Precision fluorescently dyed particles and methods of making and using same

A method of staining polymeric microspheres with two or more fluorescent dyes comprising:

• (a) combining at least two fluorescent dyes in a solvent mixture comprising at least one organic solvent in which the at least two fluorescent dyes are soluble and at least one alcoholic solvent in which the at least two fluorescent dyes are less soluble, to provide a solution of mixed dyes, which has the capacity to swell at least partially but not dissolve a plurality of polymeric microspheres brought into contact with said solution;
• (b) contacting a plurality of dehydrated and dried polymeric microspheres with said solution for a period of time sufficient to provide uniform staining of substantially all of the members of said plurality of polymeric microspheres with the at least two fluorescent dyes,
• said at least two fluorescent dyes being selected such that on isolation and excitation of said dyed plurality of polymeric microspheres, a distinct fluorescence signal is emitted from each dye, the intensity of which emitted signal is proportional to the amount of said dye in said dyed plurality of polymeric microspheres.