Photoactivation of Luminescent Centers in Single SiO2 Nanoparticles

Photobleaching of fluorophores is one of the key problems in fluorescence microscopy. Overcoming the limitation of the maximum number of photons, which can be detected from a single emitter, would allow one to enhance the signal-to-noise ratio and thus the temporal and spatial resolution in fluorescence imaging. It would be a breakthrough for many applications of fluorescence spectroscopy, which are unachievable up to now. So far, the only approach for diminishing the effect of photobleaching has been to enhance the photostability of an emitter. Here, we present a fundamentally new solution for increasing the number of photons emitted by a fluorophore. We show that, by exposing a single SiO2 nanoparticle to UV illumination, one can create new luminescent centers within this particle. By analogy with nanodiamonds, SiO2 nanoparticles can possess luminescent defects in their regular SiO2 structure. However, due to the much weaker chemical bonds, it is possible to generate new defects in SiO2 nanostructures using UV light. This allows for the reactivation of the nanoparticle's fluorescence after its photobleaching.