Using sugars as both reducing and cryoprotectants of freeze-dried silver nanoparticles for improving long-term stability

This study has proposed using maltose and lactose as reducing and cryoprotectant agents to improve silver nanoparticles' long-term stability (AgNPs). For the reducing performance, UV-vis spectroscopy revealed that both sugars could be used as reducing and eventually as capping agents of the as-synthesized AgNPs. For cryoprotective performance, the UV-vis spectroscopy and dynamic light scattering (DLS) showed that both sugars could prevent maltose-reduced (coded as AgNP-M) and lactose-reduced (coded as AgNP-L) AgNPs from irreversible aggregation under freezing and freeze-drying. For long-term stability, UV-vis spectroscopy, DLS, and transmission electron microscopy (TEM) data revealed that aged freeze-dried AgNP-M and AgNP-L were generally more stable than their non-freeze-dried counterparts under accelerated storage conditions. Likewise, the antibacterial and cytotoxic activities of aged freeze-dried AgNP-M and AgNP-L were close to those observed in their as-synthesized counterparts. Otherwise, aged non-freeze-dried AgNP-L demonstrated reduced antibac-terial and cytotoxic activities, while such behavior was not present in the aged non-freeze-dried AgNP-M. These findings proved that maltose and lactose could emerge as a green alternative to synthesize AgNPs and simul-taneously cryoprotect them during freezing and freeze-drying to achieve long-term stability.