UIUC sensor spots signs of cancer cells

07 Nov 2023

Bioinspired design combines two UV detection methods.

A project at the University of Illinois Urbana-Champaign (UIUC) has developed a bioinspired CMOS imaging sensor that could help diagnosis of cancer.

Published in Science Advances, the findings may also be valuable in remote sensing and automation, as well as the detection of biomarkers in various forms of medical imaging.

The structure of the sensor is inspired by the optics of butterfly eyes, in the latest example of specialized optical designs drawing on principles already put into practice in nature.

UIUC has its own track record in this area. Butterfly eyes provided the basis for a 2018 UIUC camera in which an array of photodetectors collected color and near-infrared fluorescence information on one imaging device.

Earlier in 2023 UIUC demonstrated an endoscopic imaging system based on the eye of the mantis shrimp able to detect both linearly and circularly polarized light, aimed at enhancing optical biopsy procedures and identification of lesions during surgery.

Both those breakthroughs involved the UIUC Biosensors Lab led by Viktor Gruev, and the Gruev Lab's latest bioinspired sensor returns to the compound eyes of butterflies and the way that ultraviolet wavelengths are detected by the insects.

The eyes of the Papilio xuthus Asian swallowtail butterfly detect blue, green and red light, but also contain violet, UV and broadband receptors, according to UIUC. In addition the eye incorporates fluorescent pigments that allow the conversion of UV into visible light which can then be easily sensed by the photoreceptors.

Overcoming the roadblock for UV imaging

UIUC replicated this UV sensing mechanism by combining a thin layer of metal-halide perovskite nanocrystals (PNCs) with a vertically tiered array of three silicon photodiodes.

The PNC layer absorbs UV photons within the UVB spectrum and reemits fluorescent light in the green spectrum, subsequently detected by the underlying silicon photodiodes, according to the project's published paper. Those photodiodes also detect UV photons in the UVA region, through direct absorption and conversion into electron-hole pairs.

"We have 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," commented Viktor Gruev. "We did this by using novel perovskite nanocrystals combined with silicon imaging technology, and this new camera technology can detect multiple UV regions."

This will be valuable in cancer diagnosis, since several biomarkers present in cancerous tissues at higher concentrations than in healthy tissues - including amino acids, proteins, and enzymes - autofluoresce in the UV and visible ranges when suitably illuminated, allowing malignancies to be differentiated from healthy cells.

In trials, UIUC found that its sensor was capable of differentiating between the wavelength responses of cancerous and healthy cells with 99-percent confidence, according to the project.

As well as human biomedical applications, the sensor may also assist investigations of animal behavior, including undersea species which detect and utilize the limited amounts of UV light that penetrate underwater.

"Imaging in the UV region has been limited and I would say that has been the biggest roadblock for making scientific progress," said UIUC's Shuming 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."