To increase stealth and evade predators, the moth has evolved a remarkable eye that, rather than reflecting light, absorbs it almost completely. Engineers have mimicked its nanostructure in the past to design better solar panel coatings and antireflective surfaces, and are now using the same principle to design a thin film that will absorb radiation from X-ray machines more effectively, exposing patients to a significantly lower risk while obtaining higher quality images.

The researchers focused on so-called scintillation materials. When they are hit by a particle, these materials first absorb its energy, and then re-emit it in the form of light. Scintillators are used in medical imaging devices to convert the X-rays reflected by the body of the patient into the visible signals that, when elaborated, make up a picture - the final scan.

Better imaging is achieved by improving the number of particles received by the scintillator. This can be done either by subjecting the patient to a higher dose of radiation (which presents severe health risks), or by tweaking the scintillator itself. The research reported here follows the latter approach by developing a film that, when applied to a scintillator, captures almost three times as many particles as before, improving the quality of the images produced without compromising the patient's safety.

The film developed by the researchers is only 500 nanometers thick. It is a crystal encrusted with tiny pyramid-shaped bumps made of silicon nitride, a ceramic that is sometimes used as an insulator in integrated circuits.

Scanning electron microscope image of the eye on a leaf miner moth (Image: Dartmouth College)

Each of these bumps is modeled after the minuscule structures that make up a moth's eye. The bumps are designed to capture and absorb as many particles as possible, partly thanks to their large surface area. The protuberances are very small in size, with 100,000 to 200,000 of them fitting in a 100-by-100 micrometer square. Incidentally, this is the same density of protuberances found in an actual moth eye.

To test its performance, the film was applied to the scintillator of an X-ray mammographic unit, and the intensity of the emitted light increased by up to 175 percent. But while the film seems promising, the researchers say they are still three to five years away from testing and perfecting the film to exploit its full potential.

A paper detailing the work was published in the journal Optics Letters.

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