This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.
Mosquito bites aren’t just a nuisance on summer hikes or backyard patios. For millions of people around the world, they can bring deadly diseases. Now, researchers have proposed a new strategy to keep our skin bite-free. Add a layer of graphene to your outerwear.
Graphene is a single layer of carbon atoms. Identified in 2004, graphene earned its two discoverers the 2010 Nobel Prize in physics. Millions of graphene layers form the graphite in school pencils. Attaching oxygen atoms to graphene produces a film known as graphene oxide (GO). And that’s the basis of the new fabric.
Cintia Castilho is a graduate student in engineering at Brown University. That’s in Providence, R.I. She was intrigued when Robert Hurt, her advisor, mentioned mosquito protection at a team meeting. “Our group had used GO in clothing that protects against chemical vapors,” Castilho recalled. “From that and other applications, we knew it’s an extremely versatile material.” Yet, could it keep a mosquito from biting?
This project showed Castilho that any idea may be worth trying, even when some of your colleagues are skeptical. Her team described its success in the September 10 Proceedings of the National Academy of Sciences.
The mosquito’s unique toolkit
Castilho learned that a mosquito’s mouth consists of more than a straw to slurp up blood. In fact, there are six mouthparts. They are, in some ways, like dinnerware. “A mosquito holds your skin with two mouthparts that act as a fork,” she explains. Another four parts have knife-like serrated edges. They cut into your skin.
Only a female needs a blood meal. It will nourish her eggs. The mouthparts of males can't penetrate skin. Some biting flies have mouthparts similar to those of a female mosquito. But none are as unique and powerful as hers.
Some female mosquitoes strongly prefer human blood. A prime example is Aedes aegypti, which transmits many dangerous diseases. They include Zika, dengue (DEN-gay) fever, yellow fever and chikungunya (Chih-kun-GUN-yah).
“We think that Aedes aegypti comes from Africa and reached other continents with our ancestors,” says Laura Harrington. People likely transported it in human-made water containers, she says. “It’s basically a domesticated animal that can't survive without people.”
Harrington is an insect scientist, or entomologist, who wasn’t involved in the new project. She works at Cornell University in Ithaca, N.Y. The mosquito A. aegypti can feed on many mammals, she’s found. But it prefers people 98 percent of the time. During millions of years of evolution, 3,500 mosquito species have developed different body adaptations and behaviors. These help them feed on whatever animal they prefer.
Female mosquitoes transmit diseases through a channel formed by their mouthparts. They inject their saliva (spit) before pumping the host’s blood out. The mosquito’s saliva contains molecules that stimulate blood flow and prevent clotting. But sometimes that spit carries viruses from a blood source on which the insect previously fed.
We try to prevent mosquito-borne disease with protective clothing, chemical repellents, bed nets — even some drugs. But those drugs are too expensive for most people in poor countries. The same is true for vaccines. They are difficult and costly to develop. And for many diseases, they don’t even exist.
Harrington is excited about the new study because graphene-based materials are a new idea. “We're losing the battle against infectious diseases,” she says. “Any promising new technology for mosquito protection is something we should pursue.”
Graphene oxide vs. mosquito
To test graphene oxide’s prowess, Castilho’s group needed human recruits willing to expose their arms to mosquitoes. The researchers covered a volunteer’s skin with cheesecloth, a light, airy fabric. Then they let 100 mosquitoes loose on the volunteer for five minutes. (The researchers made sure those mosquitoes were free of dangerous viruses.) A volunteer would end up with about 10 bites per square inch of exposed skin.
Then the researchers ran the test again. This time they used some cheesecloth to hold the GO film in place. After another five minutes with the insects, the volunteer would have no mosquito bites.
The researchers thought the film would be a mechanical barrier — like a wall. In that case, mosquitoes should still land on the arm. In fact, almost no mosquitoes landed on a GO-protected arm.
