Abstract: 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. The semiconductor nanocrystals used in the inventive “barcoding” scheme can be tuned to a desired wavelength to produce a characteristic spectral emission in narrow spectral widths, and with a symmetric, nearly Gaussian line shape, by changing the composition and size of the quantum dot. Additionally, the intensity of the emission at a particular characteristic wavelength can also be varied, thus enabling the use of binary or higher order encoding schemes.