Penn Researchers Investigate Squids' Perfect Lenses

A team led by Professor Alison Sweeney and Postdoctoral Fellow Jing Cai investigated the material structure of squid eye lenses.  These spherical lenses achieve remarkable acuity by incorporating a graded refractive index, which reproduces to a high degree of accuracy the ideal parabolic form calculated by Maxwell in 1854.  The team found that S-crystallin proteins in the squid eye accomplish this by behaving as patchy colloids—small molecules that have spots of molecular glue that they use to stick together in clusters. The parabolic gradient of the refractive index arises from differing concentrations of different forms of the S-crystalline proteins, while the patchy behavior of the particles ensures that the correct density forms at every position in the lens and that the system remains transparent and stable for the lifetime of the animal. The evolved squid system gives insight into how to engineer self-assembled systems at the nanometer scale. 

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