Mosquito bite prevention through graphene barrier layers

Abstract

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.

Keywords: graphene barriers; mosquito bite prevention; wearable technologies.

Fig. 1.

Effect of graphene films (dry state) on mosquito biting behavior. (A) Typical Aedes behavior observed during bare skin control experiments with yellow arrows showing 2 bite indicators: Left arrow, red, swollen abdomen reflecting successful blood feeding; Right arrow, head-down position indicating fascicle insertion. (B) Skin patch following an example control experiment (no graphene), showing inflammatory reaction used as a third bite indicator. (C) Structures of standard cheesecloth (Top) and GO nanosheet film of 2 cm lateral dimension (Bottom). (D) Example raw data on bite counts (bites per 5-min experiment) presented in the order in which the randomized trials were performed. No bites were recorded during any experiment with dry GO films. (E) Box plot of area-normalized mosquito bite frequency on dry GO films vs. controls. Horizontal bars indicate the median, the boxed area extends from the 25th to 75th percentiles, and whiskers show the minimum to maximum range. Statistical significance was calculated using Welch’s t test (1-tailed test). **P < 0.01. An alternative statistical model ignores the small variations in exposed areas and treats total bite numbers as count data (positive integers) that follow a Poisson distribution model based on independent bite probabilities, λ, in a given time interval. This alternative analysis yields even lower P values (SI Appendix, Fig. S5) indicating very high confidence in the inhibiting role of dry GO films. All of the graphene films were pressed onto skin with a layer of cheesecloth to prevent air gaps.

Fig. 2.

Mosquito behavioral assays and mechanisms of bite inhibition. (A) Box plot of mosquito contact frequency (landings plus walk-ons) on dry GO films compared to controls. (B) Box plot of Aedes residence times after initial contact with dry GO films compared to controls. Black circles represent individual data points. (C) Residence time distributions (10 bins) of mosquitoes on skin, cheesecloth, and dry GO. (D) Sketch of possible bite inhibition mechanisms on dry GO and wet rGO films. (Left) A selection of chemical, thermal, and optical cues reported to play a role in mosquito host sensing (19, 20). Chemical cues (CO₂, humidity, and sweat-associated organic compounds) are rendered nonbioavailable by a molecular barrier effect exerted by the overlaying (nonwetted) GO films (Center). Addition of water or sweat as an attractant on the outer surface of graphene (rGO) films successfully attracts mosquitos (Right), but still prevents biting through a mechanical penetration barrier effect (Fig. 3). Box plot interpretation is the same as in Fig. 1. Statistical significance was calculated using Welch’s t test (1-tailed test). ***P < 0.05. All of the graphene films were pressed onto skin with a layer of cheesecloth to prevent air gaps.

Fig. 3.

Effect of water or human sweat addition to the behavior of mosquitos on graphene films. (A) Experimental statistics on mosquito contact frequency on dry and wet graphene films compared to control experiments. Water or human sweat (pooled data) act as attractants that greatly increase contact frequency. (B) Box plot of mosquito biting frequency on dry and wet graphene films compared to control experiments. Aedes successfully bites through wet GO but not dry GO or wet rGO. (C) Box plot of mosquito residence time after landing on wet and dry graphene films compared to control experiments. Black circles represent individual data points. (D) Nonhuman experiment to test the effect of surface water as a mosquito attractant. A 1-um GO layer was placed between stretched Parafilm and cheesecloth and exposed to mosquitoes for 5 min in the dry and wet states. Box plot definitions and statistics are the same as in Figs. 1 and 2. *P < 0.001; **P < 0.01; ***P < 0.05.

Fig. 4.

Mechanical penetration resistance of various graphene films. (A) Measured critical penetration forces for graphene films of varying thicknesses in the dry and wet states. Data are presented as mean ± SEM (n = 9). (B) Schematic illustration of the membrane indentation model. $F$ and $a$ are the indentation force and membrane radius, respectively; the radii of the indenter tip and the circular contact area are denoted by $r_t$ and $r_c$, respectively; and $\beta$ is the local inclination angle of the membrane relative to the horizontal direction. (C) Linear relationships between the critical penetration force $\left(F_{\text{p}}\right)$ and indenter tip size predicted from finite element and analytical models. The membrane thickness is taken as $h/a=4\times {10}^{-4}$. (D) Variations of penetration force with different film thicknesses for GO–rGO films in the dry state. Dashed lines for experimental data are used for reference to show the linear relationships.