If only life was like television. The cast members of CSI enter the crime scene with their gadgets and spray bottles of Luminol, spray a bit onto a surface, and see it glow at the telltale sign of a bloodstain. Cut to commercial, and 90 seconds later when the show resumes, those same intrepid criminalists are kicking in doors at a suspect’s house.
While we’re not likely to see accurate portrayals of investigations on shows like CSI, some new research may make the real-life investigative process simpler. A paper published last September, in Analytical Chemistry by five researchers at the University of South Carolina describes a technique where infrared light is shone on the surface to be analyzed, and the light reflected from that surface filtered through a plate coated with a thin layer of the protein albumin. The albumin absorbs wavelengths of light not characteristic of blood, causing the image viewed through the filter to reveal any blood that might be present.
Unlike Luminol, this method doesn’t involve the use of any reagents or other wet chemistry. Luminol has some significant drawbacks. First, it’s expensive, at around $2.00 per ounce, and it has a limited shelf life. It’s mildly toxic, and you don’t want to be breathing it for very long or very frequently. While it does cause blood to fluoresce a blue light, the effect lasts for only about 30 seconds, and requires darkness to see it at all. Blood contaminated with Luminol is still viable for DNA analysis, but the spray can smear fingerprints and spatter patterns that are of equal evidentiary value. And Luminol isn’t specific for blood. The chemical reacts with the iron contained in blood hemoglobin, but the chemiluminescence is also activated by copper or substances containing copper, certain types of bleach, urine, and feces.
The “blood camera” envisioned by researchers Stephen Morgan and Michael Myrick would have its own infrared light source that would be shone onto the sample surface, and reflected back into the camera lens. The lens would incorporate the albumin filter. The operator would observe the surface and record images using a display like that in any other digital camera. The sample itself would remain as found until a sample was taken for DNA or other analysis.
This technique has promise for detection of substances other than blood. By altering the composition of the filter, the camera could reveal the presence of illicit drugs, explosives, sweat and lipids found in latent fingerprints, and other substances specifically. Because this research is new, no products incorporating it are on the market yet.