Structural Analysis and Intrinsic Enzyme Mimicking Activities of Ligand-Free PtAg Nanoalloys.

Nanozymes are nanomaterials with biocatalytic properties under physiological conditions and are one class of artificial enzymes to overcome the high cost and low stability of natural enzymes. However, surface ligands on nanomaterials will decrease the catalytic activity of the nanozymes by blocking the active sites. To address this limitation, ligand-free PtAg nanoclusters (NCs) are synthesized and applied as nanozymes for various enzyme-mimicking reactions. By taking advantage of the mutual interaction of zeolitic imidazolate frameworks (ZIF-8) and Pt precursors, a good dispersion of PtAg bimetal NCs with a diameter of 1.78 ± 0.1 nm is achieved with ZIF-8 as a template. The incorporation of PtAgNCs in the voids of ZIF-8 is confirmed with structural analysis using the atomic pair-distribution function and powder X-ray diffraction. Importantly, the PtAgNCs present good catalytic activity for various enzyme-mimicking reactions, including peroxidase-/catalase- and oxidase-like reactions. Further, this work compares the catalytic activity between PtAg NCs and PtAg nanoparticles with different compositions and finds that these two nanozymes present a converse dependency of Ag-loading on their activity. This study contributes to the field of nanozymes and presents a potential option to prepare ligand-free bimetal biocatalysts with sizes in the nanocluster regime.

Uptake and Intracellular Fate of Fluorophore Labeled Metal-Organic-Framework (MOF) Nanoparticles.

The uptake and the fate of Zr-based metal-organic-framework nanoparticles labeled with organic fluorophores in HeLa cells has been monitored with fluorescence detection and elemental analysis. The nanoparticles have been selected as a model system of carrier nanoparticles (here Zr-based metal-organic-framework nanoparticles) with integrated cargo molecules (here organic fluorophores), with aze that does not allow for efficient exocytosis, a material which only partly degrades under acidic conditions as present in endosomes/lysosomes, and with limited colloidal stability. Data show that, for Zr-based metal-organic-framework nanoparticles of 40 nm size as investigated here, the number of nanoparticles per cells decreases faster due to particle redistribution upon proliferation than due to nanoparticle exocytosis and that, thus, also for this system, exocytosis is not an efficient pathway for clearance of the nanoparticles from the cells.