Nanoparticle-Assisted STED Nanoscopy with Gold Nanospheres

We demonstrate stimulated emission depletion (STED) microscopy with 20 nm gold nanospheres coated by fluorescently doped silica. We demonstrate significantly improved spatial resolution down to 75 nm, which is the first time that hybrid NPs are used in STED imaging beyond the diffraction limit of confocal microscopy. Unlike previous demonstrations of super-resolution with metal nanoparticles with different techniques, this 3.3-fold resolution improvement was limited only by the particle size. The STED intensity required for this is almost twice lower than for conventional STED based on dye alone, and we observe no melting or displacement of the NPs at the utilized intensities. Moreover, we show that the nanoparticles can be imaged in an aqueous environment, demonstrating the relevance to bioimaging. Finally, we also show, for the first time in this context, an up to 3-fold reduction in the rate of photobleaching compared to standard dye-based STED, thus enabling sustainably brighter images.