A group led by Joe Wang at the University of California-San Diego, USA has developed a new forensic technique that can detect gunshot residue at the scene of the crime.  

Gunshot residue consists of a large mix of compounds including both inorganic metals from the cartridge, bullet and the gun, and more complex organic compounds from the primer and gunpowder. 

However, although gunshot residue contains this mix (including antimony, lead, barium, nitroglycerin and dinitrotoluene) it is currently detected by measuring the presence of just one component, such as antimony, which is unreliable at low concentrations as there are other sources of contamination.

In addition, tests currently involve taking a swab and then analysing it back in the lab. Being able to take the equipment out to the crime scene and perform tests without the need for specialised personnel is the eventual goal of the research, says Wang. 'We want to identify, in the field, individuals who have fired a weapon,' he explains. 

Wang's team has put together a method where both the inorganic and organic components of gunshot residue can be measured at the same time. Measuring both the heavy metal and explosive parts makes the identification of gunshot residue more definitive, which is crucial in forensic cases. 

The new detection method is based on an electrochemical technique called voltammetry - a potential is applied to a solution that includes the material you want to detect, and then the current is measured as you change the applied potential. This gives you an electrochemical signature that allows you to work out what is in your sample. One of the main advantages is that this is a cyclic method, which means very little sample is needed, but lots of detailed information can be gathered, because you are running the test over and over again. 

Damien Arrigan, an expert in electrochemistry and sensors from Curtin University, Australia, says that 'the possibilities to deploy this as a practical strategy for analysis in the field are immense, as electroanalytical methods and strategies readily lend themselves to miniaturisation and portability as well as simplicity of operation and data analysis'.  

Arrigan goes on to point out that some issues still need to be tackled before it can be successfully used in practice, including testing real gunshot residue. Wang agrees that the next step will be complete validation in the field, to really demonstrate the potential of the technique.