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.
