New Penn physics professor dives deep for research

Alison Sweeney

Shane Anderson

Alison Sweeney, as assistant professor in the Department of Physics and Astronomy in the School of Arts and Sciences, checks a spectrometer from a pool chair.

Alison Sweeney is one of the newest faculty members in the Department of Physics and Astronomy in the School of Arts and Sciences, but until she came to Penn, she didn’t fit into either of those disciplinary boxes. She mostly studied sea life, traveling to places like Palau in the western Pacific Ocean to study exotic squid and giant clams.  

This work recently earned Sweeney the Society for Integrative and Comparative Biology’s 2012 Bartholomew Award, given to young investigators for work in physiology, or functional and integrative biology. She will give a lecture at the Society’s annual meeting in San Francisco in January.

So what is a physicist doing studying giant clams?

"The biology questions I’ve been interested in ultimately required physics to answer," Sweeney says. “My intellectual lineage is in bio-optics and bio-optical materials, specifically looking at the material properties of biological systems and how they generate new and interesting optical phenomenon.”

Giant Clam

Alison Sweeney

Sweeney and her colleagues believe that the reflective structures in giant clams help them grow algae.

Those phenomena are based in a protein called “reflectin,” which is found in a variety of deep-sea squid. The reflectin in the squids’ cells creates a kind of biological reflector with features smaller than the wavelength of visible light—a feat that human technology is only just beginning to replicate in the field of metamaterials. The squid are able to use the reflectin to change the amount of light their bodies reflect as they move into brighter or darker waters, providing them effective camouflage.       

Sweeney and her colleagues theorized that reflectin would also be found in a wide variety of related sea life—mollusks—and discovered a fascinating application in a species of giant clams. “The giant clams use these sub-wavelength structures to optimize the photosynthesis of the algae living in their tissues,” she says. “They are essentially farming the algae for nutrients.”       

While Sweeney’s work is increasingly focused on the physical properties of these structures, she still has her hands in the world of the biological, studying their evolutionary roots and how animals use the properties to survive.

Originally published on October 18, 2012