2014, Böse, Katharina, Koch, Marcus, Cavelius, Christian, Kiemer, Alexandra K., Kraegeloh, Annette

Fluorescently labeled nanoparticles are widely used to investigate nanoparticle cell interactions by fluorescence microscopy. Owing to limited lateral and axial resolution, nanostructures (<100 nm) cannot be resolved by conventional light micro­scopy techniques. Especially after uptake into cells, a common fate of the fluorescence label and the particle core cannot be taken for granted. In this study, a correlative approach is presented to image fluorescently labeled gold nanoparticles inside whole cells by correlative light and electron microscopy (CLEM). This approach allows for detection of the fluorescently labeled particle shell as well as for the gold core in one sample. In this setup, A549 cells are exposed to 8 nm Atto 647N-labeled gold nanoparticles (3.3 × 109 particles mL−1, 0.02 μg Au mL−1) for 5 h and are subsequently imaged by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). Eight fluorescence signals located at different intracellular positions are further analyzed by TEM. Five of the eight fluorescence spots are correlated with isolated or agglomerated gold nanoparticles. Three fluorescence signals could not be related to the presence of gold, indicating a loss of the particle shell.

2015, Lacava, Johann, Weber, Anika, Kraus, Tobias

The ageing of spherical gold nanoparticles having 6-nm-diameter cores and a ligand shell of dodecanethiol is investigated under different storage conditions. Losses caused by agglomeration and changes in optical particle properties are quantified. Changes in colloidal stability are probed by analytical centrifugation in a polar solvent mixture. Chemical changes are detected by elementary analysis of particles and solvent. Fractionation occurs under all storage conditions. Ageing is not uniform but broadens the property distributions of the particles. Small-number statistics in the ligand shell density and the morphological heterogeneity of particles are possible explanations. Washing steps exacerbate ageing, a process that could not be fully reversed by excess ligands. Dry storage is not preferable to storage in solvent. Storage under inert argon atmosphere reduces losses more than all other conditions but could not prevent it entirely.