Polymeric nanoparticles with sufficient solid concentration could be synthesized by emulsion polymerization without using surfactants. The polymeric nano-colloids with surface functional groups were synthesized to obtain carboxylated polystyrene beads or amidine polystyrene nanoparticles. Sodium styrene sulfonate was also adopted for the synthesis of sulfonated polystyrene nanoparticles less than 50 nm in diameter using KPS as an initiator. The diameter of the carboxylated particles could be controlled by adjusting the reaction parameters such as the amount of monomer, cross-linker, and polymerization temperature. The range of the diameter of the resulting polymeric beads was 100 to 200 nm, which is useful size range for bio-sensing purposes. Amidine polystyrene nanoparticles less than 50 nm could be fabricated using a cationic comonomer, MTC. As an application of the polymeric beads, the porous inorganic particles could be synthesized by colloidal templating using emulsions as micro-reactors.