Incorporating anionic dyes into silica nanoparticles by using a cationic polyelectrolyte as a bridge

A negatively charged dye, 8-hydroxypyene-1,3,6-sulfonic acid trisodium salt (HPTS), was successfully incorporated into a silica matrix by using a positively charged polyelectrolyte, poly (diallyldimethylammoniumchloride) (PDADMAC) as a bridge. The positive charges of PDADMAC were partially neutralized by HPTS upon the formation of PDADMAC–HPTS complexes. After being introduced into a Stober system and pre-hydrolyzed for a finite time, the surface charge of the complexes was rapidly reversed from positive to negative due to the absorption of the negatively charged silica species on their surface, which was important to avoid flocculation of the complexes and allow the growth of the silica particles. Stability of the complexes and thus the size of resulting particles were tunable by changing either the positive charges of the complexes or the pre-hydrolyzation time of the Stober system. The optical performance of the silica particles was improved and the leakage of the dye from the particles was greatly suppressed due to the electrostatic interaction between the dye and polyelectrolyte.