Photoblinking upconversion nanoparticles for super-resolution imaging
Single-molecule localization microscopy (SMLM) surpasses the diffraction limit to achieve molecular-scale resolution, but conventional probes suffer from photobleaching, limiting imaging duration. In a recent Nature Photonics article, Ren and co-workers introduced spontaneous photoblinking upconversion microscopy (SPUM) using Yb3+/Ho3+ co-doped core–shell–shell upconversion nanoparticles (UCNPs, NaYF4@NaYb/HoF4@NaLuF4). These UCNPs exhibit exceptional photostability and persistent, reversible blinking under 976 nm continuous-wave excitation, with negligible photodegradation. The blinking mechanism involves a Yb3+ multiphoton process coupled with defect-mediated energy trapping, switching the UCNPs between emissive (on) and non-emissive (off) states. Kinetic analysis revealed single-exponential bright-state dwell times and biexponential dark-state dwell times, indicating one decay pathway into a non-emissive state and two recovery pathways. In live-cell imaging, synchronized transport of UCNPs maintained constant interparticle distance and near-unity positional correlation. In fixed cells, Fourier ring correlation (FRC) resolution reached 30 nm, confirming sub-50 nm performance in biological specimens. This work provides an unprecedented combination of low duty cycle and photostability, establishing a foundation for non-photobleaching luminescent nanomaterials in long-term super-resolution imaging and nanoscale tracking.