Non-bleaching Fluorescence Emission Difference Microscopy Using Single 808-nm Laser Excited Red Upconversion Emission

Optical super-resolution microscopy has become a powerful technique to help scientists to monitor the sample of interest at nanoscale. Fluorescence emission difference (FED) microscopy, a very facile super-resolution method, does not require high depleting laser intensity and is independent on the species of agents, which makes FED microscopy possess great potential. However, to date, the biomarkers applied in FED microscopy usually suffer from a photo-bleaching problem. In this work, by introducing Er activated upconverting nanoparticles with red-color emission and non-photobleaching properties, we demonstrate nonbleaching super-resolution imaging with FED microscopy. The dopant neodymium ions (Nd) can work as highly efficient sensitizing ions and enable near infrared 808-nm CW laser excitation of relatively low power, which would potentially reduce high intensity/short-wavelength light induced tissue damage. Both simulations and experiments on monodispersed NaYF:Nd/Yb/Er@NaYF:Nd UCNPs also indicate that the easy saturation of the multiphoton properties of these UCNPs is beneficial to resolution enhancement in FED microscopy.