Moth Eyes: A New Vision for Light-Harnessing Efficiency

Abstract

Moths have compound eyes, meaning they are faceted and consist of many repeated, anatomically identical unites called ommatidia (Stavenga et al., Proc Biol Sci 273(1587):661–667, 2005). Every ommatidium detects signals that are neurologically processed to form a whole image and is composed of retinula cells, a rhabdom, a crystalline cone, and a corneal lens covered in nano-scale structures called corneal nipples (Lee and Erb, Beilstein J Nanotechnol 4:292–299, 2013). Corneal nipples are covered in protuberances that are responsible for the antireflective property of moth eyes (Parker, Am Sci 87(3):248–255, 1999). This optical mechanism relies on the fact that the wavelength range of incident light is less than the dimensions of the corneal nipples. The antireflective surface of moth eyes is critical to their survival, because they allow moths to camouflage with their surroundings at night and impart superhydrophobic properties, lending anti-adhesive, anti-fogging, and self-cleaning abilities (Boden and Bagnall, Moth-eye antireflective structures. In: Bhushan B (ed) Encyclopedia of nanotechnology. Springer, Netherlands, pp 1467–1477, 2012). Moth-eye antireflective (AR) structures have been produced by engineers to enhance the surfaces of materials such as glass and silicon to an extent that surpasses the antireflective properties provided by traditional antireflection coatings, or ARCs (Boden, Biomimetic nanostructured surfaces for antireflection in photovoltaics. PhD thesis, University of Southampton, School of Electronics & Computer Science, p 18, 2009). Researchers in the solar energy field have taken particular interest in the antireflective properties of moth eyes in hopes of applying them to photovoltaic (PV) systems to increase light-efficiency and minimize energy waste (Yamada et al., Prog Photovolt Res Appl 19(2):134–140, 2010). Perhaps one of the most exciting, up-and-coming applications of the moth-eye nano-structure is an X-ray enhanced with a film of protuberances modeled after corneal nipples. Using a moth-eye based film in addition to a traditional scintillator could allow a decrease in radiation dosage and offer higher-resolution imaging—both things that would be a huge step forward for medical care and, best of all, patient treatment (The Optical Society, Insects inspire X-ray improvements: nanostructures modeled after moth eyes may enhance medical imaging, http://www.osa.org/en-us/about_osa/newsroom/newsreleases/2012/insects_inspire_x-ray_improvements_nanostructures/, 2012). Though tiny, moth eyes have the potential to contribute enormously to engineering endeavors, serving as a reminder of the infinite amount of knowledge hidden even among nature’s smallest creations.