Told in tears

May 1, 2012
This article appeared in Berkeley Engineer magazine, Spring 2012

Kelly Karns and Amy HerrGrad student Kelly Karns and Amy Herr, assistant professor of bioengineering. (Photo by Noah Berger)Tears reveal more than you think. Amy Herr (at right), assistant professor of bioengineering, and graduate student Kelly Karns have developed a microfluidic assay that tests human tears for eye disease-specific proteins. Because tear proteins are alkaline, they stick readily to conventional assay surfaces and other tear fluid proteins, making clinical testing difficult.

But Herr’s lab bypassed the problem by mixing a fluorescently labeled antibody with the tear sample—under alkaline conditions. The resulting sample was separated by protein electrophoresis, which uses an electric field applied to a gel-filled microchannel to move negatively charged proteins at speeds roughly proportional to size. The labeled antibody specifically bound to the tear biomarker, forming a large, slow-moving protein complex. In less than five seconds, they used fluorescence imaging to measure levels of the protein lactoferrin, which has been linked to the autoimmune disease Sjögren’s syndrome.