Highly functionalized, porous organosilica particles and methods of their synthesis are described that employ high amounts of functional silane such as 3-mercaptopropyl trimethoxysilane. Silane particle diameters are controlled from less than 1 μm to over 100 μm. The particles have a high surface area due to their advantageous internal structures, which consist of large pores, typically up to 10 μm that are linked by small channels of typically about 20 nm diameter. Isothiocyanate modified fluorescent dyes can enter and react with thiol groups inside the pores. The invention also provides clear silica shells of controlled thicknesses to protect fluorescent signals and provide an independent parameter for distinguishing particle types based on light scattering off different sized particles. The particles are stable and useful for many purposes, particularly for optical bar coding in combinatorial synthesis of polymers such as nucleic acid, polypeptide, and other synthesized molecules.