We humans actually have poor senses if you compare it to other animals. For example, dogs can smell much better, some birds sense the Earth’s magnetic field and butterflies can perceive many more colors, including UV light. And it is precisely with the latter that they can help us detect cancer.
Inspired by the special properties of the Papilio xuthus butterfly, scientists have developed an image sensor, that can ‘see’ UV light that is impossible for the human eye to detect. The sensor works using photodiodes and perovskite nanocrystals – more about which later – that are able to detect different wavelengths of UV light. Certain biomedical markers, which are more common in cancer cells than in healthy cells, can be detected with this. In this way, the sensor is able to detect the difference between cancer cells and normal cells with 99 percent certainty.
Three types of UV light
UV light is electromagnetic radiation with wavelengths shorter than visible light, but longer than X-rays. Of course, we mainly know it as the harmful part of sun rays, but there are three types of UV light, based on different wavelengths: UVA, UVB and UVC.
We humans cannot see UV light, let alone the differences between the three types. However, butterflies can detect these small variations in the UV spectrum. “It’s intriguing how they can see such small differences. UV light is incredibly difficult to capture, it is simply absorbed by everything and butterflies are able to do that extremely well,” says Professor Viktor Gruev of the University of Illinois.
Six instead of three photoreceptors
It is the number of photoreceptors, or light-sensitive cells, that makes butterflies so good at detecting UV light: humans have three – for red, green and blue – butterflies have at least six. For example, the Papilio xuthus, an Asian swallowtail butterfly, not only has receptors for those three colors, but also for violet, ultraviolet and broadband. In addition, they also have fluorescent pigments that allow them to convert UV light into visible light, which they can then easily perceive with their photoreceptors, which also have a unique layered structure. This way they can perceive a much larger group of colors and much more detail in their environment.
To recreate the photoreceptors as closely as possible, the researchers combined a thin layer of perovskite nanocrystals – a mineral that is also used in solar panels – with a layered series of silicone photodiodes, which produce current when light falls on them.
Detecting cancer cells
But how do you use this to detect cancer cells? Certain biomedical markers are more abundant in cancer tissue than in healthy cells. Think of amino acids, proteins and enzymes. By absorbing UV radiation, these markers emit light again, something called autofluorescence.
Because cancer and healthy cells have different concentrations of certain markers and are therefore visible in different ways by UV light, these two types of cells can be distinguished. The researchers tested their new technology and managed to see the difference between cancer cells and healthy cells with 99 percent certainty.
More applications
“Imaging UV light remained difficult and was the biggest stumbling block to scientific progress,” explains Professor Shuming Nie. “Now we have this new technology where we can image UV light with a high degree of sensitivity and also distinguish between small differences in wavelength.”
The researchers see how the sensor can be of great use during operations. One of the biggest challenges in cancer surgery is figuring out how much tissue needs to be removed to make sure it’s all gone. The sensor can aid a surgeon’s decision-making when removing a tumor. “This new imaging technology ensures that we are able to distinguish between cancer cells and healthy cells, but it also has other interesting applications,” says Nie. More animal species are now able to see UV light. The fact that this light can now be detected offers biologists the opportunity to learn more about these species.