To better understand why, the researchers added water to the film. That simulates human sweat, which is known to attract mosquitoes. And now mosquitoes did land on the arm. They also were able to bite. So while dry GO was fully protective, wet GO was not. (Mosquito bites were still less frequent with wet GO than with cheesecloth alone.)
A microscope showed what happened. Wet GO has a mushy structure that makes it a less effective shield. To restore its original protection, the researchers changed GO’s chemistry. They applied a vapor to the film. That removed most of the oxygen molecules. It was now what chemists call reduced graphene oxide (rGO). Wet rGO doesn’t get mushy. And the wet rGO film kept mosquitoes from biting, even when they landed.
These results showed that wet rGO was the mechanical barrier the researchers had expected to find. Dry GO, on the other hand, blocks some (smelly) chemicals that our skin emits with sweat. These chemicals help mosquitoes find nearby people to bite. Other attractants include heat, humidity, carbon dioxide and visual cues.
Castilho is confident that rGO will work for other kinds of mosquitoes, too. The size of the mouthparts and the sensing system are very similar in all species.
Two kinds of barriers to explore
Matthew Daly is a materials engineer who studies graphene at the University of Illinois at Chicago. He was not involved in the project but is impressed by its findings. “The science is excellent,” Daly says. “And the use of graphene for mosquito control is new and timely.”
The Brown University researchers know that rGO is not a breathable material. That’s why they plan to test if other chemical changes can keep GO fully protective in moist conditions. Daly notes that one of the challenges will be finding the right chemistry. The ideal material needs to stick together while remaining breathable.
Rakesh Joshi is also impressed with the work, especially the potential of rGO. He is a materials scientist at the University of New South Wales. That’s in Sydney, Australia. “I think it’s possible to make composite fabrics with an rGO coating,” Joshi says. Composite materials contain two or more components with different properties.
Joshi thinks teaming up with textile companies would be a great next step. More research might show which graphene-based material is the best barrier. The company could help get it into clothing that’s comfortable to wear and easy to clean.
The goal is durable and affordable clothing that deters mosquitoes and protects against diseases. Future studies of the technology also may lead to products that work directly on the skin.
adaptation (in biology) A process by which an organism or species becomes better suited to its environment. When a community of organisms does this over time, scientists refer to the change as evolution.
Aedes aegypti A species of mosquito that can transmit the viruses responsible for several tropical diseases, including dengue fever, yellow fever and West Nile disease.
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.
attractant A chemical that lures an organism, usually by odor.
behavior The way something, often a person or other organism, acts towards others, or conducts itself.
bug The slang term for an insect. Sometimes it’s even used to refer to a germ.
carbon dioxide (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.
chikungunya A tropical disease that has been crippling large numbers of people in Africa and Asia. It’s caused by a virus that is spread by mosquitoes. It recently has been spreading widely throughout warm nations. More than 3 million people have suffered through its initial flu-like symptoms. A large share may also go on to develop intense pain in their muscles and joints that can last months to years. There is no cure or vaccine.
colleague Someone who works with another; a co-worker or team member.
component Something that is part of something else (such as pieces that go on an electronic circuit board or ingredients that go into a cookie recipe).
composite A material made using two or more different building blocks, which together produce something with new and better features. Carbon fiber reinforced polymers are one example. Embedded in these hard and strong plastics are tiny fibers made from carbon. Engineers use these plastics to build lightweight bodies for race cars and airplanes, among other things.
continent (in geology) The huge land masses that sit upon tectonic plates. In modern times, there are six established geologic continents: North America, South America, Eurasia, Africa, Australia and Antarctica. In 2017, scientists also made the case for yet another: Zealandia.
dengue A potentially lethal infectious disease transmitted by mosquitoes. No vaccine yet exists to prevent infection with the virus responsible for the disease, which causes high fevers, severe headache, joint pain, pain behind the eyes, rash, bone pain and sometimes mild bleeding. A more severe form of the disease, known as dengue hemorrhagic fever can cause uncontrolled bleeding if not treated right away.
deter An event, action or material that keeps something from happening. For instance, a visible pothole in the road will deter a driver from steering his car over it.
develop To emerge or come into being, either naturally or through human intervention, such as by manufacturing. (in biology) To grow as an organism from conception through adulthood, often undergoing changes in chemistry, size and sometimes even shape.
domesticate (n. domestication) To turn a wild plant or animal species into a tame version, which can take many generations. A domesticated animal is one that has been bred in captivity for food or as a pet. A domesticated plant is one usually farmed or used for landscaping.
edge (n network mathematics) A connection or link between two people or things.
