Firefly Luciferase Fluc CircRNA incorporates the luciferase sequence and is synthesized through in vitro transcription and cyclization. After transfection into cells, Fluc-CircRNA expresses firefly luciferase (Firefly luciferase) protein within the cells. This protein was originally isolated from the firefly Photinus pyralis. Firefly luciferase is a commonly used bioluminescent reporter molecule, widely applied in studies such as gene regulation, cell viability assays, ATP level analysis, and in vivo imaging. Luciferase catalyzes the oxidation of its substrate luciferin to oxyluciferin in the presence of ATP and oxygen. During the oxidation of luciferin, bioluminescence is emitted. The bioluminescence released during this process can then be measured at a wavelength of 560 nm using a luminometer or liquid scintillation counter. This bioluminescent system, composed of luciferin and luciferase, enables extremely sensitive and efficient detection of gene expression.