Bound states in the continuum help shrimp eyes to catch more light

Optical bound states in the continuum (BICs) have recently attracted a great deal of attention as an efficient way to localize and manipulate light at nanoscale. Traditionally, generation of BICs has relied on using artificial structures where suppression of radiative losses leads to very high Q factors. Here we show that BICs may play an important biological role by boosting light-matter interaction in a biogenic nanostructure: tapetum reflector of a shrimp eye. Enveloping photosensitive units of the retina (rhabdoms), this system contains quasi-periodic arrays of spherical core-shell nanoparticles which include concentric lamellae of single-crystal isoxanthopterin nanoplates arranged around a hollow core. The radial alignment of the plates gives rise to the spherical anisotropy of the nanoparticles which provides access to quasi-BIC modes in a full visible domain. Thus, a tapetum reflector hosting BICs maximizes light interaction with rhabdoms, enhancing the eye’s sensitivity. Our findings suggest that BICs, previously associated with man-made structures only, can be generated in biogenic structures, performing crucial optical functionalities in living organisms.