Researchers showed that multilayer graphene can provide a two-fold defense against mosquito bites. The ultra-thin yet strong material acts as a barrier that mosquitoes are unable to bite through. At the same time, experiments showed that graphene also blocks chemical signals mosquitoes use to sense that a blood meal is near, blunting their urge to bite in the first place. The findings suggest that clothing with a graphene lining could be an effective mosquito barrier, the researchers say.
“Mosquitoes are important vectors for disease all over the world, and there’s a lot of interest in non-chemical mosquito bite protection,” said Robert Hurt,a professor in Brown’s School of Engineering, leader of Brown’s Superfund Research Program and senior author of the paper. “We had been working on fabrics that incorporate graphene as a barrier against toxic chemicals, and we started thinking about what else the approach might be good for. We thought maybe graphene could provide mosquito bite protection as well.”
The researchers compared the number of bites participants received on their bare skin, on skin covered in cheesecloth and on skin covered by a graphene oxide (GO) films sheathed in cheesecloth. GO is a graphene derivative that can be made into films large enough for macro-scale applications.
It was readily apparent that graphene was a bite deterrent, the researchers found. When skin was covered by dry GO films, participants didn’t get a single bite, while bare and cheesecloth-covered skin was readily feasted upon. What was surprising, the researchers said, was that the mosquitoes completely changed their behavior in the presence of the graphene-covered arm.
“With the graphene, the mosquitoes weren’t even landing on the skin patch — they just didn’t seem to care,” said Cintia Castillho, a Ph.D. student at Brown and the study’s lead author. “We had assumed that graphene would be a physical barrier to biting, through puncture resistance, but when we saw these experiments we started to think that it was also a chemical barrier that prevents mosquitoes from sensing that someone is there.”
To confirm the chemical barrier idea, the researchers dabbed some human sweat onto the outside of a graphene barrier. With the chemical ques on the other side of the graphene, the mosquitoes flocked to the patch in much the same way they flocked to bare skin.
Other experiments showed that GO can also provide puncture resistance — but not all the time. Using a tiny needle as a stand-in for a mosquito’s proboscis, as well as computer simulations of the bite process, the researchers showed that mosquitoes simply can’t generate enough force to puncture GO. But that only applied when the GO is dry. The simulations found that GO would be vulnerable to puncture when it was saturated with water. And sure enough, experiments showed that mosquitoes could bite through wet GO. However, another form of GO with reduced oxygen content (called rGO) was shown to provide a bite barrier when both wet and dry.
The mosquito is the world’s most important vector for transmission of infectious diseases, and chemical agents now used for bite prevention can have environmental or human health side effects. This work explores a nonchemical method for mosquito bite prevention based on graphene, the atomically thin sheet of carbon atoms, as a potential barrier material. We show that multilayer graphene films in the dry state completely inhibit biting by preventing mosquitos from sensing skin- or sweat-associated chemicals used to locate blood meals. In some cases, the graphene films also act as mechanical barriers to the penetration of the mosquito fascicle, its feeding apparatus. The results can guide development of graphene protective technologies on skin or within smart fabrics.
Graphene-based materials are being developed for a variety of wearable technologies to provide advanced functions that include sensing; temperature regulation; chemical, mechanical, or radiative protection; or energy storage. We hypothesized that graphene films may also offer an additional unanticipated function: mosquito bite protection for light, fiber-based fabrics. Here, we investigate the fundamental interactions between graphene-based films and the globally important mosquito species, Aedes aegypti, through a combination of live mosquito experiments, needle penetration force measurements, and mathematical modeling of mechanical puncture phenomena. The results show that graphene or graphene oxide nanosheet films in the dry state are highly effective at suppressing mosquito biting behavior on live human skin. Surprisingly, behavioral assays indicate that the primary mechanism is not mechanical puncture resistance, but rather interference with host chemosensing. This interference is proposed to be a molecular barrier effect that prevents Aedes from detecting skin-associated molecular attractants trapped beneath the graphene films and thus prevents the initiation of biting behavior. The molecular barrier effect can be circumvented by placing water or human sweat as molecular attractants on the top (external) film surface. In this scenario, pristine graphene films continue to protect through puncture resistance—a mechanical barrier effect—while graphene oxide films absorb the water and convert to mechanically soft hydrogels that become nonprotective.
SOURCES- Brown University, PNAS
Written by Christina Wong, Nextbigfuture.com
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