Dye-labeled polystyrene latex microspheres prepared via a combined swelling-diffusion technique

A series of water-insoluble, biologically compatible dyes, meso-tetraphenylchlorin, meso-tetraphenylporphyrin and chlorophyll-a, were successfully incorporated into beads composed of linear polystyrene (PS) via a tunable combined swelling-diffusion process. Dyed PS beads were prepared by the addition of a dye solution in tetrahydrofuran to an aqueous suspension of 10 μm PS beads in the presence of a poly((ethylene glycol)-b-(propylene glycol)-b-(ethylene glycol)) block copolymer surfactant. The presence of surfactant was found to be beneficial to prevent particle aggregation, especially at tetrahydrofuran contents above 30%. Dye loading was shown to be tunable by simple adjustments in dye composition. Confocal fluorescence microscopy indicated that dyes were distributed uniformly throughout the entire PS bead, but heterogeneously with ∼500 nm diameter droplets, indicative of a separate dye phase within the PS matrix. The stability of dyed beads, indicated by resistance to dye leaching in solvent, was found to be governed by the degree of swelling of PS in the solvent medium. Hence, no leaching was observed even when a good solvent for the dye was used (ethanol), as long as that solvent did not swell the carrier particle, PS. No leaching of dyes from the beads was observed during long-term (2 years) storage in water.

A series of fluorescent dyes were incorporated into unmodified PS latex beads via a solvent (THF)-controlled, combined swelling-diffusion technique.Figure optionsDownload high-quality image (65 K)Download as PowerPoint slideHighlights
► Dye-loaded PS beads are prepared by a combined swelling-diffusion technique.
► A solvent environment of 33 vol.% tetrahydrofuran maximizes dye incorporation.
► Incorporated dyes are distributed throughout the whole volume of the PS bead.
► PS beads inherit the optical properties of the incorporated dye molecules.
► The resistance of dye leaching is determined by the degree of swelling of PS beads.