US Patent 7367505 - Quantum dot dispensing and detecting

http://www.freepatentsonline.com/7367505.html

This patent from Caltech (priority June 12, 2003) teaches methodology for using quantum dots for optical coding. Claim 1 reads:

1. A method of dispensing and detecting fluorescent quantum dots, comprising:

dispensing said dots on a surface at a plurality of locations where each location includes quantum dots of a plurality of center wavelengths;

exciting said dots with a UV light until said dots fluoresce; and

analyzing said fluorescence with a spectrometer.

Unfortunately some pertinent prior art may have been overlooked such as:

US Patent 6617583- "A novel encoding system and methods for determining the location and/or identity of a particular item or component of interest is provided. In particular, the present invention utilizes a "barcode" comprising one or more sizes of semiconductor nanocrystals (quantum dots) having characteristic spectral emissions, to either "track" the location of a particular item of interest or to identify a particular item of interest. " (from abstract)