Stability Enhancement of Silver Nanoparticles Through Surface Encapsulation via a Facile Green Synthesis Approach and Toxicity Reduction

Abstract

Persuaded by the necessity of reduction of toxicity, silver nanoparticles (Ag-NPs) were synthesized from the reaction between AgNO3 solution and Mizuna (Brassica rapa var. japonica) leaf extract. This study aimed to investigate the role of synthesis temperature on particle properties. Thus, four synthesis-temperatures, 25 °C (room temperature), 60 °C, 80 °C, and 100 °C were applied. Ag-NPs were characterized using ultraviolet–visible (UV–Vis) spectrophotometer, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, atomic absorption spectrometry and dynamic light scattering techniques. The high-temperature (80 and 100 °C) synthesis showed higher stability, demostrated lowest release of silver ion (0.02 µg/mL, 0.002 µg/mL) compared to low-temperature synthesis. In addition, high-temperature synthesis showed higher C-content (> 50%) with lower Ag-content (< 30%) than low-temperature (25 and 60 °C) synthesis. Moreover, a complete surface encapsulation is found on the particles synthesised at 100 °C by TEM analysis. The synthesized Ag-NPs were exposed to Caco-2 cell lines for cytotoxicity assessment. The high-temperature synthesis Ag-NPs exerted significantly lower cytotoxicity in terms of Caco-2 cell viability and lactate dehydrogenase (LDH) activity assay. Upon exposure to 1, 5 and 10 µg/mL Ag-NPs for 48 h the cell viability (96.33%, 90.66% and 89.66%) was not changed for high-temperature synthesis particles as well as the LDH activity was unchanged. However, low-temperature synthesis showed significant cytotoxicity (81%, 66% and 44.33%) under similar experimental conditions. Thus, characterization and cytotoxicity techniques clearly demonstrate the successful synthesis of Ag-NPs with the encapsulation of bio-molecules that enhances the particle stability and reduce cytotoxicity.