A team led by Purdue Analytical Chemistry Professor R. Graham Cooks created a tool that reads and provides an image of a fingerprint's chemical signature. The technology can be used to determine what a person recently handled. The technology also can easily uncover fingerprints buried beneath others. The research is detailed in a paper published in the August 8, 2008 issue of Science.
Researchers examined fingerprints in situ or lifted them from different surfaces such as glass, metal and plastic using common clear plastic tape. They then analyzed them with a mass spectrometry technique.
Mass spectrometry works by first turning molecules into ions, or electrically charged versions of themselves, so their masses can be analyzed. Conventional mass spectrometry requires chemical separations, manipulations of samples and containment in a vacuum chamber for ionization and analysis. Cooks' technology performs the ionization step in the air or directly on surfaces outside of the mass spectrometer's vacuum chamber, making the process much faster and more portable.
The procedure performs the ionization step by spraying a stream of water in the presence of an electric field to create positively charged water droplets. Water molecules in the droplets contain an extra proton and are called ions. When the charged water droplets hit the surface of the sample being tested, they transfer their extra proton to molecules in the sample, turning them into ions. The ionized molecules are then vacuumed into the mass spectrometer to be measured and analyzed.
Researchers placed a section of tape containing a lifted fingerprint on a moving stage in front of the spectrometer. The spectrometer then sprayed small sections of the sample with the charged water droplets, obtaining data for each section and combining the data sets to create an analysis of the sample as a whole. Software was used to map the information and create an image of the fingerprint from the distribution and intensity of selected ions.
The research was performed within Purdue's Center for Analytical Instrumentation Development located at the Bindley Biosciences Center in Purdue's Discovery Park. The device, called desorption electrospray ionization or DESI, has been commercialized by Prosolia, who funded the research along with the Office of Naval Research.