09-24 Aedes aegypti mosquito

[Image above] Aedes aegypti mosquitos are known for spreading dengue fever, Zika fever, and other diseases. How can we make sure they do not bite humans? Credit: Centers for Disease Control, Free Stock Photos (Public Domain)

It’s official—fall has arrived in 2019.

Some people love autumn for pumpkin spice, crunchy leaves, and sweater weather. I love this season because it marks the beginning of the end for my mortal enemy—mosquitoes.

No matter how much bug spray I use or how many long-sleeved shirts I wear, mosquitoes always find a way to cover me in itchy bumps. I personally prefer hot summer weather, but I choose fall as my favorite season simply because I can go for evening walks without being attacked by insects.

Though genetically engineering mosquitoes to reduce their population is tempting, there may be unintended consequences (the company behind the engineered mosquitoes disputes these claims).

But does that mean we must coat ourselves in potentially dangerous chemicals to enjoy an outdoor hike?

Natural repellents offer one alternative to synthetic sprays. Robert Hurt, professor of engineering at Brown University, has another idea.

“There’s a lot of interest in nonchemical mosquito bite protection,” Hurt says in a Brown University press release. In particular, tightly woven clothing shields against a mosquito’s proboscis, but the most effective materials—polyester and nylon—do not have much stretch and can be quite sweaty.

Is there a material that is strong, thin, and flexible from which to make mosquito-repellant clothing? Yes, and the answer lies with a material not previously explored for insect bite protection—graphene.

Graphene is being explored as a component in wearable fabric-based or on-skin technologies to enable biomonitoring, UV protection, and chemical toxicant rejection, among other things. Graphene films are ultrathin and ultralight, and textured versions can mimic elasticity to match stretchable fabrics.

Hurt and his students were working on fabrics that incorporated graphene as a barrier against toxic chemicals when they started thinking about other applications for the graphene-enhanced fabric. “We thought maybe graphene could provide mosquito bite protection as well,” Hurt says.

In a paper published in Proceedings of the National Academy of Sciences, Hurt and his students worked with other researchers from Brown University to recruit brave participants willing to place their arm in a box full of lab-bred Aedes aegypti mosquitos. They measured the number of bites participants received in three conditions: on bare skin, on skin covered in cheesecloth, and on skin covered by graphene oxide (GO) films sheathed in cheesecloth.

While the first two conditions resulted in participants receiving many bites, participants did not experience a single bite when covered with GO-enhanced fabric—in fact, the mosquitos completely changed their behavior in response to the graphene-covered skin.

“With the graphene, the mosquitoes weren’t even landing on the skin patch—they just didn’t seem to care,” Cintia Castillho, a Ph.D. student at Brown and the study’s lead author, says in the press release. “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.”

GO-enhanced fabric kept mosquitos from biting the skin underneath. Credit: Brown University

To investigate the chemical barrier idea, the researchers repeated the experiments with human sweat or water dabbed on the outside surface of the GO films. The mosquitoes flocked to the patch similarly to how they converged on bare skin.

These water-and-sweat experiments led to another surprising discovery—mosquitos can sometimes bite through GO if it is wet.

“Water or sweat are clearly sufficient as an attractant, and once on the surface, the Aedes fascicle can penetrate the 1-μm-thick GO wet films to reach human skin and underlying blood vessels,” the researchers write in the paper. “GO is known to be a hygroscopic material, and contacting our films with excess liquid water causes absorption, swelling, and the formation of hydrogels without the characteristic 001 XRD peak of stacked GO nanosheets in the dry state.”

In contrast, reduced graphene oxide (rGO) proved an efficient barrier when both wet and dry.

Despite rGO’s superior protection when wet, the researchers say GO still holds distinct advantages over rGO.

“GO is breathable, meaning you can sweat through it, while rGO isn’t,” Hurt says. “So our preferred embodiment of this technology would be to find a way to stabilize GO mechanically so that is remains strong when wet. This next step would give us the full benefits of breathability and bite protection.”

I for one would love to see this technology come to market someday. And if they make tracksuits containing GO, then I know the perfect shoe to pair with it.

The paper, published in Proceedings of the National Academy of Sciences, is “Mosquito bite prevention through graphene barrier layers” (DOI: 10.1073/pnas.1906612116).