Crime scene investigations: Gunshot residue analysis on a single gunpowder particle / Eurekalert.org, 6 April 2008
http://www.eurekalert.org/pub_releases/2008-04/acs-csi031108.php
"Scientists in Texas are reporting development of an highly dependable, rapid, and inexpensive new method for identifying the presence of gunshot residue (GSR). The test fills a GSR-detection gap that results from wider use of “green” — lead free — ammunition."