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Tracking silver nanoparticles: ultra-small silver refunctionalizable with fluorescent biopolymers
(2016)
We report on the synthesis of ultra-small silver nanoparticles and their quantitative characterization by small-angle X-ray scattering. The size distribution was derived by utilizing a Monte-Carlo data evaluation procedure reported by Pauw et al. Mean volume-weighted sizes are 3 nm with a size distribution width of 18 %. The particles should be used as reference materials for comparison of the result of different analytical methods among which are field-flow fractionation (FFF), dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and electron microscopy (EM). In addition further use of the particles is foreseen for comparison of studies on the toxicology of nanoparticles. Therefore the silver nanoparticles are transfunctionalized with fluorescent marked albumin (BSA-FITC) and also thoroughly characterized. With this it is possible to track silver nanoparticles and their behavior in interaction with cells.
We report on the development of ultra-small core-shell silver nanoparticles synthesized by an up-scaled modification of the polyol process. It is foreseen to use these thoroughly characterized particles as reference material to compare the catalytic and biological properties of functionalized silver nanoparticles. 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 particles’ surface 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. The 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 a catalytic activity of 77.6 ± 0.9 and 3.47 ± 0.50 L g⁻¹ s⁻¹, respectively.