Nanotech Scientists Build on an Insect’s Odd Soccer Ball-Like Excretions to Design Ingenious Camouflage todayheadline

Nanotech Scientists Build on an Insect’s Odd Soccer Ball-Like Excretions to Design Ingenious Camouflage

By Ivan Amato edited by Gary Stix

In the early 1950s biologists at Brooklyn College were using an electron microscope to pursue a lead that the leafhopper, a common insect that is about the size of a rice grain and named after one of its signature behaviors, could be an agent of viral transmission. In their research, the scientists incidentally observed, in their words, “certain ultramicroscopic bodies, hitherto undescribed,” on the wings of leafhoppers. In a 1953 note in the Bulletin of the Brooklyn Entomological Society, they dubbed these minuscule, spherical, jacklike structures “brochosomes,” after a Greek word meaning “mesh of a net.”

Since then a thin but determined line of scientists and engineers has built a brochosome-anchored hyperspecialty. These researchers are drawn to these subpinpoints of highly structured matter by the biological wonders they embody and the technological possibilities their elaborately porous forms and physical properties suggest. Brochosome aficionados do not hesitate to share their delight at having run across such an evolutionary tour de force.

“Our group first became intrigued by brochosomes around 2015, drawn to their nanoscale dimensions and intricate, three-dimensional buckyball-like geometries,” says Tak-Sing Wong, a biomedical and mechanical engineer at Pennsylvania State University. “We were amazed by how leafhoppers can consistently produce such complex structures at the nanoscale, especially considering that even with our most advanced micro- and nanofabrication technologies we still struggle to achieve such uniformity and scalability.”

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As much as anyone interested in these structures, Wong has been working to channel his brochosome envy into the creation of a cabinet of technological curiosities based on brochosomes’ knack for absorbing specific ranges of visible and ultraviolet wavelengths. Wong, with his partners at Penn State and Carnegie Mellon University, has been granted two U.S. patents and has others pending for processes to manufacture synthetic counterparts to brochosomes.

Wong says the synthetic brochosomes are potentially suitable for a range of applications, including antireflection and camouflage materials, anticounterfeiting, data encryption and an “optical security,” tactic in which hidden information becomes visible only when it is illuminated with, say, infrared or ultraviolet light. The researchers have been able to garner grant money from the Office of Naval Research, which is always on the lookout for the next way to make it harder for adversaries to detect and track naval vessels, aircraft and other U.S. military assets.

Much of the recent brochosome-inspired R&D around the world, Wong notes, derives from the ultra-antireflective upgrade that nature-made brochosomes add to leafhoppers’ body. It’s not just cool optical physics: this trick of the light renders the insects stealthy on leaf surfaces where hungry insects, birds and spiders scan for prey.

Some of the forays into brochosome biology have revealed that these natural nanoscale innovations are composed of proteins and lipids that get assembled into the stealth-making nanospheres within specialized compartments of the insects’ Malpighian tubules, which are kidneylike excretory organs. With their hind legs, the insects groom their entire little selves with brochosome-packed microdroplets from their anus, resulting in light-absorptive cloaks that help them live another day.

But the nanospheres are good for more than just concealment. In a recent addition to the growing list of concepts and prototypes of brochosome-inspired technologies, Wong’s Penn State team joined Carnegie Mellon University researchers, led by mechanical engineer Sheng Shen, with an eye to delivering new materials not just for camouflage but for novel security and encryption devices as well. The technology leverages people’s inability to perceive infrared light.

As the researchers were making measurements of optical and other physical aspects of synthetic brochosomes, they noticed that “while these structures appeared identical under visible light, they exhibited dramatic contrasts in infrared imaging,” Shen says. And that sparked an encryption- and security-technology idea, which the researchers now are pursuing. The team is asking whether it might be possible to encode infrared information invisibly within the visible spectrum. A small dot of such an infrared-active brochosome material on currency could serve as a signature of authenticity and add an additional hurdle for would-be counterfeiters.

Researchers have explored a half-dozen ways of fabricating synthetic brochosomes of various sizes and geometries. Through the use of different polymeric, ceramic and metallic materials, the cabinet of brochosome-inspired technocuriosities is only becoming more eye-catching.

A team of Chinese researchers who are brochosome fans recently reported a process for making a vivid spectrum of color-bestowing particles by filling tiny indentations—“nanobowl” spaces—on silver brochosome structures with tiny polystyrene spheres. When the researchers tailored the sizes of the spheres with a precise etching method, they were able to tweak the electromagnetic interactions between the spheres and, thereby, the apparent colors of the synthetic brochosome-structures. In an ACS Nano paper in which the researchers rolled out their color-making strategy, they suggested this opened a pathway for producing longer-lasting and more stable colors compared with shorter-lived chemical dyes and pigments.

A different Chinese research group, attempting to emulate the master-of-disguise feats of chameleons, cephalopods and other creatures, fabricated tungsten-oxide-based brochosome structures that become less reflective when they are electrically stimulated. One possible end point for this work could be energy-saving applications—windows that could regulate the amount of solar and thermal energy that passed through them over the course of the day.

On an even more expansive and eclectic to-do list are light-harvesting electrodes that could generate and corral energized electrons to make hydrogen fuel and self-cleaning surfaces that could repel liquids and adhesives. Also on the list are sensors that could be tailored for detecting specific bacteria and proteins for environmental monitoring and health applications. Additionally, there is the prospect of brochosome-inspired particles whose pores and surfaces could be tailored to carry specific drugs to target tissues.

The promise seems enormous, but an era of brochosome-inspired technology is not an immediate prospect. “One of the major bottlenecks to the widespread use of synthetic brochosomes is the lack of scalable production technologies, as their complex 3D shapes and nanoscale dimensions remain challenging to replicate at scale,” Wong cautions.

Whether specific brochosome-inspired technologies get to the finish line or not, Wong says that he loves sharing his work with nonscientist family members and friends. “They are immediately captivated by the beauty of the brochosomes’ soccer-ball-looking structures,” he says. “When I explain that the structures are about 100 times thinner than the diameter of a hair, they can hardly believe it.”

Meanwhile Shen welcomes a humbling aspect of this research romance with brochosomes. “It’s a powerful reminder that innovation doesn’t always need to come from human ingenuity,” he says. “Sometimes nature has already solved the problems we’re working on.”