Magnets may one day cull deadly germs from blood

Tiny particles of antibody-covered iron would grab bacteria, then get mopped up by magnet
Feb 6, 2017 — 7:10 am EST
blood bacteria

In sepsis, bacteria (colored green in this illustration) can cause a deadly infection. A newly proposed method might pull the invaders out of blood (red) with iron oxide and magnets.


Sometimes the immune system overreacts to an infection. This mysterious condition is known as sepsis. Each year, more than a million people in the United States alone develop sepsis. And somewhere between a fourth and half of them will go on to die from it. But researchers have come up with a new tactic to attack these infections. They plan to filter germs from the blood. And it may only take simple tools: magnets and nano-bits of iron.

An infection anywhere in the body can trigger sepsis. Bacteria are usually to blame, although sometimes the source may be viruses or microscopic fungi. The worst cases tend to spread through the bloodstream. (That helps explain why sepsis is commonly, but wrongly, nicknamed “blood poisoning.”) Having so many possible causes makes sepsis tough to treat, says Gerald Pier. He’s a microbiologist at Brigham and Women’s Hospital in Boston, Mass. He also teaches nearby at Harvard Medical School.

Before doctors can treat sepsis, they must identify the germ responsible. So they will collect some blood and then send it to a lab. There, technicians multiply the microbes until there are enough to find them and identify them. That may take hours. And during that time, the sepsis may worsen dramatically. But Pier and some colleagues have an idea on how to start treating the bacteria even before they identify the germ.

The immune system uses antibodies to attack bacteria and viruses. These antibodies are proteins that latch onto the invaders as they’re carried around the body in blood. Like flags, antibodies make the microbes more visible to white blood cells. Then those white blood cells surround and consume the intruders.

Often, each antibody works against only one type of microbe, explains Pier. But his group developed a single antibody that is able to recognize nine of the 10 most common sepsis-causing bacteria.

magnetic nanoparticles
These magnetic iron-oxide particles could help remove infectious germs from blood.
Lattuada et al./Journal of Materials Chemistry B 2016

Still, antibodies alone aren’t enough. So others on the team invented a way to make the antibody stick to tiny particles of iron oxide. (Iron oxide is the scientific name for rust. And it is magnetic.) If those antibody-coated iron bits were mixed into a patient’s blood, the scientists reasoned, bacteria should stick to them. Then magnets could pull the iron particles from the blood — along with the bacteria that had glommed onto them.

Inge Katrin Herrmann is a chemical engineer at Empa in St. Gallen, Switzerland. (Empa is a short name for the Swiss Federal Laboratories for Materials Science and Technology.) The team that she and Pier are part of described their research in the November 28 Journal of Materials Chemistry B.

The researchers tested the concept with a blood-like solution.

Staphylococcus aureus bacteria are a major cause of sepsis. The researchers added different amounts of these germs to the liquid. Some solutions held just 100 S. aureus bacteria per milliliter. Others had 1,000 or 10,000 bacteria per milliliter. (For comparison, there are about 5 milliliters in a teaspoon.) Then the researchers added antibody-coated iron oxide particles to the solutions. The particles were about 300 nanometers (billionths of a meter) across. That’s smaller than most bacteria, which are usually a few micrometers (millionths of a meter) long.

After about 10 minutes, the antibody-coated nanoparticles had trapped at least 98 percent of the bacteria.

In the future, treating a patient would probably require using this germ-filtering strategy outside of the body, says Pier. Infected blood would be pumped through a machine. Magnets in the machine would remove the germs as they became coated with the iron-oxide and antibody mixture. The process would be a bit like dialysis, a treatment for severe kidney disease, explains Pier. In dialysis, a patient’s blood runs through a machine that removes wastes and extra water.

blood magnet
A liquid cloudy (left) with tiny floating iron particles can be cleaned with a strong magnet (block at right). Researchers hope a similar process can remove bacteria.
Lattuada et al./Journal of Materials Chemistry B 2016

This filtering may sound complicated. But it would let doctors treat patients more quickly than current methods, says Herrmann. “We can remove what is in the bloodstream without having to identify it,” she says.

Besides removing bacteria from blood, the magnetic filtering would concentrate the bacteria. And that could speed up the process of identifying them, says Pier. Once doctors know what germ they’re dealing with. Then they can choose the proper drug to treat it.

