Investigation on stability of silver nanoparticles with different ligands

Water-dispersible silver nanoparticles (Ag NPs) are widely used in the research of biology and medicine due to their unique physical, chemical, and biological properties. However, the stability of conventional water-dispersible Ag NPs is generally poor, which limits the development of their applications. How to improve the long-term stability of Ag NPs in various environments remains a challenge. The results of this work indicate that the ligands on the surface of Ag NPs (diameter: 4.3 nm) influence their stability greatly. To address the stability difficulties of Ag NPs under long-term storage and application conditions, we prepared water-dispersible Ag NPs with two different types of ligands, namely monodentates ligands 11-mercapto-undecanoic acid and polydentate ligands poly(maleic anhydride-alt-1-octadecene). The stabilities of Ag NPs to light, heat, acid, alkali, salt, and buffer solutions were investigated. Compare with Ag NPs with monodentate ligands, Ag NPs with polydentate ligands shows better stability under the same external conditions. For Ag NPs with polydentate ligands, we attribute the multiple sites provided by the ligands and their inhibition of oxygen permeation through Ag NPs as the main factors for improving their long-term stability. In addition, the presence of free carboxylic acid groups not only conferred Ag NPs high solubility in water, but also allowed them further conjugation with biomolecules such as streptavidin. Graphical abstract