Bioinspired endoscopic system offers guide for cancer surgery

31 May 2023

UIUC sensor derived from mantis shrimp captures color images while resolving two near-IR probes.

Optical diagnostic probes are set to play an increasing role in both cancer diagnosis and optical biopsies, building on current trends in miniaturization and sensitivity of fluorescence platforms.

One route to minimally invasive cancer surgery involves fluorescence-guided surgery (FGS), in which patients are injected with a fluorescent probe that preferentially binds to tumor cells, enabling surgeons to easily identify lesions when they are illuminated with light from optical endoscopes.

A project at the University of Illinois Urbana-Champaign (UIUC) has now developed a new optical endoscopic imaging system that can capture color images and resolve two near-IR probes simultaneously, employing a sensor modeled on the vision system of the mantis shrimp.

The eyes of this animal can detect both linearly and circularly polarized light, an ability that has been of interest to optics designers for some time, with implications for both imaging and data storage.

Published in Journal of Biomedical Optics, the UIUC findings point to FGS procedures able to detect tumors tagged with multiple near-IR fluorescent probes. This would overcome a current hurdle, whereby cocktails of different tracers are used to suit the heterogeneity of tumors but the endoscopes used for analysis are then only capable of detecting a single marker.

In the mantis shrimp, photosensitive cells at the top of its compound eyes preferentially register shorter-wavelength photons, while the photosensitive cells at the bottom preferentially register longer wavelengths. Using this architecture as a blueprint, UIUC designed an artificial detector employing layers of n-doped silicon and p-doped silicon along with interference filters composed of layers of different dielectric materials.

Detect small or hidden tumors more easily

"Our bioinspired imaging sensor combines vertically stacked photodetectors with pixelated spectral filters to make three observations in the near-IR spectrum while simultaneously capturing color images," commented the project in its published paper. "This approach is radically different from current state-of-the-art multispectral imaging systems, which combine multiple cameras and complex optical elements while still only imaging single molecular tracers."

The project also had to consider an appropriate excitation source for activating the fluorescent tracers, designing custom bifurcated optical fibers connected to three independent light sources: a white LED and two near-IR lasers at 665 and 785 nanometers.

In pre-clinical trials on mouse models for breast cancer injected with two markers, the system could clearly differentiate between the fluorescence signatures produced by the individual tracers and the mixture. Tests on human lung cancer nodules removed from patients, initially using just one marker to assess clinical utility, validated the simultaneous imaging of near-IR fluorescence and color targets, as well as the efficacy of detecting tumors.

"The proposed endoscopic imaging system will help doctors detect smaller or otherwise hidden tumors more easily," commented the team, which is initially targeting its device at the treatment of lung cancer but expects its device will pave the way for instrumental platforms using multi-tracer FGS becoming less bulky and easier to use in clinical practice.