US Patent 7785717 - Q-dot encoded media

http://ip.com/patent/US7785717

This patent from Life Technologies has relatively early priority (1998) and teaches forming coded patterns on media such as ID cards and currency using multi-spectral (plural color) nanocrystals. Claim 1 reads:

1. An article comprising:

a substrate having an identifiable code pattern of fluorescent water soluble quantum dots operably bound to the substrate, said identifiable code pattern including more than one color of quantum dot;

the identifiable code pattern including encoded data; and

wherein the identifiable code pattern is in a machine readable format,

wherein the quantum dot is operably bound to a molecule that provides a reactive functionality that enables the quantum dot to be soluble in water.