Analytische Chemie
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The use of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a variety of products, which range from textiles over children toys and dietary supplements. Therefore, research on silver in a nanoscale form becomes increasingly important for a high amount of studies. Unfortunately the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The central problem lies in the utilization of a wide range of silver nanoparticles, which show a broad size distribution. To overcome this problem we synthesized ultra-small core-shell silver nanoparticles by an up-scaled modification of the polyol process. The particles are highly stable and show no aggregation for more than six months. Small-angle X-ray scattering (SAXS) analysis reveal a narrow size distribution of the silver cores with a mean radius of RC = 3.0 nm and a distribution width of 0.6 nm. Dynamic light scattering (DLS) provides a hydrodynamic radius of RH = 10.0 nm and a PDI of 0.09. The surface of the particles is covered with poly(acrylic acid) (PAA) forming a shell with a thickness of 7.0 nm, which provides colloidal stability lasting for more than six months at ambient conditions. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. The stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione (GSH) and bovine serum albumin (BSA) have been performed as examples. We demonstrate that the particles effectively catalyze the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride. With PAA as stabilizer, the catalytic activity of (436 ± 24) L g-1 s-1 is the highest reported in literature for silver nanoparticles. GSH and BSA passivate the surface substantially resulting in lower catalytic activities of (77.6 ± 0.9) L g-1 s-1 and (3.47 ± 0.50) L g-1 s-1, respectively. The ultra-small particles were already used in the Nano Define project. Due to their small size it is possible to investigate the detection limits of different analytical techniques like electron microcopy, field flow fractionation or single particle tracking. In this project they serve as the calibration standard with the smallest radius.
The use of silver nanoparticles in consumer related products has significantly increased over the last decade, especially due to their antimicrobial properties. Today they are used in a variety of products, which range from textiles to dietary supplements. Thus, investigations on nanoscale silver become increasingly important in many fields like biomedicine or catalysis. Unfortunately, the results of these studies are extremely diverse and do not lead to a consistent evaluation of the toxicity of silver nanoparticles. The main problem is the use of nonuniform and poorly characterized particles with broad size distributions. To overcome this problem we modified the known polyol process to synthesize ultra-small core-shell silver nanoparticles in a large scale. The particles are highly stable and show no aggregation for more than six months. Small-angle X-ray scattering analysis reveals a narrow size distribution of the silver cores with a mean radius of 3 nm and a distribution width of 0.6 nm. Dynamic light scattering provides a hydrodynamic radius of 10.0 nm and a PDI of 0.09. The stabilizing ligand PAA can be easily exchanged by biomolecules to modify the surface functionality. Replacements of PAA with glutathione and bovine serum albumin have been successfully performed. To demonstrate the broad applicability of our particles we performed catalysis experiments with the reduction of 4-nitrophenol as model reaction. The PAA-stabilized particles show a catalytic activity of (436 ± 24) L g-1 s-1, which is the highest reported in literature for silver nanoparticles. In contrast, GSH and BSA passivate the surface substantially resulting in lower catalytic activities.