L-Cysteine as a reducing/capping/gel-forming agent for the preparation of silver nanoparticle composites with anticancer properties.

The present article reports the preparation of silver nanoparticles (AgNPs) homogeneously distributed in the gel matrix formed using only L-cysteine (CYS) as a bio-reducing agent. The physicochemical methods of analysis confirmed the formation of a gel-network from aggregates consisting of spherical/elliptical cystine-stabilized AgNPs (core) and cysteine/Ag complexes (shell) regardless of the used silver salt - AgNO, AgNO or AgOOCCH. CYS/AgNO and CYS/AgOOCCH aqueous solution systems needed the addition of electrolytes (Cl and SO) for the gelation process, but the gel-formation in CYS/AgNO occurred in one stage without any additional components. The AgNP sizes were about 1-5 nm in diameter for CYS/AgNO, 5-10 nm for CYS/AgOOCCH and 20-40 nm for CYS/AgNO systems. The zeta-potential values varied from +60 mV for CYS/AgNO to +25 mV for the CYS/AgNO system. The MTT-test showed that the obtained composites suppressed the MCF-7 breast cancer cells and the CYS/AgNO system possessed the highest activity. Flow cytofluorimetry confirmed that the cell death occurred by apoptosis and this effect was the strongest for the CYS/AgNO system. All systems were non-toxic to fibroblast cells. The novel simplest "green chemistry" approach, combining the knowledge of organic, inorganic, physical and supramolecular chemistry could open possibilities for the creation of the newest soft gel materials used in various fields of our life.