These vials may look like they're filled with colored water, but they really contain nanocrystals reflecting different colors under ultraviolet light. The tiny crystals, made of semiconducting compounds, are called quantum dots. Depending on their size, the dots emit different colors that let scientists use them as a tool for detecting particular genes, proteins, and other biological molecules. Courtesy of Shuming Nie, professor of biomedical engineering at Emory University. Featured in the April 19, 2005, issue of Biomedical Beat. High res. image (76 KB JPEG)