Abstract

“Patchy colloids” are systems in which constituent particles exhibit rich phase and assembly behavior due to the anisotropic distribution of attractive and repulsive “patches” on particle surfaces. These systems show great promise for generating sophisticated new, self-assembled material properties, but the colloidal particles used in current experimental systems are typically micron-scale or larger, limiting the range of material properties that can be explored. Globular proteins are an intuitive choice for roughly spherical particles an order of magnitude or more smaller than currently tractable colloidal patchy particle systems, but naturally evolved proteins are typically strongly selected to avoid disordered aggregation to avoid poisoning the cells which must make them. However, cephalopods have evolved a diverse array of complex optical and photonic structures that appear to self-assemble from globular proteins interacting as patchy colloids. Therefore, we explore naturally evolved, self-assembling photonic systems in cephalopods as inspiration for novel hierarchically ordered, self-assembling materials.

Our preliminary evidence suggests that the self-assembling photonic devices in cephalopods are structured in a manner consistent with theoretical predictions from the patchy colloid framework. In particular, the squid lens system appears to have evolved a system of patchy proteins of continuously decreasing average coordination number with lens radius, resulting in a graded refractive index lens from a single-index evolutionary precursor. This talk will explore experimental and modeling evidence from the diverse, living optical systems in cephalopods suggesting that the optical properties of both the graded-index lenses in the eyes, and the sophisticated reflectors in the skin evolved for camouflage may arise from proteins following patchy-colloid-like assembly rules.