Metal–Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm)

Abstract

Ultrasmall silver nanoparticles were prepared by reduction with NaBH4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver­(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver–sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL–1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag∼250GSH∼155.

Uptake of Functional Ultrasmall Gold Nanoparticles in 3D Gut Cell Models

“…Capable of being localized inside a cell or a spheroid by confocal laser scanning microscopy, fluorescing ultrasmall gold nanoparticles are well‐suited as a carrier system for various molecules into cells. [ 7b,c,13 ] We first evaluated the uptake of ultrasmall gold nanoparticles in 2D cell culture models: mouse intestinal epithelial cells (MODE‐K) as a healthy gut model and murine colorectal carcinoma cells (CT‐26) as a tumor model. Confocal laser scanning microscopy detected strong fluorescent signatures from Au‐AF647 nanoparticles inside all MODE‐K cells.…”

“…Studying the uptake of fluorescent gold nanoclusters (3.3 nm) in HeLa cells, Yang et al used inhibitors to show that clathrine‐mediated endocytosis and macropinocytosis were the primary mechanisms of nanocluster uptake, while caveolin‐mediated pathways played minor roles. [ 13d ] Larger gold nanoparticles (50–100 nm) were translocated into cells via caveolin‐mediated endocytosis. [ 24 ] In addition to relative size, the morphology of nanoparticles is a critically important factor in cellular uptake.…”

“…Doxorubicin‐conjugated ultrasmall nanoparticles have previously been applied to 2D cell cultures. [ 13c,30 ] Zhang et al reported efficient cellular uptake of ultrasmall gold nanoparticles loaded with doxorubicin, with subcellular transport of doxorubicin into nuclei occurring after having separated from the metal core. [ 13c ] In vivo mouse models bearing hepatocellular carcinomas were also treated with functionalized bioactive ultrasmall gold nanoparticles, which effectively inhibited subsequent tumor growth.…”

“…[ 13c,30 ] Zhang et al reported efficient cellular uptake of ultrasmall gold nanoparticles loaded with doxorubicin, with subcellular transport of doxorubicin into nuclei occurring after having separated from the metal core. [ 13c ] In vivo mouse models bearing hepatocellular carcinomas were also treated with functionalized bioactive ultrasmall gold nanoparticles, which effectively inhibited subsequent tumor growth. [ 31 ] Conjugating anti‐cancer drugs with ultrasmall nanoparticles results in prolonged circulation in the bloodstream and decreased renal filtration, which leads to increased bioavailability and local concentrations of the active compounds.…”

Silencing of proinflammatory NF-κB and inhibition of herpes simplex virus (HSV) replication by ultrasmall gold nanoparticles (2 nm) conjugated with small-interfering RNA

“…The ligand shell inuenced the particle size by DCS, thereby underestimating the actual particle size. 70 NMR spectroscopy which can be applied to ultrasmall nanoparticles [71][72][73][74][75][76] was used to identify and quantify GSH and N 3 bound to the ultrasmall nanoparticles. 46 Alkyne-terminated duplex siRNA was then clicked to the Au-N 3 nanoparticles.…”