Achieving high-efficiency emission depletion nanoscopy by employing cross relaxation in upconversion nanoparticles

Abstract

Stimulated emission depletion microscopy provides a powerful sub-diffraction imaging modality for life science studies. Conventionally, stimulated emission depletion requires a relatively high light intensity to obtain an adequate depletion efficiency through only light–matter interaction. Here we show efficient emission depletion for a class of lanthanide-doped upconversion nanoparticles with the assistance of interionic cross relaxation, which significantly lowers the laser intensity requirements of optical depletion. We demonstrate two-color super-resolution imaging using upconversion nanoparticles (resolution ~ 66 nm) with a single pair of excitation/depletion beams. In addition, we show super-resolution imaging of immunostained cytoskeleton structures of fixed cells (resolution ~ 82 nm) using upconversion nanoparticles. These achievements provide a new perspective for the development of photoswitchable luminescent probes and will broaden the applications of lanthanide-doped nanoparticles for sub-diffraction microscopic imaging.

Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications

“…From microscopy to nanoscopy with breaking the optical diffraction limit, UC‐STED is an emerging technology enabling extensive development of the usage of the UCNPs for subcellular fine structure imaging. In 2017, Zhan et al demonstrated the first super‐resolution imaging of the cytoskeleton of HeLa cells with UCNPs . The synthesized 11.8 nm NaGdF 4 UCNPs were highly doped with Tm 3+ , up to 10 mol%, which enabled donut beam depletion of the emission light to gain super‐resolution imaging at blue wavelength.…”

“…i–iv) Areas selected from (a) and (b) (marked by white dotted squares) and shown corresponding line profile analyses. Reproduced with permission . Copyright 2017, Macmillan Publishers Limited.…”

Photon Upconversion Kinetic Nanosystems and Their Optical Response

“…reported that the blue upconversion emission at 455 nm of Tm 3 + ions in UCNPs doped with high concentrations of thulium ions, excited at a wavelength of 980 nm, can be optically inhibited by a laser at 808 nm . Interestingly, in an independent work we observed similar optical inhibition of the 455‐nm emission band of Tm 3 + ions (excited at 975 nm) by the addition of an 810‐nm laser irradiation in high Tm 3 + ‐doped UCNPs . Based on the advancement of optical depletion of upconversion luminescence, UCNPs have been used as probes for multi‐photon super‐resolution microscopy .…”

“…Based on the advancement of optical depletion of upconversion luminescence, UCNPs have been used as probes for multi‐photon super‐resolution microscopy . Particularly, we have implemented cytoskeleton protein super‐resolution imaging of immunolabeled HeLa cells using antibody‐conjugated UCNPs . UCNP‐mediated nanoscopy provides many advantages, including low laser intensity requirement, large penetration depth, non‐photobleaching and non‐photoblinking properties, cost‐effective and simplified imaging systems.…”

Nanoparticle Probes for Super‐Resolution Fluorescence Microscopy

“…NaYF 4 nanocrystals, highly doped with ytterbium (Yb 3+ ) and thulium (Tm 3+ ) ions, have been used for STED imaging (Figure ) ,. These NPs can be excited and depleted using low‐power (<0.2 MW/cm 2 ) infrared laser beams by skillfully exploiting energy transfer processes between the ions.…”