One-step synthesis of water-dispersible silicon nanoparticles and their use in fluorescence lifetime imaging of living cells.

We report a novel method for synthesizing water-dispersible silicon nanoparticles (Si NPs) with a simple one-step procedure using mild reagents (3-aminopropyl) trimethoxysilane (APTES) and ascorbate sodium (AS). This is the first report of "green" synthesis of Si NPs on a large scale and at low cost. The method involves a quick reaction in a commonly used round bottom flask at room temperature and pressure without additional treatment and any special equipment. The as-prepared Si NPs have an average diameter of 2 nm and an emission band at 530 nm with a full width at half maximum height (FWHM) of 70 nm and a quantum yield (QY) of 0.21. Moreover, the fluorescence lifetime of these Si NPs is much longer than that of native fluorophores in living cells. Therefore, these Si NPs allow effective imaging of living cells with a fluorescence lifetime imaging microscope (FLIM). Using the time gating model in FLIM, an excellent image was obtained in which the auto-fluorescence interference of cellular fluorophores was suppressed demonstrating that the Si NPs are promising probes for cell imaging particularly using the FLIM technique.