Traditional methods for fingerprinting often utilize powders, liquids, or vapors, which can destroy fingerprints for subsequent analysis. A technique using X-rays aims to overcome this issue. 
This technique is designed to detect the salts in human sweat, which form the outline of fingerprints. If a fingerprint retains a sufficient amount of salt, the machine can identify it without interfering with the sample.
Scientists from the Los Alamos National Laboratory have employed a thin beam of X-rays to illuminate fingerprints using a method called X-ray fluorescence (MXRF). Elements such as sodium, potassium, and chlorine present in human sweat absorb the X-rays and emit light, or “fluorescence,” at a low frequency.
This technique can also identify these substances when a finger is covered with cosmetics, dirt, saliva, or sunscreen – pollutants that compromise the accuracy of traditional crime scene investigation methods.
The method can capture fingerprints on various materials, including paper, wood, leather, plastic, and even human skin. It is also useful for identifying children’s fingerprints, who have less oil on their skin. Additionally, experts may extract a wealth of information from fingerprints, such as the last food item consumed by a murder suspect.
“This is a new tool for forensic investigators, allowing them to detect fingerprints using a non-destructive method that might be overlooked by traditional techniques,” said Chris Worley, the research team leader.
The MXRF method will require another 2-5 years before it can be implemented in practice. Its limitation is that sometimes the detectable material may be too small. X-rays do not recognize lighter (and more common) elements like carbon, nitrogen, and oxygen.
