Neutron Activation Analysis (NAA) as a means for testing contaminant levels

"Elemental Analysis Inc., a privately held trace element analysis firm, today released a white paper which examines purity testing levels....(t)he white paper reveals that irradiation testing of nano-medicines and nano-delivery devices can insure detection of contaminants to levels as sensitive as one part per quadrillion for 40 trace elements, including gold." Look here and here.