Patent ID: 7255895

Claim:
A method for generating a plurality of microparticle populations of different dye concentrations wherein dye is loaded into polymer microparticles to generate said microparticle populations, comprising: (a) providing: (i) at least one first solvent in which the dye and the microparticle polymer are soluble; (ii) at least one tuning solvent in which the dye and the microparticle polymer are not or only weakly soluble, said first and tuning solvents being immiscible or at most partially miscible; (iii) at least one third solvent in which the dye and the microparticle polymer are not or only weakly soluble, said third solvent being miscible with the first and tuning solvents; (b) forming a plurality of suspensions of said polymer microparticles, each in a designated volume of a mixture including the tuning solvent and the third solvent; (c) adding to said polymer microparticle suspension a solution including the dye dissolved in said first solvent to form a homogeneous solution in the mixture of the first, tuning and third solvents; and (d) increasing the uptake of dye into the polymer microparticles in at least one of said populations relative to another of said populations by decreasing the solvency of the mixture of the first, tuning and third solvents for the dye.