water unfit to drink. The problem: The algae and their poison can be invisible to the human eye. But not to a new sensor. This new device can detect amazingly small quantities of the algal poison quickly and at low cost.

This means drinking-water officials may be able to warn people of risks before any signs of a sickening bloom become visible. They also can get to work treating the water to remove the poison before it reaches danger levels.

It’s a solution to a very real problem.

Not all algal blooms release toxins. But those that do can endanger human health. Indeed, such toxins made the drinking water supplies for one Ohio community too toxic to drink during part of 2013 and then for another city one year after that. Local officials told people to drink only bottled water for a few days. Events like these show why water-supply systems need to regularly test their water.

Algae hand
The bloom of toxic algae in this goopy green water forced officials to shut down a local drinking-water plant for a short time in 2013. Another toxic bloom occurred in 2014.
Jeff Reutter/Stone Laboratory

Today’s tests are not only expensive but also take hours to yield a result. The new low-cost sensor can cut that wait time down to just a few minutes. This device targets the same toxins — a group known as microcystins (My-kroh-SYS-tins) — that had poisoned the Ohio water supplies. One of the most potent of these poisons is microcystin-LR. It can cause rashes, headaches, diarrhea and liver damage. It some cases, it can kill people.

A guideline from the World Health Organization warns that people should not drink water containing more than 1 microgram of microcystin-LR per liter (µg/l). That’s one part per billion. U.S. Environmental Protection Agency guidelines recommend not drinking water with 1.6 µg/l or more of those poisons. Young children should get even less, EPA says — no more than 0.3 µg/l. 

Yet higher levels do show up. Levels above 1 µg/l forced the city of Toledo, Ohio, to shut down its water supplies for two days in 2014. People in Carroll Township, Ohio, were told to avoid drinking their tap water for two days in 2013. The sooner cities can treat toxin-tainted water, the fewer people will face a risk of poisoning.

But the toxin doesn’t only show up in the Great Lakes or other sources of freshwater.

Raphael Kudela is a biologist at the University of California Santa Cruz. He and his colleagues recently found microcystin in ocean-dwelling mussels. They had collected these shellfish in California’s San Francisco Bay. The poison could have come from streams that flow into the bay.

Toxin levels in the mussels were lower than California's suggested limits. Still, the state is in a  major drought. If heavy rains were to occur, higher microcystin levels could enter the bay, the researchers say. Their new study on bay mussels tainted with the toxin appears in the November 2016 issue of Harmful Algae.

Wu Lu is an electrical engineer at Ohio State University in Columbus. “What you would like to have is testing in real time,” he says. By that he means engineers would like results in seconds to minutes, not hours. And that’s what his new sensor does. It can tell if microcystin is in liquids at levels as low as one part per trillion.

Lu and his graduate student, Paul Bertani, described their work on the new sensor at a meeting on September 15 in Toledo. It was hosted by Ohio Sea Grant and Ohio State University. (Sea Grant programs at universities in 33 states do research and outreach in cooperation with the National Oceanic and Atmospheric Administration.)

Teaming up

The new sensor took lots of teamwork. Jiyoung Lee, a microbiologist at Ohio State, is a co-author of the new research. She is among those scientists anxious to know more about how harmful algal blooms affect people’s health. She also wants to keep microcystin out of drinking water. “For toxin detection,” she notes, “sensitivity, accuracy and speed are the key.”

Lee knew of Lu’s work on biosensors. These are devices that use enzymes or antibodies to detect chemical residues left behind by living organisms. Lu’s sensors hunt for chemicals that are electrically charged (called ions) within some solution, such as water. As it happens, microcystin molecules in water do have a small positive charge.

Biosensor schematic
If microcystin (red) is in water (blue), antibodies (blue Y’s) on the top layer of the biosensor will bind the poison. This will show up as an increase in the electrical current able to flow through the device.
P. Bertani et al., Ohio State University

“I thought his biosensor would work for this toxin monitoring,” Lee says. Working together, her group and Lu’s created the new sensor.

