How Luminol Works. ‘There’s a lot of unbelievable technology in cop shows and movies — computers that can zoom in and “enhance” a tiny section of a video frame; machines that can isolate a particular background voice from a muffled recording in a matter of seconds. Most of this stuff is pure fiction, fabricated by the writers to move the plot along. But one of the most outlandish TV cop tools, a special chemical that reveals invisible blood traces, is entirely real.’
Luminol: The Blood Detector: In a crime scene, large pools of spilled blood are easy to spot. But what about blood that’s been washed away? Enter luminol. Luminol is a chemical that glows greenish-blue when it comes into contact with blood — even traces that are years old. To be exact, it reacts to hemoglobin, an oxygen-carrying protein in red-blood cells. Luminol is so sensitive, it can detect blood at 1 part per million. In other words, if there is one drop of blood within a container of 999,999 drops of water, luminol will glow.