Structured illumination super-resolution imaging with lanthanide-doped upconversion nanoparticles

Super-resolution microscopy provides a high spatial resolution that is beyond the diffraction barrier and can visualize nano-sized structures and interactions in biological and material study. In recent years, lanthanide-doped upconversion nanoparticles (UCNPs) that can upconvert the near-infrared (NIR) excitation photons to visible emission photons, have been developing as a kind of novel nanoprobes for bioimaging. Here we report the recently developed NIR superresolution imaging techniques by exploring the nonlinear fluorescence responses in UCNPs. Upconversion Nonlinear Structured Illumination Microscopy (U-NSIM) employes nonlinear fluorescence, along with NIR excitation and emission light, to deliver rapid frame rates and high-resolution capabilities, enabling in-depth super-resolution imaging. The tunability of lifetime in UCNPs is also introduced to develop the multiplexed super-resolution imaging with lifetime-engineered nanoprobes. By detecting two emission channels with different nonlinear fluorescence responses, a single doughnut illumination beam is used to scan the sample to generate a Gaussian-like emission point spread function (PSF) and a doughnut-emission PSF simultaneously, which can be fused by algorithms to an optimized super-resolution nanoscopy. These upconversion super-resolution imaging techniques provide new strategies to develop deep-tissue and multiplexed super-resolution imaging and also help to achieve it in a simple optical scheme.