Topology-Engineered Upconversion Nanoparticles for Low-Power U-STED Super-Resolution Imaging

ABSTRACT

Lanthanide-doped upconversion nanoparticles (UCNPs) are attractive probes for super-resolution microscopy due to their photostability, non-bleaching emission, and compatibility with low-intensity near-infrared excitation. However, achieving efficient upconversion stimulated emission depletion (U-STED) imaging remains challenging, as conventional UCNP designs largely overlook the role of spatial ion topology, leading to inefficient energy transfer and high laser power requirements. Here, we introduce a topology-driven design strategy that engineers energy transfer networks in core–shell UCNPs to enable low-power U-STED imaging without sacrificing emission brightness. By spatially separating Yb³⁺ sensitizers and Tm³⁺ activators within 50-nm nanoparticles, we create geometry-controlled energy pathways that enhance energy migration and cross-relaxation.
This results in strong 450-nm upconversion emission and a reduced saturation intensity of 0.06 MW cm⁻². Using this optimized architecture, we achieve U-STED imaging with 65-nm lateral resolution at substantially reduced excitation and depletion powers, establishing topology-guided dopant engineering as a powerful design principle for low-phototoxicity super-resolution imaging.