Patent ID: 7912653

Claim:
A method of encoding and authenticating a nanocrystal spectral code, the method comprising: providing a composition comprising a population of nanocrystals that emit light when excited, the population comprising two or more different subsets of nanocrystals wherein each subset comprises a plurality of quantum dots of the same size and/or the same composition; determining one or more optical properties of the composition when excited with one or more select excitation wavelengths to encode a unique spectral code for the composition, the unique spectral code comprising at least one optical property defined by the interaction of optical properties of at least two of the two or more different subsets of nanocrystals, wherein the interaction comprises an interaction between the emission frequency of at least the first said subset and the emission frequency of at least the second said subset; tagging at least a first object with the composition; exciting the first object and/or a second tagged object with the one or more select excitation wavelengths; detecting emission wavelengths emitted from the composition of nanocrystals on the first and/or second tagged object; and determining whether the first or second tagged object has the unique spectral code; wherein said step of determining one or more optical properties occurs before said tagging step, and said tagging step occurs before said step of determining whether the object is tagged with the spectral code.