The preparation of stable cysteine-capped silver nanoparticles (AgNPs), via the reduction of silver ions with sodium borohydride and modification of formed nanoparticles by l-cysteine, was developed. The micrographs from transmission electron microscopy (TEM) revealed that the spherical AgNPs exhibited an average size equal to 22±4nm. Surface enhanced Raman spectroscopy (SERS) and inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed a chemisorption of cysteine molecules on the AgNPs. Additionally, dynamic light scattering (DLS) measurements showed that the AgNPs were stable for ionic strength lower than 5×10-3molL-1 and at 6.8<pH<4.5. The electrophoretic mobility measurements allowed to determine the isoelectric point of AgNPs, which appeared at pH 5.1. Below this value, the AgNPs were positively charged with the zeta potential equal to +68±3mV at pH 3.5. Under alkaline condition, the zeta potential of AgNPs was negative, attaining a value of -71±3mV at pH 9.5. The AgNPs were prone to the processes of oxidative dissolution, which was assessed using atomic absorption spectrometry (AAS). The cytotoxicity of AgNPs towards histiocytic lymphoma (U-937) and human promyelocytic (HL-60) cells was studied by the evaluation of changes in mitochondrial functions and cell membrane integrity. In the case of the HL-60 cells, apoptosis caused by the membrane damage was dominant. Furthermore, the obtained results showed the does-dependent impact of the AgNPs on the cell viability. Finally, it was found that the AgNP concentration of 15mgL-1 caused a complete destruction of cells of both types.
Keywords: amino acids; biological activity; charge inversion; cysteine; cytotoxicity; oxidative dissolution; silver nanoparticles.
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