A large-scale synthetic strategy is developed for facile one-pot aqueous synthesis of silicon nanoparticles (SiNPs) yielding similar to 0.1 g SiNPs of small sizes (similar to 2.2 nm) in the 10 min. The as-prepared SiNPs feature strong fluorescence (photoluminescence quantum yield of 20-25%), favorable biocompatibility, and robust photo- and pH-stability. Moreover, the SiNPs are naturally water dispersible, requiring no additional post-treatment. Such SiNPs can serve as highly photostable bioprobes and are superbly suitable for long-term immunofluorescent cellular imaging.