There is a continuous demand for imaging probes offering excellent performance in various microscopy techniques for comprehensive investigations. of cellular processes by more than, one technique. FluoreScent nanodianiond gold nanoparticles (END Au) constitute a new class of "all in -one" hybrid particles providing.unique features fOr multimodal imaging including optical imaging, eleCtron microscopy, and, and potentially even quantum, sensing. COnfocal and optical coherence microscopy of the END Au allow fast investigations inside living cells via emission, scattering, and photothermal imaging techniques because, the END 'emission is not quenched by AuNPs. In electron microscopy, transmission electron microscopy (TEM) and. scanning transmission electron microscopy (STEM) analysis of END Au reveals greatly enhanced contrast due to the gold particles as well as an extraordinary flickering behavior in three-diniensional Cellular environments originating from the nanodiamonds. The unique multimodal imaging characteristics of END Au enable detailed studies inside cells ranging from statistical distributions at the entire cellular level (micrometers) down to the tracking of individual particles in sub cellular organelles (nanometers). Herein, the processes of endosomal membrane uptake and release of FNDs were elucidated for the first time by the imaging of individual END Au hybrid nanoparticles with single-particle resolution. Their convenient preparation, the availability of various surface groups, their flexible detection modalities, and their single-particle contrast in combination with the capability for endosomal penetration and low cytotoxicity make FND Au unique candidates for multimodal optical electronic imaging applications with great potential for emerging techniques, such as quantum sensing inside living cells.