Nanoparticles Synthesis
The stabilized polyvinylpyrrolidone-coated silver nanoparticles
(AgNPs-PVP) were synthesized by a chemical reduction reaction as
described in the literature46. In short, silver
nitrate (AgNO3, 99.9% trace metals basis, Sigma, USA)
and polyvinylpyrrolidone (PVP, MW 40000, Sigma, USA) were dissolved in
deionized
(DI) water separately and stirred on a magnetic stir plate until the
solutions became homogeneous. Then AgNO3 and PVP
solutions were added together and stirred for 30 mins at 0°C, meantime
sodium borohydride (NaBH4, ≥98.0%, Sigma, USA) was
dissolved in DI water at 0°C in a separate flask. Next, the reducing
agent solution was added dropwise into the AgNO3-PVP
mixture solution to reduce the Ag+-PVP to AgNPs-PVP.
The color of the mixture solution became transparent bright yellow
indicating formation of AgNPs-PVP. The final molarity concentration
ratios of each component were
AgNO3:NaBH4:PVP=2:1.4:1.
The AgNPs (AgNPs) was synthesized by chemical reduction reaction as a
control to compare with the stabiliity of AgNPs-PVP, using a protocol
reported previously47. In short, 0.25 mM AgNPs was
made by adding 10 mL of 1.0 mM AgNO3 dropwise to 30 mL
of chilled 2.0 mM NaBH4. The reaction mixture was
stirred vigorously on a magnetic stir plate for 10 mins. Color of the
mixture became clear yellow indicating the formation of AgNPs.