The Imitation Game: New research shows one of the most advanced examples of using the visual system of butterflies in the latest imaging technology.
On our planet, numerous creatures possess senses more advanced than those of humans. Turtles navigate by sensing Earth’s magnetic field, mantis shrimp perceive polarized light, and elephants hear frequencies below the human auditory range. Notably, butterflies exhibit an extended visual spectrum, including ultraviolet (UV) light.
Drawing inspiration from the exceptional visual abilities of the Papilio xuthus butterfly, a team of researchers has developed an imaging sensor with the capability to perceive the UV range, a spectrum inaccessible to human vision.
This innovative sensor design integrates stacked photodiodes and perovskite nanocrystals (PNCs) for imaging various UV wavelengths. Remarkably, this advanced imaging technology can distinguish between cancer cells and normal cells with a remarkable 99% accuracy by analyzing the spectral signatures of biomarkers such as amino acids.
The groundbreaking research, spearheaded by Professor Viktor Gruev from the University of Illinois Urbana-Champaign’s electrical and computer engineering department and Professor Shuming Nie from the bioengineering department, has been recently published in the journal Science Advances.
What If We Could See Like Butterflies?
“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.
To achieve this, they employed pioneering perovskite nanocrystals in conjunction with silicon imaging technology.
“This new camera technology can detect multiple UV regions.”
UV light constitutes electromagnetic radiation with wavelengths shorter than those of visible light, though longer than x-rays. UV radiation, largely associated with the sun and its health risks to humans, is divided into three distinct regions: UVA, UVB, and UVC, each defined by specific wavelength ranges.
Given that human eyes cannot perceive UV light, capturing detailed UV information, especially distinguishing the subtle differences between these regions, presents a significant challenge.
In contrast, butterflies possess the remarkable ability to discern these slight variations within the UV spectrum, akin to how humans perceive distinctions in shades of blue and green.
Gruev remarks, “It is intriguing to me how they are able to see those small variations. UV light is incredibly difficult to capture, it just gets absorbed by everything, and butterflies have managed to do it extremely well.”
How Can Butterflies See Colors We Can’t?
In the realm of vision, humans rely on trichromatic capabilities, encompassing three photoreceptor types to perceive a spectrum of colors fashioned from the primary hues of red, green, and blue.
In stark contrast, butterflies boast compound eyes, equipped with six or more photoreceptor classes, each finely attuned to distinct spectral sensitivities.
Among these optical marvels, the Papilio xuthus, an Asian swallowtail butterfly, distinguishes itself by featuring not just blue, green, and red receptors but also violet, ultraviolet, and broadband receptors.
To further augment their visual prowess, butterflies employ fluorescent pigments, which ingeniously transform otherwise invisible UV light into a visible spectrum.
This radiant transformation is subsequently detected by their photoreceptors, enabling them to perceive an astonishing array of colors and intricate environmental details.
Beyond their multiplicity of photoreceptors, butterflies introduce a unique tiered architecture within their visual sensors. In a bid to emulate the UV-sensing mechanism of the Papilio xuthus butterfly, the University of Illinois Urbana-Champaign (UIUC) research team ingeniously replicated this process by harmonizing a slender layer of perovskite nanocrystals (PNCs) with a tiered grid of silicon photodiodes.
PNCs, or perovskite nanocrystals, belong to the class of semiconductor nanocrystals, showcasing distinctive properties reminiscent of quantum dots.
Altering the size and composition of these particles leads to significant changes in the absorption and emission properties of the material.
In recent years, PNCs have emerged as a fascinating material in diverse sensing applications, including solar cells and LEDs. What sets PNCs apart is their exceptional aptitude for detecting UV and even lower wavelengths, a feat beyond the reach of conventional silicon detectors.
Within the novel imaging sensor, the PNC layer adeptly absorbs UV photons, transforming them into visible green light. These emissions are subsequently captured by the tiered silicon photodiodes. Through signal processing, the system orchestrates the mapping and identification of UV signatures.
Can a Butterfly’s Vision Revolutionize Medical Imaging?
Within cancerous tissues, various biomedical markers, including amino acids (essential building blocks of proteins), proteins, and enzymes, are typically present at elevated concentrations compared to healthy tissues.
When exposed to UV light, these markers exhibit autofluorescence, emitting fluorescence in both the UV and a portion of the visible spectrum. This unique process has been described as the key to advancing scientific understanding.
As Dr. Nie notes, “Imaging in the UV region has been limited and I would say that has been the biggest roadblock for making scientific progress. Now we have come up with this technology where we can image UV light with high sensitivity and can also distinguish small wavelength differences.”
Distinguishing cancer cells from healthy cells becomes feasible due to their differing marker concentrations and spectral signatures, particularly in the UV spectrum. The research team assessed their imaging device’s ability to discriminate cancer-related markers and demonstrated its remarkable proficiency, achieving a 99% confidence level in distinguishing between cancerous and healthy cells.
Professors Gruev, Nie, and their collaborative research team envision the practical use of this sensor in surgical procedures. One of the most formidable challenges in surgery is ensuring that surgeons remove the right amount of tissue to guarantee clear margins, and this sensor can significantly aid the decision-making process when extracting cancerous tumors.
As Dr. Nie emphasizes, “This new imaging technology is enabling us to differentiate cancerous versus healthy cells and is opening up new and exciting applications beyond just health.”
The ability to detect UV light opens up intriguing possibilities for biologists, allowing them to gain deeper insights into species beyond butterflies that can see in the UV spectrum. This, in turn, can shed light on their hunting and mating behaviors. Submerging the sensor underwater also promises to enhance our understanding of aquatic environments. While much UV light is absorbed by water, a significant portion still penetrates, impacting various underwater species that also rely on UV light for their activities.
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