The eye is such a useful feature that it has evolved many times, often with differing structures and capacities. Now, a team of scientists has modeled cameras on two animal eyes very different from our own and each other. They found one can help surgeons remove cancers, while the other can help explain underwater migratory behavior.
For cancer surgeons, one of the greatest challenges is to not leave any cancerous cells behind when removing tumors. To do that, it is essential to be able to distinguish diseased cells from the healthy ones. Chemicals that preferentially bind to tumors and fluoresce in the near infrared can help with the process, but since this is outside the range of human vision we need machines to collect the light and convert it to something surgeons can see. These are expensive and so large they can't even fit into most operating theaters. They also only work well under low light, hindering surgeons' capacity to see the healthy cells they don't want to cut.
Dr Viktor Gruev of the University of Illinois at Urbana-Champaign turned to nature and realized the morpho butterfly found the solution millions of years ago. The butterfly can see in the near-infrared, but also at visible wavelengths, using nanoscale structures that substitute for the color detecting cones in our own retinas.
In Optica, Gruev describes the creation of a camera using similar nanostructures, which detects the infrared fluorescence and feeds a signal to surgical goggles at a frequency human eyes can see. “The surgeon puts on the goggles that have integrated our bio-inspired camera technology, and it will protect their eyes and at the same time project the fluorescent information whenever they want it,” Gruev said in a statement.
Besides eliminating the size and light limitations of current instruments, Gruev estimates that, once mass produced, the camera and goggles will be available for $200, compared to $20,000 for existing options.
Prototypes have been used successfully for surgery on mice, and to remove breast cancer in humans without taking extra tissue. Gruev also demonstrated his invention's versatility by making a dye used to identify lymph nodes for biopsies to glow in the same infrared frequencies. The technique not only enabled the surgeons to find the lymph nodes more quickly but in two patients, it located nodes the surgeons would otherwise have missed.
Remarkable as the butterfly's eye is, the mantis shrimp is the optical champion, with some species having 16 types of photoreceptors (compared to our three), and being able to differentiate all six types of polarized light. Gruev decided this too is worth replicating and produced Mantis Cam.
In Science Advances, Gruev reveals this turned out to have unexpected application as an underwater GPS. “We collected underwater polarization data from all over the world in our work with marine biologists and noticed that the polarization patterns of the water were constantly changing,” Gruev said in a statement.
The changes turned out to reflect the Sun's position in the sky at the location, which Gruev realized could be combined with the time and date, to work out the location at which images were taken. The precision of these estimates, within 61 kilometers (38 miles) is no match for satellite-based GPS, but it works at depths where satellite transmissions may not reach.
“We could use our underwater GPS method to help locate missing aircraft, or even create a detailed map of the seafloor,” said the Queensland Brain Institute's Dr Samuel Powell, who was first author on the paper. “Robots swarms equipped with our sensors could provide a low-cost means of underwater remote sensing – it would certainly be more cost-effective than current methods.”
The work could also help explain how marine migratory species find their way across oceans where there are no landmarks or identifiable scents. It is already known honeybees use polarized light for navigation, and some birds probably use it to calibrate their magnetic sensors. The authors also think the light filtering to depths is being affected by pollution, and this may affect these migrations, possibly providing one explanation for whale strandings. By being able to see what the animals see, Mantis Cam could help biologists anticipate when problems will arise as a result.