Ultrabright and Stable Luminescent Labels for Correlative Cathodoluminescence Electron Microscopy Bioimaging.

The mechanistic understanding of structure-function relationships in biological systems heavily relies on imaging. While fluorescence microscopy allows the study of specific proteins following their labeling with fluorophores, electron microscopy enables holistic ultrastructural analysis based on differences in electron density. To identify specific proteins in electron microscopy, immunogold labeling has become the method of choice. However, the distinction of immunogold-based protein labels from naturally occurring electron dense granules and the identification of several different proteins in the same sample remain challenging. Correlative cathodoluminescence electron microscopy (CCLEM) bioimaging has recently been suggested to provide an attractive alternative based on labels emitting characteristic light. While luminescence excitation by an electron beam enables subdiffraction imaging, structural damage to the sample by high-energy electrons has been identified as a potential obstacle. Here, we investigate the feasibility of various commonly used luminescent labels for CCLEM bioimaging. We demonstrate that organic fluorophores and semiconductor quantum dots suffer from a considerable loss of emission intensity, even when using moderate beam voltages (2 kV) and currents (0.4 nA). Rare-earth element-doped nanocrystals, in particular Y2O3:Tb3+ and YVO4:Bi3+,Eu3+ nanoparticles with green and orange-red emission, respectively, feature remarkably high brightness and stability in the CCLEM bioimaging setting. We further illustrate how these nanocrystals can be readily differentiated from morphologically similar naturally occurring dense granules based on optical emission, making them attractive nanoparticle core materials for molecular labeling and (multi)color CCLEM.

Stabilizer-free silver nanoparticles as efficient catalysts for electrochemical reduction of oxygen.

In this work we demonstrated the potential of the He+5% H2+1% N2 plasma jet treatment for the synthesis of surfactant-free silver nanoparticles (Ag NPs) with narrow size distribution. The obtained colloidal solutions of electrostatically stabilized Ag NPs do not show any agglomeration for several months. Apart from an atomic thin oxide layer and the relatively weakly bound OH- ions, the surface of Ag NPs can be considered as stabilizer-free. The surface charge (characterized by the zeta potential) of Ag NPs in solution was measured by electrophoretic light scattering technique. Plasmonic band position and width in the UV/VIS extinction spectra was utilized for the assessment of Ag NPs size distribution. Highly concentrated Ag NPs were uniformly deposited on the surface of the glassy carbon (GC) electrodes by vacuum-drying technique. The deposition process was monitored with a digital camera attached to a microscope. The assemblies of Ag NPs on the electrode surface were characterized by scanning electron microscopy. The Ag NP/GC catalysts were electrochemically tested in alkaline solution using the rotating disk electrode method. The Ag NP/GC electrodes exhibited high electrocatalytic activity toward the oxygen reduction reaction (ORR) in 0.1M KOH solution, indicating their potential applicability as cathode materials for alkaline fuel cells.