Fluorescent labeling of proteins such as antibodies, DNA, and lipids is widely used to investigate and better understand protein structure and function. The fluidiphore rapid amine 503 is an amine-reactive fluorescent label that, once conjugated to its binding partner, absorbs at 503 nm. The fluidiphore rapid amine 503 labeling kit is designed to bind proteins in 30 minutes rather than hours to overnight. In addition, the kit does not require a purification step, which is due to a triple-lock against background effects. There is also an observable color change from blue to red/yellow, which confirms that labeling is taking place, giving researchers additional confidence in the process.