Bioluminescence Living Imaging (BLI) visualizes light produced by luciferase within a living subject. Luciferases are unique light-producing enzymes capable of using luciferin as a substrate. The most commonly used luciferase for imaging applications is firefly luciferase, which catalyzes luciferin oxidization in the presence of oxygen and ATP. The DNA coding sequence of firefly luciferase has been identified and further optimized for mammalian expression.
With the aid of molecular biology techniques, a luciferase-expressing cassette can be genetically introduced into viruses, cancer cells, or even the whole animal (transgenic) for BLI imaging research. One great advantage of luciferase-based bioluminescence imaging is the very low background signal. Since the substrate has uniquely evolved together with its partner enzyme, D-luciferin is not a substrate for any mammalian enzymes. Thus BLI imaging is extremely specific and highly sensitive; only luciferase-expressing cells are able to generate light signal.