Silica-coating of fluorescent polystyrene microspheres by a seeded polymerization technique and their photo-bleaching property

This paper describes silica-coating of polystyrene microspheres incorporated with fluorescence dyes (fluorescent microspheres) by means of a seeded polymerization technique based on Stöber method. The silica-coating of the fluorescent microspheres was performed in the presence of 0–10 g/l polyvinylpyrrolidone (PVP), 1.13–17 M water, 0–1.2 M aqueous ammonia and 0.00038–0.2 M tetraethoxyorthosilicate (TEOS). The addition of PVP was found to suppress the generation of free silica particles and improve the uniformity of shell thickness. The silica shell thickness increased from 13 to 138 nm with an increase in TEOS concentration at 10 g/l PVP, 0.4 M aqueous ammonia and 10.9 M water. The thickness also increased with the ammonia concentration and the water concentration. However, excess ammonia and water caused aggregation of free silica particles and the polystyrene microspheres. The silica-coated fluorescence microspheres showed more stable fluorescence to laser-irradiation than uncoated microspheres.