The preparation of protein doped silica particles is impeded by the difficulty of incorporating proteins within the silica mesostructure under conditions that do not lead to denaturation. Herein, the synthesis of spherical silica particles (diameter 150 nm–550 nm) under protein friendly conditions in a one step process is described. Diglyceroxysilane (DGS) was reacted in ethanol and methanol-free conditions in pure water or in buffer solutions with or without the presence of additional glycerol. Stabilization of the particles, consistent with steric stabilization, was obtained using poly(ethylene glycol) (PEG) of various molecular weights and with various end groups, including allyl and (CH2)3Si(OEt)3 groups, as a co-reagent. The particles can be prepared at ambient temperature and are reasonably monodisperse in size. At large molecular weights, all PEG led to stable, spherical particles. At lower molecular weights, hydrophobic end groups were necessary to prepare particles. The influence of different molecular weights of PEG, additives and reaction conditions on the size and porosity of particles are analyzed with SEM, TGA and nitrogen adsorption measurements. To demonstrate the biocompatibility of the processing conditions, horse radish peroxidase (HRP) was incorporated into the particles and was observed to remain active for more than 3 months.