Patent ID: 7445844

Claim:
A population of polymeric microspheres dyed with two or more fluorescent dyes, obtained by a method comprising: treating polymeric microspheres by adding a polar organic solvent to an aqueous solution containing the polymeric microspheres to produce a mixture; and adding at least two fluorescent dyes to the mixture such that the polymeric microspheres are stained with the at least two fluorescent dyes, wherein the at least two fluorescent dyes are selected such that on isolation and excitation of the polymeric microspheres, a distinct fluorescence signal is emitted from each dye, wherein the distinct fluorescence signals have an intensity proportional to the amount of the dye in the polymeric microspheres, and wherein the distinct fluorescence signals are substantially equivalent to targeted fluorescence signals that have been used to determine a concentration ratio of the at least two fluorescent dyes added to the mixture.