Finding even small blood traces at crime scenes is often of great importance in forensic science. The most common method for this is the use of luminol, which reacts with the heme group in blood and creates a chemiluminescence effect that makes the stains glow blue. An oxidant is required to activate the luminol and usually, a solution of hydrogen peroxide and sodium hydroxide is used for this purpose. However, a range of transition metal ions and complexes can react with this mixture and cause false positives.

Guobao Xu, Chinese Academy of Sciences, Changchun, and colleagues have used artemisinin, a malaria drug, to create a more selective test. Artemisinin is a naturally occurring peroxide that is relatively stable in the presence of common metal ions, but still reacts with blood traces. The team prepared a solution of luminol, artemisinin, and a carbonate buffer and tested the mixture on dried diluted bloodstains, coffee stains, tea stains, and brown sugar stains.

The team used a smartphone camera with long exposure times to visualize the glowing stains. The method shows excellent selectivity and only produces a detectable chemiluminescence effect on the bloodstains. The sensitivity is also high and allows the detection of blood down to dilution factors of 100,000.

• Artemisinin-Luminol Chemiluminescence for Forensic Bloodstain Detection Using a Smart Phone as a Detector,
  Wenyue Gao, Chao Wang, Kateryna Muzyka, Shimeles Addisu Kitte, Jianping Li, Wei Zhang, Guobao Xu,
  Anal. Chem. 2017.
  DOI: 10.1021/acs.analchem.7b01000