Seeing the unseen: How butterflies can help scientists detect cancer

There are a lot of animals on our world that have higher developed senses than us. The magnetic field of Earth is sensed by turtles. Polarized light is detectable by mantis shrimp. Compared to humans, elephants have substantially lower frequency hearing. In addition to seeing a wider spectrum of hues, butterflies can also detect ultraviolet (UV) radiation.

Motivated by the improved vision of the Papilio xuthus butterfly, scientists have created an image sensor that can "see" into the UV spectrum that is invisible to human vision. The sensor's architecture makes use of perovskite nanocrystals (PNCs), which can image various UV wavelengths, in conjunction with stacked photodiodes. With 99% certainty, this new imaging system can even distinguish between cancerous and normal cells using the spectral fingerprints of biological markers like amino acids.

Professors of bioengineering Shuming Nie and electrical and computer engineering Viktor Gruev of the University of Illinois Urbana-Champaign spearheaded this new research, which was just published in the journal Science Advances.

Small Differences

"We've taken inspiration from the visual system of butterflies, who are able to perceive multiple regions in the UV spectrum, and designed a camera that replicates that functionality," Gruev explains. "We did this by using novel perovskite nanocrystals, combined with silicon imaging technology, and this new camera technology can detect multiple UV regions."

Electromagnetic radiation having wavelengths shorter than visible light but longer than X-rays is known as ultraviolet light. The most well-known risks to human health that UV radiation from the sun presents are. UVA, UVB, and UVC are the three zones into which UV radiation is divided according to its various wavelength ranges. Since UV light is invisible to humans, it is difficult to gather UV data, particularly when trying to identify the minute variations between each location.

But just as humans see different tones of blue and green, butterflies are able to perceive these minute changes in the UV spectrum. Gruev observes, "I find it fascinating that they can detect those minute differences. Butterfly photography is exceptionally adept at capturing ultraviolet light, which is exceedingly difficult to record since it is absorbed by everything."

The Game of Imitation

With its three photoreceptors, humans have trichromatic vision, meaning that any hue they experience may be created by combining red, green, and blue. In contrast, the eyes of butterflies are complex, including six or more classes of photoreceptors with different spectrum sensitivity. Specifically, the yellow Asian swallowtail butterfly, Papilio xuthus, possesses violet, ultraviolet, and broadband receptors in addition to blue, green, and red ones. Moreover, butterflies' fluorescent pigments enable them to transform UV radiation into visible light, which their photoreceptors can then easily detect. As a result, they are able to recognize more hues and features in their surroundings.

Butterflies have more photoreceptors than other animals, but their photoreceptors also have a distinct tiered structure. The UIUC researchers combined a thin layer of PNCs with a tiered array of silicon photodiodes to mimic the UV sensing mechanism of the Papilio xuthus butterfly.

PNCs are a particular kind of semiconductor nanocrystals that exhibit distinctive characteristics akin to those of quantum dots: altering the particle's size and composition modifies the material's absorption and emission characteristics. PNCs have become a fascinating material for many sensing applications, including solar cells and LEDs, in the past several years. PNCs are incredibly effective at detecting wavelengths in the UV and even lower ranges that conventional silicon detectors are not. The PNC layer of the novel image sensor can absorb UV photons and reemit light in the visible (green) spectrum, which the tiered silicon photodiodes subsequently pick up on. Mapping and identifying UV signatures are made possible by the processing of these signals.

Healthcare and other fields

Higher amounts of many biological indicators, including proteins, enzymes, and amino acids—the building blocks of proteins—are seen in malignant cells compared to healthy ones. In a phenomenon known as autofluorescence, these markers light up and fluoresce in the UV and portion of the visible spectrum when exposed to UV light. "Imaging in the UV region has been limited and I would say that has been the biggest roadblock for making scientific progress," says Nie. "Now we have come up with this technology where we can image UV light with high sensitivity and can also distinguish small wavelength differences."

The two types of cells may be distinguished from one another based on their fluorescence in the ultraviolet spectrum because cancer and healthy cells have distinct spectral fingerprints and marker concentrations. The researchers assessed the capability of their imaging gadget to distinguish between cancerous and healthy cells with 99% confidence by looking at indicators associated with cancer.

Gruev, Nie, and their cooperative research group hope to apply this sensor in the operating room. Knowing how much tissue to take to guarantee clear margins is one of the toughest hurdles, and a sensor like this can assist a surgeon make decisions more easily while removing a dangerous tumor.

"This new imaging technology is enabling us to differentiate cancerous versus healthy cells and is opening up new and exciting applications beyond just health," Nie continues. Beyond butterflies, there are a plethora of other species that are able to see in the ultraviolet spectrum. By developing a means of detecting this light, researchers will have intriguing chances to discover more about these species, including their mating and hunting behaviors. Moreover, submerging the sensor can contribute to a deeper comprehension of that surroundings. Even while water absorbs a large amount of UV light, enough of it still reaches the surface to have an effect, and many submerged species are also able to perceive and use UV light.