Marking Animals with Micro-Tags of Chemical Elements for Identification by X-Ray Spectroscopy

Abstract

This report describes a method of marking living organisms. As an illustration of the method, foreign chemical elements are incorporated into small salmon and the analytical technique of X-ray fluorescence spectroscopy is used to detect and measure minute quantities in the tissues. Mixtures of elements, either in equal or varying concentration, are used to generate a code. Decoding is readily accomplished by irradiating the tagged organisms and monitoring the X-ray fluorescence produced. A large number of unique combinations appear possible using the method as described. Mixtures of chemical elements (atomic numbers 37–69) were suspended in silicone rubber and injected directly into fish tissue. In this manner tags 1 mm² in area were incorporated in the tissue and decoded by nondestructive analysis.