Roger Tsien

University of California, San Diego

Roger Yonchien Tsien was an American biochemist and cell biologist at UC San Diego, celebrated for his transformative contributions to the development and application of fluorescent proteins. Building on the original discovery of green fluorescent protein (GFP) by Osamu Shimomura, Tsien engineered a diverse palette of GFP variants with shifted excitation and emission spectra — including cyan, yellow, and red fluorescent proteins — enabling researchers to simultaneously image multiple cellular components in living cells with unprecedented color discrimination. He also designed calcium-sensitive fluorescent indicators such as fura-2, which became the standard tool for measuring calcium signaling in living cells, and contributed membrane-permeable probes for imaging specific cellular organelles. Tsien shared the 2008 Nobel Prize in Chemistry with Shimomura and Martin Chalfie. His inventions are used in virtually every biology and pharmacology laboratory worldwide and have driven a multi-billion-dollar market for fluorescent reagents, imaging instruments, and drug-screening assays. Tsien passed away in 2016.