Systematic Tuning the Hydrodynamic Diameter of Uniformed Fluorescent Silica Nanoparticles

We report a facile method for systematic tuning of the hydrodynamic diameter of uniformed fluorescent silica particles in the size range from 12 to 465 nm. Dynamic light scattering and electron microscopy studies demonstrate that the hydrodynamic size distribution of the silica particles is uniform. ' We show that the initial amount of ethanol and ammonia are essential to tune the size of these particles. The hydrodynamic diameter of such a particle increases as the amount of ammonia is increased. An increase in the amount of ethanol leads to the formation of smaller particles. A higher initial amount of ethanol yields an increase in the concentration of ethoxide ions and a decrease in the concentration of hydroxide ions. Such control over the concentration of hydroxide ion, which is responsible for the formation of siloxane bonds, causes a controlled-growth of the silica particles, resulting in precise tuning of the hydrodynamic size. We confirm that a linear relationship exists between the size and brightness of particles, demonstrating that the amount of dye molecules in such particles can be regulated by the presented method. We prove that the silica network provides protection for dye molecules encapsulated in particles against solvents, fluorescence quenchers, and unfavorable pH of environments. Moreover, the fluorescent silica particles with the size of 12, 50, and 250 nm were found to not be cytotoxic against the epithelial cell lines of MCF7 and PC3, even when the dosage levels up to 1.0 mg/mL and incubation periods up to 72 h were applied.