CONTAMINATED crime-scene DNA samples that would normally be written off as forensically useless can now be rescued, thanks to amplification enzymes that tolerate pollution.

Before a profile can be obtained from a DNA sample recovered from a crime scene, it must be amplified using enzymes called polymerases. Pollutants such as tobacco or aluminium from drink cans can stop the enzyme working, but now Johannes Hedman and colleagues at the Swedish National Laboratory of Forensic Science have come up with some alternatives to the AmpliTaqGold enzyme, which is preferred by forensic labs.

The team amplified 32 polluted samples of saliva using …