It has two layers. You might think of it as a layered gelatin or a two-layered fudge. The bottom layer is gallium nitride. The top is aluminum gallium nitride. Both materials are semiconductors. That means they may, at times, relay an electrical current.

The sensor’s top layer is covered with antibodies. They bind any microcystin they encounter. So if a liquid flows over the sensor, its antibodies will latch onto the microcystins.

“In our tests, we used a 15-minute wait time,” says Bertani. Then the group put the sensor into a machine, which passes an electric current through the sensor. The machine measures the current in a process that’s a bit like the blood-sugar testers used by people with diabetes, Bertani explains.

When no microcystin is present, the current will flow at a certain low level. But if the water contains the toxin, the current increases. How much it rises will be a gauge of how much toxin was present.

Super sensitive

“The devices are highly sensitive,” Lu notes. They can detect as little as one part per trillion of microcystin in a liquid. Water-treatment plants could use the sensors to monitor levels of those toxins and how they change in response to weather or water treatment. The devices might even let researchers like Lee look for low levels of microcystins in someone’s blood. If it works, health officials could use the system to get a better idea of how algal blooms are linked to symptoms in people who drank tainted water.

Eventually, Lu’s team expects each sensor to cost only about $1 to $2. The machine to read those the sensors might cost another $1,000 or so. That equipment could make microcystin testing much easier (in part because the equipment would be portable).

Biosensor
This tiny chip can detect minute amounts of microcystin in water — as little as one part per trillion.
P. Bertani et al., Ohio State University

The sensor “looks like it’s going to be an inexpensive, very rapid way to measure microcystin concentration,” says Glenn Lipscomb. He’s a chemical engineer at the University of Toledo who did not work on the devices.

One of Lipscomb’s projects tests filters that can be sold to help homeowners remove microcystin from tainted tap water. His team wants to test and compare how well those filters work in practice. The new sensor would make the chemical tests for his project quicker and cheaper, he says. Some people might even want to use such sensors to test their home’s water, he suspects.

The biosensor might also have been useful for Kudela’s study on shellfish in San Francisco Bay. His team used a method called LCMS. That stands for liquid chromatography (KRO-mah-TOG-rah-fee) mass spectrometry (Spek-TRAH-muh-tree). LCMS is “very accurate, but probably not as sensitive as the biosensor,” Kudela says. It also takes longer to get results.   

If the test were cheap enough, commercial shellfish harvesters might use it to test local waters, he notes. High readings could provide early warning of a potential problem. The biosensor might be even more useful if it could be adapted to test shellfish tissue, Kudela says. But doing that would depend on how the tissue samples were prepared, said Young at Ohio State.

Lu’s team is now working to see how high a toxin level their sensor can measure. The engineers also are working to better calibrate those sensors. That means they’re looking to match a particular level of electrical conductivity with a particular concentration of toxin in the water.

So far, the Ohio State team has been testing the sensor in the lab. They know just how much microcystin is in the water in their tests. Out in lakes or water-treatment plants, however, other organisms and chemicals might confuse the sensor. The team will probably want to make sure those things don’t alter its sensor’s accuracy, Lipscomb says.

For now, he is hopeful, as is Lu, Lee and others. This project shows the value of researchers from different fields of science or engineering working together to solve a problem, says Lee. “It’s team science.”

Note: This story was changed on 11/7 to correct the definition for microgram per liter.

Power Words

(for more about Power Words, click here)

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

bloom     (in microbiology) The rapid and largely uncontrolled growth of a species, such as algae in waterways enriched with nutrients.

chemical     A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.

chemical engineer     A researcher who uses chemistry to solve problems related to the production of food, fuel, medicines and many other products.

concentration     (in chemistry) A measurement of how much of one substance has been dissolved into another.

current     (in electricity) The flow of electricity or the amount of electricity moving through some point over a particular period of time.

diabetes     A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).

electrical conductivity     The ability of some substance (such as water or metals) to transport an electrical charge or current.

electrical engineer     An engineer who designs, builds or analyzes electrical equipment.

