Monodispersed or narrow-dispersed melamine-formaldehyde resin polymer colloidal spheres: preparation, size-control, modification, bioconjugation and particle formation mechanism.

A two-step organic sol-gel process for the preparation of monodispersed or narrow-dispersed melamine-formaldehyde (MF) resin polymer colloidal spheres in water was developed. A modified Stöber process was used to coat the MF colloidal spheres with silica shells, which rendered the surfaces of these colloidal spheres easily modifiable. The prepared MF@silica core-shell composite colloidal spheres were then bioconjugated with bovine serum albumin to demonstrate the feasibility of using these colloidal particles as supporting materials in bioassays. The particle formation mechanism of this organic sol-gel process was investigated by time-resolved microscopic analysis. The prepared MF nano-/microscale resin polymer spheres were monodispersed or narrow-dispersed with a controllable average size ranging from 30 nm to 250 nm and from 0.8 μm to 4.5 μm. The spheres were stable in aqueous or organic solvents and after heat treatment above 300 °C. A "controlled aggregation" model was proposed to explain the influences of the key factors in this process.