Alan Cross is a doctor who specializes in infectious diseases at the University of Maryland School of Medicine in Baltimore. “This is an interesting concept, but it needs further testing,” he says. Magnetic germ removal still hasn’t been tested yet in animals or people, he notes. Such tests might reveal problems that don’t show up when using only cells or blood. For instance, the team’s tests suggest that bacteria attached to tiny iron particles stay alive. If these germs slipped by the magnets and reentered the body, they would likely migrate to the liver. (That organ is the body’s natural blood filter.) Once stuck there, the bacteria might grow and continue to foster infection.

Pier and Herrmann don’t think the germ-coated particles would get much chance to reenter the body. And even if they did, the researchers say, blood is slightly acidic. So it should soon dissolve the particles.

Cross also points to another potential problem. Treating a patient could take huge numbers of tiny iron particles. In the team’s tests, the researchers added about 10 billion particles to each milliliter of blood. But there are about 5 liters (1.3 gallons) of blood in the human body, notes Cross. So it would take about 50 trillion particles of iron to treat that much blood. “I’m astounded by the numbers,” he says.

Power Words

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acidic     An adjective for materials that contain acid. These materials often are capable of eating away at some minerals such as carbonate, or preventing their formation in the first place.

antibody     Any of a large number of proteins that the body produces as part of its immune response. Antibodies neutralize, tag or destroy viruses, bacteria and other foreign substances in the blood.

bacterial     Having to do with bacteria, single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

bacterium     ( plural bacteria ) A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.

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

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact with one another. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances.

colleague     Someone who works with another; a co-worker or team member.

dialysis     The removal of waste from blood by a machine as a substitute for the normal function of a kidney.

dissolve     To turn a solid into a liquid and disperse it into that starting liquid. For instance, sugar or salt crystals (solids) will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.

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.

germ      Any one-celled microorganism, such as a bacterium, fungal species or virus particle. Some germs cause disease. Others can promote the health of higher-order organisms, including birds and mammals. The health effects of most germs, however, remain unknown.

immune system     The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.

infection     A disease that can spread from one organism to another. It’s usually caused by some sort of germ.

infectious     An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

iron     A metallic element which is common in minerals of the Earth’s crust and in its hot core. This metal is also found in cosmic dust, and in many meteorites that fall to Earth from space.

journal     (in science) A publication in which scientists share their research findings with the public. Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send out all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

kidney     Each in a pair of organs in mammals that filters blood and produces urine.

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.

magnet     A material that usually contains iron and whose atoms are arranged so they attract certain metals.

materials science     The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.

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.

micrometer     (sometimes called a micron) One thousandth of a millimeter, or one millionth of a meter. It’s also equivalent to a few one-hundred-thousandths of an inch.

microscopic     An adjective for things too small to be seen by the unaided eye. It takes a microscope to view such tiny objects, such as bacteria or other one-celled organisms.

nano     A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.

online     A term that refers to things that can be found or done on the internet.

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 interprets nerve signals and a plant’s roots are organs that take in nutrients and moisture.

oxide     A compound made by combining one or more elements with oxygen. Rust is an oxide; so it water.

particle     A minute amount of something.

protein     Compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better-known, stand-alone proteins. Medicines frequently work by latching onto proteins.

sepsis     (also called septicemia ) Complications of an infection that can prove life-threatening. It occurs when an inflammatory reaction gets out of control and risks affecting the entire body. Immune chemicals released into the bloodstream start damaging tissues throughout the body. Tissues affected by this runaway inflammation are called septic.

Staphylococcus aureus    (also known as staph) A species of bacteria that is responsible for a number of serious human infections. It can cause surface abscesses, or boils. If it gets into the bloodstream, where it can be carried throughout the body, it may also cause pneumonia and infections of the joints or bones.

technology     The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

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

virus     Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.

white blood cells     Blood cells that help the body fight off infection.


Journal: M. Lattuada et al. Theranostic body fluid clensing: Rationally designed magnetic particles enable capturing and detection of bacterial pathogens. Journal of Materials Chemistry B. Vol. 4, November 28, 2016, p. 7080. doi: 10.1039/C6TB01272H.