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

electric current     A flow of charge, called electricity, usually from the movement of negatively charged particles, called electrons.

engineering     The field of research that uses math and science to solve practical problems.

Environmental Protection Agency (or EPA)      An agency of the U.S. government that is charged with helping create a cleaner, safer and healthier environment in the United States. Created on Dec. 2, 1970, it reviews data on the possible toxicity of new chemicals (other than food or drugs, which are regulated by other agencies) before they are approved for sale and use. Where such chemicals may be toxic, it sets rules on how much may be used and where it may be used. It also sets limits on the release of pollution into the air, water or soil.

enzymes   Molecules made by living things to speed up chemical reactions.

field      A term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.

filter     (in chemistry and environmental science) A device which allows some materials to pass through but not others, based on their size or some other feature. (in physics) A screen, plate or layer of a substance that absorbs light or other radiation or selectively prevents the transmission of some of its components.

gauge     An device to measure the size or volume of something. For instance, tide gauges track the ever-changing height of coastal water levels throughout the day. Or any system or event that can be used to estimate the size or magnitude of something else.

graduate student     Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

ion     An atom or molecule with an electric charge due to the loss or gain of one or more electrons.

liver     An organ of the body of animals with backbones that performs a number of important functions. It can store fat and sugar as energy, breakdown harmful substances for excretion by the body, and secrete bile, a greenish fluid released into the gut, where it helps digest fats and neutralize acids.

microbe     Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiology     The study of microorganisms, principally bacteria, fungi and viruses. Scientists who study microbes and the infections they can cause or ways that they can interact with their environment are known as microbiologists.

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).

National Oceanic and Atmospheric Administration (or NOAA)      A science agency of the U.S. Department of Commerce. Initially established in 1807 under another name (The Survey of the Coast), this agency focuses on understanding and preserving ocean resources, including fisheries, protecting marine mammals (from seals to whales), studying the seafloor and probing the upper atmosphere.

potent     An adjective for something (like a germ, poison, drug or acid) that is very strong or powerful.

residue     A remnant or material that is left behind after something has been removed. For instance, residues of paint may remain behind after someone attempts to sand a piece of wood; or sticky residues of adhesive tape may remain on the skin after a bandage is removed; or residues of chemicals may remain in the blood after exposure to a pollutant.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.

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.

taint        To contaminate.

tin     A metallic element with the atomic number 50.

toxic     Poisonous or able to harm or kill cells, tissues or whole organisms. The measure of risk posed by such a poison is its toxicity.

toxin     A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.

trillion     A number representing a million million — or 1,000,000,000,000 — of something.

weather     Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

World Health Organization     An agency of the United Nations, established in 1948, to promote health and to control communicable diseases. It is based in Geneva, Switzerland. The United Nations relies on the WHO for providing international leadership on global health matters. This organization also helps shape the research agenda.

NGSS: 

  • MS-LS1-5
  • MS-LS2-1
  • MS-LS2-3
  • MS-LS2-4
  • MS-ESS3-2
  • MS-ETS1-4
  • HS-PS1-1
  • HS-PS4-4
  • HS-LS2-1
  • HS-LS2-4
  • HS-LS2-6

Citation

Meeting: P. Bertani et al. GaN-based field effect transistor sensors for detection of microcystin-LR in water. Understanding algal blooms: State of the Science Conference, September 15, 2016. Toledo, Ohio.

Journal: C. Gibble et al. Evidence of freshwater algal toxins in marine shellfish: Implications for human and aquatic health. Harmful Algae. Vol. 59, November 2016, p. 59. doi: 10.1016/j.hal.2016.09.007.