Watching lanthanide nanoparticles one at a time: characterization of their photoluminescence dynamics at the single nanoparticle level

Lanthanide nanoparticles (LnNPs) feature sharp emission lines together with millisecond emission lifetimes which makes them promising luminescent probes for biosensing and bioimaging. Although LnNPs are gathering a large interest, their photoluminescence properties at the single nanoparticle level remain largely unexplored. Here, we employ fluorescence correlation spectroscopy (FCS) and photoluminescence burst analysis to investigate the photodynamics of Sm and Eu-based LnNPs with single nanoparticle sensitivity and microsecond resolution. By recording the photoluminescence intensity and the number of contributing LnNPs, we compute the photoluminescence brightness per individual nanoparticle, and estimate the actual number of emitting centers per nanoparticle. Our approach overcomes the challenges associated with ensemble-averaged techniques and provides insights into LnNP photodynamics. Moreover, we demonstrate our microscope capability to detect and analyze LnNPs at the single nanoparticle level, monitoring both photoluminescence brightness and burst duration. These findings expand our understanding of LnNPs and pave the way for their advanced biosensing applications at the single nanoparticle level.