US Patent 7972426 - Nanomaterial security mark

http://www.freepatentsonline.com/7972426.html

This patent from HP teaches nanomaterial based inks used as authentication marks on checks, documents, or other media. Some relevant prior art not considered during the examination of this patent is US Patent 6,617,583 from M.I.T. and US Patent 7,917,298 (priority 2003) from Nanosys. Claim 1 reads:

1. An ink including light-activated components utilized for printing a security mark, comprising:

a first ink component that defines a first spectral property, the first component being chosen from a nanocrystal, a quantum dot, and a carbon nanotube;

a second ink component that defines a second spectral property different from said first spectral property, the second component being chosen from a nanocrystal, a quantum dot, and a carbon nanotube; and

a solvent in which said first and second ink components are dispersed;

wherein the first and second spectral properties are each a wavelength specific feature chosen from the group consisting of an absorptive feature and a Raman feature.