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.
entomologist A biologist who specializes in the study of insects. A paleoentomologist studies ancient insects, mainly through their fossils.
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).
graphene A superthin, superstrong material made from a single-atom-thick layer of carbon atoms that are linked together.
graphite Like diamond, graphite (the substance found in pencil lead) is a form of pure carbon. Unlike diamond, graphite is very soft. The main difference between these two forms of carbon is the number and type of chemical bonds between carbon atoms in each substance.
host (in biology and medicine) The organism (or environment) in which some other thing resides. Humans may be a temporary host for food-poisoning germs or other infective agents.
humidity A measure of the amount of water vapor in the atmosphere. (Air with a lot of water vapor in it is known as humid.)
infectious An adjective that describes a type of germ that can be transmitted to people, animals or other living things.
insect A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
malaria A disease caused by a parasite that invades the red blood cells. The parasite is transmitted by mosquitoes, largely in tropical and subtropical regions.
mammal A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.
materials scientist Someone who studies 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.
microscope An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
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); water is made of two hydrogen atoms and one oxygen atom (H2O).
Nobel prize A prestigious award named after Alfred Nobel. Best known as the inventor of dynamite, Nobel was a wealthy man when he died on December 10, 1896. In his will, Nobel left much of his fortune to create prizes to those who have done their best for humanity in the fields of physics, chemistry, physiology or medicine, literature and peace. Winners receive a medal and large cash award.
oxide A compound made by combining one or more elements with oxygen. Rust is an oxide; so is water.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.
Proceedings of the National Academy of Sciences A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.
reduced (in chemistry) An adjective that describes something that has undergone a process (reduction) in which an atom gains an electron by stealing it from another atom or molecule. Reduction is the opposite of oxidation.
serrated A description for a saw-like edge, usually found on knives meant to cut through tough meat.
simulate To deceive in some way by imitating the form or function of something. A simulated dietary fat, for instance, may deceive the mouth that it has tasted a real fat because it has the same feel on the tongue — without having any calories.
skeptical Not easily convinced; having doubts or reservations.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
strategy A thoughtful and clever plan for achieving some difficult or challenging goal.
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
textile Cloth or fabric that can be woven of nonwoven (such as when fibers are pressed and bonded together).
trait A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
transmit (n. transmission) To send or pass along.
unique Something that is unlike anything else; the only one of its kind.
vaccine (v. vaccinate) A biological mixture that resembles a disease-causing agent. It is given to help the body create immunity to a particular disease. The injections used to administer most vaccines are known as vaccinations.
vapors Fumes released when a liquid transforms to a gas, usually as a result of heating.
yellow fever A disease that creates flu-like symptoms that can start with fever, chills, headache, backache and vomiting. Roughly 15 percent of patients may go on to develop more serious disease. This can lead to uncontrolled bleeding, the failure of multiple internal organs — and death.
Zika A viral disease that can be transmitted to humans via mosquitoes. About 20 percent of infected people get sick. Symptoms include a slight fever, rash and pinkeye and usually fade quickly. A growing body of evidence suggests that the virus could also cause a devastating birth defect — microcephaly. Evidence suggests it may also cause neurological conditions such as Guillain-Barré syndrome.
Journal: C.J. Castilho et al. Mosquito bite prevention through graphene barrier layers. Proceedings of the National Academy of Sciences. Vol. 116, September 10, 2019, p. 18304. doi: 10.1073/pnas.1906612116.